Equal-channel angular (ECA) pressing is a procedure having the capability of introducing an ultrafine grain size into a material. Experiments were conducted to examine the effect of the low stacking fault energy in pure Cu on microstructural development during ECA pressing at room temperature. The results show that the low 0stacking fault energy and the consequent low rate of recovery lead to a very slow evolution of the microstructure during pressing. Ultimately, a stable grain size of −0.27 μm was established in pure Cu but the microstructure was not fully homogeneous even after pressing to a total strain of ∼10. It is shown by static annealing that the as-pressed grains are stable up to ∼400 K, but at higher temperatures there is grain growth. These results lead to the conclusion that a low stacking fault energy is especially favorable for the introduction of an exceptionally small grain size using the ECA pressing procedure.
An Al-3 pct Mg-0.2 pct Sc alloy was fabricated by casting and subjected to equal-channel angular pressing to reduce the grain size to ϳ0.2 m. Very high tensile elongations were achieved in this alloy at temperatures over the range from 573 to 723 K, with elongations up to Ͼ2000 pct at temperatures of 673 and 723 K and strain rates at and above 10 Ϫ2 s Ϫ1 . By contrast, samples of the same alloy subjected to cold rolling (CR) yielded elongations to failure of Ͻ400 pct at 673 K. An analysis of the experimental data for the equal-channel angular (ECA)-pressed samples shows consistency with conventional superplasticity including an activation energy for superplastic flow which is within the range anticipated for grain boundary diffusion in pure Al and interdiffusion in Al-Mg solid solution alloys.
An Al-3 pct Mg-0.2 pct Sc alloy was fabricated by casting and subjected to equal-channel angular pressing to reduce the grain size to ϳ0.2 m. Very high tensile elongations were achieved in this alloy at temperatures over the range from 573 to 723 K, with elongations up to Ͼ2000 pct at temperatures of 673 and 723 K and strain rates at and above 10 Ϫ2 s Ϫ1 . By contrast, samples of the same alloy subjected to cold rolling (CR) yielded elongations to failure of Ͻ400 pct at 673 K. An analysis of the experimental data for the equal-channel angular (ECA)-pressed samples shows consistency with conventional superplasticity including an activation energy for superplastic flow which is within the range anticipated for grain boundary diffusion in pure Al and interdiffusion in Al-Mg solid solution alloys.
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