We design and characterize new materials to optimize both incompressibility and hardness.
Superhard materials are used in many applications, from cutting and polishing tools to wear-resistant coatings. Diamond remains the hardest known material, despite years of synthetic and theoretical efforts to improve upon it. Designing new superhard materials are not only of great scientific interest, but also could be very useful. The Tolbert group in collaboration with the Kaner group has demonstrated that valence electron density and bond covalency can be used as design parameters for creating ultra-incompressible, superhard materials.
In designing new superhard materials, we want to optimize both incompressibility and hardness. Hardness has been the traditional gauge of a material's mechanical strength and the relationships between hardness, shear strength, incompressibility, and Young's modulus have been studied extensively. Understanding the connections between these properties is an important aspect of predicting new, potential superhard materials. Through hardness tests and diffraction measurements, OsB2 has been determined to be an ultra-incompressible, hard material, whose incompressibility could rival c-BN, but can only scratch sapphire. ReB2 has been shown to scratch diamond with a high bulk modulus of 360 GPa and is able to support a remarkably high differential stress.
This combination of properties suggests that these dense metal borides may find application in cutting when the formation of carbides prevents the use of traditional materials such as diamond.