Localized plastic flow, anisotropic mechanical properties and crystallographic texture in Zircaloy sheet

Abstract

Mechanical properties of Zircaloys, like many other hexagonal close-packed (hcp) metals, are sensitive to the textures developed during fabrication processes. These alloys exhibit highly anisotropic mechanical properties, a thorough knowledge of which is needed for selecting materials with good formability characteristics as well as for the predictability of inservice behavior. This paper describes texture analysis performed on recrystallized Zircaloy-4 sheet using x-ray diffraction techniques, crystallite orientation distribution function (CODF) analysis using pole figure intensity data, predictions on mechanical anisotropy and formability using CODF and appropriate plasticity models, and experimental characterization of mechanical anisotropy using grid technique. In addition, the localized plastic flow analysis, which gives the upper limits on the strains that the material can withstand without failure, is also considered. The texture based model predictions of the anisotropy parametersR andP and the formability parameterB show an excellent agreement with the experimental measurements. Analysis of the true stress-strain behavior indicates that necking in this material starts much earlier than the maximum load, and the localized plastic flow analysis gives the maximum strains along the rolling (RD) and transverse (TD) directions of the sheet that the material can be subjected to without the initiation of diffuse or local necking. The material parameters obtained in these analyses control the formability during thermomechanical processing, and the inservice behavior of the material.