Influence of Al content and post-annealing on synthesis and mechanical properties of plasma sprayed Cr–Al–C composite coatings

Abstract

Due to ultra-high temperature and short reaction time, it was very challenging to produce high purity MAX phase by plasma spraying. In this study, Cr–Al-graphite agglomerated powders with different Al additions (x = 0.2–1.5) was used to prepare Cr–Al–C composite coatings by atmospheric plasma spraying followed with annealing. Results showed that the as-sprayed coatings displayed typical lamellar structure, mainly composed of Cr–C binary carbides (Cr7C3 and Cr23C6) and residual Al. After annealing at 700 °C, the newly formed Cr2AlC phase increased significantly in the coatings. The higher addition of Al, the more Cr2AlC phase formed after annealing. The enhanced atomic diffusion, sufficient Al source and existence of (Cr, Al)Cx contributed to the formation of Cr2AlC under annealing. Annealing treatment improved the hardness of the coating, but with the increase of Cr2AlC phase content, the hardness decreased slightly. The Al content and post-annealing had a synergistic effect on the formation of Cr2AlC phase in the sprayed coatings. This provided an effective route to control the Cr2AlC content in sprayed Cr–Al–C composite coatings.