Tensile-compression loading and pre-strain effects on the evolution of stacking fault tetrahedra, dislocation density, and free volume in crystal-amorphous thin film interface: A large-scale molecular dynamics study

Abstract

Molecular dynamics (MD) simulations are carried out to study the tensile-compression cyclic loading behavior and structural changes in Al (metal)-Cu50Zr50 (metallic glass) thin film interface model (TFIM). The model comprises of 2.88 million atoms, interactions between Al, Cu and Zr atoms are modeled using EAM (Embedded Atom Method) potential. The tensile-compression test cycles are performed at a temperature of 100 K and strain rate of 109 s−1 at two pre-strains (e = 0.033 and e = 0.2). The stress-strain curves reveal that during cycle-I tensile loading, TFIM exhibits yield strength of 266 MPa and peak strength of 760 MPa. Increase in the tensile pre-strain from e = 0.033 to e = 0.2 has no significant effect on the compressive yield stress. The deformation mechanism in Al is by slip by partial dislocation nucleation. Shockley partial dislocation density (2 × 1017–4.5 × 1017 m−2) is observed to be the highest of all the other types of dislocations. Complete SFT (stacking fault tetrahedra) is formed in Al region when strained beyond e = 0.033 and during compression cycles only. The number of SFT increases from 8 during tensile to 28 during the compression cycle indicating that compressive test assists the formation of SFT. Beyond the elastic strain, the collapse of (00120) and (0 2 8 2) polyhedral network is observed in Cu50Zr50 metallic glass region at distance of 25 Å from the interface resulting in the creation of low dense regions.