TEXTURE AND MICROSTRUCTURE DEVELOPMENT IN COPPER AFTER CRYOGENIC ROLLING AND HEAT TREATMENT

Present study aims at investigating the texture evolution and mechanical properties of bulk nanocrystalline / ultra fine grained pure Cu after cold deformation (86%) at cryogenic temperature (liquid nitrogen) and recrystallisation at different temperatures. Ctyogenic rolling of Cu has been used to produce nano-grain sizes with bimodal distribution so that total elongation is improved along with strength. A few fold increments in tensile properties were observed in this study. Both bulk and micro textures were determined using XRD and EBSD. Neither the pure brass-type nor the pure Copper-type could be observed. Both brass and near Copper (not ideal Cu-type texture) with significant strength along with S (strongest) were present. During heat treatment (180- 300 degrees C), bulk textures showed a gradual weakening with increase in temperature and time. EBSD study confirmed that significant amount of deformed structures were still present after heat treatment. But the texture of the recrystallised fraction got randomized in all the cases. This difference in texture formation in the present case and the as reported by other researcher, is attributed to higher impurity content and diffrenct rolling temperature. Significant dependence of mechanical property on grain size has been recorded. Present study indicates that conventional rolling at subzero temperature followed by controlled recrystallisation may be utilised as an effective method for development of bulk Cu, with two to three fold improvement in yield strength in comparison to its coarse grained counterpart with moderate ductility and toughness.