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

Abstract

Abstract The structural and hydriding properties have been investigated for the heat-treated MgNi alloys with nanoscale structure which consists of the Mg 2 Ni and MgNi 2 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 Mg 2 NiH 4 and MgNi 2 phases during measurement of pressure–composition isotherm. In the case of nanoscaled crystalline Mg 2 Ni (c-Mg 2 Ni)+amorphous MgNi 2 (a-MgNi 2 ) 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-Mg 2 Ni+crystalline MgNi 2 (c-MgNi 2 ) 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-Mg 2 Ni grains precipitated but also by the accumulation/release of internal stress on the precipitation process.