Substructure and strengthening of heavily deformed single and two-phase metallic materials

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Abstract
Work hardening of single-phase crystalline materials (and to some extent, coarse two-phase and dispersion hardened materials too) at low temperatures results from the competition of two dynamic processes: dislocation accumulation, during the long-range gliding of mobile dislocations and dynamic recovery, involving local rearrangements and length annihilation from mobile and stored dislocation interactions. Its complete understanding would be very useful for designing materials with maximized strength after heavy cold work. However, modelling of the strain-induced evolution of the dislocation substructure, an essential ingredient of any work hardening theory, is still far from satisfactory. On the other hand, some heavily deformed ductile two-phase in situ composites are only second to whiskers among the strongest metallic materials. At first sight, the main obstacle geometry for dislocation glide in lamellar or multifilamentary in situ composites being clear-cut, it can be thought that their strength and work hardening are completely understood. However, this is not so and several schools of thought propose different interpretations for the exaggerated departure of the stress-strain curves of in situ composites from the rule-of-mixtures curves built from those of their bulk components. This paper aims to discuss such interpretations. The composite Cu-Nb is taken as model material owing to the extensive and detailed mechanical and microstructural data available in the literature, including different deformation temperatures and two different strain paths. Fine pearlite Fe-Fe3C is the other obvious reference

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