The oxidation of TiB₂ particle-reinforced TiAl intermetallic composites

The oxidation kinetics of TiAl alloys with and without (3, 5, 10 wt.%) TiB₂ dispersoids were studied between 1073 and 1273 K in atmospheric air. The inert TiB₂ dispersoids effectively increased the oxidation resistance of TiAl alloys. The higher the TiB₂ dispersoids content, the more pronounced the effect. The oxide scale formed on TiAl-TiB₂ composites was triple-layered, consisting mainly of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner (TiO₂ + Al₂O₃) mixed layer. No B₂O₃ was observed within the oxide scale because of its high vapor pressure. A thin Ti₃Al sublayer and discrete TiN particles were found at the oxide-substrate interface. During the oxidation of TiAl alloys with and without TiB₂ dispersoids, titanium ions diffused outwardly to form the outer TiO₂ layer, while oxygen ions transported inwardly to form the inner (TiO₂ + Al₂O₃) mixed layer. The increased oxidation resistance by the addition of TiB₂ was attributed to the enhanced alumina-forming tendency and thin and dense scale formation.