ELASTIC STRAINS DURING DECOMPOSITION OF HOMOGENEOUS SOLID SOLUTIONS - PERIODIC DISTRIBUTION OF DECOMPOSITION PRODUCTS

A decomposition is considered of an elastically anisotropic homogeneous solid solution in two phases having the same structure as that of the original solution. The following assumptions are made: 1. The phases differ in their composition and the specific volume only. 2. The inclusions of precipitating phases are coherent and have the same elastic moduli as those of the matrix. The configuration and inclusion shape is assumed to be determined by minimizing the elastic energy associated with the difference in specific volumes of the phases. A theoretical analysis for the alloys with negative elastic anisotropy leads to the configuration with a minimum of the elastic energy when the inclusions are distributed periodically. In this case the mechanism of the formation of periodic distributions differs considerably from that proposed by Cahn. Three types of metastable periodic distributions are possible, enumerated below in order of increasing elastic energy. Firstly, there is an one‐dimensional distribution representing the system of similar parallel laminated inclusions, regularly spaced along a cubic plane (e.g. (001)). Secondly, there is a two‐dimensional distribution which may be viewed as a planar square macro‐lattice formed by inclusions. The two basic translation vectors lie along the 〈100〉 orthogonal cubic directions. Finally, there is a three‐dimensional distribution, representing a primitive cubic macro‐lattice, the site of which are inclusions of equilibrium phases and of the partially decomposed matrix. Copyright © 1969 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim