Structure and tribological properties of AlCrTiN coatings at elevated temperature

In this study, we analyzed the high temperature tribological behavior of AlCrTiN coatings deposited on WC substrates by low cathodic arc technique. The coatings chemical composition, Al 31 at.%, Cr 16 at.%, Ti 7 at.% and N 46 at.%, and the bonding state were evaluated by X-ray photoelectron spectroscopy. The mechanical properties of the coatings were studied by scratch-test and nanohardness depth sensing indentation. The morphology of the coatings surface, ball scars, wear tracks and wear debris as well as the oxidized samples was examined by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The structure was analyzed using X-ray diffraction (XRD). Wear testing was carried out using a high temperature tribometer (pin-on-disc) with alumina balls as counterparts. The evaluation of the friction coefficient with the number of cycles (sliding distance) was assessed at different temperatures and the wear rates of the coatings and balls were determined; the maximum testing temperature was 800 °C. The coating showed an excellent thermal stability and wear resistance. The friction reached a maximum at 500 °C and then decreased, whereas the wear rate was negligible up to 600 °C and increased significantly at higher temperatures.