Thermal stability and hardness of ReB2 type hexagonal OsB2 with the addition of W

This work attempts to understand the effect of W addition on microstructure, thermal stability, and hardness of ReB₂ type hexagonal osmium diboride (h-OsB₂). h-OsB₂ samples with W atomic concentration of (Os+W) from 0% to 30% were synthesized by mechanochemical method combines with pressure-less sintering. The XRD patterns of the as-synthesized powders indicate the formation of Os_1-xW_xB₂ (x?=?0, 0.1, 0.2 and 0.3) solid solution, which has a ReB₂-type hexagonal structure. After being high temperature sintered, part of the h-OsB₂ phase of the pure OsB₂ transformed to orthorhombic (o) phase, while the h-OsB₂ phase was maintained with the addition of W, which suggests that the thermal stability of the sample was remarkably improved. A macroscopically homogeneous structure with some pores can be found from all groups of the as-sintered Os_1-xW_xB₂ (x?=?0, 0.1, 0.2, 0.3) samples, with some B-rich areas distributed in the W doped samples. The lattice parameters of the Os_1-xW_xB₂ (x?=?0, 0.1, 0.2 and 0.3) solid solutions linearly decreased with the increase of the W concentration. The micro-hardness of the OsB₂ sintered samples is 25?±?2?GPa under an applied load of 0.49?N, which increased to 34?±?2?GPa, 38?±?2 and 37?±?2?GPa, respectively when the W concentration increased from 10, 20 and 30?at%. The increased hardness of the h-OsB₂ can be mainly attributed to the improvement of thermal stability with the addition of W.