Influence of stoichiometry on indentation-induced plasticity in CuZr glasses

Abstract

Plasticity in metallic glasses depends on their stoichiometry. We explore this dependence by molecular dynamics simulations for the case of CuZr alloys using the compositions Cu64.5Zr35.5, Cu50Zr50, and Cu35.5Zr64.5. Plasticity is induced by nanoindentation and orthogonal cutting. Only the Cu64.5Zr35.5 sample shows the formation of localized strain in the form of shear bands, while plasticity is more homogeneous for the other samples. This feature concurs with the high fraction of full icosahedral short-range order found for Cu64.5Zr35.5. In all samples, the atomic density is reduced in the plastic zone; this reduction is accompanied by a decrease of the average atom coordination, with the possible exception of Cu35.5Zr64.5, where coordination fluctuations are high. The strongest density reduction occurs in Cu64.5Zr35.5, where it is connected with the partial destruction of full icosahedral short-range order. The difference in plasticity mechanism influences the shape of the pileup and of the chip generated by nanoindentation and cutting, respectively.