Enhanced stress relaxation behavior via basal 〈a〉 dislocation activity in Zircaloy-4 cladding

This work evaluates the stress relaxation behavior of textured Zircaloy-4 cladding to understand how mechanical anisotropy influences pellet-cladding interactions. Uniaxial and biaxial stress relaxation tests are performed using full-tube axial tension and internal pressurization, respectively, aiming to achieve 0.25 %, 1 %, and 2 % equivalent strains in the cladding samples at a temperature of 300 °C. Internal pressure relaxation test results display enhanced stress relaxation compared to axial testing results, particularly for samples loaded beyond yield. Results of electron backscatter diffraction indicate increased deformation microstructure during loading and increased strain homogenization and recovery during relaxation for samples loaded via internal pressurization. Analysis indicates that the increased production and activity of basal 〈a〉 dislocations play a significant role in the enhanced relaxation measured in samples subjected to internal pressurization.