Preparation And High Temperature Oxidation Resistance Of Anti-Oxidation Coating On High Nb-Tial Alloy Surface

High Nb-Ti Al alloy,as a new kind of high temperature structural materials with the light weight,has an important application prospect in the field of aerospace due to its low density,high specific strength,high specific stiffness,good resistance to creep and fatigue at high temperature.However,the oxidation resistance of the Ti Al alloys decreases sharply at their service temperature,hindering their engineering application.The alloying and surface modification of bulk materials,as two ways to overcome the problem,have been developed.In comparison,the surface modification can improve the high temperature oxidation resistance without affect the mechanical properties of the substrate,which has attracted wide attention.In this paper,the Cr coating,CoNiCrAlTaY coating,and Cr/CoNiCrAlTaY composite coating were prepared on the surface of high Nb-Ti Al alloy by plasma surface metallurgy technology.The phases,microstructure,composition distribution and binding force of the modified layer were studied.The formation and growth of oxides,morphology and microstructure,interface phases,element diffusion and binding force were studied through initial and isothermal oxidation at 900?.Besides,the mechanism of high temperature oxidation resistance of coatings was discussed.The main contents and conclusions are as follows:(1)The Cr coating including diffusion and deposition layers was prepared on the surface of high Nb-Ti Al by plasma surface metallurgy technology,and it had high adhesion.The binding force was of?140 N.Compared with the uncoated substrate,the Cr₂O₃formed and covered the whole surface of the coated substrate after oxidation at 900?,which significantly reduced the oxidation rate of the alloy.The binding force between the oxide film and substrate was as high as?59 N due to gradient distribution of element diffusion.It indicates that the Cr coating can effectively improve the oxidation resistance and bonding property of the alloy.(2)The CoNiCrAlTaY coating was fabricated at 850?,which had a binding force of?172 N.The Al₂O₃and Cr₂O₃generated at the beginning of oxidation at 900?.However,the spinel oxides of Co Cr₂O₄,Ni Cr₂O₄and Cr₂Ti O₅formed with the increasing oxidation time,which is useful to improve the oxidation resistance of the alloy.(3)The Cr/CoNiCrAlTaY composite coating with the interlayer of CoNiCrAlTaY layer between Cr coating and high Nb-Ti Al alloy was fabricated by plasma surface metallurgy,which consisted of the deposited Cr coating,inter-diffusion layer between Cr coating and CoNiCrAlTaY layer,CoNiCrAlTaY layer,inter-diffusion layer between CoNiCrAlTaY layer and high Nb-Ti Al substrate.The bonding force increased to?192 N.The oxidation weight rate of this coating was half of the uncoated substrate oxidation at 900?.At the initial oxidation stage,the Cr₂O₃formed on the surface to protect the substrate.With increasing of the oxidation time,the spallation occurred on the local region of the coating.However,the Al₂O₃formed on the subsurface,which can continue to protect the substrate.The bonding force between this coating and the substrate was of?77 N after oxidation for 300 h,which suggests the excellent oxidation risistance and bonding property.