Improving high-temperature oxidation resistance of TiAl-based alloys by MnCl2 surface treatment

The effects of chlorine on the high temperature (900–1115 °C) oxidation resistance of γ-TiAl-based alloys were studied by applying MnCl2 on the sample surfaces of the Ti47Al, Ti55Al, Ti47Al3V and Ti47Al2Cr2Nb alloys. The oxidation rates of these alloys decreased remarkably after treating the sample surfaces with MnCl2. The oxide scales formed on TiAl based alloys generally consisted of a TiO2-rich outer layer and a TiO2+Al2O3 mixed inner layer. After surface treatment with MnCl2, a very convoluted scale consisting of a thin discontinuous TiO2 outer layer and continuous Al2O3 inner layer with a small amount of TiO2 formed on the four alloys. At the initial stage of oxidation the continuous Al2O3 layer had formed on the MnCl2 treated samples. It is suggested that occurrence of chlorination of aluminium during the initial stage promoted the formation of the continuous Al2O3 layer.