Diffusion of nickel through copper twist grain boundaries and influence of diffusion-induced recrystallization on volume diffusion in copper-nickel couples

A systematic study of the heterodiffusion of the Cu-Ni system along symmetric twist grain boundaries was performed. A total of six Cu bicrystals were grown using the vertical Bridgman technique. The Cu bicrystals were grown such that the grain boundary in each sample had a nominal twist misorientation, two with a low angle (10°), two with a special angle (Σ5 = 36.87°), and two with a high angle (45°). The grain boundary plane in all cases was (100).; The bulk bicrystals were then cut into 2 mm thick samples, ground and polished, and electroplated with Ni to provide for an infinite source for subsequent diffusion anneals. The plated bicrystal samples were annealed for 120 hours and 200 hours at temperatures ranging from 500°C up to 650°C. Areas of diffusion induced recrystallization (DIR) and areas devoid of DIR were observed in the vicinity of the Cu-Ni interdiffusion zone.; Transmission electron microscopy (TEM) specimens were extracted from the non-DIR regions of the interdiffusion zone using the focused ion beam in-situ lift-out technique. Concentration profiles were obtained from the TEM specimens using x-ray energy dispersive spectrometry in scanning transmission electron microscopy mode. Regions exhibiting DIR at the Cu-Ni interface resulted in the acquisition of an effective volume diffusivity that varied with grain size. The volume diffusivity of Ni into Cu was determined from non-DIR regions and found to be D = (2.64E-7 m2/S) exp(−207 kJ/RT) in the temperature range 500°C–650°C.; Grain boundary diffusion profiles were acquired by secondary ion mass spectrometry. Grain boundary diffusivities were determined using the volume diffusion data from this research. The Ni diffusion through Cu twist boundaries increases with grain boundary misorientation. The misorientation dependence is minimized at higher temperatures. The grain boundary activation energies for the 10°, Σ5, and 45° twist grain boundaries are 188, 156, and 88 kJ, in the temperature range 500°C–650°C, respectively. The associated grain boundary pre-exponential terms for the 10°, Y-5, and 45° twist grain boundaries are 8.60E-13, 2.17E-14, and 4.00E-18 m 3/s, in the temperature range 500°C–650°C, respectively. The Ni diffusion along Cu twist grain boundary data supports the prediction that diffusion along twist grain boundaries is approximately two orders of magnitude slower than diffusion along tilt grain boundaries of similar misorientation.