Molecular Dynamics Simulation of Nano-indentation Studies on Zr-based Metallic Glass Matrix Composites

Abstract

In the present investigation molecular dynamics (MD) simulations of nano-indentation on Zr50Cu50, Zr50Cu30Al20 metallic glasses (MGs) and Zr50Cu50, Zr50Cu30Al20 glass matrix composites (GMCs) with 14%, 30% and 50% crystalline volume fraction have been studied. Nano-indentation tests are conducted at varying strain rates (2.5 × 109 s-1, 2.5× 1010 s-1, 1.25 × 1011 s-1 and 2.5 × 1011 s-1) and temperatures (100K, 300K and 500K) to investigate the deformation behaviour and response on the mechanical properties such as yield point, maximum load, and hardness through load-displacement plots. Also, the effect of crystallite distribution (single-spherical and multi-spherical) and shape (spherical and cylindrical) on the load-displacement response have been studied. Structural analysis during deformation has been done by centro-symmetry parameter (CSP) studies. It is found that all curves have linear elastic behaviour and non-linear plastic behaviour with load varying linearly with displacement of the indenter following Hertz’s contact theory in the elastic region. After the first “pop in” or initiation of plastic deformation, serrations are observed to be irregularly spaced in amorphous alloys because of their short range order arrangement of atoms. With compared to that of MGs. This may be due to delay in load transfer from amorphous phase to crystallites which can be observed in the atomic position snapshots of CSP studies. The increase of temperature leads to the decrease in the yield point and maximum loads in MG and GMCs. This may be due to the fact that atoms are displaced far away and so the interatomic interaction force decreases causing softening of the alloy. Studies on the effect of crystallite distribution show that single-crystallite (14%) reinforced composite exhibits higher strength as compared to multi-spherical crystallite composite (14%). Also, studies on the shape of the crystallite reveal that composite reinforced with cylindrical shaped crystallites (14%) offer better strength than that of the composite with spherical crystallites (14%). From this study, it can be concluded that GMCs have better strength compared to MGs. Zr50Cu50 with 30 % crystalline volume fraction has better strength and in case of Zr50Cu30Al20 GMC with 50% crystalline volume fraction exhibits superior properties.