Slip behaviour near a grain boundary in high-cycle fatigue of poly-crystal copper

Abstract

In order to investigate the characteristic slip behaviour near a grain boundary in high-cycle fatigue, a high-cycle fatigue test is carried out using a copper poly-crystal specimen, which consists of several tens of grains. Seventeen persistent slip bands (PSBs) are observed along the grain boundaries. Their location and the activated slip system are different from those expected by the Schmid factor. After the fatigue test, the crystalline orientation and the three-dimensional shape of each grain are specified by the repetition of polishing and observation by means of an orientation-imaging microscope (OIM). A finite-element method (FEM) analysis is also conducted for the specimen with the same orientation and shape of grains taking into account the anisotropy. This analysis reveals that the shear stress concentrates near the grain boundaries where the PSBs are formed. The activated slip systems predicted by the maximum resolved shear stress agree well with those observed in the fatigue experiment. Thus, the characteristic slip near the grain boundary in the polycrystal is governed by the concentrated resolved shear stress on the specific slip system due to the deformation constraint by neighbouring crystals.