Research Of Plasma Sprayed CoCrAlYTaSi-TiB₂ Oxidation Resistant Coating On TiBw/TC4 Composite

Due to its superior properties such as high specific strength, high specific stiffness at high temperature properties, titanium matrix composites（TMCs） are of special significant in the hot parts such as aviation and space field. However,as is well-know, titanium and titanium alloys are very active chemically. They are vulnerabled to hot corrosion and high temperature environment,especially when TMCs serve in the atmosphere of more than 600℃. In order to improve the high temperature performance and maximum service temperature of TMCs, CoCrAlYTaSi-TiB₂ composite powder was used to prepare the coating by air-plasma sprayed（APS）. The microstructure of surface and as-cross of coating, interfacial bond strength between coating and substrate and porosity of coati ng was investigated. Optimized the plasma spraying process of the coating was found. Isothermal oxidation test were carried out in air furnace at 700℃、800℃and 900℃ for 100 h with weight measurement and oxidation rate, respectively. The phase analysis and composition analysis of coating and substract after Isothermal oxidation test show that oxidation resistance of substrate with coating can be effectively improved.The optimized the plasma spraying process of the coating showed tha t spraying power was 27.5³3k W, spraying distance was 90mm¹30mm and coating thickness should be less than 250 μm. CoCrAlYTaSi-TiB₂ coating could effectively improve the interface bonding strength and the porosity of CoCrAlYTaSi-TiB₂ coating was only 4.67%, which is obviously lower than CoCrAlYTaSi coating. According to corrosion resistance between TC4 alloy and Ti B, substrate surface is covered with a large number of Ti B whisker after chemical etching. The size of Ti B whisker was about 3μm and width was about 0.8μm. Interfacial bond strength between coating and substrate was about 26.85 MPa after APS. For Ti Bw/Ti composite with network microstucture, etching surface pretreatment could replace traditional surface roughen methods for improve the coarsening of substrate surface.Four typical phases can be seen and confirmed according microstructure of surface and as-cross of coating. They are Al203, Ta C, γ-（Co,Cr） and β-（Co,Cr）Al solid solution, respectively. The morphology of coating major area is comp letely melting area. What’s more, solid sintering area and liquid sintering area are presented in the coating.After oxidation for 100 h at 700℃,800℃ and 900℃,Ti Bw/TC4 composites exhibited the mass gain about 10.5 mg/cm2, 14.9 mg/cm2 and 24.5 mg/cm2, respectively and the surface was covered Al₂O₃ and Ti O2. From the analysis of oxidation kinetics of these temperatures, substract was unstable oxidation stage and the surface oxidation film did not have protective.After oxidation for 100 h at 700℃,800℃ and 900℃,Ti Bw/TC4 composites coated CoCrAlYTaSi-TiB₂ exhibited the mass gain about 2.5 mg/cm2, 4.0 mg/cm2 and 5.4 mg/cm2, respectively. Oxidation rate of coating was about 0.061mg2?cm4·h、0.164mg2?cm4·h2、0.289mg2?cm4·h2, respectively. Oxidation weight gain rate decreased obviously after coated CoCrAlYTaSi-TiB₂ coating.Phase tended to be stable after 20 h oxidation at various temperatures. Al₂O₃ and Cr₂O₃ presented on the surface of coating after 100 h oxidation. Element diffusion behavior occurred between coating and substract. With the increasing of oxidation temperature, width of interface diffusion zone increased. Oxygen content in the substract was very low due to coating. Thus, CoCrAlYTaSi-TiB₂ coating can observably improve the oxidation resistance of Ti Bw/TC4 composites.