A new method for evaluating the size of plate-like precipitates by small-angle scattering

A methodology is presented for extracting the thickness and length of plate-like precipitates from streaking that appears in the small-angle scattering pattern of moderately textured polycrystalline samples. This methodology builds upon existing work on single crystals but is extended to polycrystals through a modeling of the streaking misalignment distribution. It is also shown that it is essential to take into account the Ewald sphere curvature. The protocol is applied to an in situ small-angle X-ray scattering study of the transition between θ′ and T1 in an Al–Li–Cu system, where the contributions of both phases are well separated, and the size, volume fraction and number density are monitored.