Characterization of Strain Rate Sensitivity, Plastic Anisotropy, and Dislocation Content in Zircaloy-2

Abstract

Zirconium alloys are used broadly throughout the nuclear industry due to a combination of its mechanical properties, low neutron absorption cross section, and resistance to corrosion. Understanding the process of plastic deformation in these alloys is important both for predicting in-service behaviour in operating and accident conditions, as well as for optimizing the manufacturing of components. This thesis presents a body of work based around using advanced materials characterization techniques to study the deformation properties of Zircaloy-2, and how those properties are dependent on the rate of deformation and the history of previously imparted deformation.

This thesis is presented in a manuscript format, composed of four manuscript chapters. Chapter 3 presents a series of experiments using x-ray diffraction to investigate the effect of changes in the direction of applied strain on the deformation mechanisms and mechanical properties of Zircaloy-2. Chapter 4 introduces a technique for extending the analysis of conventional stress relaxation experiments to incorporate in situ x-ray diffraction data. The technique is applied to Zircaloy-2 to demonstrate a dependence of the strain rate sensitivity and activation volume on crystallographic orientation. Chapter 5 presents a newly developed Matlab computer code for calculating geometrically necessary dislocation density from electron backscattering diffraction data. The code is applied to measurements performed on the samples from Chapter 3, and validated against an established state of the art technique for measuring dislocation density via x-ray diffraction. Chapter 6 applies a polycrystalline plasticity model to the experimental data from Chapter 3 to quantify the dislocation density of the material and the work hardening parameters of the individual deformation mechanisms (the former of which is compared with experimental measurements performed in Chapter 5). Following the manuscript chapters, is Chapter 7, which summarizes the main conclusions of the manuscript chapters, discusses how they relate to one another, and provides suggestions for future work.