Quaternary diborides—improving the oxidation resistance of TiB2 ± z coatings by disilicide alloying

Abstract

To overcome the limited oxidation resistance of the emerging class of transition metal borides, we suggest within this study novel quaternary diborides, Ti-TM-Si-B2 ± z (TM = Ta, Mo), achieving the compromise between excellent oxidation resistance and requirements of hard coatings. Single-phase AlB2-type structured Ti-TM-Si-B2 ± z films (3–5 µm) are sputter-deposited from TiB2/TMSi2 targets. The Ti-Ta-Si-B2 ± z coatings exhibit 36 GPa in hardness, while maintaining strongly retarded oxidation kinetics till 1000°C. Ti-Mo-Si-B2 ± z coatings preserve a hardness up to 27 GPa, although outperforming all their counterparts by featuring outstanding oxidation resistance with 440 nm oxide scale thickness after 1 h at 1200°C.