EFFECTS OF ELEMENT Si ON OXIDATION RESISTANCE OF TiAl ALLOYS

The effects of alloying element Si on oxidation resistance of several 7-TiAl based alloys containing different Nb contents have been studied. The results reveal that the lower the Nb content of the alloy, the more obvious the beneficial effect of Si. The improvement of oxidation resistance by Si is mainly attributed to promoting the formation of continuous and dense Al2O3 layers in the binary alloy. In addition, more homogeneous and finer oxidation products appear on the surface of higher Si-bearing alloys than on lower Si-bearing alloys, leading to further improvement of oxidation resistance in Nb-containing alloys. As a result, the parabolic rate constant decreases with increasing Si content. Isothermal oxidation experiment, X-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis of the oxidation products are presented.