Reaction diffusion in Ni–Al diffusion couples in steady magnetic fields

Abstract

The effect of a steady magnetic field on reactive diffusion in Ni–Al diffusion couples was investigated. The diffusion couples prepared by the electrodeposition technique were annealed in the temperature range of 530–590°C with and without the magnetic field of 6T. Regardless of the magnetic field, two intermetallic compounds, i.e., Ni2Al3 and NiAl3, were present in the product layers of diffusion couples. NiAl3 phase shows island-like structures at relatively lower temperatures while the Ni2Al3 phase forms a typical layered structure. The growth of Ni2Al3 layer was found to be parabolic. When the diffusion direction was perpendicular to the direction of the magnetic field, the external magnetic field reduced the growth rate of the Ni2Al3 phase. Whereas the magnetic field had no obvious effect on the growth rate of Ni2Al3 layers in the diffusion configuration of mutually parallel directions. The magnetic field intensity and direction dependence of growth rate of Ni2Al3 intermetallic layers can be attributed to the change in number of collision of an atom with neighbors during diffusion due to spiral motion under the action of the Lorentz force, which leads to change the frequency factor, not activation energy, for layer growth.