High-temperature tribological behavior of nanolayered TiAlN/TiSiN coating deposited on WC-Co cemented carbide

In this study, high-temperature tribological behavior of nanolayered TiAlN/TiSiN coating was evaluated against the Al2O3 counter-body using a pin-on-disk tribometer. The coating was deposited on the WC-Co substrate, in an industrial unbalanced magnetron sputtering system. Tribological tests were conducted at room temperature, 500, 600, 700, and 760 degrees C, in air and nitrogen atmospheres. After the tests, the coating was examined using confocal microscopy, tactile profilometry, scanning electron microscopy, focused ion beam, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy and secondary ion mass spectrometry. The coating retained its microstructure and mechanical properties after exposure to high temperatures. At lower temperatures coating exhibited abrasive and adhesive wear mechanisms, while at higher temperatures abrasive and oxidative wear mechanisms were observed. In high-temperature tests, Al-O, Ti-O and Si-O were detected inside of wear tracks, in both atmospheres. However, the oxide thickness was significantly lower in tests with nitrogen atmosphere. Additionally, the top of the oxide layer was enriched in Al-O with respect to Ti-O and Si-O. The enrichment of Al-O was more pronounced in nitrogen atmosphere. The coating tested in air exhibited slightly higher and more unstable coefficient of friction (COF) values, than in nitrogen atmosphere. This is attributed to the increased oxidation in air atmosphere. At room temperature tests in nitrogen, the wear rate was approximately 3 times lower than in air. At higher temperatures the wear rate was lower than at room temperature, in both atmospheres, due to formation of protective oxides. However, with the increase in testing temperature the wear rate increased. The reason for such behavior is the loss of substrate's and coating's hardness at high temperatures, and thickening of the oxide layer which accelerated its removal. The latter effect is not so pronounced in nitrogen atmosphere due to thinner oxide layer, which agrees with the lower wear rate in nitrogen atmosphere at high temperatures than in air.