Investigation on the Initial Oxidation Behavior of TiAl Alloy

In this paper, the initial oxidation behaviors of alpha(2), gamma and beta phase in the newly developed TNM alloy (Ti-44Al-4.0Nb-1.5Mo-0.1B-0.01Y) were investigated. The oxidation tests were performed at 800 degrees C for 3 min, 5 min, 20 min, 1 h, 2 h and 4 h respectively. The alloy has a good oxidation resistance below 800 degrees C. The antioxidant capacity of the three phases decreases as follow order: gamma > alpha(2) > beta. Within the lamellar colony, the values of atom ratio (Ti/Al) in alpha(2) lath and gamma lath remain within the range of 1.11-1.16, indicating that atom diffusion occurs at the initial stage of oxidation. The microstructure observations also confirmed the segregation of Y element at grain boundaries of primary coarse alpha grains and segregation of Nb element in massive gamma phases. The peeling off of the oxide from beta phase and oxygen diffusion at grain boundaries are detrimental to the oxidation resistance of the alloy.