Microstructural Evolution and Recrystallization Behavior in Copper Multi-Directionally Forged at 77 K
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.
T. Chandra, K. Tsuzaki, M. Militzer and C. Ravindran
Y. Nakao et al., "Microstructural Evolution and Recrystallization Behavior in Copper Multi-Directionally Forged at 77 K", Advanced Materials Research, Vols. 15-17, pp. 649-654, 2007