Fatigue-cracking characteristics of a copper bicrystal when slip bands transfer through the grain boundary

Abstract

We reported the fatigue cracking characteristics of a special copper bicrystal with a tilt ∑ 19b grain boundary (GB) and a coplanar primary slip system between the two grains. It is found that the primary slip bands of the two adjacent grains have a good continuation across the GB on the four surfaces of the bicrystal specimen in the axial plastic strain range of 1.5×10 −4–2.13×10 −3. It indicates that the surface slip bands had transferred through the GB during cyclic deformation. When cyclic plastic strain was continued to be applied on the bicrystal specimens, fatigue cracks always initiated and propagated along the GB at all the applied strain amplitudes. By using electron channeling contrast (ECC) technique in scanning electron microscopy (SEM), the dislocation patterns near the GB of the bicrystal were observed. The ladder-like persistent slip bands (PSBs) did not transfer through the GB continuously, no matter what the surface or the common primary slip plane of the bicrystal. Instead, a dislocation affected zone (DAZ) or piling-up of dislocations near the GB was observed. Based on the results above, the fatigue cracking mechanism of the bicrystal was discussed and the GB cracking was attributed to the difference in the slip directions of the two adjacent grains.