GRAIN-BOUNDARY DIFFUSION AND MOTION ASSOCIATED WITH PRECIPITATION ANDDISSOLUTION IN METALLIC SYSTEMS

The microstructural evolution resulting from the combination of grain boundary diffusion-controlled phase transformations in typical alloy s ystems is described. For this purpose discontinuous precipitation lame llar products in Cu-In and Ni-Sn binary alloys have been subjected to dissolution treatments, Examination of the resulting microstructures h ave shown that, depending on the alloy composition and annealing tempe rature, the dissolution could be discontinuous or continuous. In the f ormer, the dissolution process is controlled by diffusion along migrat ing grain boundaries. In the latter, it is dominated by volume diffusi on while the grain boundaries remain stationary. The most striking fea ture 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 grain s, giving rise to a localized grain refinement. In the absence of any plastic deformation applied to the material, the role played by the in ternal stresses and the lamellar interfaces generated during the preci pitation process is discussed, particularly as the energetic potential far the observed recovery and recrystallization phenomena.