Erosion behaviors and the control of fiber structure in Al₂O_3,f/TiAl composites

Continuous Al₂O₃ fiber reinforced TiAl composite (Al₂O_3,f/TiAl) is expected to be promising to satisfy the tougher conditions in space industry. However, the thermostability of Al₂O₃ fibers in TiAl alloy has not been well studied. In this work, continuous Al₂O₃ fibers (containing 28 mol.% SiO₂) have been introduced in Ti-48Al-4Nb-2Cr alloy by powder metallurgy technology at different hot pressing temperatures. The erosion reactions of Al₂O₃ fibers in TiAl matrix have been investigated by thermodynamic calculation. A evolution model of the interface regions has been established. It has been determined in this study that micropores can be eliminated completely at hot pressing temperature of 1050 °C while ensuring the integrity of Al₂O₃ fibers. Thermal exposure tests revealed the erosion reaction of fibers was mainly dominated by element diffusions of Ti and Si, and the erosion product was determined to be Ti₅Si₃. Based on the regulation of erosion reactions, a novel multilayer fiber structure with higher modulus has been achieved which could be matched with TiAl alloy and expected to improve strength/toughness of the Al₂O_3,f/TiAl composite.