Change in Dynamic Restoration Rate of Nickel with Dynamic Recrystallization

Abstract

Hot compression tests of Ni were conducted in the range of temperature from 973 to 1223 K at strain rates from 3.3×10⁻⁴ to 8.6×10⁻³ s⁻¹. Single and multi peak behaviours associated with dynamic recrystallization were observed in flow stress-strain curves under the present experimental conditions. The dynamic restoration rate (r=−∂σ⁄∂t) and the work hardening rate (h=∂σ⁄∂ε) were measured as a function of strain by means of stress relaxation analysis. Values of r and h sharply increased at a strain of about 0.7ε_p (ε_p is the strain to the flow stress peak). They reached maximum values at ε_p and sharply decreased before the softening of flow stress came to an end. r and h values remained constant during steady states. These behaviours of r and h were plausibly interpreted as follows: (1) The production rate of dynamically recrystallized grains is maximum around a peak strain. (2) Newly formed fine grains are liable to be deformed preferentially since they are much softer than old grains around them.