| Summary: | Several appropriately treated alloys (Pb-6.5vol.%Cd, Pb-28vol.%Cd, Cd-6vol.%Pb and Zn-lwt.%Al) were investigated for their superplastic properties, and documented in terms of three-stage strain rate sensitivity curves in which stage II, the region of maximum superplasticity, was of prime interest. The investigation included analysis of: creep and tensile test data, surface deformation markings, activation energy tests and Instron inferences of a "backstress".
The rate controlling and prime strain-producing process in stage II was identified to be diffusional grain boundary sliding with slip accommodation at triple lines. Several interpretations were feasible for stage I, all involving processes concurrent with, and dependent on, grain boundary sliding. Stage III was identified as "normal" coarse-grained creep (adapted to permit considerable recovery in the vicinity of grain boundaries), operating independently of superplastic processes, and dominating at high flow stresses and strain rates. === Applied Science, Faculty of === Materials Engineering, Department of === Graduate
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