| Chemically induced recrystallization occurs when Fe atoms are added to Mo-Ni grains in liquid phase sintered Mo-Ni alloys. Alloy specimens of 90Mo-10Ni by wt have been heat-treated at 1400℃ after replacing their liquid matrix by Cu-Fe melts of varying Fe concentration. When the Fe concentration in the Cu-Fe melt is 3 wt%, chemically induced grain boundary migration(CIGM) occurs. When the Fe concentrations are 5 and 10 wt%, chemically induced recrystallization(CIR) occurs at the grain surface with the recrystallized grain density increasing with the Fe content. The recrystallized grains contain Fe with the average amount increasing wigh the Fe content in the matrix, but the Ni concentration is reduced to 0 because of Ni depletion into the Cu-rich matrix. With advance of the recrystallization front, the Fe concentration in the recrystallized region decreases because of Fe depletion in the matrix. The density of misfit dislocations produced by diffusion of Fe atoms at the critical concentration required to nucleate CIR is estimated to be close to that for the recrystallization in cold worked solids. The result thus appears to be consistent with the theory that the nucleation of CIR is induced by solute diffusion producing misfit dislocations upon coherency breaking. When the specimen is sintered at 1540℃ and heat-treated at 1540℃ with Cu-10wt% Fe matrix, the recrystallization front stops when the Fe concentration decreases to such a level that the coherency strain is reduced to 0 due to simultaneous decrease of Ni concentration. The grain boundaries formed by recrystallization then move back to the specimen surface and disappear, leaving behind regions enriched with Fe and depleted of Ni. This behavior is consistent with the theory that the diffusional coherency strain energy acts as the driving force for the growth of grain nuclei formed in the recrystallization process. |
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