Mesoscale numerical investigation of the multi-cracking behavior of Cr coatings on Zr alloys

Abstract

Chromium (Cr)-coated zirconium (Zr) alloys are considered candidate materials for accident-tolerant fuel (ATF) claddings in light-water reactors. However, the multi-cracking behavior of the Cr coating under external loading might be a potential threat to the integrity of the coated claddings during operation. Comprehensive mechanistic research on this temperature- and microstructure-dependent microcracking behavior is lacking. In this study, a mesoscale numerical model was built to study the cracking behavior of the Cr coating on Cr-coated Zr alloys based on a crystal plasticity finite element model (CPFEM) combined with the extended finite element method (XFEM). The results indicated that the nucleation site of the initial coating crack is governed by the grain orientation distribution, and the magnitude of the local misorientation influences the initiation rate. The evolution and saturation of the coating cracks are determined by the grain characteristics and island length. Grain orientation dictates crack positioning, whereas island length determines whether cracks can propagate through the coating thickness. A method for estimating the saturated crack density in coatings based on the stress field distribution is proposed, and the saturation crack predictions are consistent with direct crack simulation results. The observed reduction in coating saturation crack density at 400 °C is directly attributed to enhanced substrate plasticity, which results in strain localization and significant crack tip blunting.