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 Os1-xWxB2 (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 Os1-xWxB2 (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 Os1-xWxB2 (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.