Atomic mechanisms for the fracture of AlMo0.5NbTa0.5TiZr refractory high entropy superalloy

Refractory high entropy superalloys (RHESs), known for their excellent high temperature performance, exhibit promising characteristics but are challenged by significant brittleness. Efforts to enhance plasticity through microstructure regulation have achieved only limited success, largely due to the unclear underlying fracture mechanisms of the superstructure. In this study, we systematically investigate the fracture mechanisms of the AlMo_0.5NbTa_0.5TiZr RHES from microscopic to electronic scales. Interestingly, both experimental and simulation results reveal that the ordered B2 phase demonstrates non-negligible plastic deformation capabilities during fracture, including deformation twinning and amorphization. Despite this, the fracture resistance of the B2 phase is lower compared to the A2/B2 interface and disordered A2 phase, even though the A2 phase shows less twinning and amorphization. Ab initio molecular dynamics simulations, combined with electronic behavior analysis, indicate that bonds involving Al and Zr in the B2 phase often exist in an anti-bonding state, making them more prone to breaking under load. This study provides deeper insights into the fracture mechanisms of the A2/B2 superstructure and its constituent phases at both atomic and electronic levels, offering a systematic approach to improving the fracture properties of such RHESs.