Structure, mechanical and tribological properties of Ti–B–N and Ti–Al–B–N multiphase thin films produced by electron-beam evaporation

Abstract

Titanium-based multiphase ceramic coatings were deposited by electron-beam plasma-assisted physical vapor deposition, evaporating mixtures of Ti, TiB2, and (Ti0.6Al0.4)B2.19N1.47 material in Ar or Ar/N2 plasmas. All exhibited dense microstructures, however varying amounts of droplets or spits incorporated in the coatings produced could be observed for the different evaporation materials depending on their fabrication route. Results on the chemical composition of the coatings, obtained from glow discharge optical emission spectroscopy and Auger electron spectroscopy, showed no preferential evaporation of any element from the different evaporation source materials used, resulting in very similar compositions between evaporant and coating. Hardness values of up to 40 GPa were found for Ti–B–N based coatings containing both TiB2 and c-BN phases. Lower hardness values of around 30 GPa were observed for coatings deposited within the quaternary Ti–Al–B–N system, due to the presence of h-BN. Two micron thick Ti–Al–B–N coatings showed only minimal wear in pin-on-disk sliding wear tests against cemented tungsten carbide balls and, with increasing h-BN content, a slight decrease in “stick–slip” oscillation and friction coefficient. In contrast to Ti–Al–B–N coatings (whose impact adhesion was relatively poor) Ti–B–N coatings approximately 1.5 μm thick showed no coating spallation in impact tests against cemented tungsten carbide balls and consequently superior impact wear resistance.