Grain Boundary Dislocations and Stacking Defects in the 9R Phase at an Incoherent Twin Boundary in Copper

Abstract

Experiment and modeling show that there is a general mode of grain boundary dissociation, common in low stacking fault energy FCC metals, that can be well understood in terms of the emission of arrays of stacking faults from the grain boundary plane. Most extensively studied of such dissociated interfaces are the Σ=3 incoherent twin boundaries. Numerous observations now exist of grain boundary dissociation at such interfaces showing a layer that is well described as a narrow, several nanometer wide slab of 9R stacked material. The 9R stacking sequence is equivalent to a close-packed stacking of FCC ﹛111﹜ planes with an intrinsic stacking fault inserted every three planes (i.e., a stacking sequence of ABC/BCA/CBA …). The width of the 9R layer is sensitive to the local stress state. Figure 1 shows results of an atomistic calculation simulating the effect of an applied shear strain parallel to the boundary.