First-principles prediction of thermodynamic and mechanical properties of ZrCr2 under extreme conditions

Abstract

The cubic C15 and hexagonal C14/C36 phases of ZrCr₂ are typical phases formed in the newly developed Cr-coated Zr alloy cladding, and their formation and transformation significantly affect the system's service performance. However, their crystal structures and associated thermodynamic and mechanical properties under high temperatures and pressures are not fully elucidated. This work comprehensively explores the phase stability, thermodynamic, and mechanical properties of these three ZrCr₂ polymorphs over a temperature range from 0 to 2500 K and pressure from 0 to 30 GPa using first-principles calculations. The calculated lattice parameters agree well with experimental values. It is confirmed that C15 is the stable phase at low temperatures, C36 serves as an intermediate phase, and C14 is relatively prevalent at high temperatures. Above 10 GPa, C14 is no longer stable in the temperature range studied. Temperature and pressure significantly influence the thermodynamic and mechanical properties of the three ZrCr₂ phases. All three phases are ductile, but their ductility decreases as temperature rises and pressure decreases, accompanied by volume expansion, suggesting that ZrCr₂ formation during a loss of coolant accident could significantly increase the risk of cracking. These results advance our understanding of the thermodynamic and mechanical behavior of the ZrCr₂ phases under high temperatures and pressures, providing essential insights for designing high-performance Cr-coated Zr alloy cladding in nuclear engineering.