Decomposition kinetics in Ti1-xAlxN coatings as studied by in-situ X-ray diffraction during annealing

The influence of the microstructure of the as-deposited cathodic arc evaporated Ti1-xAlxN coatings and, in particular, the influence of the intrinsic lattice strains on their thermal stability were investigated by in-situ synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments up to 850 °C. The microstructure of the as-deposited coatings was adjusted by the bias voltage (UB = −40 V, UB = −80 V and UB = −120 V) and by the [Al]/([Ti] + [Al]) ratio (0.4, 0.5 and 0.6) of the used Ti-Al targets. The microstructure evolution during annealing was described in terms of the phase composition of the coatings, the aluminium content, aluminium distribution and residual lattice strains in fcc-(Ti,Al)N. Independent of the deposition parameters ([Al]/([Ti] + [Al]) ratio and bias voltage), all coatings contained a mixture of fcc-(Ti,Al)N, fcc-AlN and w-AlN after annealing at 850 °C. The [Al]/([Ti] + [Al]) ratio was found to control the amount of fcc-(Ti,Al)N, whereas the bias voltage was mainly responsible for the relative amount of fcc-AlN and w-AlN. Finally, the interplay between lattice strains and the kinetics of the spinodal decomposition of fcc-(Ti,Al)N was illustrated.