Grain Boundary Evolution and Its Interaction with Shear Band in Continuous Columnar Crystal Cu-ECAP
GUO Tingbiao1,2, WEI Shiru1, WU Yibo1, WANG Bing1, MA Di1
1 State Key Laboratory of Advanced Processing and Recycling of Nonferrous Metals, Lanzhou University of Technology, Lanzhou 730050 2 Key Laboratory of Non-ferrous Metal Alloys and Processing, Ministry of Education, Lanzhou University of Technology, Lanzhou 730050
Abstract: The shear band of metals formed during plastic deformation will be divided into a twinning and matrix lamellar structure under high strain condition, and the nano-scale twin boundary can achieve a high degree of matching between strength and plasticity of metals. Accordingly, it will provide an effective support for the strength and plasticity matching of materials through studying the formation and action of shear bands by means of equal channel angular extrusion (ECAP) technique. In this work, one pass ECAP was conducted on the continuous columnar crystal pure Cu with special grain boundary angle, the evolution of grain boundary during deformation was studied, the formation mechanism of shear band as well as its interaction with grain boundary during deformation were analyzed, and the mechanical properties of samples with different orie-ntations were tested. As could be seen from the results, after ECAP deformation, the 0° grain boundary was bent, the grain boundary at the inner corner rotated 50° clockwise, 30° grain boundary rotated 5° clockwise, 45° grain boundary was also bent and showed a "spoon" shape, the center of 60° grain boundary was bent, and there was no deformation occurred at 90° grain boundary. Multiple stress regions with diverse stress states appeared during the deformation process of the sample. Alternating action of various stresses brought about the nonuniform strain distribution during the deformation process, resulting in great differences in macroscopic deformation. The tensile test results indicated that the crystal with 0° grain boundary possessed the highest tensile strength of 325 MPa, followed by the crystal with 45° grain boundary (295 MPa), and the crystal with 60° grain boundary held the lowest tensile strength of 230 MPa. A large number of shear bands were formed in the grains after deformation, and the interaction between the shear bands and the grain boundary results in the bending of the grain boundary. The difference of grain orientation and grain boundary angle between the shear band and the grain boundary is one of the factors that cause the great difference in tensile strength after deformation.
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2019, Vol. 33 
