- The present work is concerned with the grain structure and grain growth in some cerium– neodymium alloys. The grain size in a Ce–10 wt.% Nd alloy is determined by the rate of cooling through the two-phase γ+ δ region. Grain growth in the upper γ-phase is a diffusion- controlled process with activation energy close to that associated with self-diffusion of cerium. In the course of spontaneous oxidation, epitaxial CeO 2 layers grow on the Ce-alloy surface. The presence of such layers has been previously observed on a variety of substrate materials but not on the parent metal cerium. As these layers become thicker, coherency strains give rise to a network of cracks that develop within the oxide layer. The coherence between the cerium–substrate and the oxide layer is maintained even across the initially formed intermediate sub-oxide layers.