Erosion behaviors and the control of fiber structure in Al2O3,f/TiAl composites

Abstract

Continuous Al2O3 fiber reinforced TiAl composite (Al2O3,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 Al2O3,f/TiAl composite. This structure contains a core of original fiber and coated by three composite ceramic layers, which can be obtained at hot pressing condition of 1050 °C/50 MPa/2 h and thermal exposure of 1050 °C/60 min