Irradiation-induced spinodal decomposition in alloys

Abstract

Studies of homogeneous phase transformations induced by irradiation are aimed at developing materials for nuclear applications and understanding basic mechanisms of decomposition. Spinodal decomposition, one of the major modes of homogeneous phase separations, induced by electron irradiation is investigated with respect to the basic mechanism and to the confirmation of its inducement with a large increase in the coherent spinodal temperature. The inducement of spinodal decomposition is successfully clarified by analyses of the induced modulated structure using the theory of spinodal decomposition. The increase in spinodal temperature up to its chemical limit under irradiation is shown to be due to the relaxation of the coherent strain associated with the modulated structure. The process of relaxation of the coherent strain under irradiation is investigated through high resolution electron microscopy. Interstitials and vacancies produced by irradiation accumulate in a spatially modulated structure possessing a definite wavelength. The elastic interaction between the strain fields around point defects themselves and the coherency maintained in compositional fluctuations are associated with the spatial modulation. It is emphasized that the periodic distribution of excess point defects under irradiation contributes remarkably to the relaxation of the coherent strain without destruction of coherency between atoms, resulting in inducement of the spinodal decomposition up to the chemical spinodal temperature.