Fabrication And Properties Of Layered Ternary Ceramic Cr₂AlC Coating By Multi-arc Ion Plating Technique

Layered ternary ceramics, Mn+1AXn phases, combine the merits of metals and ceramics. Such unique properties make them of great interest for potential applications in many industrial fields. Cr2AlC attracted extensive attentions due to its excellent oxidation and hot corrosion resistance. However, its applications are limited because of the difficulty of the synthesis of bulk Cr2AIC with big dimensions; And the synthesis of Cr2AlC coating can overcome this limitation of synthesis of bulk, which is significant for promoting its applications.Up to now, phase pure Cr2AIC coating has been successfully prepared. However, all of the works concentrated on the synthesis using magnetron sputtering. No literitures related to the synthesis of the Cr2AIC coating using cathodic arc deposition method has been reported.In present work, we investigated the preparation of the Cr2AlC coating using multi-arc ion plating method from a sintered Cr2AIC target. The following conclusions were drawn:(1) The used phase pure Cr2AIC target was sintered using in-situ reaction/hot pressing method. XRD results demonstrated that the coating prepared at RT was mainly amorphous.(2) Serious Al and C deficiency has been detected in the as-deposited coating from single Cr2AlC target. Therefore, two extra Al and C targets were used to supplement the lost Al and C elements. During the experimental procedure, the power of the Al and C targets were carefully adjusted to satisfy the Cr2AIC stoichiometry.(3) Post annealing was needed to crystallize the RT-deposited amorphous coating. It was found that high annealing temperature (higher than the melting temperature of Al660℃) could result in the volatilization of the Al element in the coating, further the formation of the chromium carbides. And620℃was proved to be a proper annealing temperature in present work. Crystalline coating, with Cr2AlC as the main phase, could be acquired by post annealing at620℃for20h in Ar atmosphere.(4) The mechanical properties and the high temperature oxidation resistance of the post annealed coating at620℃for20h was investigated in present work. It was found that the coating had good adhesion to the M38G substrate, with the adhesive strength up to69MPa. In addition, the existence of the large particles and the CrAl phase in the coating endowed the coating with high hardness. At the initial stage of the oxidation process, the weight gain of the coating was higher than that of the bared alloy. After15hours oxidation, the weigh gain of the coating slowed down, which was smaller than that of the bared alloy. This phenomenon could be related to the microstructure of the coating. At the initial stage, O in the atmosphere could diffuse quickly along the large number of the grain boundaries existed in the coating, react with the coating and result in the large weight gain. With the proceeding of the oxidation, a dense Cr2O3layer could formed on the surface of the coating, which blocked the inter-diffusion of the O and protected the underlying coating from further oxidation.