A comparative study on the microstructure and cycling stability of the amorphous and nanocrystallization Mg60Ni20La10 alloys

Amorphous and nanocrystalline Mg60Ni20La10 alloys were prepared by melt-spun and crystallization of the amorphous alloy respectively. Microstructural evolution of the amorphous and crystallized (CA) alloys during hydrogenation/dehydrogenation cycles was studied and compared in the present work. The CA alloy exhibits homogeneous and fine (<50 nm) multiphase microstructure composed of LaMg2Ni, Mg2Ni and LaMgNi4. The CA alloy has slightly lower hydrogenation ability but far excellent cycling stability compared with the amorphous alloy. The amorphous and CA alloys have identical phase constitution including Mg2Ni and LaH3 after cycling. While, microstructures of the two cycled alloys show dramatically distinct characters. Grain size of the cycled CA alloy is almost unchanged compared with the original alloy, which contributes to the better cycling stability. However, grain growth especially coarsening of Mg2Ni is severe in the cycled amorphous alloy, leading to difficulty to dehydrogenation. The better coarsening resistance of the CA alloy is attributed to the crisscrossed distribution of Mg2Ni and LaH3 and well-matched interfacial configuration between Mg2Ni and LaH3 that (113)Mg2Ni (111)LaH3. However, hydrogenation of the amorphous alloy leads to large and inhomogeneous microstructure which is ascribed to the preferential recrystallization and growth of Mg2Ni, contributing to rapid degradation of the amorphous alloy. The present work illumines a potential way to prepare stable nanocrystalline by introducing secondary phase with interlaced microstructure and well-matched interfacial configuration using nanocrystallization method. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.