Softening and heating behaviors during the nonlinear viscous flow in a Zr-based bulk metallic glass

Abstract Heat evolution of stress-induced structural disorder Δ H s ( e ) of a Zr 55 Al 10 Ni 5 Cu 30 bulk metallic glass (BMG) during compressive constant ram-velocity deformation in the glass transition region ( T g = 680 K) was deduced from in situ measurements of temperature change Δ T ( e ) of deforming samples, where e is true strain. At transition from the linear to nonlinear viscoelasticity, i.e., a softening phenomenon, viscosity η ( e ) does not change consistently with Δ T ( e ) but with Δ H s ( e ). Therefore, it is concluded that the stress-induced structural disorder triggered this softening phenomenon. The viscous frictional heating of the softened alloy brings about the increase in Δ T , which also influences Δ H s . Because Δ T is determined by relationship between the power of the frictional heating and heat convection to the sample-surroundings, Δ H s and η can be positively controlled with varying thermal conductivity D of the surrounding materials, especially after the transition period.