Isothermal Oxidation Behavior of TiAl-Nb-W-B-Y Alloys with Different Lamellar Colony Sizes

The oxidation behavior of full-lamellar Ti-42.5Al-8Nb-0.2W-0.2B-0.1Y alloys with different colony sizes was investigated by a thermogravimetric method at 900 °C for 100 h in air. The microstructure and composition of the alloy as well as the oxide scales were analyzed by OM, SEM, EDS and XRD. It is found that the oxidation kinetic of the present TiAl alloys accords with the parabolic law, and the alloy with larger lamellar colony has a better oxidation resistance than the one with smaller lamellar colony. The mass gain of the two samples with large and small lamellar colony after 100 h oxidation is 6.45 and 7.62 g/cm2 respectively. And correspondingly the thickness of oxide scale is about 5 and 7 μm, respectively. Based on the analysis of oxidation kinetic and microstructure characterization, we conclude that the structural differences between the two samples which affect the diffusion rate of O element into the matrix result in different oxidation behavior.