Fe/Ni diffusion behavior in the shear-extrusion solid state bonding process

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• A diffusion layer about 3 μm thick can be formed through Fe/Ni interdiffusion during the SEB process. • The main composition of the diffusion layer is Fe-Ni substitutional solid solution distributed in Ni base. • The maximum actual interdiffusion coefficient of Fe/Ni atoms can achieve 5.4 × 10 −13 cm 2 /s during the SEB process. • Relative diffusion layer thickness increases with the increase of deformation degree with a linear relationship. The shear-extrusion bonding (SEB) of pure iron (99.9 %) and pure nickel (99.5 %) are carried out under the experiment condition of heating temperature 1050℃, top die speed 12 mm/s with different deformation degrees. The Fe/Ni diffusion behavior is analyzed through experimental studies and theoretical analysis. The results indicate that a diffusion layer about 3 μm thick is formed through Fe/Ni interdiffusion and the main compositions of the diffusion layer are Ni and Fe-Ni solid solution. It is found a large number of vacant clusters are formed at the Fe/Ni interface in the SEB process. The diffusion of matrix atoms or substitutional solute atoms is mainly realized by vacancies, so the diffusion mechanism of Fe/Ni in SEB process is vacancy diffusion mechanism or vacancy pair diffusion mechanism. The actual interdiffusion coefficient of Fe/Ni in SEB process is 100∼1000 times higher than the interdiffusion coefficient of Fe/Ni atoms under thermal action. So the plastic deformation provides additional vacancies to promote the formation of diffusion layer. The relative diffusion layer thickness increases from 6.02 μm to 12.01 μm when the deformation degree increases from 50 % to 74.2 %, and the relative diffusion layer thickness increases linearly with the increase of deformation degree.