Comparison of cyclic deformation behavior between copper bicrystals and their component crystals

In this article, the cyclic deformation behavior of a combined copper bicrystal (CB), a naturally grown copper bicrystal (RB), and their component crystals (G1 and G2) was investigated under total strain amplitude control at room temperature in air. The bicrystal CB without grain boundary (GB) was prepared by joining the two single slip-oriented component crystals G1 and G2 in the gage. The results showed that the cyclic hardening rates and the axial stresses increased, in order, in the component crystal G2, the bicrystal CB, the bicrystal RB, and the component crystal G1. The cyclic stress-strain curves (CSSCs) of the component crystals G1 and G2 and the bicrystal CB exhibited a plateau behavior under the selected strain range. However, the cyclic saturation stress of the bicrystal RB increased with strain amplitude and did not show a plateau in its CSSC. Surface observations of the copper bicrystals and the component crystals revealed that the cyclic plastic strains were carried by the primary slip (B4) within the component crystals in the bicrystal CB and its component crystal G1 and G2. However, an additional slip (A3) within the component crystal G2 was observed in the vicinity of the GB in the bicrystal RB. The width of the additional slip region increased with strain amplitude and varied in the range from 265 to 650 μm. In order to compare the CSSCs of the copper bicrystals and their component crystals, an “orientation factor” for the copper bicrystal was introduced and the effect of the GB on the bicrystal RB is quantified during cyclic deformation.