Metals Microstructure Improving under Hard Cyclic Viscoplastic Deformation
Annealed pure copper was subjected to equal-channel angular pressing (ECAP) by route Bc for different passes number. Tensile test specimens were manufactured and subjected to hard cyclic viscoplastic (HCV) deformation by means of the materials testing installation Instron 8516 in strain control regime at room temperature. The specimens were cyclically deformed with a frequency of 0.5Hz at different strain amplitudes, step-by-step increased from ±0.05 to ±2.5% for 30 cycles, up to seven test series in this study. The microstructure of ECAP and HCV deformed samples were characterized by optical- and transmission electron microscope, X-ray diffraction, tensile- and hardness testing methods. The ECAP processed metal has mainly elongated subgrains with low-angle grain boundaries and texture, oriented in direction of metal flow during latest pressing. We demonstrate that during HCV deformation the dislocations density of ECAP processed UFG copper was decreased. The ECAP texture was reoriented under cyclic load applied as elongated subgrains were jointed to small pieces under this same angle to axis as texture before. The grain- and crystallite sizes were decreased, which were accompanied with dislocation ribbons forming nearby new formed high-angle grain boundaries. This paper builds on knowledge that the combined treatment by ECAP and followed HCV deformation enable to improve UFG microstructure and ductility with lowering the strength and hardness of UFG metals due to the lower dislocation density while coarse grained copper exhibits increasing the strength and hardness.
Yuri Estrin and Hans Jürgen Maier
L. A. Kommel "Metals Microstructure Improving under Hard Cyclic Viscoplastic Deformation", Materials Science Forum, Vols. 584-586, pp. 361-366, 2008