Diffusion-controlled deformation of particulate composites

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Abstract
Unusual mechanical effects at elevated temperatures have been observed in a composite system of zinc containing large volume fractions (0·05 to 0·30) of small (< 1 μm) Al<2O3 or W particles. These materials are dispersion-weakened in the temperature range 0·3 to 0·7T m, and show marked insensitivity of flow stress to changes in strain rate or temperature at about 0·7T m. Strain-ageing yield points are also observed at 0·6T m. An explanation for such behaviour proposes that, above a threshold stress, mobile dislocations are generated at particle–matrix interfaces by local incompatibility stresses, and that these dislocations have a dominant effect on the nominal flow stress in the region 0·3 to 0·7T m. A constitutive equation reminiscent of the Ansell–Weertman theory for creep of dispersion-strengthened materials is derived from the model, and compared with experimental creep data.