The Corrosion of Titanium Aluminides in H2/H2S/H2O Atmospheres at 800–1000°C

Abstract

The corrosion behavior of three Ti–Al intermetallics containing 20, 30, and 40 wt.% Al was studied over the temperature range 800–1000°C in a H2/H2S/H2O gas mixture. Ti–20Al and Ti–40Al alloys had the single-phase structure of Ti3Al and TiAl, respectively, while Ti–30Al was a two-phase mixture of Ti3Al+TiAl. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants increased with increasing temperature, but decreased with increasing Al content. The Ti–40Al alloy exhibited the best corrosion resistance among all alloys studied. The scales formed on Ti–Al intermetallics were heterophasic and duplex, consisting of an outer-scale layer of pure α-TiO2 and an inner layer of α-TiO2 with minor amounts of α-Al2O3 and Til-xS. The amount of α-Al2O3, which increased with increasing Al content, is responsible for the reduction of the corrosion rates as compared with those of pure Ti oxides.