Use of repeated indenter sliding coupled with finite element computations to investigate the tribological response of nano-twinned 316L stainless steel

Abstract

The wear response of dynamically deformed 316 L austenitic stainless steels with varying percentages of compressive strain has been investigated. A relatively high strain rate of 80 s−1 has been used while compressing 316 L at engineering strains of 20 % and 80 %. Nano-indentation coupled with inverse algorithm approaches were used to extract the yield strength and strain hardening exponent of all the specimens. The strain hardening exponent decreased with deformation percentage while the strength enhanced, and these properties have been used in the finite element model (FEM) to find out the stresses and strains during repeated sliding to make scratches. A depth-sensing instrumented nano-indenter with a conical tip was used to make multiple scratches on all the specimens, and the damage in the form of scratch groove depth and width was characterized using a combination of profilometry and scanning electron microscopy. The results showed that the 80 %deformed sample exhibited the least wear damage evident in the form of thinnest scratch profiles, shallowest scratch depths and hence the least specific wear rate. However, after multiple cycles of sliding, undeformed and 20 % deformed samples showed similar wear rates. The friction coefficient decreased with an increase in the percentage deformation, but the dynamic friction coefficient for all the specimens saturated after about 30 passes of sliding. Cross-sectional scanning electron microscopic (SEM) imaging of the scratches revealed refinement and alignment of the microstructure along the shape of the bottom of the groove after repeated sliding. We discovered through the utilization of transmission electron microscopy imaging and selected area diffraction pattern that the region affected by scratching exhibited partial transformation of the initial austenitic phase into martensitic phase.