Effect of ternary elements on the oxidation behavior of aluminized TiAl alloys

Abstract

The effects of ternary elements added to TiAl on the coating layer formed by the pack-aluminizing process was studied with respect to oxidation resistance and mechanical properties. All the TiAl specimens, with various amounts of Nb, Cr, Fe, and V, were pack aluminized under identical conditions using a high-activity process. Among the ternary alloying elements tested, Nb showed the best property of the TiAl3 coating layer formed on the surface and, consequently, the best oxidation resistance. The TiAl3 coating layer becomes thicker and has a finer grain size as the content of Nb or Cr is increased. Microhardness tests revealed that the addition of Nb or Cr improved the toughness of the coating layer and thus improved the cracking resistance. Cyclic oxidation tests showed that the TiAl3 coating layer formed on the TiAl alloy has better oxidation resistance with increasing Nb content. The ductility and oxidation resistance of the TiAl3 coating layers improved with Nb addition, which contributes to the grain refinement of TiAl3. The Nb present in the TiAl3 coating layer inhibits grain growth by the solute-drag effect and retards inward diffusion of Al to the TiAl matrix by forming (Nb, Ti)Al-3 precipitates during high-temperature oxidation.