Thermal stability and hydriding properties of nanocrystalline melt-spun Mg63Ni30Y7 alloy

Nanocrystalline Mg-2(Ni,Y) hydrogen storage alloy (with exact composition Mg63Ni30Y7) was prepared by rapid solidification, using a melt-spinning technique. Thermal stability and phase transition in the as-quenched alloy were studied by TEM, DSC, X-ray and electron diffraction. It was found that the as-cast material consists of mainly hexagonal :Mg,(Ni;Y) nanocrystals with an average size of 2-3 nm and a significant amount of amorphous phase with similar composition located between them. During heating the alloy crystallizes completely by three dimensional nanocrystal growth, with an activation energy of 140 +/- 7 kJ mol(-1). The hydriding properties of the as-quenched nanocrystalline alloy were studied as well. The maximum hydrogen absorption capacity (about 3.0 wt.%) and hydrogenation kinetics of the melt-spun Mg-2(Ni,Y) were found to exceed those of the conventionally prepared polycrystalline Mg2Ni alloys and to be comparable to the hydrogen absorption characteristics of nanocrystalline ball-milled Mg2Ni. Hydrogenation of the as-cast alloy causes a change in the crystallization mechanism during annealing, as the microstructure remains nanocrystalline (15-20 nm) even after complete crystallization of the alloy. (C) 1998 Elsevier Science S.A. All rights reserved.