High-temperature tribological properties of CrAlN, CrAlSiN and AlCrSiN coatings

Cr-Al-Si-N coatings with high and low Cr/Al ratios (CrAlSiN and AlCrSiN, respectively) were deposited on WC substrates by cathodic arc and compared with a reference Cr-Al-N coating. The silicon content was close to 3 at.%. X-ray diffraction analysis showed that CrAlN and CrAlSiN coatings exhibited the cubic Cr(Al)N structure, whereas in AlCrSiN a mixture of cubic Cr(Al)N and wurtzite-type AlN was identified. All three coatings showed excellent thermal stability and oxidation resistance up to 800 °C. The tribological properties were evaluated by ball-on-disk tribometer in the temperature range 25-600 °C. Two materials were used as counterparts: alumina and 440C steel. Sliding against 440C steel balls led to the extensive wear of the balls and transfer of the ball material to the surface of the coatings. The coatings were not damaged. When sliding against alumina balls, the coating wear was low up to testing temperature 300 °C. At 400 °C, CrAlSiN coating was partially worn through. CrAlN and AlCrSiN coatings were almost immediately worn out at 600 °C. The analysis of the wear debris identified high-temperature adhesive failure of the coatings.