Study On Plasma Sprayed Chromium Carbide Composite Coatings

Chromium carbide has the advantages of high hardness,low density,good wear resistance,and good corrosion resistance.However,plasma sprayed single-phase chromium carbide coating has low density,low bonding strength with the substrate,low wear resistance,and poor high temperature oxidation resistance.In this paper,composite powders of Cr₇C₃-CrSi₂,Cr₇C₃-CrSi₂-Al₂O₃,Cr-SiC and Cr₂O₃-SiC-Al system were first prepared by spray drying,and then chromium carbide composite coatings were prepared by plasma spraying.The microstructure and properties of chromium carbide composite coatings of four systems were compared and studied.The reaction mechanism of Cr-SiC and Cr₂O₃-SiC-Al systems during plasma spraying and the formation mechanism of chromium carbide composite coating were revealed.The influence of raw material composition on the microstructure and properties of Cr₂O₃-SiC-Al composite coating was studied.During the plasma spraying of Cr₇C₃-CrSi₂ and Cr₇C₃-CrSi₂-Al₂O₃system composite powders,the phase of the raw materials did not change significantly,and the resulting coating had obvious pores and low density.However,a composite coating of Cr₇C₃and CrSi₂as the main phases was prepared by plasma spraying Cr-SiC system composite powder.Chromium carbide composite coatings with Cr₇C₃,CrSi₂and?-Al₂O₃as main phases were prepared by plasma spraying Cr₂O₃-SiC-Al system composite powder.Comparing four systems of chromium carbide composite coating found that the river pattern of Cr₂O₃-SiC-Al system coating was more obvious,the structure was more uniform,and the coating quality was significantly better than the other three system coatings.Direct plasma spraying of Cr₇C₃-CrSi₂ and Cr₇C₃-CrSi₂-Al₂O₃system composite powders to prepare coatings mainly includes two stages:melting and deposition.The formation mechanism of coatings prepared by plasma spraying Cr-SiC composite powder was solid phase diffusion-reaction-melt-deposition:Cr and SiC undergo solid-phase diffusion to form Cr₇C₃and CrSi₂.The reaction heat and the heat of the plasma flame superimpose to promote the melting of particles,and the molten droplets hit the substrate to form the coating.The formation mechanism of coatings prepared by plasma spraying of Cr₂O₃-SiC-Al composite powder was melt-diffusion-reaction-deposition:Al first melts and reacts with Cr₂O₃to produce solid-liquid diffusion reactions to generate Cr atoms and Al₂O₃,and then Cr atoms react with SiC to form Cr₇C₃and CrSi₂.Finally,the molten droplets hit the substrate under the action of a plasma flame to form a dense coating.By studying the influence of raw material components on the structure and properties of the Cr₂O₃-SiC-Al system,it is found that the coating quality is the best when the quality of the raw material powder is Cr₂O₃:SiC:Al=65:12:23.It has the lowest porosity,the highest hardness,the best toughness and abrasion resistance.The results show that the Cr₂O₃-SiC-Al coating has more obvious fluvial pattern,the highest density and the most uniform microstructure distribution,and the Cr₂O₃-SiC-Al coating has the lowest porosity,the highest microhardness,the best toughness and the best wear resistance.The results of ablation experiments show that the synergistic effect of Cr₂O₃,Si O₂and(Al_0.9Cr_0.1)₂O₃solid solution in the Cr₂O₃-SiC-Al system can effectively prevent oxygen from entering the coating and has better ablation resistance.