High strength-high conductivity fibre-reinforced copper alloys

Abstract
High strength copper-based alloys reinforced with fibres of a bcc metal such as Cr,Nb,Ta, produced by very high strain drawing of cast eutectic mixtures, have been studied for some time. Fine bcc fibres leading to high strength can be produced, but only for thin sheets or fine wires because the drawing strains necessary are so high (>99.99%). Ultra-fine microstructures are produced here by using spray deposition techniques to give a finer starting microstructure than obtained by conventional casting, followed by high strain drawing to achieve high strengths in wires of reasonable diameters. The microstructures produced by these procedures are analysed by electron metallographic techniques and shown to be highly refined. Grain widths in the range 50-100nm are produced with bcc metal fibres of thickness below 10nm. Once this nanometric level is attained the strength of the composite depends only on the scale of the component phases - that have no further internal structure - and strengthening mechanisms operating can be more easily determined. The fibres are seen to behave as an ideally-strong, dislocation-free material but which contribute only a small part of the composite strength. The most significant strengthening contributions arise from the refinement of the scale of the copper matrix, a refinement that is induced by the fibres stabilising grain boundaries.