Microstructure characterization of Cu processed by compression with oscillatory torsion

High purity Cu (99.9%) was subjected to severe plastic deformation up to a total effective strain εft = 130 through compression with the oscillatory torsion method at room temperature. This method produces an ultrafine grain microstructure. The microstructure evolution was investigated with respect to the value of the total effective strain using a scanning electron microscope with an electron-backscattered diffraction technique and a scanning transmission electron microscope. The results of the structural analyses show that increasing εft from 2 to 50 causes progress in the grain refinement. A quantitative study of the microstructure parameters, such as fraction of high angle boundaries, grain and subgrain diameter, and the area fraction of grains up to 1 μm, shows that deformation at εft = 45 guaranteed the best conditions for refining the microstructure of Cu. Using high values of εft in the range 60 to 130 restricts grain refinement because intensive recovery begins to dominate in the microstructure.