Characterisation of orthorhombic (Ti25Al25Nb)/SiC intermetallic composites for advanced space applications

Intermetallic Matrix Composites (IMC) represent a relatively new area in the field of advanced materials. The combination of an intermetallic matrix and continuous reinforcements provides exceptional levels of room and elevated temperature strength, stiffness as well as low density. In particular, titanium aluminide composites reinforced with continuous fibres have recently received considerable attention due to their potential to replace titanium and the higher density nickel based superalloys for some applications. Aerospace structures and components in both jet engines and hypersonic vehicles -in which specific strength and stiffness, environmental conditions and working temperatures are paramount- could benefit from the development of these IMCS. Hot-skin, structural components and structures within the propulsion area of reusable vehicles are some of the potential components already identified for these advanced IMCS. Taking into account this scenario, the present work has developed and optimised the diffusion bonding technique for manufacturing orthorhombic titanium aluminide matrix composites, with a nominal composition of Ti-25Al-25Nb (at%) reinforced with continuous SiC fibres. The composite was manufactured comprising 4 unidirectional plies of SiC monofilaments (SM1140+ type from DRA) by uniaxial hot pressing through the foil/fibre/foil technique. Fibre/matrix interface and composite microstructure were examined by means of optical and electronic microscopies showing much lower reactivity than other titanium aluminide and titanium alloy based composites. The analytical electronic microscopy was mainly used for chemical analysis at the matrix/reinforcement interface in order to identify possible reaction compounds formed as well as the chemistry of the phases surrounding them. Three point bending tests were also performed with samples obtained from the panels manufactured.