Deposition and characterisation of TiAlBN coatings produced by direct electron-beam evaporation of Ti and Ti-Al-B-N material from a twin crucible source

TiAlBN coatings were synthesised by evaporating Ti and hot isostatically pressed TiAl0.68B3.67N2.44 material from a twin crucible sourer: in an Ar plasma at 450 degrees C. A combination of optical emission spectroscopy and partial pressure control was utilised to control the Ti and TiAl0.68B3.67N2.44 evaporation rates and hence the Ti-Al-B-N composition in the coating. The goal of this investigation was to study the influence of composition on the structural and mechanical properties of these coatings. The influence of the Ti/B ratio (in the range of 0.34-2.31) in TiAlBN coatings containing approximately 12 at.% Al and 40 at.% N (calculated from glow discharge optical emission spectroscopy data) is described. All coatings, consisting of two hard phases TiB2 and TiN, and a soft hexagonal BN phase, showed dense structures and a decrease in roughness values with increasing Ti/B ratios. The hardness and elastic modulus increased with increasing Ti/B ratios from 0.34 to 2.31 up to 37 Gpa and 320 GPa, respectively. Coatings with Ti/B = 1.73-2.31 showed a twofold increase in wet cutting performance compared to commercially available TiN and TiAlN. However, due to the rather low amount of Al in the TiAlBN coatings no significant improvement in dry cutting compared to TiN was observed. (C) 1999 Published by Elsevier Science Ltd. All rights reserved.