Studies of Mg film and substrate coupling effects on hydrogenation properties

Changes of microstructure, phase composition and surface morphology were investigated for 1.5–2 μm thick nanocrystalline Mg films, which were sputter-deposited on quartz and stainless steel substrates and hydrogenated at 600 kPa in the temperature range 200–260 °C. The volume fraction of MgH2 in Mg and changes of the surface topography were analyzed using X-ray diffraction and scanning electron microscopy analysis, respectively. Coupling processes occurring between the Mg film and the substrate were registered and correlated with hydrogenation properties. Due to strong coupling to stainless steel substrate, a fast and complete transformation of Mg into MgH2 accompanied by film cracking and spontaneous crushing into nanometer-size powder was observed. For Mg films weakly coupled to the quartz substrate, a slow and partial transformation of Mg into MgH2 and simultaneous film buckling followed by film detachment and flaking was registered.