Hydriding properties of the mechanically deformed Mg-Ni alloys

Mechanical deformations with/without elemental substitutions have been carried out on Mg-Ni-based alloys to improve their hydriding properties. The alloys Mg-x at.%Ni (x = 33, 38, 43 and 50) with different nanometer-scale structures were successively synthesized by mechanical milling of Mg ₂Ni mixed with various amounts of additional Ni, and the relations between their structural and hydriding properties were investigated in detail. By milling only Mg₂Ni, nanostructured Mg₂Ni composed of the intra- and inter-grain regions was obtained (x = 33). Amorphous MgNi (a-MgNi) as a third region was dispersed around the nanostructured Mg ₂Ni by milling of Mg2Ni mixed with additional Ni (x = 38 and 43), and the pure amorphous MgNi was homogeneously synthesized in equivalent composition (x = 50). The coordination numbers and interatomic distances of the Mg-D and Ni-D correlations in the amorphous MgNi-D show that deuterium occupies the interstitial tetrahedral site composed of nearly [2Mg2Ni]. According to the specific structural properties, there is obvious miscibility gap (plateau) pressure higher than 1 × 10^-4 MPa at room temperature even in the amorphous phase, and the total hydrogen content reached up to 2.2 mass%. Further studies on an amorphous MgNi-based system were carried out to clarify the effect of the short-range ordering on the structural and hydriding properties due to substitution of Mg- and Ni-sites by various elements.