Chemically induced migration of liquid films and grain boundaries in MoNi(Fe) alloy

Abstract

The liquid films and grain boundaries in liquid phase sintered 90 Mo-10 Ni alloy (wt%) migrate when Fe is added to the molten matrix. The growth of MoNiFe ternary solid solution at the expense of the MoNi solid initially formed during the liquid phase sintering is clearly revealed by a strong etching. The alloy formed behind the migrating liquid films is shown to have a uniform distribution of Fe atoms by an electron microprobe analysis. The increase of the migration rate with the amount of Fe added and with the estimated change of the lattice parameter from MoNi to MoNi-Fe solid solutions is parabolic in agreement with the prediction of the coherency strain model. An estimate of the driving force from its balance against the interface curvature also agrees in order of magnitude with the coherency strain energy. The observed grain boundary migration is identical to the diffusion induced grain boundary migration (DIGM) with a liquid solute source. The results demonstrate that it is possible to vary the migration rate systematically by manipulating the coherency strain through the amount of solute added to the liquid matrix in this type of experiments.