Structural effects of energy input during growth of Ti1 - xAlxN (0.55 ≤ x ≤ 0.66) coatings by cathodic arc evaporation

Effects of growth conditions on structural properties are investigated for the case of Ti-1 (-) xAlxN (0.55 <= x <= 0.66) deposition by cathodic arc evaporation. The evolution of residual stress, stress free lattice parameter, crystalline content, grain size, growth rate, and ion irradiation is studied as functions of the following parameters: Al content, process temperature, substrate bias potential, arc current, and magnetic field in front of the cathode. The evolution of residual stress is explained in terms of generation and annihilation of defects. Generation of defects, as indicated by increased compressive stress and stress free lattice parameter, is found to be directly connected to an increased ion energy caused by either higher bias potential or increased (estimated) average charge state of the depositing species. Annihilation of defects, indicated by decreased compressive stress and stress free lattice parameter, is observed as process temperature or arc current is raised, where the effect of arc current becomes stronger at higher magnetic field strength. It is concluded that the most likely explanation is thermal activation caused, directly or indirectly, by the applied process parameters. The results also show a strong decrease in grain size as either of the studied parameters is increased. The grain refinement is found to be correlated to an increase in the amount of wurtzite phase, in addition to the majority NaCl phase, as detected by X-ray diffraction. It is proposed that the probability of forming wurtzite becomes higher as either the energy available increases (due to thermal activation) or the energetic difference between the two phases becomes smaller (e.g., as the Al content is increased from x = 0.55 to x = 0.66). This explanation is consistent with the evolution of grain size and phase content as functions of process conditions or Al content, and is further supported by the results on residual stress evolution. (C) 2013 Elsevier B.V. All rights reserved.