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 p otential 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 ha nd, 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 additi on 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 investi gate the effects of the additional third element X on the properties of coa ting layer that provides the TiAl with high temperature oxidation resistanc e. Manganese, chromium, silver and copper were chosen as the additional elemen t in this study. Vickers hardness of the Ti(AI, X)(3), in which X is Mn, Cr or Ag, becomes s imilar 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 coati ng 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 c ouple, it was found that phase separation occurs in the Ti(AI, X)(3) materi al added with Ag or Cu. In the case of Mn or Cr added Ti(AI, X)(3), the con centration of each element changes gradually and no intermediate phase form s 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 g rowth rate of the diffusion layer is, the more effective it is for the coat ing 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 tempe rature oxidation resistance among the four materials.