Synthesis and characterization of MAX phase Cr2AlC based composite coatings by plasma spraying and post annealing

Abstract

In this work, a simple two-step method was developed to produce thick Cr2AlC based coatings. Firstly, atmosphere plasma spraying was employed to deposit Cr-A-C coatings with Cr/Al/graphite mixtures. Then Ar-annealing treatment was conducted on as-sprayed coatings to in situ achieve Cr2AlC. Microstructure evolution and mechanical performance of composite coatings was investigated. The as-sprayed coating exhibited a lamellar feature with mainly Cr7C3 and residual Al. With increasing temperature, the residual Al decreased and the newly formed Cr2AlC phase increased. Especially, high temperature annealing (>700 °C) led to remarkable increasing amount of Cr2AlC phase due to the enhanced atom diffusion. The annealing treatment enhanced both of hardness and fracture toughness of coatings due to the formation of Cr2AlC. However, the increasing amount of Cr2AlC phase resulted in slight decrease of hardness. Thus, the content of Cr2AlC phase played a significant role in mechanical performance of composite coatings, which was adjusted by post-annealing.