The physical interpretation of the activation energy for hot deformation of Ni and Ni–30Cu alloys

Abstract

Hot compression tests on pure Ni and Ni–30Cu at 950–1150 °C and strain rates of 0.001–1 s⁻¹ were performed to identify the physical interpretation of the apparent activation energy (Q_d). For pure Ni, Q_d was constant and identical to that of the self-diffusion. However, for Ni–30Cu, it decreased steadily with strain. The value of Q_d was separated into thermal and mechanical parts. The thermal part was necessary to propel diffusion. For pure Ni, the mechanical part was zero at low and medium strain rates of 0.001–0.1 s⁻¹ and the self-diffusion was the controlling mechanism. However, at 1 s⁻¹, both the thermal and mechanical parts were needed to provide Q_d. For Ni–30Cu, Q_d was greater than that for the interdiffusion of Ni and Cu. The value of mechanical part decreased with increasing temperature and strain rate. Although the thermal parts for pure Ni and Ni–30Cu were nearly identical, the mechanical part for the latter was considerably higher. The difference was attributed to the strengthening effect of Cu atoms and the sluggish dynamic softening with respect to pure Ni.