Cyclic deformation behavior and intergranular fatigue cracking of a copper bicrystal with a parallel grain boundary

Abstract

Abstract Cyclic deformation behavior and intergranular fatigue cracking of a [4 9 16]/[4 9 27] copper bicrystal with a grain boundary (GB) parallel to the stress axis were investigated under constant plastic strain control at room temperature in air. It was found that cyclic saturation stresses of the bicrystal increased with increasing strain amplitude, and were higher than the plateau stress of 28–30 MPa, if modified by an orientation factor ΩB of the bicrystal. Surface observations showed that a GB affected zone (GBAZ) with secondary slip formed owing to plastic strain incompatibility near the GB. As cyclic deformation was continued, fatigue cracks always initiated at the intersection sites of persistent slip bands (PSBs) with the GB. Gradually, they linked each other along the GB, leading to intergranular cracking. However, fatigue crack nucleating along slip bands was not observed as intergranular cracking occurred. It is indicated that intergranular fatigue cracking is the major damage mode even though the GB was parallel to the stress axis. Based on the results above, the GB strengthening effect and intergranular fatigue cracking mechanism were discussed in combination with the GBAZ and the interaction between PSBs and GB.