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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
Results 51–75 of 123
Results 51–75 of 123