Characterization and reaction mechanism of in-situ micro-laminated Cr2AlC coatings by plasma spraying Cr3C2/Al/Cr powder mixtures

Large-scale fabrication of MAX phase coatings such as Cr2AlC and Ti2AlC by plasma spraying is extremely challenging, owing to the ultra-high temperature and insufficient reaction time. In this research, the Cr2AlC coatings were produced by plasma spraying from Cr3C2@Al-Cr agglomerates. The influence of Al contents on microstructure and mechanics properties of coatings were investigated. Results showed the as-deposited coatings displayed a typical layered structure, mainly composed of Cr2AlC, Cr7C3, Cr23C6 and sub-stable (Cr, Al)C-x. Rapid deposition resulted in an imperfect reaction of raw powders, thus generated sub-stable (Cr, Al)C-x. The adequate Al and nonstoichiometric carbides CrCx were the main key to promote the presence of MAX-Cr2AlC phase. Nevertheless, excessive Al would create extra (Cr, Al)C-x, thus reduce the Cr2AlC content. Notably, the coatings retained high hardness (>10 GPa) and good fracture toughness (similar to 2.5 MPa center dot m(1/2)). The micro-lamellar structure, nano-layered Cr2AlC and microcrack-toughening ensured the good mechanical properties of coatings.