The primary objective of this research program is to develop a systematic method to determine the intrinsic physical properties of transition metal nitrides. The project uses a combination of experiments and density functional calculations, to determine intrinsic elastic properties, hardness, and oxidation resistance values for binary nitrides. Stress-free single crystal layers of unexplored nitrides are deposited using ultra-high vacuum reactive sputter epitaxy. Intrinsic mechanical properties and high temperature oxidation rates are measured and directly correlated to results from first-principles calculations. This correlation is used to develop a complete property dataset for all binary transition metal nitrides by classifying them according to their electronic structure and atomic bonding, using theoretically computed anisotropic elastic constants and oxygen replacement energetics and measured hardness and oxidation rates. The knowledge from binary nitrides is used to develop a quantitative model that relates composition of ternary and off-stoichiometric nitrides to mechanical properties, using both measured and calculated electron density of states and the composition-dependent Fermi level, which determines charge transfer and bond directionality. The project also explores first-level microstructural features by measuring mechanical properties in a model system with coherent interfaces and calculating strain-dependent shear moduli and dislocation energetics at the boundary between two nitrides.
This project is expected to provide a systematic understanding of the fundamental properties of all transition metal nitrides, based on their electronic structure. This understanding represents the knowledge base that has the potential to transform the multi-billion-dollar hard coating industry with a new coatings design approach. Thus, it provides the basis to accelerate discovery of hard, wear and corrosion resistant coatings and transform the evolutionary trial-and-error development of protective coatings into a Coatings-by-Design approach, resulting in rapid deployment of new coating materials for emerging applications including fuel-efficient jet engines and gas turbines, environmentally-friendly lubricant-free cutting tools, high-temperature concentrating solar power plants, and wind turbines. Graduate and undergraduate students are trained in this interdisciplinary collaborative research program which links two research groups with complementary experimental and computational expertise at two institutions. An integral part of the proposed effort is the development of an online virtual nitride-property tool including a research-community-driven database for intrinsic properties of transition metal nitrides relevant to hard protective coatings.
