Improving high-temperature oxidation resistance of TiAl-based alloys by MnCl 2 surface treatment

Abstract

The effects of chlorine on the high temperature (900–1115 °C) oxidation resistance of γ-TiAl-based alloys were studied by applying MnCl 2 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 MnCl 2. The oxide scales formed on TiAl based alloys generally consisted of a TiO 2-rich outer layer and a TiO 2+Al 2O 3 mixed inner layer. After surface treatment with MnCl 2, a very convoluted scale consisting of a thin discontinuous TiO 2 outer layer and continuous Al 2O 3 inner layer with a small amount of TiO 2 formed on the four alloys. At the initial stage of oxidation the continuous Al 2O 3 layer had formed on the MnCl 2 treated samples. It is suggested that occurrence of chlorination of aluminium during the initial stage promoted the formation of the continuous Al 2O 3 layer.