Microstructural Evolution and Recrystallization Behavior in Copper Multi-Directionally Forged at 77 K

Y. Nakao; Hiromi Miura; Taku Sakai

doi:10.4028/www.scientific.net/AMR.15-17.649

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Microstructural Evolution and Recrystallization Behavior in Copper Multi-Directionally Forged at 77 K
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Microstructural Evolution and Recrystallization Behavior in Copper Multi-Directionally Forged at 77 K

Abstract:

Microstructural evolution in pure copper during multi-directional forging (MDF) at temperature of 77 K was studied. Flow stress during MDF at 77 K showed a monotonical increase at all strain. Ultra fine (sub)grains of 0.15μm in diameter were evolved, which was accompanied by deformation twinning, at strain of Σε = 2.4. In higher strain region, Σε = 6.0, lamellar-look structure of twins extensively appeared. The lamellar spacing was 10-100nm. For comparison, samples were also MDFed at 300 K. The flow stress curves showed an apparent steady state flow at above strain of Σε =2.0, which implies occurrence of dynamic recovery. The evolved (sub)grain size was 0.3 μm at high strain of Σε = 6.0. Therefore, grain refinement seems to take place more easily by MDF at 77 K compared with that at 300 K due to effect of deformation twin. Microstructures evolved under MDF at 77 K and 300 K showed different annealing behavior. Static recrystallization started earlier and faster in the samples MDFed at 77K than those MDFed at 300K.