Effect of rapid solidification on hydrogen solubility in Mg-rich Mg–Ni alloys

The hydrogenation properties of Mg100−xNix alloys (x = 0.5, 1, 2, 5) produced by melt spinning and subsequent high-energy ball milling were studied. The alloys were crystalline and, in addition to Mg matrix, contained finely dispersed particles of Mg2Ni and metastable Mg6Ni intermetallic phases. The alloys exhibited excellent hydrogenation kinetics at 300 °C and reversibly absorbed about 6.5 mass fraction (%) of hydrogen. At the same temperature, the as prepared Mg99.5Ni0.5 and Mg95Ni5 powders dissolved about 0.6 mass fraction (%) of hydrogen at the pressures lower than the hydrogen pressure corresponding to the bulk Mg–MgH2 two-phase equilibrium, exhibiting an extended apparent solubility of hydrogen in Mg-based matrix. The hydrogen solubility returned to its equilibrium value after prolonged hydrogenation testing at 300 °C. We discuss this unusually high solubility of hydrogen in Mg-based matrix in terms of ultrafine dispersion of nanometric MgH2 precipitates of different size and morphology formed on vacancy clusters and dislocation loops quenched-in during rapid solidification.