Modeling the micromechanical behaviors of Zircaloy-2 alloy under large deformation

The orientation distribution of grains (so-called texture) and its evolution almost decisively govern the inservice performance of a polycrystalline material, especially for materials with low crystallographic symmetry. As an important nuclear material, zirconium and its alloys have a hexagonal-close-packed ( hcp ) crystallographic structure and multiple plastic deformation mechanisms. Among them, deformation twinning, reorienting the basal poles 85.22 degrees, could result in an abrupt and drastic change in the texture. As simulation plays a more and more important role in the design, manufacturing, and service of an endproduct, a reliable twinning model is essential for zirconium alloys. Two twinning models, namely the Twinning and De-twinning (TDT) and Predominant Twin Reorientation (PTR) models, were implemented in an Elastic Viscoplastic Self-consistent (EVPSC) framework with the thermal effect accounted for. The EVPSC-TDT and EVPSC-PTR models were applied to study the deformation behavior of a Zircaloy-2 slab under different strain paths. A predictive capability of the two twinning models was assessed by both the macro-mechanical behavior of stress-strain response and Lankford coefficient and the micro-mechanical behavior of texture evolution in terms of both pole figure and texture coefficient. It was found that the TDT model exhibits superior performance to the PTR model, especially in predicting texture development.

Automated summary

The orientation distribution of grains plays a decisive role in the performance of polycrystalline materials, especially those with low crystallographic symmetry. A reliable twinning model is essential for the design and service of zirconium alloys. In this study, two twinning models were implemented and evaluated, with the TDT model showing superior performance in predicting texture development.