Kirkendall Effects Of Cu-ni Couples Under High Magnetic Field Conditions

High magnetic fields can transfer high intensity magnetization energy to substances on the scale of atom or molecule, and change its arrangement,matching,migration and even change the thermodynamics state of the materials without any contacting. Under the high magnetic field conditions, materials will be affected by the strong magnetic force which is large enough even for non-ferrous magnetic materials. Therefore, in the fields of materials fabrication processing, the application of high magnetic fields could be a good substitute method for research comparing with conventional methods.In this paper, the Kirkendall Effects under high magnetic field on conditions atomic diffusion of Cu-Ni diffusion couples have been investigated by using optical microscope, digital microscopy and electronic microprobe analysis. The changes of marker movement and diffusion layer thickness of Cu-Ni diffusion couples under various high magnetic field conditions were investigated. Boltzmann-Matano plane solution method was used to calculate the interdiffusion coefficient, followed by the intrinsic diffusion calculation of copper and nickel atoms using Darken equations. By investigating the diffusion behavior under the effects of magnetic field intensity, gradient and direction, the mechanism of high magnetic field on diffusion process of Cu-Ni diffusion couples was discussed. The main results are presented as the followings:When specimens of Cu-Ni diffusion couples were annealed under the uniform high magnetic field conditions, the atom diffusion speeds were strongly affected by the magnetic field direction. It was found that magnetic field direction is the key factors to influence the atomic diffusion speed. In the DPB directions (parallel to B), with high magnetic field strength increasing, the distance of marker migration increased. However, in the DVB directions (vertical to B), the marker movement had no significant change with high magnetic field strength increasing.During diffusion annealing, the marker migrated from the interface to the nickel side of Cu-Ni diffusion couples. Due to the diffusion velocity of nickel atom was more rapidly than that of copper atom, In the DPB direction, the thickness of diffusion layer was increased with the enhancement of magnetic field strength under various magnetic flux densities. Taking these results together, a uniform high magnetic field accelerated markedly the interdiffusion speed of copper and nickel atoms. Comparing with the copper atom diffusion velocity, intrinsic diffusion of nickel was significantly faster than that of copper with magnetic field intensity increasing, which could attribute to that high magnetic intensity, changed atomic relative diffusion speed.Moreover, it was found that gradient high magnetic fields could significantly inhibit the interdiffusion between copper and nickel atoms and clearly retard the movement of Mo-markers in Cu-Ni diffusion couples. The effects of magnetic field were different in DPB and DVB directions for the movement of Mo-markers under gradient high magnetic field conditions. It can be concluded that the retarding effect of the vertical directions on diffusion are greater than that in the parallel directions.