In-situ study on the microstructure and cracking behavior of annealed Cr coated Zr-4 alloy

•Deformation and cracking of Cr coating were studied by in-situ tensile tests.•450 °C annealed coating fractured in a brittle manner, similar to the as-deposited.•800 °C annealed coating was crack-free under tension due to recrystallization.•Improvement in interface deformation compatibility helps to hinder cracking. Uncovering the deformation and cracking behavior of Cr coating were essential for the integrity of accident-tolerant fuel (ATF) claddings during both operating and accident conditions. In the present work, the crack resistance of Cr coated Zr-4 alloys was improved by an annealing process. By using novel in-situ tensile tests, the 450 °C annealed Cr coating with enlarged columnar grains fractured in a brittle manner under tension, similar to the as-deposited. But the crack density of annealed sample was reduced. For the 800 °C annealed Cr coating with large equiaxed grains, despite the formation of thin brittle ZrCr2 interlayer, Cr coating was crack-free under even severe deformation, which benefited from recrystallization and grain growth at high temperature. Besides, the improvement in deformation compatibility between ductile Cr coating and Zr-4 substrate also played an important role in hindering initiation and propagation of surface cracks in Cr coating.