Study On Processes And Oxidation Resistance Of TiAl Aloy Prepared By Plasma Treated Technique

TiAl alloys are one of the most promising high temperature structural materials for aerospace and automobile industries due to their advantages, such as low density, high melting point and good mechanical property. However, their insufficient wear resistance and oxidation resistance become the major obstacles for their wide applications. Great efforts including surface treatment and alloying addition have been made to enhance their wear and oxidation resistance, but excessive addition of alloy elements produces some negative effects on the mechanical property.At present, the surface treatment becomes more attractive to improve the performance of TiAl alloys. Previous investigations demonstrated that its oxidation resistance and wear resistance were enhanced after the duplex treatment, i.e. double glow plasma surface niobizing and plasma carburization. The research still found that the thickness of the niobizing alloyed layer greatly influenced on the thickness and structure of the plasma carburized layer. Therefore this paper studied the influence of the niobizing layer on the carburized layer, and investigated the cycled oxidation behavior of the TiAl samples, the carburized samples, the niobizing samples, and the niobizing and carburized samples. The oxidation mechanism is also discussedThe research results show that: (1) The thickness and composition of the alloyed layer is related to an alloying temperature and duration on the condition of the constant pressure and sample-cathode gap. A deposit layer formed on the surface of TiAl is resulted from both too low alloying temperature and too long alloying time. By an optimized processing parameter, an appropriate thickness and gradient component distribution of the alloyed layer is gained on the TiAl surface. (2) The process of the plasma carburization after the plasma niobizing can greatly accelerate plasma carburization. The thicker the niobizing layer is, the deeper the carburized layer is. (3) The oxidation behavior is related to the characteristics of the niobizing layer. A definite thickness of alloyed layer or a proper content of niobium can improve the oxidation resistance of TiAl alloys. (4) The plasma carburization can to some extent improve the oxidation resistance of TiAl alloys, but whose long-term effect is not good. (5) The plasma niobizing and carburization can greatly improve the oxidation resistance of TiAl alloys. The niobium content of niobizing layer and its thickness greatly influence the oxidation capability of the carburized layer. In addition, the surface hardness of the niobizing and carburized layer is higher than that of TiAl alloys, causing a good wear resistance of TiAl alloys.