Study by elastic theory of the clustering of solute atoms during the early stage of solid solution decomposition

Abstract

Khachaturyan's expression for the elastic strain energy of a coherent inclusion of arbitrary shape in an anisotropic medium is derived from both macroscopic and microscopic theoretical approaches. This expression can be simplified for the case of a very thin disk-shaped inclusion, which enables one to analytically calculate the preferred orientations of Guinier-Preston (G.P.) zones in aluminum-copper alloys and carbide precipitates in iron-carbon martensite. The results are in good agreement with the experimental data. However, this thin plate theory breaks down badly when it is applied to the case of thick plate inclusions, such as the nitride precipitate (Fe,gN 2) in iron-nitrogen martensite. A method which takes the thickness effects into account has been developed in order to solve this problem. The calculated minimum strain energy orientation of the disk-shaped nitride precipitate in iron-nitrogen martensite, obtained with this method shows excellent agreement with experimental observation.