A study of recovery, recrystallization, grain growth and phase transformations during the annealing of cold-worked zircaloy-4

The annealing behaviour of 60% tube reduced Zircaloy-4 nuclear fuel cladding is examined over the temperature range 300 C to 1000 C. The annealing effects (recovery, recrystallization, grain growth, phase transformations, and texture changes) were monitored by Knoop microhardness measurements, optical metallography, x-ray texture, and thermoelectric power (TEP) measurements. For annealing temperatures up to 500 C, there was little change in crystallographic or mechanical anisotropy, the tubing becoming slightly softer due to recovery. From 500 C to 800 C, recrystallization and grain growth occurred, and recrystallization texture was formed and the tubing was more mechanically anisotropic than in the cold-worked condition. At temperatures above 800 C, there is a phase transformation (β-Zr forms at temperature and transforms to α' on cooling) and the tubing becomes more crystallographically and mechanically isotropic. (orig.)