Exploring the structural stability and mechanical properties of TM5SiB2 ternary silicides

Abstract

The improvement of the balance between ductility and strength is still a big dilemma for high-temperature materials. To improve the correlation between ductility and strength, we apply the ab-initio calculations to investigate the crystal structure, elastic properties and ductile-or-brittle behavior of TM5SiB2 ternary silicides. The calculated results show that Mo5SiB2, Cr5SiB2, W5SiB2 and Re5SiB2 are dynamically stable. In comparison to binary silicides, TM5SiB2 shows the strong volume deformation resistance and high elastic stiffness. In particular, TM5SiB2 exhibits better ductility. The calculated electronic structure reveals that the high elastic modulus of TM5SiB2 is attributed to the formation of TM‒B bond and B‒B covalent bond. However, the ductility of TM5SiB2 derives from the weak TM‒Si bond along the shear direction. Therefore, we propose that the adjustment of bond type, bond orientation and bond strength of ternary silicides by controlling the crystal structure is beneficial for improving the balance between strength and ductility.