Hybrid reactive sputtering of transition metal aluminum oxynitrides

Abstract

Transition metal aluminum nitrides like CrAlN and TiAlN coatings are widely used to improve performances of cutting tools. Incorporation of oxygen leads to the transition metal aluminum oxynitrides CrAlON and TiAlON, resulting in reduced friction against steel compared to nitride coating and further improved cutting performance. In previous studies, over stoichiometric chemical compositions with increased non-metal to metal ratios of z > 1 were observed in oxynitride CrAlON and TiAlON coatings. Nevertheless, the reason for the non-metal to metal ratios of z > 1 is not clarified yet. The current study aims to contribute to this issue. For this purpose, CrAlON and TiAlON coatings were deposited with four different oxygen to reactive gas flow ratios jO2/(jO2+jN2) using a direct current magnetron sputtering (dcMS) / high power pulsed magnetron sputtering (HPPMS) hybrid process. The plasma composition was investigated at the substrate side in front of both, the dcMS and HPPMS cathode. Subsequently, the chemical and phase composition of the deposited coatings was examined. It can be concluded that a higher oxygen content of reactive gas mixture jO2/(jO2+jN2) increases non-metal to metal ratios z in the plasma. This results in higher non-metal to metal ratios z in the coating. The findings reported in this study expand the understanding of the reason for over stoichiometric chemical composition of transition metal aluminum oxynitrides.