Microstructure characterization of ultra-fine grained Cu-0.17wt%Zr

The first part of the study was dedicated to investigate the recrystallization behavior of the samples subjected to high levels of strain via high pressure torsion. The deformed structure revealed the simple shear texture components of the FCC materials. The strongest texture components with increasing the strain level kept the same character from strain levels of about 9. The grain size decreased at the first increasing levels of the strain and then reached the saturation in refinement of the microstructure. The microstructure evolution of the heat-treated samples showed that there were some grains, growing discontinuously during heat treatment of the samples. Due to the high fraction of high angle grain boundaries, it was expected that the material shows homogenous changes of microstructure during heat treating, which was not the case. Accordingly the stored energy evolution depicted that the stored energy decreases during annealing processes. The texture results demonstrated the dominance of the B component and B components in the annealed state. The stored energy of each texture component existing in the deformed microstructure was approximated using the kernel average misorientation, however there was no correlation between the stored energy of the texture components and their appearance during heat treatment. A correlation between the grain size and the stored energy was observed. During annealing of the samples the larger grains yielded the smallest stored energy. This could be explained by the fact that grains reducing their stored energy grow in the deformed microstructure and develop a bimodal structure. The driving force for formation of these grains was obtained most probably from the stored energy of the dislocations. This can be an indication of primary recrystallization. But the preferable domination of specific texture components was not related to their stored energy but is probably caused by the character of grain boundaries. Since the driving force for the discontinuous grain growth and primary recrystallization is in the same order of magnitude, it can be concluded that both processes are active during heat treatment of the strongly strained samples.