Site-occupation behavior and solid-solution hardening effect of rhenium in Mo₅SiB₂

The site-occupation behavior of Re in Mo₅SiB₂ (T ₂) was studied both theoretically and experimentally, and the effect of Re on the solid-solution hardening of T₂ was investigated by taking into account the off-stoichiometry of the T₂ phase. Mo-Si-B quaternary alloys containing 1.4 at.% Re were produced using a conventional Ar arc-melting technique, and the cast samples were homogenized at 1800 °C for 24 h in an Ar atmosphere. High-resolution high-angle annular dark-field scanning transmission electron microscopy observations strongly suggest that Re preferentially occupies the Mo sites in the Mo-B layers of the T₂ unit cell, which was confirmed by the site-occupation behavior predicted by first-principles calculations. Nanoindentation measurements indicate that the hardness of the T₂ phase is affected by both the off-stoichiometry and Re addition.