High Temperature Oxidation Mechanism Of Ti₂AlNb Alloy And Its Effect On Mechanical Properties

As a new generation of high-temperature structural materials,Ti₂AlNb alloy has high high-temperature yield strength,high creep resistance,and fracture toughness,as well as low notch sensitivity.Under a high-temperature environment,a protective Al₂O₃ protective film will be formed on the surface of the Ti₂AlNb alloy.However,when the temperature rises to 750℃,The oxidation resistance of the alloy matrix decreases,which makes the titanium alloy unable to serve normally under these conditions,and restricts the application and development of the alloy.In this paper,the Ti-22Al-24Nb-0.5Mo alloy plate as the original material,through constant temperature oxidation treatment of the alloy plate,makes it under thermal exposure conditions.First,through the oxidation weight gain test,it was found that Ti₂AlNb alloy continuously oxidized for 60h,when the anti-oxidation coating was not sprayed,the linear law was in line with the three temperatures,and the oxidation resistance was poor.When the anti-oxidation coating is sprayed,the temperature at 850℃and 900℃conforms to the parabolic law,while the temperature at 950℃conforms to the linear law,and the oxidation resistance decreases sharply with the increase in temperature.Then,the oxidation layer of Ti-22Al-24Nb-0.5Mo alloy was obtained from the surface to the sample matrix by using SEM and EDS detection methods.It can be roughly divided into the outermost layer of Ti O₂-based Al₂O₃ and Ti O₂ loose oxide film mixing zone,the outer layer of dense oxide film composed of Ti O₂ and AlNb O₄,and the inner Ti O₂ oxygen diffusion layer zone.According to Fick’s second law and the solution method at a constant temperature,the activation energy Q of oxygen diffusion in Ti₂AlNb alloy is 251771.965J/mol.In the range of 850℃～950℃,the curve of oxygen diffusion depth was obtained.Through the analysis of the fracture of the high-temperature tensile specimen after constant temperature oxidation at different temperatures,it was obtained that the unsprayed protective coating showed good plasticity after 60h oxidation at 850°C constant temperature,and the fracture morphology was dominated by a large number of tenament sockets,which was characterized by ductile fracture.When the oxidation temperature is increased to 900℃,the fracture is characterized by dimple+quasi cleavage,which is a mixed fracture mechanism with ductile fracture.When the oxidation temperature is 950℃,both strength and plasticity decrease,showing typical brittle cleavage fracture characteristics.