Electron microscopy of modulated and ordered alloys

Abstract

Modulated and ordered alloys are of interest not only from a basic standpoint but also because they often possess interesting properties or form the basis of commercial materials. Transmission electron microscopy (TEM) provides much unique and valuable information in the study of phase transformations in such alloys but, as this overview of the applicable methods will try to illustrate, the experimental work is often challenging and data interpretation is rarely straightforward.In alloys with a modulated structure, spinodal decomposition is the transformation process of most interest. In cubic crystals, elastic anisotropy usually leads to triaxially modulated structures with composition modulations along <100>, whereas in isotropic systems, randomly oriented, highly interconnected structures are formed. TEM has most commonly been used to image the spinodal microstructure and to measure wavelength and waveshape. The observations are often only qualitative because of the complex nature of the image, but quantitative measurements of coarsening behavior have been attempted.