Effect of annealing on the microstructure, mechanical and electrochemical properties of CrAlC coatings

The CrAlC coating has broad application prospects as a high temperature protective material due to its unique properties. However, it is difficult to control the properties of CrAlC coating due to the multiphase structure produced by thermally induced solid-reaction. In this paper, the CrAlC coating was prepared by filtered cathodic vacuum arc (FCVA) technology. In order to elucidate the relationship between the phase structure evolution and the properties, the structure, mechanical and electrochemical properties of the CrAlC coating before and after annealing were systematically investigated. The results illustrated that the CrAlC coating changed from amorphous structure to crystalline structure after annealing, and the phase composition varied with the increases of annealing temperature. As the annealing temperature increased from 700 °C to 800 °C, the content of Cr23C6 and Al4C3 increased. However, with further increasing the annealing temperature to 900 °C, the content of Al4C3 gradually decreased, and the Cr23C6 phase was transformed into Cr7C3 and Cr3C2 phases. In addition, the hardness and corrosion resistance of the coating first increased and then decreased with the increase of annealing temperature. When the annealing temperature was 800 °C, the CrAlC coating had the highest hardness (18.28 GPa) and the best corrosion resistance with the smallest corrosion current density (8.54 × 10-9 A/cm2).