Materials Science and Engineering

Biography

Biography: Lev Rapoport

Abstract

Friction and wear are the crucial problems affecting the life time of moving mechanical parts. The main goal of this work is to study: the evolution of the microstructure after friction with lubricant of four fcc metals (Ag, Cu, Ni and Al and the effect of stacking fault energy (SFE) on grain size and wear loss. Friction surfaces were carefully examined with a field emission scanning electron microscope. The cross sectional TEM lamellae were prepared from the pins using a focused ion beam (FIB). Cross-sectioning of the specimens was done in the longitudinal and transverse directions (parallel and perpendicular to direction of friction).Deformation twinning followed by a limited recovery within a surface of Ag led to formation of relatively thick top layer of ultra-fine equiaxial grains. Surface regions of Cu and Ni  samples consisted of inhomogeneous microstructure with wide range of grain sizes. With a depth lamellar structure was formed parallel to direction of friction for Ag, Cu and Ni. Subdivision of grains into subgrains with high dislocation density is clearly observed within a lamellar structure. Steady state values of grain size, ds and hardness, Hs after friction in lubricant conditions are explained by a balance between hardening and dynamic recovery in surface layers strongly depending on the g_SFE and temperature.

Typical HAADF STEM images of Ag presenting general view of deformation microstructure with a gradient of grain size. The white arrow shows direction of friction. Black arrows show the pores in top layers.