Synthesis and characterization of CrZrAlN films using unbalanced magnetron sputtering with segment targets

In this work, CrZrAlN thin films with various Al contents were synthesized with an unbalanced magnetron sputtering technique using segment targets. Microstructure, surface morphology, and film hardness were investigated as functions of the Al content; X-ray diffraction, atomic force microscopy, and a microhardness tester were used to carry out the investigations. The thermal stability of the films as a function of the Al content was evaluated by annealing the films at temperatures up to 500 °C for 30 min in air. The synthesized CrZrAlN thin films with Al content from 0 to 12.9 at.% consisted mainly of the crystalline NaCl B1 fcc solid solution phase. With the addition of Al to the CrZrN thin film, the microstructure of the film changed from dense and compact to a columnar structure, and the preferred orientation of the films changed from (111) to (200) plane. The hardness of the film decreased slightly as the Al content increased, and the thermal stability of the CrZrAlN thin films deteriorated. The columnar microstructure in the CrZrAlN thin film is believed to provide a fast route for oxygen to diffuse, resulting in a poor oxidation resistance of the film. Contrary to expectations, the addition of Al to the CrZrN thin film did not improve the oxidation resistance of the film. A way to break the columnar microstructure of the CrZrAlN thin film should be developed in order to improve the oxidation resistance of the film.