Optimisation of a multiphase intermetallic metal–metal composite material

Abstract

Metal–metal composites (MeMeCs) manufactured by coextruding β[Ni(Al,Ti)], β′[Ni₂AlTi] and γ′[Ni₃(Al,Ti)] show promise as high strength, heat resistant materials. The best combination of strength and plasticity are obtained by using a high fraction (0·8) of γ′ as the matrix phase combined with equal fractions of β and β′ reinforcement. Further improvements in properties may be obtained by increasing the fracture strength of the matrix phase following the methods used in monolithic γ′ alloys. Boron additions are shown to lead to significant improvements in tensile fracture strength. The highest levels of plasticity were obtained in an MeMeC material which had a matrix composition designed to allow the more ductile γ phase to precipitate in the γ′, as well as containing boron to increase grain boundary cohesion. Fractography suggests that tensile failure occurs in this material in a much more ductile way, with evidence of local plastic deformation and a largely transgranular failure mode rather than the intergranular fracture observed in the other MeMeC materials.