Influence of Nb on the phase stability of Ti–Al–N

Metastable solid-solution Ti1−xAlxN thin films synthesized by plasma-assisted vapour deposition crystallize in the cubic NaCl structure with AlN mole fractions x ⩽ 0.7. Based on X-ray diffraction and ab initio calculations, we reveal that this critical value only slightly decreases to 0.69 with the addition of up to n = 0.125 mol fraction NbN to form cubic Ti1−x−nAlxNbnN. During annealing in vacuum to 1450 °C, the as-deposited single-phase cubic coatings decompose to form cubic Ti1−nNbnN and wurtzite AlN.