| A systematic study is presented in order to study the effects of Bi grain boundary segregation on the grain boundary diffusion of Ni into three ⟨100⟩ Cu symmetric twist grain boundaries (10°, 36.87°(Σ5), and 45°). Six ⟨100⟩ Cu symmetric twist bicrystals were grown, two each for the 10°, 35.87(Σ5), and 45° misorientations. The bicrystals were diffusion doped with Bi to 96 ± 11.8 at. ppm, then annealed between 500–650°C to allow for segregation to the Cu grain boundaries. The Bi segregation was quantified utilizing x-ray energy dispersive spectroscopy (XEDS) in transmission electron microscopy/scanning transmission electron microscopy (TEM/STEM). An average grain boundary coverage of Γ Bt = 4.2 ML was obtained for all samples. However, the amount of Bi segregation depends on both the grain boundary misorientation angle and the crystallography of the grain boundary plane. Concentration profiles were obtained using quadrupole secondary ion mass spectrometry (SIMS). The Whipple-LeClaire solution for Type B grain boundary diffusion was utilized to determine the grain boundary diffusion coefficient sδD bo and the activation energy Qb from each of the ⟨100⟩ Cu twist grain boundaries. The presence of the Bi grain boundary segregation had the effect of both enhancing or reducing the grain boundary diffusion of Ni into the Bi segregated Cu grain boundaries. The enhancement or reduction of the Ni diffusion varied with the grain boundary structure, Bi composition at the boundary and temperature. It is suggested that the enhancement or reduction of the Ni diffusion through the Bi segregated ⟨100⟩ Cu twist grain boundaries depends on the amount of Bi and the type of phase that is present in the grain boundary. An empirical model is presented to account for the effects of Bi segregation on the grain boundary diffusion of Ni in ⟨100⟩ Cu twist grain boundaries. |
