Influence of applied electric field on atom diffusion behavior and mechanism for W/NiFe interface in diffusion bonding of Steel/NiFe interlayer/W by spark plasma sintering

Abstract

Influence of applied electric field on atom diffusion behavior and mechanism for W/NiFe interface in diffusion bonding of Steel/NiFe interlayer/W by spark plasma sintering was studied using the first-principles calculations. The result indicates that applied electric field reduces d-orbital electron concentrations of W atom and Ni atom effectively, and then weakens W-W metallic bonding/Ni-Ni metallic bonding and Nisp-W metallic bonding/Wsp-Ni metallic bonding for W/NiFe diffusion interface, which decides the vacancy formation energy and solute atom migration energy. Therefore, the diffusion activation energy composed by vacancy formation energy and solute atom migration energy was reduced and leading to the increasing interfacial atom diffusion coefficient. Moreover, because W atom is more susceptible to applied electric field due to the smaller stability of d-orbital electrons than Ni atom, the decline degrees of W-W and Nisp-W metallic bonding strength are larger than those of Ni-Ni and Wsp-Ni metallic bonding strength. Therefore, the accelerating effect for Ni atom diffusing into W slab is larger than W atom diffusing into NiFe slab on W/NiFe interface, presented as that the diffusion activation energies for them decrease by 0.37 eV and 0.07 eV, and the diffusion coefficients at 1400 K increase by 26.72 times and 2.23 times, respectively.