THE INFLUENCE OF TERNARY ELEMENT ADDITION ON THE OXIDATION BEHAVIOR OF TIAL INTERMETALLIC COMPOUND IN HIGH-TEMPERATURE AIR

A variety of ternary element additions were made to a binary TiAl (Ti- 34.5 wt% Al) intermetallic compound and the oxidation behaviour was st udied with particular interest in the influences of the ternary elemen ts. As a result of the oxidation tests in air at temperatures between 1073 and 1273 K, the effect of various elements was classified into th ree groups, i.e. (a) detrimental-Cu, Y, V. Cr and Mn; (b) neutral-Sn, Zr, Hf, Ta, Ni and Co; (c) beneficial-Si, Nb, Mo and W. Their influenc e was very significant, the difference in the weight gain between the best and the worst alloys being approximately two orders of magnitude. Particularly, the W- and the Mo- modified alloys were approximately 2 00 and 100 K more resistant than the binary alloy. The mechanism for t he improvement by the W and Mo additions may be explained as follows: the elements are enriched on the metal side of the scale/metal interfa ce and may cause the formation of beta and/or delta phases in which Al diffusion may be fast and oxygen solubility may be small. This leads to Al-enriched scale formation and/or Al2O3 layer formation along the interface.