PORTEVIN-LeCHATELIER EFFECT AND OBSERVATION OF SLIP BAND GROWTH IN Cu-Al SINGLE CRYSTALS

By measuring macroscopic quantities (stress, strain rate, temperature) and observing simultaneously through the light microscopie the evolution of slip bands (their number, height, arrangement) on single crystals of Cu-2...15at% Al in the temperature range from room temperature to 500 °C, the details of the microprocesses which dermine the flow stress in stage I are studied, in particular those occurring at the onset and during serrations in the Portevin-LeChatelier regime. With increasing temperature the number of simultaneously active slip band bundles decreases until during each serration only a single bundle grows very rapidly by adding a group of slip bands at its margin. A one to one correlation is found for the drop in load and the increase of the number of slip bands in the observed small region of the crystal. The observations are used to interpret the differences in strain rate sensitivities (activation volumes) measured by strain rate change and stress relaxation experiments.

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