Research On Preparationand High Temperature Oxidation Resistance Properties Of Al₂O₃-Y₂O₃/Al-Y Composite Coating On The Surface Of γ-TiAl Alloy

γ-TiAl alloy is a kind of high-quality and high-temperature structural material,its relative density is half less than nickel-based alloy,with many salient features,such as light,high strength,abrasion and so on.Therefore,it is widely used in many industrial fields including aerospace.However,due to the limited high temperature oxidation resistance,the use ofγ-TiAl has been greatly restricted.In order to overcome this problem,this project uses magnetron reactive sputtering technology to prepare Al₂O₃-Y₂O₃/Al-Y composite coating onγ-TiAl alloy to achieve high temperature protection.Based on the previous studies,we prepared the Al-Y coating on the surface ofγ-TiAl alloy by radiofrequency magnetron sputtering technology,its parameters are:the sputtering power is 200W;The working pressure is 4Pa;The pole spacing is 20mm;Holding time:3h.Then,Al₂O₃-Y₂O₃coating was prepared on the surface of Al-Y coating by radiofrequency reactive sputtering,and the orthogonal experiment was designed to analyze the influence of sputtering parameters such as sputtering power,oxygen partial pressure,electrode spacing and holding time on the coating performance.Taking the sputtering rate and cohesion of the coating as the evaluation criteria,the optimal process parameters were obtained by the analysis of the range method.Finally,the annealing process was performed to prepare the Al₂O₃-Y₂O₃/Al-Y composite coating.The microstructure,elemental distribution and phase composition of the coating were analyzed by SEM,EDS and XRD.And the mechanical properties and thermal shock resistance of the coating were characterized and measured.The oxidation behaviors of Al₂O₃-Y₂O₃/Al-Y composite coating at different temperatures（750℃,850℃,950℃）and different time（50h,100h,150h）were studied.The results show that:（1）The optimum technological parameters of Al₂O₃-Y₂O₃ coating prepared by radiofrequency magnetron reactive sputtering are:sputtering power:300W;partial pressure of oxygen:30:1;pole spacing:15mm;olding time:4h.Annealing process parameters are diffusion temperature:800℃;Diffusion time:15h.（2）The prepared Al₂O₃-Y₂O₃/Al-Y composite coating has a dense surface with no obvious holes and cracks.From outside to inside the elements were in gradient distribution,total thickness is 35μm.The outside Al₂O₃-Y₂O₃layer thickness is 7μm;the middle layer is Al-Y coating thickness is 20μm;the inside diffusion layer thickness is 8μm.The main phase of Al₂O₃-Y₂O₃/Al-Y composite coating is Al₂O₃and Y₂O₃phase.（3）The hardness of Al₂O₃-Y₂O₃/Al-Y composite coating is 433.4 HV0.1;the bonding strength is 58.7N;the bonding strength is between 37.88 and 40.03 MPa;the nano hardness is 12965 Mpa;the elastic modulus is245Gpa,which is increased by about 2 times compared to the baseγ-TiAl alloy.（4）Al₂O₃-Y₂O₃/Al-Y composite coating failed after 100 thermal shock test failure,the coating surface still has good integrity after 50 cycles of thermal shock,so the coating has better resistance of thermal shock performance.（5）After being oxidized at 750℃,850℃and 950℃for 100h,the Al₂O₃-Y₂O₃/Al-Y composite coatings onγ-TiAl alloy formed a different diffusion layers due to element diffusion.The ceramic layer Al₂O₃-Y₂O₃on the initial oxidation layer plays a protective role,Y₂O₃acts as a pinning layer,the Al-Y metal layer alleviates the stress between the Al₂O₃-Y₂O₃ layer and the substrate,and the layers are connected in a folds-like structure.In the late oxide coating peeling,the appearance of Kendal holes and cracks accelerated the diffusion of Ti and O elements,and the TiO₂oxides formed,eventually it coating failed.（6）Cracks and voids appeared on the surface of Al₂O₃-Y₂O₃/Al-Y composite coating and the high temperature oxidation resistance of the coating was weakened at different temperatures（50h,100h and 150h）at 1050℃.