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 a nd MgNi2 phases. The alloys were fabricated by mechanical alloying (MA) and heat treatment (HT), the so called MA/HT method. For the as-alloyed amorph ous MgNi (a-MgNi) alloy, the maximum hydrogen content reaches 1.72 mass% at 473 K. The hydride, however, gradually decomposes into Mg2NiH4 and MgNi2 p hases during measurement of pressure-composition isotherm. In the case of n anoscaled crystalline Mg2Ni (c-Mg2Ni)+amorphous MgNi2 (a-MgNi2) multiphase alloy, the maximum hydrogen content reaches only 0.35 mass% at 473 K. No pl ateau-like behavior is observed in the desorption process. In the case of n anoscaled c-Mg2Ni+crystalline MgNi2 (c-MgNi2) multiphase alloy, the maximum hydrogen content reaches 1.45 mass% at 473 K. A well-defined plateau regio n is observed of nearly 0.012 MPa at 473 K in the desorption process. There fore, it is concluded that the hydriding properties of the nanoscaled MgNi multiphase alloy will. be strongly affected by not only the structural prop erties of the matrix surrounding the c-Mg2Ni grains precipitated but also b y the accumulation/release of internal stress on the precipitation process. (C) 1999 Elsevier Science S.A. All rights reserved.