Optimisation of a multiphase intermetallic metal - metal composite material

Metal-metal composites (MeMeCs) manufactured by coextruding beta [Ni(Al,Ti) ], beta'[Ni2AlTi] and gamma'[Ni-3(Al,Ti)] show promise as high strength, he at resistant materials. The best combination of strength and plasticity are obtained by using a high fraction (0.8) of gamma' as the matrix phase comb ined with equal fractions of beta and beta' reinforcement. Further improvem ents in properties may be obtained by increasing the fracture strength of t he matrix phase following the methods used in monolithic gamma' alloys, Bor on additions are shown to lead to significant improvements in tensile fract ure strength. The highest levels of plasticity were obtained in an MeMeC ma terial which had a matrix composition designed to allow the more ductile ga mma phase to precipitate in the gamma', as well as containing boron to incr ease grain boundary cohesion. Fractography suggests that tensile failure oc curs in this material in a much more ductile way, with evidence of local pl astic deformation and a largely transgranular failure mode rather than the intergranular fracture observed in the other MeMeC materials.