Phase transformations in Ti1xA1xN thin films

• We report ageing phenomena in arc-deposited Ti1-xA1xN (0≤x≤0.66) thin films probed by X-ray diffraction, differential scanning calorimetry, four-point probe sheet resistance, and transmission electron microscopy measurements. Annealing Ti1-xA1xN films at 500-900°C results in residual stress recovery through annihilation of deposition-induced lattice defects, followed by spinodal decomposition at 900-1400°C into coherent nanometer-size domains of [NaCl]-TiN, and [NaCl]-AIN that eventually transform into the stable [wurtzite]-AIN phase. Kinetics measurements reveal activation energies of 2.0-2.9 eV for lattice recovery processes, and 2.9-3.5 eV for transformation processes, indicating grain boundary and defect-assisted segregation of Ti and Al. The composition was shown to have large influence on the thermal stability of Ti1-xA1xN films. The results show that the phase transformations are initiated at lower temperatures with increasing Al content.

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