Evolution of FCC/BCC interface and its effect on the strengthening of severe drawn Cu–3 wt.% Cr

Abstract

Metal composites have attracted great interest for the combination of high strength and high electrical conductivity. We take the Cu–3wt.% Cr composite as a model system to reveal the structure–property relations in a large range of drawing strains (η), and propose the strengthening mechanism during cold drawing. At small and moderate drawing strains, the incoherent and semi-coherent interfaces are effective barriers for dislocation motion and pile-up. The mechanical behaviors are described well by the Hall–Petch relation. The work hardening at η<4.5 is the direct consequence of the grain refinement and the increasing density of phase boundaries, which can be well modelled by a linear rule of mixture. Deviation is observed at η>4.5, when the strength gradually reaches a plateau. Microstructural analysis reveals that further refinement can hardly occur at high drawing strains due to the dynamic recovery process. Another characteristic of the turning point is the structural homogenization, i.e. the mechanical alloy induced inter-mixing and the full coherency. The transition of the interface coherency is clearly identified by both electron diffraction and high resolution transmission electron microscopy. The structural homogenization at the interface may alleviate the interfacial blockage to the dislocation slipping, indicating the existence of an interfacial strength limit. The linear rule of mixture is modified to account for this effect at η>4.5. The complete mechanical behavior of the Cu–3wt.% Cr composite is captured by a piece-wise function.