Role of interfacial interaction in the temperature-dependent fatigue behavior of Cr-coated Zr-4 alloy

Abstract

This study systematically investigates the temperature-dependent fatigue mechanisms of Cr-coated Zr-4 alloy, focusing on interfacial interactions under cyclic loadings. At 25 °C, channel cracks occurred in the brittle Cr coating, propagating into the Zr-4 substrate and inducing localized stress concentrations at the interface that accelerated fatigue failure. In contrast, at 400 °C, the Cr coating exhibited remarkable ductility, suppressing substrate plastic deformation and crack initiation at the interface. Crystal plasticity simulations demonstrated that the Cr coating reduced accumulated energy dissipation in the interfacial region at 400 °C, delaying crack nucleation. A critical discovery was the formation of a 300–500 nm-thick nanocrystalline Zr layer at the interface, triggered by dynamic recrystallization during cyclic loading. This layer featured refined grains (∼100 nm), which mitigated dislocation accumulation, redistributed strain, and enhanced interfacial cohesion. Furthermore, the presence of {$10\overline{1}2$} deformation twins within the nanocrystals synergized with slip, expanding the pathways for plastic deformation and consequently enhancing the plastic deformability of the nanocrystalline layer. The interplay of Cr coating ductility, grain morphology transition (columnar-to-equiaxed), and interfacial nano-crystallization synergistically improved fatigue resistance at 400 °C. These findings underscore the critical role of temperature-modulated interfacial deformation mechanisms in governing fatigue performance, providing a foundation for optimizing Cr-coated Zr-4 alloys in high-temperature nuclear applications.