Microstructure of alloy MlNi(3.75)Co(0.75)Mn(0.3)Al(0.2) (Ml-La-rich mischmetal) during electrochemical hydriding-dehydriding process

Evolution of microstructures of alloy MlNi(3.75) Co-0.75 Mn-0.3 Al-0.2 (Ml-La-rich mischmetal) during the electrochemical hydriding-dehydriding process was studied by using in-situ X-ray diffraction method. It is indicated that both the crystallite sizes of alpha phase (solid solution phase) and beta phase (hydride phase) decrease with the hydrogen content increasing during this process. beta phase is found to be composed of the plate-like and the needle like crystaltites, while the crystallite size of the former changes more rapidly than that of the later during the hydriding-dehydriding process. It's also clearly found that strains along (110) plane and (001) plane of alpha phase and beta phase are higher in the alpha+beta region than those in the corresponding single phase region. Based on the microstructural studies, mechanism for the hydride growth has also been proposed.