Oxidation Behavior of a Spark Plasma Sintered Ti–48Al–2W–0.1B Alloy at 800 °C
Résumé
Spark plasma sintering (SPS) enables the manufacturing of TiAl alloys with an exceptional combination of low density and mechanical properties such as acceptable ductility at room temperature and high strength at high temperature. However, TiAl alloys are known to exhibit low oxidation resistance above 700 °C. The oxidation of a Ti–48Al–2W–0.1B (at. %) processed by SPS was investigated at 800 °C. Coupons were oxidized in air and in Ar-21O2 (vol%), in isothermal and cyclic tests. In air, the alloy formed a mixture of Ti and Al oxides, but oxidation was slower than typically observed for W-free alloys. The oxide scale and underlying alloy were characterized by X-ray diffraction and electron microscopy in order to examine the beneficial role of W in the oxidation resistance. The main constituents of the reaction product after reaction in air may be described as follows (from gas to alloy): TiO2/porous Al2O3/TiO2 + Al2O3/TiN + Al2O3 + W/TiAl2 + W/TiAl. Close examination suggests that the relatively good oxidation resistance of the alloy is related to W doping of TiO2 in the mixed Al2O3 + TiO2 layer. The alloy formed an Al-rich oxide scale with much slower kinetics in Ar-21O2, confirming the detrimental role of N in the oxidation process.
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