EXPERIMENTAL INVESTIGATION OF CREEP BEHAVIOUR OF ALUMINIUM ALLOY (LM25) AND ZIRCONIUM DIOXIDE (ZRO2) PARTICULATE MMC

8/20/2019 EXPERIMENTAL INVESTIGATION OF CREEP BEHAVIOUR OF ALUMINIUM ALLOY (LM25) AND ZIRCONIUM DIOXIDE (ZRO…

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International Journal of Mechanical Engineering and Technology (IJMET)Volume 6, Issue 8, Aug 2015, pp. 126-138, Article ID: IJMET_06_08_012Available online athttp://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=8ISSN Print: 0976-6340 and ISSN Online: 0976-6359© IAEME Publication

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EXPERIMENTAL INVESTIGATION OF

CREEP BEHAVIOUR OF ALUMINIUMALLOY (LM25) AND ZIRCONIUM DI-

OXIDE (ZRO2) PARTICULATE MMC

A. R. Sivaram

Assistant Professor, Department of Mechanical Engineering,

AMET University, Chennai, India.

K. Krishnakumar

Assistant Professor, EGS Pillay Engineering college,

Nagapattinam, India.

Dr. R. Rajavel

Professor and HOD, Department of Mechanical Engineering,

AMET University, Chennai, India.

R. Sabarish

Assistant Professor, Dept. of Mechanical Engineering,Bharath University, Chennai, India.

ABSTRACT

Aluminium metal matrix composites are one of the new materials used forvarious applications due to their less cost and light weight. Creep is the

tendency of solid material to slowly move or deform permanently under the

influence of stresses when subjected to high temperatures for long duration oftime. So creep is one of the major considerations while analyzing the

materials which are used for high temperature for long durations. Creepanalysis of composite material has a wide scope of research. In this paper, an

Aluminum composite material is produced by mixing high strength low weightmaterial with zirconium di-oxide for different proportions (0%, 3%, 6%, and9%) by using stir casting technique. In this paper experimental tests were

carried out to determine the creep strength for different proportions (0%, 3%,6%,9%) of Zirconium-di-oxide with LM25 by creep testing machine. SEM and

microstructure analysis was also done to see the distribution and presence of

ZrO2 particles in aluminium alloy.


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Experimental Investigation of Creep Behaviour of Aluminium Alloy (LM25) and ZirconiumDi-Oxide (ZrO2) Particulate MMC


Key words: Composite material, Aluminium alloy composite, SEM, Elapsedstrain.

Cite this Article: Sivaram, A. R., Krishnakumar, K., Dr. Rajavel, R. andSabarish, R. Experimental Investigation of Creep Behaviour of Aluminium

Alloy (LM25) and Zirconium Di-Oxide (ZrO2) Particulate MMC. International Journal of Mechanical Engineering and Technology , 6(8), 2015, pp. 126-138.

http://www.iaeme.com/IJMET/issues.asp?JTypeIJMET&VType=6&IType=8

1. INTRODUCTION:

Composite material is a material composed of two or more distinct phases (matrix phase and reinforcing phase) and has bulk properties significantly different from those

of any of the constituents. Many of common materials (metals, alloys, doped ceramicsand polymers mixed with additives) also have a small amount of dispersed phases in

their structures, however they are not considered as composite materials since their

properties are similar to those of their base constituents (physical property of steel aresimilar to those of pure iron) . Favorable properties of composites materia ls are high

stiffness and high strength, low density, high temperature stability, high electrical andthermal conductivity, adjustable coefficient of thermal expansion, corrosion

resistance, improved wear resistance etc. Metal Matrix Composites are composed of ametallic matrix (Al, Mg, Fe, Cu etc) and a dispersed ceramic (oxide, carbides) ormetallic phase( Pb, Mo, W etc). Ceramic reinforcement may be silicon carbide, boron,

alumina, silicon nitride, boron carbide, boron nitride etc. whereas MetallicReinforcement may be tungsten, beryllium etc . MMCs are used for Space Shuttle,

commercial airliners, electronic substrates, bicycles, automobiles, golf clubs and avariety of other applications. From a material point of view, when compared to

polymer matrix composites, the advantages of MMCs lie in their retention of strengthand stiffness at elevated temperature, good abrasion and creep resistance properties.Most MMCs are still in the development stage or the early stages of production and

are not so widely established as polymer matrix composites. The biggestdisadvantages of MMCs are their high costs of fabrication, which has placedlimitations on their actual applications. There are also advantages in some of the

physical attributes of MMCs such as no significant moisture absorption properties,non-inflammability, low electrical and thermal conductivities and resistance to most

radiations. Li Xu-Dong et al [1] have carried out a experimental investigation toestimate the reliable effect of prior corrosion state on fatigue micro-crack initiationand early stage propagation behaviour of aluminum alloy based on scanning electron

microscopy (SEM) in situ observation. Results indicated that multi-cracks initiationoccurred almost at the corrosion pits and the early stage of fatigue micro crack

propagation behaviour can be described by KI/KII-mixed mode. Ashley D. Spear et al[2] have carried out a experimental investigation to study the effect of alkalinechemical milling used for dimensionally reducing aluminum-alloy structures in terms

of total fatigue life and crack-initiation mechanisms. Chemically milled Al – Mg – Sispecimens exhibited a 50% reduction in average fatigue lives compared to

electropolished Al – Mg – Si specimens at comparable peak-applied loads abovemacroscopic yield. D. Q. Peng et al [3] have studied the effect of aluminum ionimplantation on the aqueous corrosion behavior of zirconium, specimens were

implanted with aluminum ions with fluence ranging from 1×1016

to 1×1017

ions/cm2

,using a metal vapor vacuum arc source (MEVVA) at an extraction voltage of 40 kV.


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A. R. Sivaram, K. Krishnakumar, Dr. R. Rajavel and R. Sabarish


The valence states and depth distributions of elements in the surface layer of thesamples were analyzed by X-ray photoelectron spectroscopy (XPS) and auger

electron spectroscopy (AES), respectively. LUO Yun-rong et al [4] have studied theEffects of Strain Rate on Low Cycle Fatigue Behaviors of High-Strength Structural

Steel. S. Huang et al [5] have carried out a experimental study to investigate Effects

of laser energy on fatigue crack growth (FCG) properties of 6061-T6 aluminum alloysubjected to multiple laser peening (LP) were investigated. LP experiments and

typical FCG experiments were performed on the compact tension (CT) samples. Theresults showed that compressive RS induced by LP can effectively decrease FCG rate

and increase FCG lives of CT samples. The fatigue behavior of aluminium alloy wasinvestigated under d ifferent conditions [6 – 9]. K. Mori et al [10] have studied the staticand fatigue strengths of mechanically clinched and self-pierce riveted joints in

aluminium alloy Sheets and compared with those of a resistance spot welded joint. D.Khireddine et al [11] have carried experimental tests to investigate the Low cycle

fatigue behaviour of an aluminium alloy with small shearable precipitates. V.Balasubramanian et al [12] have studied Influences of pulsed current welding and post

weld aging treatment on fatigue crack growth behaviour of AA7075 aluminium alloy joints. The role of microstructural variability on the fatigue behavior aluminum metalmatrix composites were studied by using different techniques [13 – 17]. In this paper,

an Aluminum composite material is produced by mixing high strength low weightmaterial with zirconium di-oxide for different proportions (0%, 3%, 6%, and 9%) byusing stir casting technique. In this paper experimental tests were carried out to

determine the creep strength for different proportions (0%, 3%, 6%, and 9%) ofZirconium-di-oxide with LM25 by creep testing machine. SEM and microstructure

analysis was also done to see the distribution and presence of ZrO 2 particles inaluminium alloy.

2. EXPERIMENTAL WORK

2.1. Stir casting process

Three steps are involved in this casting process are,

1.

Heating metal till it becomes molten

2.

Pouring the molten metal into a mould

3.

Allowing the metal to cool and solidify in the shape of the mould.

Stir Casting is a liquid state method of composite materials fabrication, in which adispersed phase (ceramic particles, short fibers) is mixed with a molten matrix metal

by means of mechanical stirring. Stir Casting is the simplest and the most costeffective method of liquid state fabrication. Liquid state fabrication of Metal MatrixComposites involves incorporation of dispersed phase into a molten matrix metal,

followed by its Solidification. In order to provide high level of mechanical propertiesof the composite, good interfacial bonding (wetting) between the dispersed phase and

the liquid matrix should be obtained. Wetting improvement may be achieved bycoating the dispersed phase particles (fibers). Proper coating not only reducesinterfacial energy, but also prevents chemical interaction between the dispersed phase

and the matrix. The aluminium alloy is casted in a stir casting machine as shown inFigure 2.1. When setting up the stir caster before an experiment the rotor was first

lowered into the crucible, its height was accurately adjusted to form a partial seal at

the exit such that it was held concentrically during stirring. Only a partial sealing ofthe outlet was allowed to ensure that torque pick-up from the rotor-crucible was


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negligible. An external plug attached to the batch casting trolley provided a full seal atthe exit. After the caster set-up, metal melted in an induction furnace was transferred

to a resistance holding furnace where it was stabilized at a temperature 20 °C abovethe liquidus temperature. The melt was then poured into the stir caster furnace which

had been preheated to 570 °C for A356 and to 595 °C for Al – 4% Si. Once the

temperature of the semi-solid melt (T ss) was stabilized, giving the desired f s, via theelement controllers, rotation of the stirrer was started. After shearing the alloy at the

specified shear rate and for the specified length of time, the rotor was raised, the plugon the batch casting trolley. Stir casting setup consists of digital control muffle

furnace and a stirrer made of graphite as shown in Figures 2.2 and 2.3 which isconnected to electric motor with speed range of 22 – 840 rpm. SiC particles wereartificially oxidized in air at 1000 °C for 150 min to form a layer of SiO2 on them and

improve their wet ability with molten aluminium. This treatment helps theincorporation of the particles while reducing undesired interfacial reactions. Batches

of the matrix alloy were melted in a clay-bonded graphite crucible of 1.5 kg capacityusing a small muffle furnace. The temperature of the alloy was first raised to about

800 °C and then stirred at 540 rpm using an impeller fabricated from graphite anddriven by a variable ac motor.

2.1.1. Synthesis of composite

The synthesis of composite is done by stir casting route. The parameters which areimportant in this work are stirrer design, preheating temperature for particulate andstirring speed. These parameters are d iscussed below.

2.1.2. Sti rrer design

It is essentially requires for vortex formation for the uniform dispersion of particles.

There is a no uniform dispersion of particles in case of no vortex formation.

2.1.3. Parti cl e preheati ng temperature

Preheating of particulate is necessary to avoid moisture from the particulate otherwise

there is chance of agglomeration of particulate due moisture and gases. Along this SiC particles are heated at 1000 °C to form a oxide layer on the SiC particles which make

it chemically more stable and by the oxide layer formation wet ability will increase so particles will get effectively embedded in aluminium matrix and there will be onlyless number of porosities in casting. After oxide layer formation preheating of

particulate is done on temperature of 400° C.

2.1.4. Sti rri ng speedIn this process, stirring speed was 240 rpm which was effectively producing vortexwithout any spattering. Stirring speed is decided by fluidity of metal speed, dispers ionof particulates are not proper because of ineffective vortex.


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Figure 2.1 Aluminium Stir casting Machine

Figure 2.2 Muffle furnace

Figure 2.3 Graphite stirrer

2.2. Materials

The Percentage of composition on each phase and the number of specimens required

are listed below. The specimens are as shown in Figure 2.4. The specimens are,a) 0.97 weight fraction of LM25 and 0.03 Weight fraction of ZrO 2,


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b) 0.94 weight fraction of LM25 and 0.06 Weight fraction of ZrO2,

c) 0.91 weight fraction of LM25 and 0.09 Weight fraction of ZrO2,

d) 100% weight fraction of LM25.

The heat-treated alloy has fairly good machining properties, but tools should

preferably be of high speed steel and must be kept sharp. A moderately high rate oftool wear may be expected. Liberal cutting lubricant should be employed. Aswith LM6, resistance to corrosive attack by sea water and marine atmospheres is high

with this alloy. A protective anodic film can be obtained by either the sulphuric orchromic acid process, but the grey opaque character of coatings of normal thickness

precludes their colouring in light shades for decorative purposes. There are threecommon heat treated conditions for LM25: TE (precipitation treated), TB7 (solutiontreated and stabilized, and TF (fully heat treated).

Figure 2.4 LM25 + 0% ZrO2, LM25 + 3% ZrO2, LM25 + 6% ZrO2, LM25 + 9% ZrO2

2.3. Microstructure analysisThe well-polished samples as shown in Figure 2.5 were then observed under anoptical microscope. Micrographs were taken with the help of CCD camera attached tothe optical microscope which is shown in Figure 2.6 and are further viewed on

computer with optical image analyzer software at magnificat ion of 200X.

Figure 2.5 Al +3%ZrO2, Al +6%ZrO2, Al +9%ZrO2

http://www.mrt-castings.co.uk/aluminium-diecasting-lm6.htmlhttp://www.mrt-castings.co.uk/aluminium-diecasting-lm6.html


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Figure 2.6 Optical Microscope

2.4. Creep Test

Creep occurs as the result of long term exposures to levels of stress that are below theyield strength of material. Creep always increases with temperature. The rate of this

deformation is a function of material properties, exposure time, exposure temperature,and the structural applied load. The creep testing machine and the testing of thespecimen in the creep testing machine is shown in Figure 2.7.

Figure 2.7 Creep Testing Machine


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3. RESULTS & DISCUSSIONS

3.1. Microstructure Analysis by Optical Microscope

The images of the micro structural characterization carried out by optical microscope

for the 3% , 6%, 9% weight fraction of the particle reinforced composite is shown in

Figures 3.1, 3.2, 3.3.

Figure 3.1 Optical Image of LM25 & 3%ZrO2



The grain size estimation for LM25 & 3%, 6%, 9% weight fraction of the particlereinforced composite is shown in Table 3.1.


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Table 3.1 Grain Size Estimation

ParameterLM25 & 3%

ZrO2LM25 & 6%

ZrO2LM25 & 9%

ZrO2

Field measured 2 1 1

Total area 0.88474 sqmm 0.44237 sqmm -Standard ASTM E1382 ASTM E1382 ASTM E1382

ASTM GRAINSIZE#

1.5 0.6 3.3

INTERCEPTS 286 85 3

MEAN Int.LENGTH

190.2425 256.6118 13969.6

STANDARDDEVIATION

0.117 - 5018.157

95%CI 0.229 - 8042.722

RA% 120.248 - 57.573

3.1.1. MICROSTRUCTURE ANALYSIS BY SCANNING ELECTRON

MICROSCOPE

The micro structural characterization carried out by scanning electron microscope for

the 3%, 6%, 9% weight fraction of the particle reinforced composites are shown inFigures 3.4 – 3.10.

Figure 3.4 SEM Image of LM25 & 3%ZrO2 for 250 k

Figure 3.5 SEM Image of LM25 & 3%ZrO2 for 250 SE


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From the micro structural analysis, it is found that the Zirconium di-oxide particles are of non-uniform size, irregularly shaped and randomly dispersed in the

alloy matrix. Agglomeration or clustering of the part icles is also observed, resulting in particle-rich and particle depleted regions. This material in homogeneity is generallyhigher in these types of composites than the unreinforced matrix alloy. This was

probably formed during composite fabrication, by reaction between the Zirconium di-oxide particles and LM25 matrix aluminum alloy. Moreover the particle clusters are

found to be more when compared with others. These results, also often reported for particle reinforced composites, are generally related to the intrinsic micro structural inhomogeneity of these materials, as regards to distribution.

3.2. Creep Test Analysis

Figure 3.11 Comparison on variation of displacement with respect to load for different proportions of particle reinforced composite.

160

165

170

175

180

185

190

195

200

0 2 4 6 8 10

D i s p l a c e m e n t

( m m )

Load(kg)

Pure LM25

LM25 & 3%

ZrO2


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From the Figure 3.11, it can be observed that, the creep strength is low for LM25& 3% of ZrO2. LM25 & 6% ZrO2 have same creep strength as that of pure LM25.

LM25 & 9% ZrO2 have the highest creep strength of all the samples. It is seen thatwith the increase in addition of ZrO2 with LM25 the creep strength of the composite

material increases. It is also seen that with the increase in load displacement increases.

4. CONCLUSION:

Based on the experimental investigations of the role of ZrO 2 particulates with LM25

aluminum alloy metal matrix composites, the following conclusions can be made.

1.

The Creep strength of the Aluminium alloy (LM25) reinforced with Zirconium di-oxide (ZrO2) particulate composites is generally higher than that of unreinforcedAluminium alloy and consistent with other studies on particle reinforced metal matrixcomposites.

2.

The beneficial effect of particle addition on Creep strength is more evident at lowerstress levels and there is no appreciable change in creep strength with increasingweight fraction of particulates at higher stress level.

3.

The Creep strength of the Aluminium alloy (LM25) - Zirconium di-oxide (ZrO 2) particulate composite, which may be attributed to its coarser grain size and inhomogeneity of particle distribution and this also consistent with micrographs of thecomposites.

4.

It is seen that with the increase in addition of ZrO 2 with LM25 the creep strength ofthe composite material increases. It is also seen that with the increase in loaddisplacement increases. Moreover, the weight fraction of above 3% particlereinforcement has no appreciable effect on creep properties.

In future, the results of this study can be compared with other combination of

matrix and reinforcement to develop cost effective material with respect to

applications.

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EXPERIMENTAL INVESTIGATION OF CREEP BEHAVIOUR OF ALUMINIUM ALLOY (LM25) AND ZIRCONIUM DIOXIDE (ZRO2) PARTICULATE MMC