Grain boundary diffusion and motion associated with precipitation and dissolution in metallic systems

Overview & Synopsis

The microstructural evolution resulting from the combination of grain boundary diffusion-controlled phase transformations in typical alloy systems is described. For this purpose discontinuous precipitation lamellar products in Cu-In and Ni-Sn binary alloys have been subjected to dissolution treatments. Examination of the resulting microstructures have shown that, depending on the alloy composition and annealing temperature, the dissolution could be discontinuous or continuous. In the former, the dissolution process is controlled by diffusion along migrating grain boundaries. In the latter, it is dominated by volume diffusion while the grain boundaries remain stationary. The most striking feature of the post-dissolution microstructure in these alloys is related with two phenomena observed within the previously transformed product : generation of dislocation arrangements or new dislocation-free grains, giving rise to a localized grain refinement. In the absence of any plastic deformation applied to the material, the role played by the internal stresses and the lamellar interfaces generated during the precipitation process is discussed, particularly as the energetic potential for the observed recovery and recrystallization phenomena.