Development of New Generation OfCoatings with Strength-Ductility

Relationship, Wear, Corrosion andHydrogen Embrittlement Resistance

Beyond the Current Materials

Accomplishments till date

n As the structural scale reduces to the nanometer range,one accomplishesn High strengthn High interface–to-volume ration Enhancement of the interface-driven processes which

will extend the strain to failure and plasticityn Mechanical strength is controlled by the Hall-Pitcher

relationship σ =kd-1/2 + σo. A limitation of current inengineering materials is that gain in strength results in aloss of ductility

Accomplishments till date

n Reducing thestructural scale tothe nanometerrange one canextend thestrength-ductilityrelationshipbeyond thecurrent materialslimit

Accomplishments till date

n Nanostructured powders with increased strength andductility have been produced by plasma processing wherethe reactor vaporizes coarse meat particles; bycombustion synthesis where redox reaction takes place atelevated temperature, followed by quenching; and bymechanical alloying with gas atomization

n Cu/Nb composites (Han at al 1998) showed a completesuppression of the wire brittle fracture.

n Au-single crystals surfaces have dramatic effects on theyield strength

Accomplishments till date

n Erb et al. found that the passive current density ofnano crystalline Ni is higher than conventional Niwhich showed higher susceptibility to localizedcorrosion

n Erb et al., synthesized nanocrystalline Ni-Fe withincreased hardness, wear resistance and improvedcorrosion performance in terms of localized corrosion

Objectives for the Next decade

n Development of the next generation of protective coatingswith high corrosion, wear and erosion resistance, integrityunder thermal stress and complete inhibition of hydrogenpermeation and embrittlement

n Development of theoretical models which will explain howthe shape and the size of the nanostructure affect itsproperties and optimize the materials surface and bulkproperties

n Development of novel treatment for synthesis ofnanostructured materials.

n Development of monolayers and the nanometer rangecoatings in order extend the strength-ductility relationshipbeyond the current materials limits

n Development of procedures capable by using oxidenanoparticles to convert metals into material with wearresistance equal of that of the bets bearing steel. 

n Development of advanced scratch free resistant films, withhigh strength, wear resistance and ductility (Cu coatingsfor printing industry).

Objectives for the Next decade

Why electrodeposition ?

n Multilayer structures with nanometer-scale thickness havebeen produced by various deposition processes, such assputtering, molecular beam epitaxy, and chemical vapordeposition.

n While, versatile, the vacuum deposition techniques requireexpensive equipment; they cannot be used for fabricationof large structures with complex shapes and in most of thecases are difficult to control.

n Molecular beam epitaxy is well controlled depositiontechnique; however, this is not a volume productionmethod.

n Multilayer structures with specific textures can also be easilysynthesized using the chemical reduction andelectrodeposition processes

n For example, 3D nanostructured, crystallites can beprepared using this method by utilizing the interface of oneion with the deposition of the other.

n Also, the size of the particles can be controlled precisely bythe use of various micellar structures and lyotrophic phasesin the solution phase during deposition.

Why electrodeposition ?

Why electrodeposition ?

n Pulse and pulse reversal deposition of multilayerstructures with nanometer scale requires minimal capitalinvestment and can be applied to fabrication of parts ofany shape or size.

n The deposition rates at 10 nm layer level are about 0.05nm/h, however, the process is non-labor intensive and canrun automatically for long periods of time.

n Multi layer structures with specific textures can also beeasily synthesized using the electrodeposition process

A Novel Autocatalytic Reduction Process(ARP) for deposition of nanostructuredcomposites

n One step process

n No external current for deposition.

n Nanosized amorphous layers of Co-P, Ni-P, Co-Ni-P ,deposition of amorphous nanostructured multilayers ofNi-Mo-P, Ni-W-P, Ni-Ce-P, Ni-Mo-B can be deposited bycontrolling the concentration of the electroactive speciesin the electrolyte and by controlling the factors whichcontrol the deposition rate

Factors controlling the deposition rates

n Substrate pretreatmentn pH and temperaturen Concentration of the reducing agentn Presence of leveling agentsn Presence of dendrimersn Presence of any of the three liquid crystalline

phases exhibited by nonionic surfactantoctaethylene glycol monohexadecyl ether (OGME)

A Novel Pulse and Pulse Reversal Plating of Nickel-Iron,Co-Ni, Zn-Ni, Zn-Ni-P alloys and Zn-Ni-SiO2

Composites Procedures are Under Development atUSC

Why Pulse or Pulse Reversal Technique?n The deposit particle size is proportional to the crystal

growth rate while inversely proportional to the nucleationrate. decreases with increasing the nucleation rate.

n The crystal growth is proportional to the surface adatomconcentrations surrounding the site.

n The nucleation rate is enhanced by increasing theoverpotentials.

n Using Pulse technique, leveling agents, dendrimers andnonionic surfactant the nucleation rate dramaticallyincreases due to increased overpotential

Why Pulse or Pulse Reversal Technique?

n Since the surface adatom concentration is proportional to thesolution concentration in the vicinity of the surface one can expecta controlled pulse of less than milliseconds or micro seconds todeposit in the presence of additives in the electrolyte layers ofmetals, alloys and composites which have lower growth rate thatDC technique.

n Nanosized layers of Zn and Zn-Ni alloys are deposited bycontrolling, the average current , the pulse duration, theconcentration of Zn and Ni ions in the electrolyte and by controllingthe factors which control the deposition rate such as:n substrate pretreatmentn pH and temperaturen the presence of leveling agentsn the presence dendrimers, and nonionic surfactant octaethylene

glycol monohexadecyl ether (OGME).

Why Pulse or Pulse Reversal Technique?

n Pulse and pulse reversal technique can be used do depositmultilayer structures composed of hundreds (up to onethousand) layers (5-10 nm) of Ni//Ni-Zn-P//Ni//Ni-Zn-P; Ni-Mo//Ni-Cu-Mo; Ni-Mo-Si//Ni-Cu-Mo-Si; and Ni-Mo-Ti//Ni-Mo-Cu-Ti nanostructured composites

n The specific objectives should be:n to develop coatings with very large interfacial surface area

and with superior ductility, strength and hardness,n microstructural and mechanical characterizaton andn fundamental modeling of crack initiation and propagation.

Also, theoretical studies should be carried out which willcorrelate and tailor both strength (Koehler effect) and elasticmodulus by varying the number of layers the layer thicknessof nanostructured coatings

Under Potential Deposition of Metals (UPD)

n UPD occurs with a formation of monatomic layers atpotentials more noble the an the reversible Nernst potential

n UPD has been engineered at USC for Zn, Pb and Bi by usingthe work functions of these metals and the work functions ofthe substrates

n The underpotential shift (∆E) in volts when the monatomiclayers are formed is determined by the work functions inelectron volts of both metals.

n In situ polarization experiments showed that UPD formedmonoatomic layers of Pb, Zn, and Bi on steel surfaces inhibitcorrosion, hydrogen penetration and embrittlememnt due tolowering of the binding energy of the hydrogen adatoms onZn, Pb and Bi adsorbates

Under Potential Deposition of Metals (UPD)

Future work is necessary which willn Characterize the nature of the deposits plated when pulse

and DC technique at overvoltages between UPD potentialand Nernst potentials in the presence of leveling agents,dendrimers and nonionic surfactant octaethylene glycolmonohexadecyl ether (OGME). With an objective ton deposit monolayers of metals or alloys on large

surfaces, carbons or carbon nanotubes.n to increase the adhesion and the strength of the

deposits

Structural Studies

n In the layered andfilamentary nanostructures,the nature of the interfaceshas not been studied indetails and there is notmuch information in theliterature.

n The microstructure shouldbe investigated by highresolution TEM, scanningtunneling microscopy (STM)and neutron diffractiontechniques

The Jeol 100 CX II is a transmission electronmicroscope capable of accelerating voltagesfrom 20-100kv. It can provide magnification from100x to 600000x and a resolution of 0.2nm

Structural Studies

n The microstructural features should includen the nature and morphology of grain boundaries and

interfacesn grain size and morphologyn the nature of intergrain defects,n composition profiles across grains and interfaces and

identification of residual trapped species from processingn The electrodeposited multi layered nanostructures should be

studied in order to evaluaten composition profiles across interfacesn nature of defects andn coherency and thickness of interfaces

Mechanical Characterization Studies

n Hardness of the deposit defines the abrasion resistanceand general wear and tear qualities of the coating. Vickersand Knoop hardness tests are generally used to determinethe hardness. Knoop hardness should be used since this isideally suited for thin electrodeposits.

n The ductility, the resistance to fatigue damage, abrasion(wear) resistance, porosity, bending and cup impact testwill be done using standard methods.

n Coefficient of Sliding Friction will be determined bymeasuring the coefficient of sliding friction according to theCoulomb’s Law

n The adhesion test should be based on ASTM B571-97Standard Practice for Qualitative Adhesion Testing ofMetallic Coatings.

N R µ=

Mechanical Characterization Studies

n The ductility, the resistance to fatigue damage, abrasion(wear) resistance, porosity, bending and cup impact testshould be done using standard methods.

n The strength properties of multilayered depositssuggested in this proposal should be evaluatedtheoretically and experimentally.

n A mathematical model should be developed which willpredictn the dislocations as a function of the elastic constants

and the thickness of the multi layered nanostructuresand

n the susceptibility to plastic deformation and brittlefracture as a function of the deposit layer thickness