When Co-20 wt.\% 20 Cu specimens liquid phase sintered at 1150℃ are heat-treated at 1300℃, the liquid films migrate very rapidly, leaving behind new solid solutions enriched with Cu and soon the reversal of migration direction occurs. The calculated driving force for liquid film migration from the coherency strain model in the case of low strain limit is almost same the coherency strain energy of frontal diffusion layer using the Gibbs free energies of solid and liquid phase in Co-Cu system. Also, it is worthwhile to mentioning that even when it is not in the limit of low strain, the origin of the driving force for LFM is the coherency strain of frontal diffusier layer ahead of migrating liquid film. When the liquid phase sintered Co-20Cu specimens are heat-treated with the powder mixtures added 10Sn at 1300℃, the liquid film migration is not observed. But when the amount of Sn in the powder mixture increases or the experiment temperature is 1150℃, the liquid films migrate. the inhibition of LFM at high temperature is ascribed to the loss of the coherency strain energy, resulting from the coherency breaking because of high D/v. Here, D is the lattice diffusivity of solute and v is the migration rate of liquid films.
When Co-20Cu specimens liquid phase sintered at 1300℃ are heat-treated at 1150℃, the precipitation of Cu-rich liquid occurs as well as CIIM because of the retrograde solubility of Co-rich solid solution. The shape of the liquid precipitate is sphereical at very early heat-treatment and changes into the cuboid and sphere with the heat-treatment times. The cuboidal shape observed only during growing in the supersaturated solid solution is caused by the anisotropy of the diffusional coherency strain energy due to the concentration gradient around the liquid precipitate. After a long heat-treatment, when the coherency strain becomes zero because of the supersaturation decrease, the shape of the precipitate has changed to the spherical one.
