Flow state in molecular-dynamics-simulated deformed amorphous Ni0.5Zr0.5 -: art. no. 184205

Results are reported from molecular dynamics simulations about the deformation behavior of amorphous metallic Ni0.5Zr0.5 alloys near their glass transition temperature. Constant shear strain rate and constant shear stress deformations are analyzed. Stress-strain curves from constant shear strain rate deformations reveal different stages of deformation, first a regime with approximately linear stress-strain relation, then a transient regime with pronounced strain softening, and finally, for large strains, a nearly strain-independent flow stress region. The strong stress overshoot in the transient regime is ascribed to a delayed transition under steady-state deformations from the initial glassy state into a structurally and dynamically different one. This flow state shows a decreased viscosity, an increased potential energy per atom, and a loss of short-range order, the latter being deduced from the radial distribution functions. In the flow state, the self-part of the intermediate scattering function reveals an unchanged vibration spectrum of the system but a faster decay of density correlations compared to the starting structure. Creep curves from constant shear stress deformations show a nearly linearly increasing strain for moderate shear stresses and moderate deformations. The strain rate depends in a non-Newtonian manner on stress with an activation volume of 7-8x10(-29) m(3). Deformation simulation with large constant shear stress leads to an instability, identified as the transition into the flow state.