Tool steel coatings based on niobium carbide and carbonitride compounds

Although Physical Vapor Deposition (PVD) is extremely versatile in the palette of coating materials and substrates to which it can be applied, many potentially viable hard coating materials have yet to be explored for deposition on tool steels via PVD processing. Here one family of such coatings is explored: the niobium carbide and carbonitride system. By changing process variables, including bias voltage and working pressure, evaluating the mechanical properties through nanoindentation and correlating the results to microstructural observations by transmission electron microscopy, a preliminary survey of these coating materials and the preferred conditions for their production is presented. Under some conditions of deposition bias and pressure, niobium carbide can be produced with hardness and elastic modulus superior to titanium nitride films, reaching up to 37 GPa and 400 GPa, respectively, for coatings produced under deposition conditions that reduce intrinsic porosity. Nitrogen substitution for carbon leads to intermediate carbonitride compositions with mechanical properties that depend roughly linearly on composition, permitting a degree of tunability of the coating properties.