Thermal-induced blister cracking behavior of annealed sandwich-structured TiN/CrAlN films

Sandwich-structured TiN/CrAlN films were rationally designed using metallic Ti and Al-Cr alloy targets by RF-pulsed magnetron sputtering. After obtained films were annealed at diverse temperatures at atmospheric pressure for 1 h, the hardness reveals an apparent decrease evolution from 29.2 to 15.7 GPa and H/E* ratio declines below 0.1 with increasing annealing temperature. Meanwhile, the grain size gradually becomes larger from 16.3 to 130.0 nm with increasing annealing temperature. Interestingly, it is observed that cracking behavior of sandwich-structured composite TiN/CrAlN films at elevated temperature is originated from the top of the blisters where main component is alumina on the surface, in virtue of intrinsically induced stress during oxidation, thermal expansion mismatch and phase transformation of the oxide layer. No cracks, nevertheless, are yielded in the film between any two blisters. Herein, these findings provide some beneficial references for preparing high quality films and coatings in high temperature service.