Oxidation behaviour and tribological properties of arc-evaporated ZrAlN hard coatings

Zr1 − xAlxN hard coatings were synthesised by cathodic arc-evaporation from ZrAl targets with different Al contents and applying two bias voltages, –40 and − 120 V, during deposition. Subsequently, the coatings were annealed in ambient air up to a temperature of 900 °C. According to measurements by scanning electron microscopy, X-ray diffraction and Raman spectroscopy, the onset temperature for oxidation was in the range from 700 to 800 °C while higher Al contents in the coating resulted in an improved oxidation resistance regardless of structural changes. Ball-on-disc tests at temperatures up to 700 °C were performed to study the tribological properties of the synthesised ZrAlN coatings. The coefficient of friction against the used alumina balls was generally high with values between 0.5 and 1.0 depending on the chemical composition and the testing temperature. In terms of wear resistance, the Zr-rich coatings showed the lowest wear coefficient at 500 °C, whereas the Al-rich coating revealed a constant wear coefficient for all testing temperatures.