Effect of lubrication on the evolution of microstructure and texture during rolling and recrystallization of copper

Two polycrystalline copper specimens were deformed by cold rolling with and without lubrication so as to achieve different deformed microstructures. The effect of the different rolling procedures on the evolution of microstructure and texture during rolling and recrystallization was studied by microstructural observations and X-ray texture analysis. In addition, local orientations in the as-deformed state were determined by selected area diffraction (SAD) in a transmission electron microscope (TEM) and, after recrystallization, by electron backscattering diffraction (EBSD) in a scanning electron microscope (SEM). Whereas the rolling textures of the two differently rolled sheets were surprisingly similar, the microstructures strongly differed in so far as the sample rolled without lubrication contained a much larger amount of shear bands. The present results suggest that the shear component ε₁₃ caused by friction during dry rolling can effectively be dissipated by shear band formation, resulting in a rather homogeneous overall rolling texture. With regard to nucleation of recrystallization, shear bands are known to cut the typical nucleation sites of the cube-orientation, the main recrystallziation texture component of rolled copper, but they are also able to act as new nucleation sites. Furthermore, growth of the new recrystallized grains is hindered by the shear bands because of microstructural and orientation discontinuities at the matrix-shear band interfaces. This led to a strong retardation of the recrystallization process and gave rise to a very fine grained microstructure and a weak recrystallization texture in the specimen cold rolled without lubrication.