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

Heat evolution of stress-induced structural disorder Delta H-s(epsilon) of a Zr55Al10Ni5Cu30 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 Delta T(epsilon) of deforming samples, where e is true strain. At transition from the linear to nonlinear viscoelasticity, i.e., a softening phenomenon, viscosity eta(epsilon) does not change consistently with Delta T(epsilon) but with Delta H(epsilon). 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 AT, which also influences Delta H-s. Because Delta T is determined by relationship between the power of the frictional heating and heat convection to the sample-surroundings, Delta H-s and eta can be positively controlled with varying thermal conductivity D of the surrounding materials, especially after the transition period. (c) 2007 Elsevier B.V. All rights reserved.