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

The site-occupation behavior of Re in Mo5SiB2 (T2) 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.