Phase transition and properties of Ti-Al-N thin films prepared by rf-plasma assisted magnetron sputtering

Pseudobinary (Ti1-xAlx)N films were synthesized by a new inductively combin ed rf-plasma assisted planar magnetron sputtering method. From X-ray diffra ction measurement, the deposited (Ti1-xAlx)N films were identified as havin g the B1 structure up to 50 mol% Al (x = 0.5). In the range from x = 0.6 to x = 0.7, two phases with the B1 and B4 structures were observed. These res ults suggest that the critical composition for the phase change from B1 to B4 structure is located between 50 mol% Al and 60 mol% Al. The critical com position decided experimentally shows a discrepancy with the theoretically predicted value (65 mol% Al), which may arise from a somewhat high substrat e temperature (450 degrees C) in this study. Oxidation resistance increases with increasing the Al content in the (Ti1-xAlx)N films up to 70 mol% Al, irrespective of coexistence of the B1 and B4 phases in the (Ti1-xAlx)N film s with x = 0.6 and x = 0.7, while both the hardness and Young's modulus sho w a maximum value, respectively. Thus, it is indicated that the existence o f the (Ti1-xAlx)N films with the B1 structure is quite effective for improv ing the oxidation resistance, and the appearance of the B4 phase in the pse udobinary nitride films degrades mechanical properties such as the hardness and Young's modulus. (C) 1999 Elsevier Science S.A. All rights reserved.