The high temperature oxidation behaviour of high and low alloyed TiAl-based intermetallics

The oxidation behaviour of the γ-TiAl based intermetallic alloys Ti–42Al–8.5Nb–0.2W–(Si,B,Y), Ti–46Al–8.5Nb–1Ta–(C,Si,B,Y), and Ti–47Al–2Cr–2Mo–(Si,B) (composition in at.%) in air at 700, 800 and 900 °C was studied in comparison with Ti–48Al–2Nb–2Cr. Isothermal oxidation tests were performed in humidified synthetic air for 150 h. Cyclic oxidation experiments were executed in static laboratory air with each cycle corresponding with a period of 1 h at test and 12 min at ambient temperature. The results revealed for Ti–47Al–2Cr–2Mo–(Si,B) a lower isothermal and cyclic oxidation resistance than for Ti–48Al–2Nb–2Cr. This was explained by a lower beneficial effect of molybdenum (compared with niobium) on the oxidation resistance of this type of γ-TiAl based alloy. An improvement of the isothermal and cyclic oxidation resistance, when compared with that of Ti–48Al–2Nb–2Cr, was obtained with both high niobium-containing alloys Ti–42Al–8.5Nb–0.2W–(Si,B,Y) and Ti–46Al–8.5Nb–1Ta–(C,Si,B,Y). Here, Ti–46Al–8.5Nb–1Ta–(C,Si,B,Y) showed the lowest isothermal oxidation rate and highest cyclic oxidation resistance.