Incompressibility and Hardness of Solid Solution Transition Metal Diborides: Os1−x Ru x B2

Interest in new ultraincompressible hard materials has prompted studies of transition metal diboride solid solutions. We have synthesized pure RuB2 and solid solutions of Os1−x Ru x B2. The mechanical properties of these materials are investigated using in situ high-pressure X-ray diffraction and Vickers hardness testing techniques. Both bulk moduli and hardness vary linearly with composition in accordance with Vegard’s law, whereas the differing behavior among end-members can be explained by relativistic effects, core electron density, and differences in the cohesive energy of the parent metals. The results provide a refinement of the rules previously reported for the design of new superhard materials.