Orientation-dependent hardness of Mo3Si studied by cube-corner nanoindentation

Abstract

Mo$$_{3}$$ 3 Si crystals having crystallographic out-of-plane orientations close to $$(0\,0\,1)$$ ( 0 0 1 ) , $$(0\,1\,1)$$ ( 0 1 1 ) and $$(1\,2\,3)$$ ( 1 2 3 ) were studied by nanoindentation to better understand the hardness anisotropy. The Mo$$_{3}$$ 3 Si precipitates were grown in a Mo-17.5Si-6B alloy and identified by electron backscatter diffraction. Pronounced material pile-up around the indents was observed, which causes inaccuracies in the projected contact area determined using the Oliver–Pharr method of around 30% compared to the real one. Based on the analysis of scanning electron micrographs, the projected contact areas and thus the hardness values were determined. To rationalize the observed pronounced orientation dependence of the hardness of Mo$$_{3}$$ 3 Si, we suggest an easy-slip-cutting model accounting for the available slip systems as well as the upward flow of material along the surface of the cube-corner indenter tip.