Study On Plasma Sprayed Zirconium Carbide Composite Coatings

Zirconium carbide has the advantages of high melting point,high hardness,high elastic modulus,low resistivity and good radiation resistance.However,the coatings prepared by single-phase zirconium carbide have many defects such as low deposition efficiency,high porosity,low hardness and poor high temperature oxidation resistance.In this paper,four kinds of composite powders of ZrC-ZrSi₂,ZrC-ZrSi₂-Al₂O₃,Zr-SiC and ZrO₂-SiC-Al were prepared by spray granulation,and then zirconium carbide composite coatings were prepared by plasma spraying.The microstructure and properties of zirconium carbide composite coatings of four systems were compared and studied.The reaction mechanism of Zr-SiC and ZrO₂-SiC-Al system in plasma spraying process and the formation of composite coatings were revealed.The effect of ZrO₂content on the microstructure and properties of the composite coating prepared by ZrO₂-SiC-Al reaction system was studied.In the process of plasma spraying ZrC-ZrSi₂composite powder,the phase of raw material changed a little.The main phase of the coating was ZrC and Si O₂,with many holes.In the process of plasma spraying ZrC-ZrSi₂-Al₂O₃composite powder,the phase of raw material did not change,and the coating density was low.Zirconium carbide composite coating with ZrC as the main phases and ZrSi₂and SiC as the main phase was prepared by plasma spraying Zr-SiC system composite powder,and zirconium carbide composite coating with ZrC,ZrSi₂and Al₂O₃as the main phases was prepared by plasma spraying ZrO₂-SiC-Al system composite powder.Compared with the four kinds of zirconium carbide composite coating,the coating of the plasma sprayed ZrO₂-SiC-Al composite powders has obvious layered structure and is uniform and dense,and the quality of coating is better than the other three systems.Only melt-deposition of ZrC,ZrSi₂and Al₂O₃occurred during the coating process of plasma sprayed ZrC-ZrSi₂and ZrC-ZrSi₂-Al₂O₃composite powders.The formation mechanism of plasma sprayed Zr-SiC system coating is solid diffusion reaction,melting and deposition.ZrC and ZrSi₂are formed by the solid-phase diffusion reaction of Zr and SiC,and the melting of ZrC and ZrSi₂particles impact the substrate surface to form coating under the action of high-speed gas flow.The formation mechanism of plasma sprayed ZrO₂-SiC-Al system coating is melt,diffusion,reaction and deposition.At first,ZrO₂and SiC particles are wrapped by heat-melted Al,and then Al₂O₃,Al₂Zr and active Zr atoms are formed by solid-liquid diffusion reaction between the molten Al atom and ZrO₂particles.Then,Al₂Zr and active Zr atoms react with SiC to form ZrC and ZrSi₂.Under the action of high-speed gas flow,the droplets impact on the substrate surface to form coating.By studying the influence of ZrO₂on the structure and properties of ZrO₂-SiC-Al system,it is found that when the mass ratio of ZrO₂-SiC-Al=66.5:14:19.5,the coating has the best quality,the lowest porosity and the highest hardness.Compared with the ZrC composite coatings obtained by plasma spraying ZrC-ZrSi₂,Zr-SiC,ZrC-ZrSi₂-Al₂O₃composite powders,the ZrC composite coating obtained by plasma spraying ZrO₂-SiC-Al composite powders has the best toughness,scratch resistance,friction and wear and ablation performance.The reason is that ZrO₂-SiC-Al composite powder reacts fully in the spraying process and and melts better.,and the layer structure of the coating is more obvious and the structure is more uniform and dense.