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Sliding friction in electrodeposited nanocrystalline Ni Alloys : transitional behavior associated with grain size, sliding speed, and contact stress

Padilla, Henry A.; Prasad, Somuri V.; Battaile, Corbett C.; Kotula, Paul G.

Metallic materials in sliding contact typically undergo dislocation-mediated plasticity, which results in stick-slip frictional behavior associated with high coefficients of friction ({mu} > 0.8). Our recent work on two electroplated nanocrystalline Ni alloys reveal that under combined conditions of low stress and low sliding velocity, these metals have very low friction ({mu} < 0.3). The observed frictional behavior is consistent with the transition from dislocation-mediated plasticity to an alternative mechanism such as grain boundary sliding. Focused ion beam cross-sections viewed in the TEM reveal the formation of a subsurface tribological bilayer at the contact surface, where the parent nanocrystalline material has evolved in structure to accommodate the frictional contact. Grain growth at a critical distance below the contact surface appears to promote a shear-accomodation layer. We will discuss these results in the context of a grain-size dependent transition from conventional microcrystalline wear behavior to this unusual wear behavior in nanocrystalline FCC metals.

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TYPE Conference YEAR 2010
OSTI

The role of crystallography and nanostructures on metallic friction

Prasad, Somuri V.; Michael, Joseph R.; Battaile, Corbett C.; Kotula, Paul G.

In ductile metals, sliding contact is often accompanied by severe plastic deformation localized to a small volume of material adjacent to the wear surface. During the initial run-in period, hardness, grain structure and crystallographic texture of the surfaces that come into sliding contact undergo significant changes, culminating in the evolution of subsurface layers with their own characteristic features. Here, a brief overview of our ongoing research on the fundamental phenomena governing the friction-induced recrystallization in single crystal metals, and how these recrystallized structures with nanometer-size grains would in turn influence metallic friction will be presented. We have employed a novel combination of experimental tools (FIB, EBSD and TEM) and an analysis of the critical resolved shear stress (RSS) on the twelve slip systems of the FCC lattice to understand the evolution of these friction-induced structures in single crystal nickel. The later part of the talk deals with the mechanisms of friction in nanocrystalline Ni films. Analyses of friction-induced subsurfaces seem to confirm that the formation of stable ultrafine nanocrystalline layers with 2-10 nm grains changes the deformation mechanism from the traditional dislocation mediated one to that is predominantly controlled by grain boundaries, resulting in significant reductions in the coefficient friction.

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TYPE Conference YEAR 2010
OSTI

Application of diamond-like nanocomposite tribological coatings on LIGA microsystem parts

Journal of Microelectromechanical Systems

Prasad, Somuri V.; Scharf, Thomas W.; Kotula, Paul G.; Michael, Joseph R.; Christenson, Todd R.

The major focus of this study was to examine the feasibility of applying diamond-like nanocomposite (DLN) coatings on the sidewalls of Ni alloy parts fabricated using lithographie, galvanoformung and abformung (LIGA: a German acronym that means lithography, electroforming, and molding) for friction and wear control. Planar test coupons were employed to understand the friction mechanisms in regimes relevant to LIGA microsytems. Friction tests were conducted on planar test coupons as well as between LIGA-fabricated test structures in planar-sidewall and sidewall-sidewall configurations. Measurements were made in dry nitrogen and air with 50% relative humidity by enclosing the friction tester in an environmental chamber. In contrast to bare metal-metal contacts, minimal wear was exhibited for the DLN-coated LIGA NiMn alloy parts and test coupons. The low friction behavior of DLN was attributed to its ability to transfer to the rubbing counterface providing low interfacial shear at the sliding contact. The coating coverage and chemistry on the sidewalls and the substrate-coating interface integrity were examined by transmission electron microscopy, Automated eXpert Spectral Image Analysis, and electron backscatter diffraction on cross sections prepared by focused ion beam microscopy. The role of novel characterization techniques to evaluate the surface coatings for LIGA microsystems technology is highlighted. © 2009 IEEE.

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TYPE Journal Article YEAR 2009
ScopusOSTI

Characterization of the mechanical behavior of wear surfaces on single crystal nickel by nanomechanical techniques

Journal of Materials Research

Cordill, Megan J.; Moody, Neville R.; Prasad, Somuri V.; Michael, Joseph R.; Gerberich, W.W.

In ductile metals, sliding contact induces plastic deformation resulting in subsurfaces, the mechanical properties of which are different from those of the bulk. This article describes a novel combination of nanomechanical test methods and analysis techniques to evaluate the mechanical behavior of the subsurfaces generated underneath a wear surface. In this methodology, nanoscratch techniques were first used to generate wear patterns as a function of load and number of cycles using a Hysitron TriboIndenter. Measurements were made on a (001) single crystal plane along two crystallographic directions, <001> and <011>. Nanoindentation was then used to measure mechanical properties in each wear pattern. The results on the (001) single crystal nickel plane showed that there was a strong increase in hardness with increasing applied load that was accompanied by a change in surface deformation. The amount of deformation underneath the wear patterns was examined from focused ion beam cross-sections of the wear patterns. © 2009 Materials Research Society.

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TYPE Journal Article YEAR 2009
ScopusOSTI

Synthesis and tribological behavior of silicon oxycarbonitride thin films derived from poly(Urea)methyl vinyl silazane

International Journal of Applied Ceramic Technology

Cross, Tsali J.; Raj, Rishi; Prasad, Somuri V.; Tallant, David R.

A process for deposition of silicon oxycarbonitride films from poly(urea)methyl vinyl silazane (PUMVS) by spin coating precursor solutions onto a substrate, followed by polymerization, cross-linking and pyrolysis has been developed. The cross-linked polymer films (350 nm thick), deposited on variety substrates (e.g., silicon, sapphire, zirconia), were pyrolyzed in nitrogen or ammonia environments either in a hot isostatic press or in a tube furnace. Their microstructure was characterized using infrared and Raman spectroscopy. The tribological (friction and wear) behavior was evaluated in dry nitrogen and air with 50% relative humidity using a unidirectional linear wear tester in a ball-on-disk configuration. Wear surfaces, transfer films and wear debris were analyzed by scanning electron micrograph (SEM)/energy dispersive spectroscopy (EDS). © 2006 The American Ceramic Society.

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TYPE Journal Article YEAR 2006
ScopusOSTI
Results 51–100 of 123
Results 51–100 of 123