Relaxation of interphase stresses on the later stages of the heterogeneous decomposition of solid solutions: III. Conditions for the infiltration of feeding dislocations

Abstract

In this paper, we have studied the relaxation processes that occur upon the decomposition of solid solutions at the stage of coalescence in the regime of dislocation-matrix diffusion using the precipitated-phase-particle-feeding-dislocations system as an example. The cases of linear and nonlinear interrelations between the controlling parameters of the system (the fraction of the relaxed regions of the interphase surface and the number of edge dislocations that supply the alloying component to the precipitated phase) have been analyzed. It has been established that in real cases it is advantageous for the system to reduce its total energy via the “infiltration” of feeding dislocations, i.e., the escape of segments of edge feeding dislocations localized in the precipitate outside the limits of the precipitate with the formation of structural dislocation loops at the interphase surface by the reaction of the following type: 1 feeding dislocation = 1 structural loop + 1 matrix dislocation. In the presence of an enhanced density of feeding dislocations, this reaction is blocked, and the relaxation of interphase stresses is accomplished as a result of sequential acts of the loss of coherence, which are accompanied by a partial “escape” of edge feeding dislocations. For the edge dislocations that remain unescaped, there is formulated a condition for the subsequent “leakage” of their segments localized in the precipitate outside the limits of the precipitate according to the following reaction: 2 feeding dislocations = 1 structural loop + 2 matrix dislocations.