Oxidation behavior of TiAl-X (X = Cr, V, Si, Mo or Nb) intermetallics at elevated temperature

Oxidation behavior of TiAl intermetallic compounds with the additions of Cr, V, Si, Mo, or Nb was investigated at 900--1,100 C under the atmospheric environment. The reaction products were examined by XRD and SEM equipped with WDX. The weight gain by continuous oxidation increased with the addition of Cr or V, but there was less weight gain when Mo, Si or Nb was added individually. Thus, it is concluded that the addition of Cr or V did not improve the oxidation resistance, whereas the addition of Si, Mo or Nb improved it. Nb strengthened the tendency to form Al2O3 in the early stage of oxidation, due to the formation of the continuous Al2O3 and dense TiO2+Al2O3 layers. According to the Pt-marker test of TiAl-5wt%Nb, oxides were formed mainly by inward diffusion of oxygen. Upon thermal cyclic oxidation at 900 C, it was shown that the addition of Cr or Nb improved the adherence of oxide scale to the substrate