Cyclic deformation features of a copper bicrystal with an embedded grain and surrounding grain boundary

Cyclic stress-strain response, surface slip morphology and saturation dislocation patterns in a copper bicrystal with an embedded grain G(E) and a surrounding grain boundary (GB) were investigated and compared with those of its matrix monocrystal by multi-step cyclic straining at room temperature in air. The experimental results showed that the cyclic stress-strain (CSS) curve of the matrix monocrystal exhibited a plateau region with the saturation resolved shear stresses of 28.8-29.4 MPa in the plastic resolved shear strain range of 4.7 x 10(-4)-3.18 x 10(-3). However, the copper bicrystal displayed relatively higher saturation stresses of 32.2-36.0 MPa, if modified by the orientation factor of the matrix grain, indicating no apparent plateau region in its CSS curve. Surface observations revealed that the primary slip system was dominant in both grains G(M) and G(E) except near the surrounding GB. By the electron channeling contrast (ECC) technique in scanning electron microscopy (SEM), the dislocation patterns of the bicrystal and the matrix monocrystal were observed. It was found that the two-phase structure of persistent slip bands (PSBs) and dislocation veins can nucleate in both grains G(M) and G(E) after cyclic deformation of the bicrystal. Based on the experimental results above, the effects of the surrounding GB and the embedded grain G(E) on the cyclic stress-strain response of the bicrystal were discussed. Those results might provide an experimental evidence for understanding the difference in CSS curves between copper single- and poly-crystals. (C) 1999 Elsevier Science S.A. All rights reserved.