Magnetron sputtering of hard Cr–Al–N–O thin films

The design and synthesis of advanced wear resistant coatings combining metallic or covalent bonded hard materials and oxide phases in a novel metastable or nanocomposite thin film structure is an emerging new field of materials research. In this paper, the phase formation, microstructure evolution and correlation between the constitution, microstructure and growth conditions of magnetron-sputtered hard Cr–Al–N–O thin films are described. The deposition experiments were carried out with a Leybold Z 550 PVD machine following a combinatorial materials science based approach for the sputtering from a segmented target, composed of bulk ceramic CrAlN and Al2O3 pieces. In each experiment, six coatings of different composition, constitution and microstructure were obtained simultaneously by placing six substrate samples in individual positions relative to the target. Both non-reactive and reactive deposition processes (in a nitrogen/argon atmosphere) were applied. No substrate bias was used and the substrate temperature was kept constant below 200 °C. The constitution, microstructure and Vickers microhardness of the coatings is discussed in dependence of their chemical composition. While non-reactive deposition processes resulted in the growth of nanocrystalline thin films of moderate hardness but brittle character, the reactive deposition led to the growth of nanocrystalline coatings with high hardness (up to 2500 HV0.05) and toughness.