Hydriding properties of the heat-treated MgNi alloys with nanostructural designed multiphase

The structural and hydriding properties have been investigated for the heat-treated MgNi alloys with nanoscale structure which consists of the Mg₂Ni and MgNi₂ phases. The alloys were fabricated by mechanical alloying (MA) and heat treatment (HT), the so called MA/HT method. For the as-alloyed amorphous MgNi (a-MgNi) alloy, the maximum hydrogen content reaches 1.72 mass% at 473 K. The hydride, however, gradually decomposes into Mg₂NiH₄ and MgNi₂ phases during measurement of pressure-composition isotherm. In the case of nanoscaled crystalline Mg₂Ni (c-Mg₂Ni)+amorphous MgNi₂ (a-MgNi₂) multiphase alloy, the maximum hydrogen content reaches only 0.35 mass% at 473 K. No plateau-like behavior is observed in the desorption process. In the case of nanoscaled c-Mg₂Ni+crystalline MgNi₂ (c-MgNi₂) multiphase alloy, the maximum hydrogen content reaches 1.45 mass% at 473 K. A well-defined plateau region is observed of nearly 0.012 MPa at 473 K in the desorption process. Therefore, it is concluded that the hydriding properties of the nanoscaled MgNi multiphase alloy will be strongly affected by not only the structural properties of the matrix surrounding the c-Mg₂Ni grains precipitated but also by the accumulation/release of internal stress on the precipitation process.