Laser Surface EngineeringLaser surface engineering is an emerging surface engineer-ing technique which involves tailoring of the microstructure and/or composition of the near surface

Laser Surface Engineering

Jyotsna Dutta Majumdara* and Indranil Mannaa,b*aMetallurgical and Materials Engineering Department, Indian Institute of Technology, Kharagpur, WB, IndiabIIT Kanpur, Kalyanpur, Kanpur, Uttar Pradesh, India

Abstract

Surface engineering aims at tailoring the microstructure and/or composition of the near surfaceregion of a component for improving surface dependent engineering properties. Conventionally,surface engineering may broadly be classified into two categories: surface modification (where thetreated layer is part of the substrate) and coating (adding another layer onto the surface). Laser asa clean source of heat may be used for modification of microstructure and/or composition of the nearsurface region of the component by heating/melting or by deposition and alloying/cladding.Especially, because of its exponentially decaying energy distribution profile, laser enjoysa prominent position for its application in surface engineering. Laser surface engineering may beclassified as surface transformation hardening, surface melting, laser surface alloying, and lasersurface cladding. In this chapter, the application of laser for surface modification like laser trans-formation hardening, melting and homogenization of surface microstructure, changing compositionby laser surface alloying for improving surface properties for structural application and laser surfacecladding techniques will be discussed in detail. With a brief introduction to the individual technique,the principle of its operation will be discussed. Finally, the examples of application of laser surfaceengineering will be discussed in detail.

Introduction

Surface microstructure and composition control the serviceability and functionality of the compo-nent to a significant extent. Hence, an optimum designing of the microstructure and composition ofthe near surface region is necessary for tailoring the surface dependent structural and functionalproperties of any component (ASM 1982). Furthermore, in real components, the properties neededon the surface are often different from those in the bulk. Surface engineering aims at modifying/changing the microstructure and/or composition of the near surface region of a component toimprove surface dependent engineering properties (ASM 1982). The advantages of surface engi-neering over bulk manufacturing techniques include conservation of strategic and expensivealloying elements, improved functionality, and improved service life without altering the propertiesof the bulk, and hence, economic in energy and cost. There are a large number of techniquesavailable for altering the surface chemistry and microstructures of the component. However, the

*Email: [email protected]

*Email: [email protected]

Handbook of Manufacturing Engineering and TechnologyDOI 10.1007/978-1-4471-4976-7_27-1# Springer-Verlag London 2014

Page 1 of 32

choice of the technique depends on the required microstructure, composition, thickness, environ-mental impact, and economic viability. Laser surface engineering is an emerging surface engineer-ing technique which involves tailoring of the microstructure and/or composition of the near surfaceregion of the component using laser as a source of heat (Dutta and Manna 2011).

When a laser beam interacts with matter, there is absorption of photons from the incident laserbeam which excites the electrons from the valence/conduction bands to states of higher energy. Theexcited electrons may get back to their original state by emitting photons which are equivalent to thedifference in energies between excited and de-excited states. These emitted photons interact withphonon to generate heat. The time duration for the electron excitation to electron phonon interactionis as short as 10�9 s. As a result, there is instantaneous transfer of heat during the laser matterinteraction process. Figure 1 illustrates the energy distribution profile with depth during laserirradiation of solid surface. For laser irradiation, the beam intensity (I) at any depth (z) for thenormally incident beam of initial intensity Io (in W/m2) is given by (Picraux and Follstaedt 1983):

I z; tð Þ ¼ Io tð Þ 1� Rð Þexp �azð Þ, (1)

where Io is the incident intensity, t is time, R and a are the reflectivity and absorption coefficients,respectively. Since a is very high (~106 cm�1) for metals, light is totally absorbed within a depth of10–20 nm. The efficiency of optical coupling is determined by the reflectivity (R). R for metals isrelatively low at short wavelengths, rises abruptly at a critical wavelength, then remains very high atlong wavelength (Picraux and Follstaedt 1983). Due to the exponential energy distribution profile ofthe laser beam it is able to uniquely heat the near surface region of the component for modification ofits microstructure without changing composition (hardening, remelting, shocking, texturing, andannealing), or both microstructural as well as compositional modification of the near-surface region(alloying, cladding, etc.) of the component (Dutta and Manna 2011). The advantages of applicationof laser in surface engineering over conventional techniques include a rapid rate of heating/cooling(104–1011 K/s), a very high thermal gradient (106–108 K/m) and ultra-rapid solidification velocity(1–30 m/s) achievable during laser assisted surface processing (Molian 1989). These extremeprocessing conditions could develop metastable microstructures and compositions in the nearsurface region with large extension of solid solubility.

Figure 2 shows the general classification of laser surface engineering. The processes are dividedinto three major classes, namely the process involving only heating (without melting), melting

Fig. 1 Energy distribution profile with depth during laser irradiation of solid surface


Page 2 of 32

(without vaporizing), and vaporizing. The regime for individual laser surface engineeringtechnique as a function of applied power density and interaction time is illustrated in Fig. 3(Dutta and Manna 2011). It may be noted that transformation hardening needs only surface heatingand requires low power density. Surface melting, cladding, glazing, and reclamation involve meltingand require a moderately high power density. Cleaning and shock hardening demand removal ofmaterials as vapor, hence, delivery of a very high power density is needed. Therefore, a carefulcontrol and optimization of several important process parameters are needed for achieving a desiredmicrostructure and composition of the surface. The main process parameters active in controlling themicrostructure and composition of the surface include the type of laser used (wavelength of laser),power density, beam size, geometry, working distance, powder feed rate, and deposition angle.

In this chapter, with a brief description of laser surface engineering techniques like lasertransformation hardening, melting and homogenization of surface microstructure, laser surfacealloying, and laser surface cladding, the role of process parameters in controlling the microstructureand composition of the surface engineered samples will be discussed in detail. Finally, the examplesof application of laser surface engineering techniques will be stated.

Laser Surface Engineering

Heating Melting Evaporation

Transformation hardening

Paint stripping

Coloring

Remelting

Cladding

Alloying

Cleaning

Texturing

Shock hardening

Fig. 2 General classification of laser surface engineering

Fig. 3 Processing regime of different laser surface engineering (Dutta and Manna 2011)


Page 3 of 32

Laser Transformation Hardening

Laser transformation hardening is a process where a high power laser beam (either in continuouswave mode or in pulsed mode) is used as a heat source to austenitize the surface of Fe-C alloys(steel, cast iron, etc. with a carbon content higher than 0.4 %) and is subsequently, quenched toa temperature below martensitic start temperature (Ms) to induce martensitic transformation by self-quenching or by spraying external quenchant. Figure 4 presents the laser surface transformationhardening technique schematically, with the temperature distribution in different regions markedand labeled. The steps in transformation hardening include (a) austenitization, which takes place ata temperature of 50–100� above AC3 temperature. The transformation to austenite from the initialmicrostructure during the heating cycle is generally assumed to occur in two steps: in the first steppearlite transforms to austenite followed by transformation of ferrite into austenite. Ferrite trans-forms at higher temperature as it has low solubility of carbon (b) homogenization, it is important thatsufficient time should be available for the diffusion and distribution of carbon all throughout themicrostructure, and (c) quenching at temperature below martensitic start (Ms) temperature fortransformation from austenite to martensite. The kinetics of transformation hardening is dictatedby the kinetics of dissolution of carbon into matrix. Under equilibrium conditions, as soon as thetemperature during heating reaches above eutectoid temperature, pearlite starts to transform intoaustenite. The diffusion distance for carbon in pearlite is small; due to this the pearlite transformationto austenite is very rapid and sometimes assumed to be instantaneous. The reaction then proceeds tothe remaining ferrite after all the pearlite is consumed. This step occurs within a temperature rangewhich is limited by the eutectoid line and the transition temperature. During laser transformationhardening, the surface temperature should be as high as possible to shorten the time to complete thetransformation to austenite while a high temperature gradient is required to heat a sufficient thicksurface layer in a short time. A short time and high temperature gradients are also required to preventheating of the bulk material.

The parameters for laser transformation hardening include type of laser used, beam shape, appliedlaser power density, relative scan speed between the laser and substrate or pulse time, mode of itsoperation (pulsed or continuous mode), surface composition, topography, and absorptivity. Theeffect of process parameters responsible in controlling the microstructure and composition of thelaser processed zone will be discussed briefly in the later part of the process description.

Depth of the transformation hardening plays an important role in determining the service life ofany component. The higher the depth of hardening is, the greater the durability of the component

Fig. 4 Schematic of laser transformation hardening technique


Page 4 of 32

under wear will be. The depth of transformation hardening depends on the choice of applied powerdensity and interaction time along with the chemical composition of the material used for hardening.The maximum depth of hardening achieved by laser surface hardening can be as high as 0.8 mm.However, for some industrial applications, a hardened depths of up to 2.0 mm is needed whichnecessitates a proper designing of the process and application of external quenchant. Typicalhardened case depths of up to 1.6 mm have been reported by Schuöcker for type 50NiCr13 material(1998). Due to the high reflectivity of metal surfaces to the CO2 laser (wavelength of 10.6 mm), ananti-reflective coating is often applied onto the metal surface to increase absorptivity.

A detailed review of laser surface hardening and its comparison with conventional surfacehardening technique is described by Kennedy et al. (2004). The characteristics of laser surfacehardening over conventional hardening include economic in time and energy, scope of full automa-tion, minimum macro distortion, and hence, reduced need for additional machining, a precisionthickness of the hardened layer, no need for external quenchant and environmental cleanliness. Theapplication of high power lasers in surface hardening has already been proven to be feasible and isapplied on real components for automobile and aerospace industries for hardening the surface layersof turbine blades, crankshafts, and tractor engine components. Benedek et al. (1980) carried out casehardening of carbon steel, armco iron, alloyed steel, and high-speed steel using a CO2 laser beam.Processing at optimal conditions yielded a hardening depth of up to 0.7 mm and a surface hardnessof up to 720 HV. Prior microstructure of the substrate influences the final microstructure of the lasersurface hardened steel to a significant extent. Grum and Slabe (2005) observed the formation ofnanometric precipitates with a diverse microstructure up to varying depth following laser surfacehardening of maraging steel. Heidkamp et al. (2004) studied the effect of laser beam hardening onthe properties of TiN-coated AISI 4140 (EN 42CrMo4), AISI A2 (EN X100CrMoV5-1), and AISID2 (EN X153CrMoV12) substrates by CVD. A composite material with flat strength and hardnessgradients from the interface to the core, together with a high surface hardness, increased wearresistance, and an increased material resistance against high mechanical load was achieved.

Surface conditions (roughness, residual stress, phase aggregate) play a significant role in deter-mining the characteristics of hardened layer. The effect of different types of absorbing coating onlaser surface hardening of C45E steel was determined by Grum and Kek (2004). Heitkemperet al. (2003) showed that the fatigue and fracture behavior of laser heat treated high nitrogenmartensitic tool steel (X30CrMoN15) with a 3 kW Nd:YAG laser was significantly improved ascompared to that of the untreated one. The residual stresses generated during laser treatment hada significant influence on crack initiation, while those generated during the transformation ofretained austenite had a minor influence on crack propagation. Iordanova et al. (2002) carried outlaser surface melting of 0.46-mm-thick cold-rolled low carbon steel by pulsed Nd:glass laser up toa thickness of 80 mm. Prior cold rolling developed residual tensile stress both along rolling and intransverse directions. It was observed that laser melting does not affect the residual stress along therolling direction, but significantly increases it along the transverse direction with a weaker andscattered texture.

Amulevicius et al. (2000) studied the influence of simultaneous laser irradiation and ultrasound onthe phase evolution in the Fe–Si–C system (gray cast iron) by means of Mössbauer spectroscopy.The application of ultrasound reduced the amount of retained austenite in the samples by two to threetimes due to active dissolution and re-distribution of carbon between austenite and iron–carbonclusters. Chen and Shen (Chen and Shen 1999) optimized the process parameters for laser trans-formation hardening of SNCM 439 steel using Taguchi methodology and fuzzy evaluation method.It was concluded that there was improvement in hardness from HRC 52.5–63.9; with an increase inhardening width 0.43–0.89mm, with a reduction in erosion loss from 69.55 to 40.94mgwhen a long


Page 5 of 32

pulse Nd-YAG laser was used for surface hardening. It was concluded that both the fuzzy evaluationmethod and Taguchi methodology were effective and applicable for evaluating the usefulness oflong pulsed Nd-YAG laser transformation hardening processes quantitatively. Laser surface treat-ment of pearlitic gray and ductile cast irons using a 5 kW continuous wave CO2 laser improved theerosion resistance of gray iron by 5 times and the same for ductile iron by 26 times (Tobaret al. 2006). Molian (1981) studied the effect of laser surface hardening on the microstructure ofAIS14340 steel and compared it with the conventional hardened one. The microstructure exhibiteda mixture of dislocated and twinned martensites with an enhanced volume fraction of retainedaustenite as compared to the conventional furnace heat treated (870 �C treatment) specimens,though, prior austenite grain size and martensitic substructure remained essentially the same. Royand Manna (2001) have demonstrated that laser surface hardening (LSH), instead of laser surfacealloying (LSA) or laser surface melting (LSM) is more effective in enhancing the wear resistance ofaustempered ductile iron (ADI), attributed to the development of martensitic surface with residualcompressive stress. Adel et al. (2009) studied the effect of neodymium yttrium (Nd-Yag) pulsedwave laser assisted heat treatment on the coefficient of friction and wear resistance of acicularbainitic ductile iron and observed a significant refinement of microstructure with an improved wearresistance and reduced coefficient of friction.

In spite of ample advantages of laser surface hardening as compared to conventional hardening,a large thermal stress is generated in the laser irradiated surface resulting from the high cooling rateand thermal gradient associated with the process (Mura 1982). The magnitude of residual stress andits vector depends on laser parameters. The residual stress arrested due to laser transformationhardening may be due to combined influence of (a) quench stress, which is tensile in nature and(b) transformation stress, which is compressive in nature. Compressive residual stress is beneficial inimproving fatigue property, however, tensile residual stress is detrimental as it deteriorates wear,corrosion, and fatigue properties of material. Hence, process parameters should be carefully chosento minimize the residual stress arrested due to laser transformation hardening. Prediction of theresidual stress on the surface necessitates a quantitative knowledge of the thermal history of thealloyed zone. Furthermore, the microstructure of the hardened zone developed by LSH is closelyrelated to the thermal history of the process. The parameters which play a role in controlling thethermal history and residual stress are laser power density and scan speed. Time-resolved measure-ment of temperature during this process of transient heating and cooling within the short laserinteraction time (ti), is extremely difficult and confined only to the top surface. As an alternative,mathematical modeling of the heat transfer process accompanying laser surface hardening is

Fig. 5 Variation of temperature with time during laser heating and subsequently, cooling of laser surface hardened 0.6%C steel at a scan speed of 50 ms


Page 6 of 32

a convenient tool to predict the thermal history of the alloyed zone with reasonable accuracy. In thepast, several studies have been attempted to predict the temperature distribution during laser surfacehardening (Ashby and Easterling 1984; Mazumder et al. 1996). A one dimensional unsteady stateheat transfer model based on explicit finite difference method of solution was developed to simulatethe thermal profile in laser surface hardening and subsequently, the residual stress developed on thesurface has been calculated considering thermal stress and transformation stress.

Figure 5 presents the distribution of temperature as a function of time at different applied power(on the surface and at a depth of 40 mm from the surface) for laser surface hardened 0.6 % C steel atthe surface (solid line) and at a depth of 40 mm from the surface (dashed line). From Fig. 5, it isapparent that the top surface experiences the maximum or peak temperature (Tpeak), and Tpeakdecreases as depth (z) below the surface increases. It is interesting to note that the time (tpeak) toreach Tpeak (except at the top surface, i.e., at z ¼ 0) gradually increases as depth increases. In fact,tpeak> ti at all z rather than z¼ 0. From Fig. 5 it is relevant that temperature developed at the surfaceand at a certain depth is dependent on applied power. The higher the applied power, the more thetemperature develops in each layer because of a higher energy input (and hence, absorbed energy).Hence, laser power density should be carefully chosen to optimize the depth of austenitization. Toohigh or too low a temperature is not desirable as they lead to melting and improper homogenizationof austenite, respectively. It may be pointed out that tpeak at a given z is always larger than the timeneeded to reach TRT from Tpeak on cooling. In other words, it suggests that the cooling rate is higherthan the corresponding heating rate in each layer. The apparent difference within the same volume ofmaterial may be attributed to the fact that, the effect of thermal gradient during heating cycle issmaller than the same during cooling cycle. The present model predicts heating and quenching todevelop the hardened zone within a very short period of time.

Figure 6 shows the variation of temperature with depth from the surface during cooling of lasersurface hardened 0.6 % C steel. From Fig. 6 it is evident that temperature is maximum at the surfaceand decreases as the depth from the surface increases. The higher the interaction time, the higher thetemperature is in each layer, though the temperature gradient does not seem to vary significantly withthe interaction time. Figure 7 reveals the variation of thermal gradient (dT/dz) with depth (z) duringcooling cycle of laser surface hardening of 0.6 % C steel (a) lased with a power of 0.95 kW fordifferent interaction times (ti) and (b) with different power but at an interaction time of 40 ms. FromFig. 7 it may be noted that the thermal gradient is maximum at the top surface and decreases as thedepth from the surface increases. This is anticipated because the structure below 500 mm provides aninfinite heat sink which allows easy and unidirectional conduction of heat vertically downward.Furthermore, it is apparent that the higher the ti, and P, the greater the thermal gradient at a givendepth (z). However, the thermal gradient decreases with depth and follows a uniform and almost

Fig. 6 Variation of the temperature in the hardened layer as a function of the depth from the surface lased at differentpower and an interaction time of 10 ms


Page 7 of 32

identical rate for the range of ti studied in this investigation. Similarly, thermal gradient at a particulardepth increases with an increase in applied power.

Figure 8 shows the variation of the depth of hardening with (a) applied laser power and(b) interaction time for laser surface hardened 0.6 % C steel. Depth of hardened layer was foundto increase with an increase in applied power and an increase in interaction time. Increasedhardening depth with increase in applied power and interaction time are attributed to an increasedquantity of absorbed energy. However, too high of an applied power or too low interaction timemight lead to melting of the surface. On the other hand, application of inadequate power andinteraction time might cause inhomogeneous dissolution of carbon within the matrix. Hence, laserpower and interaction time should be chosen so as to obtain a homogenous hardened layer with thedesired depth of hardening.

Figure 9 shows the distribution of residual stress along the depth from the surface of laser surfacehardened 0.6 % C steel. From Fig. 9 it is evident that there is introduction of residual compressivestress on the surface, the magnitude of which decreases as the depth from the surface increases andgradually changes to tensile residual stresses at a depth of 10 mm from the surface. Furthermore, themagnitude of residual compressive stress increases with increase in interaction time which isattributed to an increased volume fraction of martensite formed on the surface at a higher interactiontime. On the other hand, increasing the power increases the surface compressive stress and the

Fig. 7 Variation of thermal gradient (dT/dz) with depth (z) during cooling cycle of laser surface hardening of 0.6 %C steel (a) lased with a power of 0.95 kW for different interaction times (ti) and (b) with different power but at aninteraction time of 40 ms


Page 8 of 32

maximum tensile stress at the sub-surface region. Increasing the power causes rapid cooling froma higher temperature, thus increasing the volume fraction of martensite in the microstructure. Inaddition to that, increasing the power causes heating to a larger depth, and hence, plastic flow will

Fig. 8 Variation of the depth of hardening with (a) applied laser power and (b) interaction time for laser surfacehardened 0.6 % C steel

Fig. 9 Variation of residual stress along the depth from the surface of laser surface hardened 0.6 % C steel


Page 9 of 32

increase a bit in the lower layer which increases the maximum tensile stress value. As thecompressive stresses are very much desirable on the surface (they increase the fatigue strength ofthe material) their variations with power and interaction time have been studied in detail. It is easilyseen that for a constant power increasing the interaction time increases the surface compressivestresses. On increasing the power, there is an increased cooling rate causing an increased areafraction of martensitic transformation, and hence, more of the transformational stress dominationleading to even higher values of compressive stresses at the surface. Figure 10 summarizes thevariation of residual compressive stress developed on the surface of laser surface hardened 0.6 %C steel with (a) applied power and (b) scan speed. From Fig. 10 it is evident that the magnitude of theresidual compressive stress on the surface increases with increase in applied power. Furthermore, therate of increase in compressive stress with applied power is higher when laser surface hardened ata higher interaction time. Similarly, it is also observed that increasing the scan speed increases themagnitude of compressive residual stress on the surface, the rate of which is higher at a higher power.From the above mentioned discussion it appears that increasing both the laser power and theinteraction time is a desirable feature as they increase the compressive residual stress on the surface.However, a detailed calculation of the influence of laser parameters on the maximum tensile residualstress at the sub-surface region shows that maximum residual stress increases with increase inapplied power, though the interaction time does have a marginal influence on it.

From the above discussions, it may be concluded that even though surface hardening may beachieved by austenetizing followed by cooling with application of a wide range of laser power-scanspeed combinations, residual stress distribution at the near surface and sub-surface regions varieswith laser parameters. Hence, optimum choice of laser parameters is essential to ensure a highcompressive stress at the surface and low tensile stress at the sub-surface regions. In this regard, it isrelevant to note that application of inadequate power density or low interaction time will lead toincomplete austenitization and very low compressive stress at the surface, while application of very

Fig. 10 Variation of residual compressive stress developed on the surface of laser surface hardened 0.6 % C steel with(a) applied power and (b) scan speed


Page 10 of 32

high powder density and high interaction time will cause a very large sub-surface tensile stress andoverheating/melting of the surface.

Laser Surface Melting

Laser surface melting (LSM) also proved to be an important technique to modify the microstructureand composition of the near surface region of a component. In laser surface melting, a high powerlaser beam is used as a source of heat to melt a thin surface layer of substrate made of metals/alloysfor microstructural refinement and homogenization. Laser surface melting aims at increasing thehardness of the surface and improving corrosion resistance and fatigue property. Laser surfacemelting leads to the following changes on the surface of metals and alloys:

(a) Polishing of surface(b) Grain refinement and homogenization

In the present section, both laser polishing and grain refinement and homogenization will bediscussed in detail.

Laser Polishing of MetalsPolishing is an integral part of manufacturing which involves smoothening of the surface bymaterials removal. Manual polishing alone accounts for 37 % of the total production time and30 % of production cost in mold and die making industries (Nusser et al. 2011). Moreover, manualpolishing is time consuming and involves a high production cost. The polishing process can beautomated to reduce the cycle time. However, polishing of materials with complex size and shapeoften restricts the application of automatic polishing unit. Laser beam irradiation may be applied forpolishing of materials which involves the process of reducing surface roughness by (a) surfacemelting or (b) ablation of materials from the surface. The advantages of laser surface polishing overconventional polishing techniques include a reduction in polishing time from 3.5 h to 10 min, theability to polish objects of complex geometry, microstructural refinement, and associated improve-ment in properties of the object. Over the last decade, laser polishing (LP) process applicability wasdemonstrated on glass, lens, fibers, and diamond polishing and it has been extended towardpolishing of metallic materials recently (Bol’shepaev and Katomin 1997). The parameters influenc-ing the quality of the polishing include topography, thermal, and optical properties of the substrate,laser power, pulse duration, pulsing frequency, beam shape, speed, tool path trajectory, number of

Fig. 11 Schematic showing laser assisted surface polishing of metals


Page 11 of 32

passes, percentage of overlap, etc. Among all these parameters energy density plays an importantrole to determine the quality to a maximum extent.

Figure 11 shows the schematic of laser melting assisted surface polishing technique. In laserpolishing, a laser beam with sufficient energy is applied on the surface leading to surface melting ofa thin layer of the work-piece which subsequently, flows and redistributes under the action of surfacetension, which evens out the surface asperities and reduces the surface peak to valley heights afterrapid solidification.

Grain Refinement and HomogenizationWhen a laser beammelts the surface it causes a significant refinement of microstructure due to a veryfast quenching rate associated with the process, due to the presence of the underlying substratewhich acts as quenchant. The microstructural refinement leads to a significant improvement inhardness, wear, and corrosion resistance properties. The morphology of the microstructure isdetermined by the ratio of temperature gradient of the liquid at the solid–liquid interface (G) andsolidification velocity (R); i.e., G/R. During laser surface melting, a high solidification velocity isattained and it at times exceeds the local diffusion rate and due to it, equilibrium at the interface cannot be established and the solute atoms are frozen into a solid at the same composition as they arriveat the interface (solute trapping). However, at a lower solidification rate (slower than the diffusionrate), local equilibrium can be established and the interface composition can achieve the samecomposition as that at the melt. During laser surface melting, due to a rapid cooling there ismicrostructural homogenization, extension of solid solubility and dissolution/redistribution of pre-cipitates or inclusions in the matrix. During laser surface melting, when the cooling rate exceeds thecritical cooling rate for glass forming, there may be formation of glassy phase for the alloys witha high glass forming ability. Laser surface melting with a high intensity laser beam at a very rapidtraverse rate may be applied to do surface glazing of ceramics and metals.

Laser surface melting has been successfully employed on tool steel, titanium, and magnesiumsubstrates to refine and homogenize the microstructure and subsequent improvement in its corrosionresistance property. In the past, laser surface melting was reported to improve the corrosionresistance (in NaCl solution) of 440C martensitic stainless steel by refinement of carbides and itsre-distribution (Lo et al. 2003). De-sensitization of AISI 304 stainless by laser surface melting hasbeen successfully reported on AISI 304 stainless steel which is achieved by complete dissolution ofM23C6 type of carbides and subsequently, homogenization of microstructure (Yanez et al. 2002).DuttaMajumdar et al. (2010) surface melted AISI 52100 steel using a high power (2 kW) continuouswave CO2 laser (with a beam diameter of 3 mm) with a linear scan speed of 1–2 m/min, usingdifferent proportions of argon (Ar) as shrouding atmosphere and observed an improvement in wearand corrosion resistance. A detailed microstructural investigation shows a significant refinement ofthe microstructure (grain size) with the presence of lath martensite (Dutta Majumdar et al. 2010).The wear behavior of the surface treated component against hardened steel ball (of 3 mm diameter)at an applied load of 2 kg and at 15 numbers of revolution showed a marginal improvement in wearresistance of laser surface melted surface as compared to as-received SAE 52100, which is attributedto improvement in hardness due to grain refinement, refinement of carbides, and presence ofmartensite in the microstructure. The corrosion behavior of laser surface melted SAE 52100 steelswas evaluated by potentiodynamic polarization studies in a 3.56 wt% NaCl solution. From thecalculated values of corrosion parameters, it was observed that corrosion voltage (Ecorr) does notvary significantly with laser surface melting, however, there was a marginal reduction in corrosionrate (2.32 mm/year for laser surface melting in comparison to 2.60 mm/year for as-receivedsubstrate) and an improvement in critical potential for pit formation (Epit) (�270 mV (SCE) for


Page 12 of 32

laser surface melting in comparison to�430 mV(SCE) for as-received substrate). Tsay et al. (2001)studied the effect of laser annealing of aged 17-4 PH (AISI 630) steel (aged at 482 �C) using a 5 kWRofin–Sinar CO2 laser on its properties. Laser annealing led to an improved fatigue propertypredominantly because of the presence of residual compressive stresses.

Weld decay in austenitic stainless steels is caused by the precipitation of chromium carbides alonggrain boundaries when the material is subject to a thermal cycle as is the case in the welding process.For example, cooling rate involved in MIG welding is sufficiently low to form such carbides alongthe grain boundaries within the HAZs, leading to intergranular corrosion within the HAZs, calledsensitization. Laser surface melting of the HAZs dissolves these carbides, homogenizes the distri-bution of Cr through liquid state diffusion and convection. Then the rapid cooling is sufficiently highto avoid the re-precipitation of the carbides, thus desensitizing the material.

Magnesium and its alloys are widely used in automotive and aerospace application because of itslight weight. However, poor wear and corrosion properties are of serious concern for its applicationas structural components. Laser surface melting was found to be an effective tool to enhance wearand corrosion properties of magnesium based alloys (Dutta andManna 2011). Laser surface meltingof a magnesium alloy (MEZ) using a continuous wave CO2 laser was reported to improve itsmechanical and electrochemical properties (Dutta et al. 2003). Figure 12 shows scanning electronmicrograph of the cross section of the laser surface melted MEZ alloy, lased with a power of 2 kWand scan speed of 200 mm/min, which shows the presence of refined columnar grains growing

Fig. 12 Scanning electron micrograph of the cross section of the laser surface melted MEZ alloy, lased with a power of2 kW and scan speed of 200 mm/min

Fig. 13 Microhardness profiles of the laser surface melted MEZ as a function of vertical distance from the surface(Dutta et al. 2003)


Page 13 of 32

epitaxially from the liquid–solid interface (Dutta et al. 2003). The precipitates observed along thegrain boundaries of MEZ are Mg/Zr/Ce-rich compound (confirmed by energy dispersive spectros-copy). Furthermore, the melted zone-substrate interface is crack/defect-free and well compatiblewith practically no noticeable amount of heat-affected zone. Figure 13 presents the microhardnessprofiles of the laser surface melted MEZ as a function of vertical distance from the surface measuredon the cross sectional plane and shows that microhardness of the melted zone has significantlyincreased by two to three times (85–100 VHN) that of the substrate (35 VHN) primarily due to grainrefinement and solid solution hardening (Dutta et al. 2003). The average microhardness of thesurface melted zone was found to vary with laser parameters. Figure 14 compares the kinetics of pitformation in terms of cumulative area fraction pits as a function of time in a 3.56 wt% NaCl solutionfor as-received (plot 1) and laser surface melted MEZ (plot 2) lased with a power of 2 kWand scanspeed of 200 mm/min (Dutta et al. 2003). From Fig. 14 it may be noted that in as-received MEZ, theextent and rate of pitting are significantly reduced following laser surface melting, where, visible pitsare observed in laser surface melted MEZ only after 12 h of exposure. Furthermore, the pits in thelaser surface melted samples are both smaller in dimension and remain isolated compared to largerand interconnected pits in as-received MEZ. However, the rate of pitting is initially fasterand decreases after 30 h of immersion time in as-received MEZ. Schippman et al. (1999) reportedthe improvement of corrosion resistance of AZ91 substrate by grain refinement due to excimer lasersurface treatment of AZ91 substrate.

Several attempts have been made to improve corrosion resistance of Al-based alloys by lasersurface melting by grain refinement and microstructural homogenization (de Mol van Otterloo andDe Hosson 1994). Yue et al. (1999) surface melted 7075-T651 Al alloy using an excimer laser witha pulse energy of 8 J/cm2 to develop a melt layer free from any grain boundary precipitates, andhence, a significant improvement in inter-granular corrosion along with stress corrosion cracking.A similar response was also observed in excimer laser surface melted (using an excimer laser (KrF)with a wavelength of 248 nm) 7075-T651 aluminum alloys with a reduction in both the number andsize of constituent particles and a refinement of the grain structure resulting in improvement incorrosion resistance. Li et al. (1996) surface melted 2024-T351 aluminum alloy using a continuouswave CO2 laser and showed an improvement in both general corrosion and pitting corrosionresistance. Badekas et al. (1998) irradiated an Al-4.5%Cu alloy with an excimer laser. The residualstress of the treated surface changed from tensile to compressive with an improved microhardness.Gremaud et al. (1990) laser surface melted Al-Fe alloy (with Fe content varying from 0.25 to 8 wt%)

Fig. 14 Kinetics of pit formation in terms of cumulative area fraction pits as a function of time in a 3.56 wt% NaClsolution for as-received (plot 1) and laser surface melted MEZ (plot 2) lased with a power of 2 kW and scan speed of200 mm/min (Dutta Majumdar et al. 2010)


Page 14 of 32

using a 1.5 kW continuous wave CO2 laser and observed significant influence of process parameterson the morphology and degree of fineness of the precipitates/grains.

Hari Prasad and Balasubramaniam (1997) laser irradiated an A1-Li-Cu alloy (of nominal com-position 2.5 % Li, 1 % Cu, and 0.12 % Zr) with a Nd:YAG laser for the purpose of surfacemodification and studied its oxidation behavior at 450 �C in air by thermogravimetry and comparedit with the untreated specimen. Parabolic oxidation kinetics was observed for both the laser-treatedand untreated specimens. The laser-treated specimen exhibited improved oxidation resistance. X-raydiffraction analysis indicated that the major component of the scale was Li2CO3. The improvedoxidation behavior of the laser-treated specimenwas related to the compact oxide structure producedon its surface during oxidation. Wang et al. (2002) melted a series of Al-Si alloys with various Sicontents using a 2 kWCO2 continuous wave laser. It was found that laser treatment refined the grainsand altered the morphology of eutectic silicon from lath-like to coralline-like with a higher Si contentin Al matrix as compared to equilibrium Si content in Al. X-ray diffraction analysis illustrated thatthe lattice parameter of Al was reduced after laser melting. A series of Al-transition metal alloys(Al–Cu, Al–Si, Al–Zn, Al–Fe) were melted by Watkins et al. (1998) leading to an improvedhardness, wear and pitting corrosion resistance under optimum process parameters.

Fig. 15 Schematic illustration of (a) laser surface alloying with a continuous wave laser, (b) stage in alloy formation byintermixing of the substrate and alloying elements (Dutta and Manna 2011)


Page 15 of 32

Laser Surface Alloying

Laser surface alloying involves melting of a pre-deposited coating layer or simultaneously addedalloying ingredients along with a part of the underlying substrate to form an alloyed zone forimprovement of wear, corrosion, and oxidation resistance. Surface alloying may be achieved by thedeposition of coating materials on the surface prior to laser melting which may be termed aspre-deposition or by feeding of alloy ingredient simultaneously during melting of surface, whichmay be termed as co-deposition. Figure 15a illustrates the schematic of laser surface alloying witha continuous wave laser, consisting of three major components, namely a laser source with a beamfocusing and delivery system and a CNC controlled sweeping stage, where the specimen is mountedfor lasing, the provision for introducing controlled atmosphere and a powder delivery systemthrough which alloy powders are delivered (Dutta and Manna 2011). The process consists of threesteps: melting of alloying elements (pre-deposited or deposited simultaneously during processing),melting of substrate, intermixing of the substrate and alloying elements in molten stage, and a fastquenching forming the alloyed zone on the top of the substrate (Fig. 15b). Usually, a 20–30 %overlap of the successive molten/alloyed tracks is intended to ensure microstructural/compositionalhomogeneity of the laser treated surface. The parameters influencing the quality of the alloyed zonein terms of depth, chemistry, microstructure, and surface properties include incident power/energy,beam diameter/profile, interaction time/pulse width, pre or co-deposition thickness/composition,and concerned physical properties like reflectivity, absorption coefficient, thermal conductivity,melting point and density.

The main characteristic of this process is the possibility of producing a surface layer withextended solid solubility, a refined and homogeneous microstructure, and no restriction in theselection of alloying elements. However, attention needs to be paid to the relative melting temper-ature, vaporization temperature, and vapor pressure of the alloying elements and the substrate. Laserprocessing will be difficult if the added element vaporizes at a temperature lower than the substratematerial. For example, it would be difficult to surface alloy copper with zinc due to a lowertemperature of vaporization of Zn (900 �C) than the melting point of copper (1,100 �C) at 1 atm.

Laser surface alloying was reported to improve the structural properties of material like wear,corrosion, and oxidation resistance on a large numbers of systems (Dutta Majumdar and Manna2003). Laser surface alloying of Mo on AISI 304 stainless steel by plasma spray deposition of Moand subsequently, laser surface melting significantly improved the pitting corrosion resistance ofAISI 304 stainless steel substrate (Dutta and Manna 1999). However, optimization of process

Fig. 16 Potentiodynamic anodic polarization tests in a 3.56 wt% NaCl solution (both in forward and reverse potential)(Dutta and Manna 1999)


Page 16 of 32

parameters was essential for the formation of a homogeneous microstructure and composition forimprovement in pitting corrosion resistance and mechanical property (Dutta and Manna 1999).Potentiodynamic anodic polarization tests in 3.56 wt% NaCl solution (both in forward and reversepotential) showed that the critical potential for pit formation (EPP1) and growth (EPP2) weresignificantly (two to three times) improved to 550 mV(SCE) after laser surface alloying as comparedto 75 mV(SCE) in the substrate (Fig. 16) (Dutta and Manna 1999). EPP2 has also been found to benobler in as-lased specimens than that in the stainless steel substrate. The improvement in pittingcorrosion resistance of laser surface melting as compared to plasma spray deposited surface and thesubstrate is attributed to sealing of porosities (as observed after plasma spray deposition) andenrichment of surface with Mo, respectively. Erosion corrosion behavior of the laser surface alloyedAISI 304 stainless steel was compared to the as-received one by evaluating the kinetics of materialloss by circulating (at 750 rpm) the specimen in a medium containing 20 wt% sand in 3.56 wt%NaCl solution as a function of time. Figure 17 compares the kinetics of material loss in terms ofvariation of mass loss (Dm) with time (t) for AISI 304 stainless steel and laser surface alloyedstainless steel with Mo, SS(Mo) under erosive corrosion condition (Dutta and Manna 1999). Lasersurface alloying reduces the magnitude of Dm by over an order of magnitude and decreases thekinetics of erosive corrosion loss in SS(Mo) more than that in 304-SS, especially beyond 20 h.Therefore, it appears that the present LSA routine is capable of imparting an excellent superficialmicrohardness and resistance to corrosion and erosion–corrosion to 304-SS.

Oxidation is another serious mode of surface degradation that gets aggravated at an elevatedtemperature. Unlike electrochemical corrosion, oxidation occurs through dry reaction and solid stateionic transport through the oxide scale. In the past, several attempts have been made to enhanceresistance to oxidation by laser surface alloying, cladding, and similar LSE techniques. Laser surfacealloying of Ti with Si, Al and Si + Al (with a ratio of 3:1 and 1:3, respectively) was conducted toimprove the wear and high temperature oxidation resistance of Ti (Dutta et al. 2002; Dutta-Majumdar et al. 1999). Figures 18a–c show the (a) scanning electron micrograph of the top surfaceof laser surface alloyed titanium with silicon, (b) isothermal oxidation behavior showing thevariation of weight gain due to oxidation per unit area as a function of time for as-received (plot1) and laser surface alloyed titanium with (b) silicon, (c) 3Si + Al and (d) Si + 3Al and (c) wearbehavior in terms of depth of scratching (zw) with load (L) due to scratching of pure Ti and lasersurface alloyed Ti with Si, Al and Si + Al with a hardened steel ball. Figure 18a reveals the hyper-eutectic microstructure on the top surface of the alloyed zone consisting of uniformly distributedfaceted Ti5Si3 phase in a two-phase eutectic aggregate of a-Ti and Ti5Si3 (Dutta-Majumdaret al. 1999). The high volume fraction of the primary phase and degree of fineness of the eutectic

Fig. 17 Cumulative loss of material per unit area (Dm) due to erosion as a function of time (t) for as-received and lasersurface alloyed AISI 304 stainless steel with molybdenum (with a pre-deposit thickness of 250 mm and energy density of38.1 MJ/m2) (Dutta and Manna 1999)


Page 17 of 32

products signify complete dissolution and uniform intermixing of Si in the alloyed zone, and a rapidquenching experienced by the latter, respectively. Subsequent oxidation studies conducted at873–1,023 K showed that LSA of Ti with Si and Si + Al significantly improved the isothermaloxidation resistance (Fig. 18b) (Dutta et al. 2002). The effect of laser surface alloying of Si and Al onthe wear resistance of titanium was also studied. Figure 18c shows the variation of depth ofscratching (zw) with load (L) due to scratching of pure Ti and laser surface alloyed Ti with Si, Aland Si + Al with a hardened steel ball (Dutta et al. 2000). It may be noted that scratch depth varieslinearly with load for all the cases. The effect of load on scratch depth is more prominent at highernumber of scratching (�1,000) than that at a lower value of the same (¼ 25). Under comparableconditions of scratching, Ti undergoes the most rapid wear loss followed by that in laser surfacealloyed specimens. Laser surface alloyed sample with Si undergoes the minimumwear loss, which isattributed to the formation of hard Ti5Si3 precipitates in the alloyed zone (Dutta et al. 2000).

Sicard et al. (2001) reported enhancement of mechanical and chemical properties of aluminumalloys (AlSi7Mg0.3) by excimer laser assisted nitriding treatment. The special nitriding treatmentrequires an excimer laser to irradiate the sample placed inside the cell with 1-bar nitrogen pressureallowing expansion of the vapor plasma, dissociation/ionization of nitrogen by laser generated shockwave, and subsequent penetration (adsorption and diffusion) of nitrogen from plasma up to somedepth. While adequate laser fluence is required to create the plasma, but this fluence must be limitedto prevent laser-induced surface roughness. The resultant polycrystalline nitride layer is severalmicrometers thick and comprises pure AlN columns (200–500 nm thick) on top of equiaxed AlNgrains in the diffusion layer. Heat conduction calculations show that a 308-nm laser is better suitedfor greater nitride thickness, as it corresponds to a weaker reflectance value for aluminum. Tang andMan (2006) observed that laser surface alloying of manganese–nickel–aluminum bronze with Al

Fig. 18 (a) Scanning electron micrograph of the top surface of laser surface alloyed titaniumwith silicon, (b) isothermaloxidation behavior at 1,050 K showing the variation of weight gain due to oxidation per unit area as a function of time foras-received (plot 1) and laser surface alloyed titanium with silicon, Ti(Si) 3Si +Al Ti(3Si+Al) and Si + 3Al Ti(Si+3Al)and (c) wear behavior in terms of depth of scratching (zw) with load (L) due to scratching of pure Ti and laser surfacealloyed Ti with Si, Al and Si + Al with a hardened steel ball (Dutta et al. 2000, 2002; Dutta-Majumdar et al. 1999)


Page 18 of 32

was more effective in enhancing corrosion and cavitation erosion resistance in a 3.56 wt% NaClsolution than that after laser surface melting.

Manna and Dutta Majumdar (1999) attempted to enhance the wear and erosion resistance of Cuby laser surface alloying with Cr (electrodeposited with 10 and 20 mm thickness, tz). Total Cr content(XCr), Cr in the form of precipitates ( fCr ), and Cr in solid solution with Cu (CuCr) in the alloyed zonewas determined by energy dispersive spectrometry, optical microscope, and X-ray diffractiontechnique, respectively. Laser surface alloying extended the solid solubility of Cr in Cu to as highas 4.5 wt% as compared to less than 1 wt% equilibrium solid solubility. The microhardness of thealloyed zone was found to improve significantly (as high as 225 VHN) following laser surfacealloying as compared to 85 VHN of the base metal. Figure 19 shows the variation of averagehardness in the alloyed zone (Hv

av) as a function of CuCr, fCr, and XCr for laser surface alloyed copperwith chromium with a pre-deposit thickness of 20 mm (Majumdar and Manna 1999). From Fig. 19 itmay be noted that average microhardness of the alloyed zone increases with increase in totalchromium content, and hence, with solid solution, and with dispersoids. However, the contributionof solid solution is higher than dispersoids.

Laser Composite Surfacing

Metal matrix composite possesses an enhanced wear resistance greater than that of the base substrateor the matrix. However, volume fraction of reinforcement is restricted as a substantially higheramount of reinforcement reduces the toughness. Development of composite layer on the surface byconventional means is extremely difficult. Laser melting of substrate and subsequent feeding ofceramic particles into the molten matrix is an effective means of development of composite layer onthe surface through a process called laser composite surfacing. Several attempts have been made todevelop a composite layer on metallic matrix by this technique (Dutta and Manna 2011). Attemptswere made to develop sub-micron sized titanium boride dispersed surface on AISI 304 stainless steelsubstrate by melting the surface of sand blasted AISI 304 stainless steel substrate using a continuouswave CO2 laser and simultaneous deposition of a mixture of K2TiF6 (potassium titaniumhexafluoride) and KBF6 (potassium hexafloroborate) (in the weight ratio of 2:1) at a flow rate of4 g/min using Ar as shrouding environment (Dutta and Manna 2011). The microhardness of thesurface was improved 250–350 VHN as compared to 220 VHN of the AISI 304 stainless steel

Fig. 19 Variation of average hardness in the alloyed zone (Hvav) as a function of CuCr, fCr and XCr for laser surface

alloyed copper with chromium with a pre-deposit thickness of 20 mm (Majumdar and Manna 1999)


Page 19 of 32

substrate and found to vary with laser parameters. The improved microhardness of the compositelayer is attributed to both grain refinement and dispersion strengthening. However, laser parametersshould be precisely controlled to achieve an improved microhardness of the composite layer.A detailed wear behavior of as-received and laser composite surfaced AISI 304 stainless steelagainst hardened steel ball shows that rate of wear is lower in laser composite surfaced AISI304 stainless steel as compared to the as-received one. A detailed investigation of the surfacefollowing wear shows that the mechanism of wear was mainly a combination of adhesive andabrasive in as-received stainless steel, however, predominantly abrasive for laser composite surfacedstainless steel. Similar observation was also noticed in laser surface alloyed Al with titanium boride(Dutta and Manna 2011). In the past, several attempts were made to develop a ceramic dispersedmetal matrix composite surface on stainless steel substrate by laser surface alloying (Dutta andManna 2011). However, a poor wettability of ceramic particulates in metallic matrix necessitates theapplication of binder for improving the particle-matrix bond strength. Dispersion of carbide basedceramic particles (WC, Cr2C3, SiC, TiC) on austenitic stainless steel UNS S31603 was reported toimprove the cavitation erosion characteristics of the surface-modified specimens in 3.56 % NaC1solution considerably (Cheng et al. 2001). St-Georges (2007) studied the effect of laser surfacecladding of Ni-Cr-WC on the wear resistance of steel substrate (AISI 1020, Fe + 0.2C, wt%). In thepast, laser surface alloying of AISI 304 stainless steel with WC, Ni, and NiCr was reported todevelop a defect-free and homogeneous microstructure under optimum processing conditions(Anandan et al. 2012). It was observed that laser parameters played a crucial role in determiningthe microstructures of the alloyed zone. The average microhardness of the alloyed zone was found tobe improved to 700–1,350 VHN (with laser parameter) as compared to 220 VHN of as-receivedg-stainless steel. It was observed that application of low scan speed developed a graded microstruc-ture. Figure 20 shows the scanning electron micrographs (FESEM) of the top surface of laser surfacealloyed AISI 304 stainless steel subjected to laser surface alloying using a 5 kW fiber optics deliverycontinuous wave (CW) Nd:YAG laser (with a beam diameter of 3 mm) by simultaneous feeding of70WC-15Ni-15NiCr in the molten pool (at a powder feed rate of 10 g/s) with a power of 1.5 kWandscan speed of 0.008m/s using Ar as shrouding environment (at a flow rate of 5 l/min). From Fig. 20 itis evident that, in the microstructure, partially dissolvedWC in grain refined matrix with precipitatesof secondary carbides like M23C6 (M¼ Cr, Ni, Fe, and W) (which is confirmed by X-ray diffraction

Fig. 20 Scanning electron micrograph (FESEM) of the top surface of laser surface alloyed AISI 304 stainless steel with50WC-30Ni-20NiCr lased with a power of 1.5 kW and scan speed of 0.008 m/s


Page 20 of 32

analysis) and the eutectic mixture of austenitic steel (Fe–Ni–Cr) and M23C6 are present. Thedifferent carbides as detected by EDS analysis are labeled in Fig. 20. A detailed study of the effectof process parameters on the microstructures was reported elsewhere (Anandan et al. 2012). Fig-ure 21 shows the wear behavior of (a) as-received and laser surface alloyed AISI 304 stainless steelslased with a (b) 1.50 kW, 0.016m/s, (c) 1.50 kW, 0.008m/s, and (d) 2.00 kW, 0.008m/s, respectivelyagainst WC ball at an applied load of 10 N and under fretting motion (at a frequency of 10 Hz) interms of cumulative depth of wear with time. From Fig. 21 it is evident that there is a significantimprovement in wear resistance property of laser surface alloyed samples (plots b-d) as compared tothe as-received one (plot a). Furthermore, laser parameters also play an important role in determiningthe degree of wear. A careful observation of different curves in Fig. 21 also reveals that in the case ofas-received AISI 304 stainless steel, the kinetics of initial wear rate is higher as compared to lasercomposite surfaced state which is attributed to hardening of surfaces due to laser surface alloying,and hence, less degree of abrasive and fretting wear. Laser parameters play an important role indetermining the rate of wear. It is observed that the effect of scan speed is more significant in

Fig. 21 Wear behavior in terms of cumulative depth of wear with time for (a) as-received and laser surface alloyed AISI304 stainless steels lased with a (b) 1.50 kW, 0.016 m/s, (c) 1.50 kW, 0.008 m/s and (d) 2.00 kW, 0.008 m/s, respectivelyagainst WC ball at an applied load of 10 N and under fretting motion (at a frequency of 10 Hz)

Fig. 22 Coefficient of friction with number of cycles for (a) as-received and laser surface alloyed AISI 304 stainlesssteels with (b) 1.50 kW, 0.016 m/s, (c) 1.50 kW, 0.008 m/s, (d) 2.00 kW, 0.008 m/s, respectively against WC ball at anapplied load of 10 N and under fretting motion (at a frequency of 10 Hz)


Page 21 of 32

contributing to wear rate as compared to applied power. The wear resistance property is improvedwhen the scan speed is reduced which is predominantly due to enhanced hardness of the alloyedzone achieved because of the increasing area fraction of WC particles in the microstructure (plotb vis-à-vis plot c). Increase in applied power reduces the kinetics of wear at the initial state, however,under steady state, increased power does not cause any significant change in steady state wear value.The decreased wear rate at high power level is possibly due to the dissociation of WC at high powerlevel and its redistribution to homogenize the microstructure and formation of a larger volumefraction of secondary carbides (Anandan et al. 2012). Figure 22 shows the variation of coefficient offriction with number of cycles for (a) as-received and laser surface alloyed AISI 304 stainless steelswith (b) 1.50 kW, 0.016 m/s, (c) 1.50 kW, 0.008 m/s, (d) 2.00 kW, 0.008 m/s, respectively againstWC ball at an applied load of 10 N and under fretting motion (at a frequency of 10 Hz) obtained bywear testing. From Fig. 22 it may be noted that the coefficient of friction is very high initially for boththe as-received and laser surface alloyed samples which is attributed to a strong adhesive bondformed betweenmating surfaces. Following an initial high value, the coefficient of friction decreasespossibly due to dislodgement of the materials from the worn surface and subsequently, covering theinterfaces between meeting surfaces and acting as lubricant. In laser surface alloyed sample, thecoefficient of friction reaches the steady state value thereafter. However, in AISI 304 stainless thereis further increase in coefficient of friction from 0.5 to 0.55, following which it reaches the steadystate. The hike in coefficient of friction for the second time in as-received AISI 304 stainless steel isattributed to damage of the surface and its roughening due to fretting action. From Fig. 22 it is alsoobserved that coefficient of friction under steady state is significantly lower in laser surface alloyedsamples as compared to that of the as-received one, which is attributed to its high hardness (Anandanet al. 2012). In this regard, it is also relevant to note that increased scan speed reduces the coefficientof friction under steady state which is possibly due to an increased hardness at reduced scan speed.On the other hand, increase in power does not contribute significantly to the coefficient of friction atsteady state.

Table 1 summarizes the corrosion parameters of as-received and laser surface alloyed AISI304 stainless steels derived from potentiodynamic polarization study in a 3.56 wt% NaCl solution.From Table 1 it is evident that laser composite surfacing shifts the corrosion potential toward thenobler direction which is attributed to the presence of Cr and Ni in solution with AISI 304 stainlesssteel, hence, increasing the corrosion resistance properties. Application of very low scan speedincreases the area fraction ofWC in the matrix, whichmay increase the probability of galvanic attackat the interface, and hence, makes the matrix prone to corrosion. On the other hand, there issignificant reduction of corrosion rate when applying a higher scan speed. The comparison ofpotential for pit formation (Epit1) shows that Epit1 shifts toward nobler direction for laser surfacealloyed samples and it is more significant when applying a higher scan speed. Hence, it may beconcluded that the pitting corrosion resistance is improved due to laser surface alloying due to thepresence of more Cr and Ni in solution and microstructural homogenization. The presence ofcarbides might have detrimental influence in corrosion resistance property as corrosion resistance

Table 1 Summary of corrosion parameters of as-received and laser surface alloyed AISI 304 stainless steel derivedfrom potentiodynamic polarization study in a 3.56 wt% NaCl solution

S.No Laser power (kW) Scan speed (m/s) Ecorr V(SCE) Epit1 V(SCE) Corrosion rate

1 Base metal �0.937 �0.015 7.8 � 10�3

2 2.00 0.008 �0.844 �0.003 5.62 � 10�3

3 2.00 0.030 �0.513 0.032 2.687 � 10�3


Page 22 of 32

property is increased by reducing carbide content in the alloyed zone. A systematic study of theeffect of laser parameters on the corrosion behavior however shows that a maximum improvement incorrosion resistance is achieved when lased with a power of 2 kW and scan speed of 0.030 m/s.

In another effort, laser surface alloying of AISI 304 stainless steel was carried out using a 5 kWfiber optics delivery continuous wave (CW) Nd:YAG laser (with a beam diameter of 3 mm) bysimultaneous feeding of WC-Co-NiCr (in the weight ratio of 20:40:40) in the molten pool (at apowder feed rate of 10 g/s) and using Ar as shrouding environment (at a flow rate of 5 l/min).Figure 23 shows the scanning electron micrograph of the top surface of laser surface alloyed AISI304 stainless steel with WC–Co–NiCr lased with a power of 0.75 kW, scan speed of 0.012 m/s.From Fig. 23 it may be noted that the microstructure of the alloyed zone consists of the presence oflarge grains (of size ranging from 5 to 7.5 mm) with very fine sub grains with average grain size.25–.5 mm. Furthermore, there is the presence of very fine nano-size precipitates of carbidesdispersed randomly within the grains. Few carbide precipitates are also observed along the grainboundary region. The area fraction of carbide precipitated inside the grains were also reduce byapplication of higher power. The morphology of microstructure was changed from equiaxed tocellular, when applied power was higher. Detailed X-ray diffraction profile analysis of the alloyed

Fig. 23 Scanning electron micrograph of the top surface of laser surface alloyed AISI 304 stainless steel with WC-Co-NiCr lased with a power of 0.75 kW, scan speed of 0.012 m/s

Fig. 24 Microhardness profiles as a function of depth from the surface along the cross section of laser alloyed304 stainless steel lased with an applied power of 2.5 kW, scan speed of 12 mm/s (plot a); 2.5 kW, 16 mm/s (plot b);and 2.0 kW, 12 mm/s (plot c)


Page 23 of 32

zone shows that there are WC, W2C, M23C6 phases in austenite matrix, the mass fraction ofindividual phase was found to vary with laser parameter.

Figure 24 shows the micro hardness profile with depth from the surface of laser surface alloyed inAISI 304 withWC–Co–NiCr laser with a power of (a) 2.5 kW, scan speed .012 m/s; (b) 2.5 kW, scanspeed .016 m/s, and (c) 2.0 kW, scan speed .012 m/s. From Fig. 24 it may be noted that there is animprovement of hardness from 250 VHN to 320 VHN due to laser surface alloying. Furthermore,a maximum hardness is achieved on the surface which decreases gradually with depth from thesurface. Decrease in micro hardness is attributed to coarsening of micro structure with increase indepth and also due to the decrease inmass fraction of precipitated with depth. A comparison of microhardness values with process parameter shows that laser parameters do have marginal influence onthe hardness and its distribution. With an increase in scan speed and a decrease in applied power,there is a marginal improvement in microhardness value.

Laser Surface Cladding

Laser surface cladding is a technique, where, a high power laser beam is used as a source of heat tomelt a pre-deposited coating layer or simultaneously added cladding ingredients along with a partialmelting of the underlying substrate to form a clad zone with a minimum dilution at the interface forimprovement of wear, corrosion, and oxidation resistance (Dutta andManna 2011). In laser claddingprocess, the coating materials in the form of powder or wire is melted using a high power laser andsubsequently deposited on the surface of the substrate, leading to the development of depositedsurface with aminimum dilution at the interface. The characteristic features of laser cladding processinclude (a) development of a refined microstructure, (b) negligible heat affected zone, (c) a strongbonding at the interface due to chemical interaction of the clad layer with substrate and flexibility ofcladding on substrate of any shape and size.

Table 2 compares the characteristics of laser cladding with conventional weld surfacing andcoating by thermal spraying. From Table 2 it may be noted that being a high intensity, well focused,and controllable heat source, laser clad offers a defect free clad zone with a minimum dilution at theinterface and is an emerging technique for the development of clad zone with a higher productivity.

Table 2 Summary of thermal spraying, weld overlaying, and laser cladding processes

Coating process Thermal spraying Weld overlaying Laser cladding

Heat source Combustible fuel, electric arc orplasma arc

Combustible fuel, electric arc orplasma arc

High intensity laserirradiation

Bond strength Moderate, mechanical interlocking High, metallurgical bond High, metallurgicalbond

Coating structure Splat like, porous Dense, solidified Dense, refined

Thermal load tosubstrate

Minimum Very high Minimum

Dilution Nil Moderate to high Low

Heat affected zone Nil Wide Very shallow

Coating thickness 25 mm to few mm Several mm 50 mm to several mm

Productivity Low to high Low to very high Low to moderate

Cost Low to high Low to moderate Moderate to high


Page 24 of 32

Laser cladding on pure Al substrate was carried out using a continuous wave Nd:YAG laser anda coaxial powder injection system to develop composite coatings of 0–40 wt% Si and 0–30 wt% TiCparticles in Al matrix (Dubourg et al. 2005). The microstructure of the coatings was homogeneousand crack/pore free with uniform distribution of carbides. The addition of Si and TiC reinforcementincreased the bulk hardness and wear resistance of the coatings. Katipelli et al. (2000) have achievedconsiderable improvement in oxidation resistance of 6061 Al alloy by laser surface alloying withAl + TiC.

Aihua et al. (1993) developed a graded coating consisting of a Ni-clad Al bond layer, a 50 wt%Ni-clad Al + 50 wt% (A12O3-13 wt%TiO2) intermediate layer and an A12O3-13 wt%TiO2 over-layer (or ceramic layer) on an Al-Si alloy substrate by plasma spraying followed by laser surfaceremelting. While the plasma-sprayed coatings seem prone to spallation at the different depthsoriginating from macrocracks in the ceramic layer during thermal cycling, the laser-remeltedcoatings, containing a network of microcracks in the ceramic layer reveals a significantly reducedtendency of spallation at the interface between the intermediate and bond layer. Thus, laser remeltingimproved the spalling resistance of plasma-sprayed coating to thermal shock, though cracking due tothermal shock remains a problem to be solved. An aluminum oxide layer of 100 mm thickness hasbeen successfully coated on aluminum alloy 6061 and pure aluminum using a powder mixture ofsilicon oxide and aluminum by laser cladding using a continuous wave CO2 laser. A strongAI/A1203 interface was formed possibly due to an exothermic chemical reaction between SiO2

and A1 (Zhou et al. 1993). Uenishi and Kobayashi (1999) obtained Al3Ti dispersed intermetallic-matrix composite (IMC) on Al by laser surface cladding.

Process Parameters in Laser Surface Engineering

The quality of the surface engineered product is defined by the following parameters:(a) microstructural and compositional homogeneity, (b) surface topography, (c) residual stressdistribution, and (d) thickness of the treated layer. All the above mentioned parameters are depen-dent on the following variables:

(a) Type of laser used(b) Laser power(c) Beam size(d) Beam configuration from the laser cavity(e) Travel speed of the workpiece(f) Mode of alloy addition(g) Pre-treatment of the substrate

Types of Laser UsedDepending on the type of laser and wavelength desired, the laser medium could be solid, liquid orgaseous. Different laser types are commonly named according to the state or the physical propertiesof the active medium. Consequently, there are glass or semiconductor, solid state, liquid, and gaslasers. Gas based lasers can be further subdivided into neutral atom lasers, ion lasers, molecularlasers, and excimer lasers. Among the commercially available lasers, the lasers commonly appliedfor surface engineering include Nd:YAG laser, semiconductor laser (AlGaAs, GaAsSb, andGaAlSb), CO2 laser and excimer laser (XeCl, KrF). The intensity of the laser beam together with


Page 25 of 32

the interaction time dictates the interaction phenomena’s effectiveness. Absorption of laser radiationis also determined by the wavelength (l) of the incident laser beam. Figure 25 summarizes the effectof wavelength of laser on the absorptivity of different materials graphically. The materials in Fig. 25are summarized into three categories, i.e., metals 1 with full inner shells electron (Au, Ag, Cu, etc.),metals 2, i.e., transition metals (Fe, Ni, Cr, etc.), and insulator with the wavelength of laser (Fig. 2).From Fig. 25 it may be noted that for metallic materials with full inner shells electrons, absorptivitydecreases from 90 % to 5–7 % at a wavelength of 0.35 mm. For metals 2 (i.e., transition metals),absorptivity decreases gradually with increase in wavelength of laser. In insulators, absorptivitydecreases from 100 % to 4–5 % at a wavelength of 0.3 following which it remains the same up toa wavelength of 2.5 and again it starts rising sharply to 90 % at a wavelength larger than 5 mm.

Applied PowerLaser power necessary for surface melting of metallic materials is generally high due to reflectanceof the laser beam and high thermal conductivity. Reflectivity of the metal surface is actually relatedto electrical conductivity. For instance, it is difficult to surface melt aluminum or copper with a CO2

laser beam because these materials absorb little laser power. For metallic materials, laser power forsurface alloying should exceed 0.5 kW.

Beam DiameterThe beam diameter determines the power density on the specimen surface (power density is definedas the power divided by the cross sectional area of the laser beam). Typical values of power densityduring laser surface alloying are 10–103W/cm2. The beam diameter is difficult to measure. A simplemethod is to measure the distance of the focal point from the workpiece surface and relate it to thebeam size. Increasing the beam size by defocusing or other means decreases the heat input per unitvolume, reduces melt penetration, and increases melt width.

Beam ShapeThe energy distribution and shape of the beam is described by the beam configuration or beamprofile. Four beam profiles are made available by the lasers in the conjunction with beam deliverysystems. These include Gaussian, multimode, square (or rectangular), top hat (Fig. 4). It is seldompossible to produce Gaussian beam configuration (TEMP00) at high power although many highpower laser manufacturers claim it can be done. A Gaussian beam is most suitable for cutting andwelding applications rather than surface treatment because, being a “sharp tool,” it tends to vaporize

Fig. 25 Graphical presentation of variation of absorptivity of different materials with wavelength of laser


Page 26 of 32

and melt the substrate deeply. In contrast, multi-mode, top hat, and square profiles (“blunt tool”) arepreferred for surface alloying. These beam profiles offer alloyed casings with wider coverage ratesand uniform case depths.

Square and rectangular beam profiles are generated by using an optical integrator or scanner.Oscillating a Gaussian beam at high frequency using a rotational mirror in the beam delivery systemmay produce a square or rectangular profile because of the power.

Relative Speed Between the Laser Beam and Work-pieceThe travel speed of the workpiece during laser surface alloying is a very important parameter as itcontrols the diffusion time of the alloying elements, changes the melt depth, width, and profile, anddetermines the microstructures of surface alloys to a greater extent than other variables.

Mode of Alloy AdditionAlloying elements in the laser melt pool may be introduced by means of pre-deposition methods orcodeposition methods. Predeposition methods include electroplating, thermal spraying, vacuumevaporation, etc., which are done prior to laser melting. Co-deposition involves injecting powder,wire, or rod forms of alloys into the laser generated melt pool of the substrate. The one stepco-deposition method is more attractive than the two step deposition technique, which also offersthe advantage of real time control on the supply of alloying element. Pre-deposition variablesinclude thickness, particle size, composition, and method application.

Shield GasShield gas serves two functions in laser surface treatments: (a) it shields the heated/melt zone fromoxidation and (b) it protects the focusing optics from the fumes. Argon and nitrogen shield gases arenormally used and typical flow rates are around 20 l/min. The flow rate will depend on the method ofshielding and also diameter of nozzle that is being used to deliver the gas.

Applications of Laser Surface Engineering

Because of the directional nature of laser light, laser surface engineering may be applied to specificareas of a work piece. However, the main disadvantages of laser surface engineering with respect tothe other technologies are the high initial cost of the equipment and inability to apply on large areas.However, laser surface engineering is an environmentally friendly technique which is flexible andversatile in nature. In this regard, it is relevant to mention that in spite of the large number ofadvantages associated with laser surface engineering, the process is yet to be industrially popular-ized due to lack of available information on laser-matter interaction phenomena in differentmaterials and the change in materials, microstructures, and properties developed in the hardenedor alloyed/clad zones.

In this regard, it is relevant to mention that, among all the existing surface engineering techniques,laser surface hardening and laser surface cladding are two important techniques which are enjoyingmarket status for the development of wear and corrosion resistance surfaces for automotive andaerospace application. Notable examples of applications of laser surface engineering include thefollowing.


Page 27 of 32

Hardening of Steering Gear AssembliesThe first commercial production application of laser heat treating is the hardening of steering gearassembly (Ready and Farson Dave 2001). Originally designed as a batch furnace heat treatmentprocess, automobile power steering pumps became a subject for process improvement as the cost ofenergy made a 24-h furnace schedule expensive. Rather than heating 5 kg of ferritic malleable castiron, engineers at the steering gear division of a U.S. automotive company decided to producea localized wear-resistant surface on the inner bore of the pump housing, as protection againstexpected wear from the piston operating under heavier loads. Experiments with a defocused CO2

laser beam indicated that a series of five hardened tracks, strategically placed, would producesufficient wear resistance without part distortion. In practice, the beam from a kilowatt-level CO2

laser is directed through a rotating optic device to the inside bore of the pump housing. A disposable,piston-mounted, mirror is sequenced up and down so that the beam produces vertical stripes on thesteering gear bore. A large-diameter, low-power density spot of laser light produces the heat requiredto transformation harden a 2.5-mm-wide track to a depth of 0.35 mm.

Diesel Engine Cylinder LinersFuel used in railroad diesel engines contains abrasive residues such as vanadium which causesexcessive scuffing on the bore wall of malleable cast iron cylinder liners. One of the most logicalchoices to obtain the desired wear resistance was chrome plating to provide a smooth, tough, andchemically resistant, surface. Unfortunately, the chrome plating process has severe environmentalproblems, specifically with regard to treating the effluent from the process. Laser transformationhardening is an effective route to improve wear resistance of the surface with its capability indevelopment of precision hardened layer with a minimum heat affected zone and minimumdistortion of the substrate.

Turbine BladesHardening of blades for steam turbines, which can be eroded by water droplets during turbineoperation, is another area of application of laser surface hardening. Other approaches to increase thehardness of the blades, like flame hardening or cladding with a hard metal, like StelliteTM, hadvarious disadvantages, as indicated by Ready and Farson (2001). Laser surface hardening of turbineblades have been used in several countries for a number of years, as indicated by Ready andFarson (2001).

Stub AxlesThe selective laser hardening of large stub axles used for industrial dump trucks proved to be aneconomically viable alternative compared to other bulk hardening processes. A type AISI 4140medium carbon steel is used for the manufacturing of the ~45 kg components, with specified areasrequired to have high wear and fatigue resistance.

Application of Laser Surface Alloying/CladdingLaser cladding may be applied for the manufacturing of spare parts and maintenance and repair ofworn components and equipment. Laser surface cladding is used to produce surfaces which areresistant against abrasive, erosive and adhesive wear, wet corrosion, high temperature oxidation andcorrosion, etc. Typical applications of laser coatings are in shafts, rods and seals, valve parts, slidingvalves and discs, exhaust valves in engines, cylinders and rolls, pump components, turbine compo-nents, wear plates, sealing joints and joint surfaces, tools, blades, and molds.


Page 28 of 32

The future scope of research activities of laser surface engineering include (a) development ofmultifunctional graded surface for structural application, (b) nano-structuring of the surface toimprove mechanical and electrochemical properties, (c) development of nano-composite surface,and (d) possibilities in research activities for the application of hybrid coating techniques foroptimum microstructures and properties.

References

Adel KM, Dhia AS, Ghazali MJ (2009) The effect of laser surface hardening on the wear and frictioncharacteristics of acicular bainitic ductile iron. Int J Mech Mater Eng (IJMME) 4(2):167–171

Aihua W, Beidi Z, Zengyi T, Xianyao M, Shijun D, Xudong C (1993) Thermal-shock behaviour ofplasma-sprayed Al2O3-13 wt%TiO2 coatings on Al-Si alloy influenced by laser remelting. SurfCoat Technol 57:169–172

Amulevicius A, Mazeika K, Daugvila A (2000) Mössbauer studies of Fe-Si-C system structurechanges by laser and ultrasound treatment. J Phys D Appl Phys 33:1985–1989

Anandan S, Pityana S, Dutta Majumdar J (2012) Structure property-correlation in laser surfacealloyed AISI 304 stainless steel with WC + Ni + NiCr. Mater Sci Eng A 536:159

Ashby MF, Easterling KE (1984) The transformation hardening of steel surfaces by laser beams-I.Hypo-eutectoid steels. Acta Metall 32:1935–1948

ASM (1982) Metals handbook, 9th edn. Surface cleaning, finishing & coating, vol 5. ASM, MetalsPark

Badekas H, Koutsomichalis A, Panagopoulos C (1998) The influence of excimer laser treatment onan aluminium alloy surface. Surf Coat Technol 34:365–371

Benedek J, Shachrai L, Levin L (1980) Laser beam. Opt Laser Technol 12:247–253Bol’shepaev OY, Katomin NN (1997) Laser polishing of glass articles. Glass Ceram

54(5–6):141–142Chen SL, Shen D (1999) Optimization and quantitative evaluation of the qualities for Nd-YAG laser

transformation hardening. Int J Adv Manuf Technol 15:70–78Cheng FT, Kwok CT, Man HC (2001) Laser surfacing of S31603 stainless steel with engineering

ceramics for cavitations erosion resistance. Surf Coat Technol 139:14–24de Mol van Otterloo JL, De Hosson JTM (1994) laser treatment of aluminium copper alloys:

a mechanical enhancement. Scripta Metallurgica 30:493–498Dubourg L, Ursescu D, Hlawka F, Cornet A (2005) Laser cladding of MMC coatings on aluminium

substrate: influence of composition and microstructure on mechanical properties. Wear258:1745–1754

Dutta Majumdar J, Manna I (2003) Laser processing of materials. Sadhana 28:495–562, Parts 3 &4, June/August

Dutta Majumdar J, Nath AK, Manna I (2010) Studies on laser surface melting of tool steel – part I:surface characterization and its electrochemical behavior. Surf Coat Technol204(1321–1325):1326–1329

Dutta MJ, Manna I (1999) Laser surface alloying of AISI 304-stainless steel with molybdenum forimprovement in pitting and erosion-corrosion resistance. Mater Sci Eng A 267:50–59

Dutta MJ, Manna I (2011) Laser material processing. Int Mater Rev 56(5–6):341–388Dutta MJ, Mordike BL, Manna I (2000) Friction and wear behavior of Ti following laser surface

alloying with Si, Al and Si + Al. Wear 242:18–27


Page 29 of 32

Dutta MJ, Mordike BL, Roy SK, Manna I (2002) High temperature oxidation behavior of lasersurface alloyed Ti with Si, Al. Oxid Metals 57:473–498

Dutta MJ, Galun R, Mordike BL, Manna I (2003) Effect of laser surface melting on corrosion andwear resistance of a commercial Mg alloy. Mater Sci Eng A 361:119–129

Dutta-Majumdar J, Weisheit A,Mordike BL,Manna I (1999) Laser surface alloying of Ti with Si, Aland Si + Al for improved oxidation resistance. Mater Sci Eng A 266:123–134

Gremaud M, Carrard M, Kurz W (1990) Microstructure of rapidly solidified Al-Fe alloys subjectedto laser surface treatment. Acta Metallurgica Materiallia 38:2587–2599

Grum J, Kek T (2004) The influence of different conditions of laser-beam interaction in laser surfacehardening of steels. Thin Solid Films 453–454:94–99

Grum J, Slabe JM (2005) Nanoscale evaluation of laser-based surface treated 12Ni maraging steel.Appl Surf Sci 247:458–465

Hari PN, Balasubramaniam R (1997) Effect of laser surface modification on the oxidation behaviorof an Al-Li-Cu alloy. J Mater Process Technol 68:117–120

Heidkamp M, Kessler O, Hoffmann F, Peter M (2004) Laser beam surface hardening of CVDTiN-coated steels. Surf Coat Technol 188–189:294–298

Heitkemper M, Bohne C, Pyzalla A, Fischer A (2003) Fatigue and fracture behaviour of a lasersurface heat treated martensitic high-nitrogen tool steel. Int J Fatigue 25:101–106

Iordanova I, Antonov V, Gurkovsky S (2002) “Investigation of surface oxidation of low carbonsheet steel during its treatment with Nd:Glass pulsed laser. Surf Coat Technol 153:267–275

Katipelli LR, Agarwal A, Dahotre NB (2000) Interfacial strength of laser surface engineered TiCcoating on 6061 Al using four-point bend test. Mater Sci Eng A 289:34–40

Kennedy E, Byrne G, Collins DN (2004) A review of the use of high power diode lasers in surfacehardening. J Mater Process Technol 155–156:1855–1860

Li R, Ferreira MGS, Almeida A, Vilar R, Watkins KG, McMahonMA, SteenWM (1996) Localizedcorrosion of laser surface melted 2024-T351 aluminium alloy. Surf Coat Technol 81:290–296

Lo KH, Cheng FT, Man HC (2003) Laser transformation hardening of AISI 440C martensiticstainless steel for higher cavitation erosion resistance. Surf Coat Technol 173:96–104

Majumdar D, Manna I (1999) Laser surface alloying of copper with chromium – II. Improvement inmechanical properties. Mater Sci Eng A 268:216–226 (Part 1); ibid: 268, 227–235 (Part 2)

Mazumder J, Mohanty PS, Kar A (1996) Mathematical modelling of laser materials processing. IntJ Mater Prod Technol 11:193–252

Molian PA (1981) Laser Surface Heat Treatment of AISI 4340 Steel: a Microstructural Study. MaterSci Eng A 51:253–260

Molian PA (1989) In: Sudarshan TS (ed) Surface modification technologies-an engineers guide.Marcel Dekker, New York, p 421

Mura T (1982) Micromechanics of defects in solids. Martinus Nijhoff, The HagueNusser C,Wehrmann I,Willenborg E (2011) Influence of intensity distribution and pulse duration on

laser micro polishing. Phys Procedia 1:462–471Picraux ST, Follstaedt DM (1983) In: Narayan J, Brown WL, Lemons RA (eds) Laser-solid

interactions and transient thermal processing of materials, vol 751. North-Holland, New York


Page 30 of 32

Ready JF, Farson Dave F (2001) LIA handbook of laser materials processing. Laser Institute ofAmerica Magnolia Publishing, Orlando, pp 37–38, 190, 321, 329–330, 343, 359

Roy A,Manna I (2001) Laser surface engineering to improve wear resistance of austempered ductileiron. Mater Sci Eng A 297:85–93

Schippman D,Weisheit A, Mordike BL (1999) Short pulse irradiation of magnesium based alloys toimprove surface properties. Surf Eng 15:23–26

Schuocker D (1998) Handbook of the Euro Laser Academy, vol 2. Chapman & Hall, CambridgeSicard E, Boulmer-Leborgnel C, Andreazza-Vignolle C, Frainais M (2001) Excimer laser surface

treatment of aluminum alloy in nitrogen. Appl Phys A 73:55–60St-Georges L (2007) Development and characterization of composite Ni Cr + WC laser cladding.

Wear 263:562–566Tang CH, Cheng FT, Man HC (2006) Corrosion behavior of AISI 316 L stainless steel surface-

modified with NiTi. Surf Coat Technol 200:2606–2609Tobar MJ, Álvarez C, Amado JM, Ramil A, Saavedra E, Yáñez A (2006) Laser transformation

hardening of a tool steels: simulation-based parameter optimization and experimental results. SurfCoat Technol 200:6362–6367

Tsay LW, Yang TY, Young MC (2001) Embrittlement of laser surface-annealed 17-4 PH stainlesssteel. Mater Sci Eng A 311:64–73

Uenishi K, Kobayashi KF (1999) Formation of surface layer based on Al3Ti on aluminum by lasercladding and its compatibility with ceramics. Intermetallics 7:553–559

Wang XF, Takacs J, Krallics G, Szilagyi A, Markovits T (2002) Research on the thermo-physicalprocess of laser bending. J Mater Process Technol 127:388–391

Watkins KG, Liu Z, McMahon M, Vilar R, Ferreira MGS (1998) Impudence of the overlapped areaon the corrosion behaviour of laser treated aluminium alloys. Mater Sci Eng A 252:292–300

Yanez A, Alvarez JC, Lopez AJ, Nicolas G, Perez JA, Ramel A, Saavedra E (2002) Modelling oftemperature evolution on metals during laser hardening process. Appl Surf Sci 186:611–616

Yue TM, Wu YX, Man HC (1999) Laser surface treatment of aluminium 6013/SiCp composite forcorrosion resistance enhancement. Surf Coat Technol 114:13–18

Zhou XB, De Hosson J, Th M (1993) A reaction coating on Aluminium alloys by laser processing.Scripta Metallurgica 28:219–224


Page 31 of 32

Index Terms:

Laser composite surfacing 19, 22Laser surface alloying 16Laser surface cladding 24–25, 28Laser surface engineering 2, 27Laser surface melting (LSM) 11–12Laser transformation hardening 4, 6Polishing 11


Page 32 of 32

Documents

Laser Surface EngineeringLaser surface engineering is an emerging surface engineer-ing technique which involves tailoring of the microstructure and/or composition of the near surface