Taku Sakai and Zhou Xu
Department of Mechanical and Control Engineering, The University of Electro-Communications, Chofu, Tokyo
Effect of purity on static softening and grain growth taking place after dynamic recrystallization (DRX) was studied by means of interrupted compression tests and metallographic observations for the three kinds of polycrystalline coppers, the purities of which were 99.9(3N), 99.99(4N) and 99.9999(6N) mass%. The fractional softening-holding time (X-t) curves after dynamic recovery consist of two stages, followed by complete softening. In contrast, the softening curves for DRX matrices consist of three distinct stages accompanied with three plateaus, followed by incomplete softening (stage I, II and III). The X-t curves for DRX 3N and 4NCu are almost the same, but clearly different from that for 6NCu. The static softening for DRX 6NCu takes place one order of magnitude faster than that for 3N or 4NCu and finally approach X=1 after a long period of annealing time in stage III. The average rate of grain growth in stage III is always smaller than that for normal grain growth, although both the rates are controlled by grain boundary diffusion irrespective of purity of copper. This results from the stable existence of metadynamically recovered grains which have many-sided irregular shapes as well as high density dislocations. As these grains are metastable in thermodynamics, however, DRX matrices only for 6NCu finally replace fully recrystallized ones, followed by the occurrence of normal grain growth.
(Received September 8, 1994)
hot deformation, dynamic recrystallization (DRX), growing DRX grain, metadynamic recovery and recrystallization, static grain growth, copper, purity
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