Study On Corrosion Resistance Of A Kind Of Ti₃Al Based Alloy

Ti₃Al based alloy has many advantages, such as high specific strength, high corrosion resistance, low density, etc. Ti₃Al based alloy are applied in the field of aeronautics and astronautics, military, automotive, especially in aeronautics and astronautics fields. In addition, Ti₃Al based alloy has great potential application in the ocean engineering field. However, the high temperature oxidation resistance and wear resistance of Ti₃Al based alloy are poor, which limits its wider application. So it is of great significance to study on corrosion resistance of Ti₃Al. TD3 alloy is a kind of three-phase（α2+O+B2） Ti₃Al based alloy with moderately niobium content. At present, the research on TD3 alloy is mainly focused on the microstructure and mechanical properties, but few researches about corrosion resistance are carried out.Aim at the poor property of high temperature oxidation of the alloy, the high temperature oxidation behavior of TD3 alloy was studied at 800 oC, 850 oC and 900 oC. The phase structure, microstructure and morphology of oxide films were investigated by means of XRD and SEM equipped with EDS. It shows that the oxidation weight gain rate of TD3 alloy significantly increase with the oxidation temperature and time. The oxide products are mainly composed of Al2O3 and TiO2.In consideration of the application of TD3 alloy in marine environment, electrochemical experiment was carried out. The corrosion behavior in 3.5% NaCl solution was investigated. Besides, 2% and 5% NaCl solution were prepared as contrast tests. Through the polarization curves, some electrochemical parameters were obtained, such as corrosion potential, corrosion current density, passive current density, etc. The corrosion morphology is observed by optical microscope. Corrosion on TD3 alloy was comparatively analyzed in different concentrations of NaCl solution.This thesis also performed 500 oC, 600 oC and 700 oC thermal oxidation and ionitriding treatment for TD3 alloy, and compared the electrochemical corrosion results of treated samples with untreated sample in 3.5% NaCl solution. The results show that thermal oxidation and ionitriding treatment can effectively improve the corrosion resistance of TD3 alloy, and the sample shows the best corrosion resistance under 500 oC thermal oxidation.Due to the poor wear resistance of Ti₃Al based alloy, the measurement of wear-resistance of the TD3 alloy was performed under the case of surface treated and untreated. Choose the to-and-fro wear way, with the load of 20 N and friction time of 5 min, the friction coefficient of every sample was measured. The wear morphology was observed by optical microscope and comparatively analyzed the result. It shows that the thermal oxidation treatment and ionitriding are effective method to improve the wear resistance of the TD3 alloy.