Abnormal grain growth in TD-nickel

Abstract

Characteristics of the coarse grain transformation occurring in TD-nickel 1 in. bar under certain conditions of deformation and annealing were examined. The transformation exhibits Avrami-type kinetics, with an activation energy of 250 kcal per mole. Characteristics of untransformed regions are like those of the as-received state. The transformed grain size increases with increasing deformation and decreasing annealing temperature. Transformed grains have a {7, 5, 15} 〈•5, •1•4, 7〉 annealing texture. The coarse grain transformation is significantly different from primary recrystallization in pure nickel. Its characteristics cannot be rationalized in terms of primary recrystallization concepts, but may be explained in terms of an abnormal grain growth description. This provides support for the suggestion, deduced from the previous electron microscopy investigation, that the coarse grain transformation in TD-nickel is abnormal grain growth rather than primary recrystallization. The analysis suggests an explanation for the effect of “thermomechanical history” on the deformation and annealing behavior of TD-nickel.