Ti1−xAlxN coatings by Reactive High Power Impulse Magnetron Sputtering: film/substrate interface effect on residual stress and high temperature oxidation

To withstand oxidation at a temperature≥850 °C, an optimized Ti1−xAlxN coating was grown via reactive High Power Impulse Magnetron Sputtering (HiPIMS) technology on three identical Ti0.48Al0.48Cr0.02Nb0.02 billets. Different substrate surface pre-treatments were designed to increase performance: i) mechanical polishing, ii) mechanical polishing combined with a strong plasma etching, and iii) mechanical polishing coupled to both a weak plasma etching and a Ti1−yAly metallic interlayer deposition. Then, all the specimens were cyclically heat treated up to 200 cycles at 950 °C, using a Burner Rig (BR) facility. The chosen Ti1−xAlxN/substrate interface architecture considerably influenced average compressive residual stress (Sres) and adhesion of just deposited films. Moreover, it was possible to identify a clear relationship between Sres behavior and each coating comportment after BR tests. It became clear that the weak plasma etching/ Ti1−yAly interlayer match helped improving the system stability (i.e. very low average residual stress thermal relaxation) thus guarantying high temperature oxidation resistance.