Grain refinement and improved hydrogen storage performance of nanostructured Mg-Ni-La alloys by amorphous crystallization exerting hydrogen atmosphere

Hydrogen storage property of Mg based alloys can be effectively improved by nanocrystalline microstructure. Here we presented an attractive finding that ultrafine and homogeneous microstructure, with a size of around 10 nm, could be fabricated by nanocrystallization of amorphous Mg-Ni-La alloy under hydrogen atmosphere. Crystallization annealing exerting hydrogen atmosphere promoted the formation of LaH2 at the early stage of the phase transformation before the crystallization of the amorphous matrix. The formed ultra-fine LaH2 particles presented excellent dimensional stability and well matched crystallography relationships with Mg and Mg2Ni, therefore providing intense secondary phase pinning effect to yield remarkable grain refinement. By regulating the hydrogen pressure and heating rate, the size and amount of formed LaH2 particles could be tailored to achieve optimal pinning effect. The corresponding mechanisms were discussed based on the experimental characterization and theoretical calculation. Positive hydrogen storage properties were obtained by the formed fine nanocrystalline microstructure.