On the strength of heavily cold worked in situ composites

Document Type


Publication Date



Department of Materials Science and Engineering


The strengths of heavily deformed two phase materials are much in excess of those expected on the bases of the strain hardening behavior of the phases comprising such a composite. In this paper a model is developed to explain the strengths of this class of materials and the predictions of it are compared to results obtained in several systems. The basis for the model is that additional (geometrically necessary) dislocations are generated during deformation of two, as compared to single, phase materials as a result of the inherently greater strain incompatibility between adjacent grains in a two phase material. Thus the model predicts that, other factors being the same, the greater the disparity between the flow curves of the composite constituents, the greater the excess strength generated. The strain hardening behaviour of the individual phases influences also the strengths obtained in a composite. Composites comprised of materials for which dynamic recovery processes are particularly effective do not display large incremental strengths as these processes eliminate both geometrically necessary and statistical dislocations. Conversely, composites containing materials which do not dynamically recover (e.g. iron which work hardens linearly) display rather impressive excess strengths as a result of the complementary interaction between statistical and geometrical dislocations. The agreement between the model developed and experimental results is good. The two adjustable parameters of the model (one concerning the partitioning of the geometrical dislocations between the phases and the other a measure of the inherent strain incompatibility between them) have physically plausible numerical values.

Publication Title

Acta Metallurgica