Fabrication and properties of continuous unidirectional Mo fiber reinforced TiAl composites by slurry casting and vacuum hot pressing

TiAl matrix composites reinforced by continuous fibers are potential structural materials for application in aerospace industry. However, the complicated fabrication procedures and high cost limit their applications. In this paper, slurry casting was proposed to simplify the fabrication procedures, and metallic Mo fibers instead of brittle ceramic fibers were applied to improve the room temperature brittleness and high temperature strength of the TiAl matrix, due to molybdenum's low price, good toughness and excellent high temperature mechanical properties. Firstly, slurries were prepared by mixing Ti and Al elemental powders with organic binder (polymethyl methacrylate) and solvent (acetone); and then a monolayer of preform was fabricated by coating a layer of aligned Mo fibers with a certain thickness of slurry; after reaching the expected number of layers the preform were cut and finally degassed and consolidated by vacuum hot pressing to produce composites. 20 vol.% Mof/TiAl composites with Mo fibers distributing uniformly in the matrix without bending were obtained. The matrix and fibers are well bonded through a reaction zone which consists of a thin δ-(Mo, Ti)3Al inner layer and a thick β'-(Mo, Al)Ti outer layer. The composite consolidated at 1100 °C exhibits a good balance of room temperature and high temperature (800 °C) strength, 721 MPa and 731 MPa, respectively. The Mo fibers' plastic deformation, necking and debonding contribute to the toughening of the composites. And the composites are greatly strengthened at high temperature due to the good properties of Mo fibers.