Effect of glow cleaning bias voltage on microstructure and properties of ion nitriding/multiarc ion plating CrTiAlN composite coatings

In order to address the issue of engine valve failure caused by high temperatures and oxidation during operation, ion nitriding was first applied to TC4 (Ti-6Al-4V) alloy, followed by the deposition of CrTiAlN coatings by multiarc ion plating. The results indicated that the surface grains of the nitrided TC4 alloy were progressively refined after ion nitriding. With the glow cleaning bias voltage increased from −600 to −900 V, the surface of the CrTiAlN coatings initially became more refined but then developed a rougher microstructure. Correspondingly, the surface roughness decreased and then increased with the rising bias voltage. At a bias voltage of −800 V, the coatings exhibited a minimum surface roughness of 0.377 μm, with a uniform microstructure and gradually refined particles. The CrTiAlN coatings mainly had optimum growth along the CrN (111) crystal plane. Under high-temperature oxidation experiments, the CrTiAlN composite coatings were classified as complete antioxidants at 600 and 700 °C, with a minimum average oxidation rate of 0.012 g m−2 h−1, and they were classified as antioxidants at 800 °C. Postoxidation analysis showed that the CrTiAlN composite coatings retained a dense and uniform surface structure with only shallow pits, and no defects such as cracking or delamination were observed. These results demonstrate a significant enhancement in the high-temperature oxidation resistance of the CrTiAlN composite coatings.