Boron nitride has generated much scientific interest due to the outstanding material properties of its cubic modification (c-BN) which can be compared with those of diamond, and to its metal (M) boron nitride compounds (MBN) which have extraordinary mechanical properties such as high hardness and high elasticity. This paper compares and discusses both of these thin film materials, concentrating in particular on their preparation and their mechanical properties in view of future applications as wear-resistant coatings.
There is a strong indication that the mechanism of c-BN film formation by commonly used physical vapour deposition (PVD) methods is based on recoil implantation of surface atoms into deeper layers. This process creates considerable compressive stress compromising the production of technologically valuable coatings of c-BN composition. On the other hand BN-based transition metal films can be made as hard as or even harder than c-BN films if suitable preparation methods are applied which promote nanometric grain sizes and a mixed phase composition. This paper discusses: (1) Ti implantation into hexagonal BN layers; and (2) co-sputter deposition from a Ti and Hf target, respectively, and from a BN target; and (3) Ti/BN multilayer interdiffusion. MBN films show good adhesion to metallic substrates such as HSS steels, and preliminary wear tests with a pin-on-disk tribometer indicate promising characteristics.
Bonding and chemical composition of the films were investigated by electron spectroscopy for chemical analysis (ESCA)-Auger spectroscopy, the structure and crystallite size by glancing angle x-ray diffractometry, and the hardness and elasticity by the nanoindentation technique.