Behavior of high temperature oxidation of Ti(Al, X)3(X=Mn, Cr, Ag, Cu) and diffusion of TiAl/Ti(Al, X)3 joints

TiAl intermetallic compound has attracted considerable interest for their potential as new heat-resisting material, because of its lightness and high strength at elevated temperature. Using TiAl as automobile engine parts and so on, it is necessary to modify the oxidation resistance. On the other hand, TiAl3 has more excellent oxidation resistance than TiAl, but it is too brittle to be a structural material. Tt has been reported that the crystal structure of TiAl3 changes from D0(22) type into Lit type due to the addition of the third element X. This study was carried out considering that L1(2) type Ti(Al, X)(3) is used as a coating material on the TiAl. The purpose of this study is to investigate the effects of the additional third element X on the properties of coating layer that provides the TiAl with high temperature oxidation resistance. Manganese, chromium, silver and copper were chosen as the additional element in this study. Vickers hardness of the Ti(AI, X)(3), in which X is Mn, Cr or Ag, becomes similar value to that of TiAl. From this result, these materials may be good for the coating layer. From the oxidation test, it was found that all the four materials have more excellent oxidation resistance than TiAl and they can play a role of coating layer that provides the TiAl with high temperature oxidation resistance. Especially, Mn or Ag added material has good oxidation resistance. From the observation of diffusion behavior of TiAl/Ti(Al, X)(3) diffusion couple, it was found that phase separation occurs in the Ti(AI, X)(3) material added with Ag or Cu. In the case of Mn or Cr added Ti(AI, X)(3), the concentration of each element changes gradually and no intermediate phase forms at the interface. The growth rate of the diffusion layer of Mn added Ti (AI, X)(3) material is lower than that of Cr added material. The lower the growth rate of the diffusion layer is, the more effective it is for the coating layer. From these results, it is considered that Mn added Ti(Al, X)(3) material is most suitable for the coating layer that provides the TiAl with high temperature oxidation resistance among the four materials.