POWDER PRODUCTION BY HYDROGEN PULVERIZATION OF FUNCTIONAL INTERMETALLICS AND DEVELOPMENT OF CLOSED SYSTEM FOR POWDER CONSOLIDATION

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In order to develop a powder production process of structural intermetallics via hydrogen pulverization and to improve cycling lifetime of hydrogen absorption and desorption in hydrogen absorbing intermetallics, hydrogen pulverization mechanisms have been investigated using Nb_3Al and NbCr_2 base intermetallic alloys. Since the ability of hydrogen absorption is sensitive to the surface oxide film covering intermetallics, all samples were prepared without exposing to air in a specially designed closed system. In this system a glove box is attached to a vacuum furnace. Hydrogen absorption-desorption curves were measured, lattice constants were calculated before and after hydrogenation, and shape and size of pulverized particles were observed by optical and scanning electron microscopy. In Nb-Al binary alloys pulverization occurs only in two phase alloys, Nb_3Al/Nb and Nb_3Al/Nb_2AI.Monolithic Nb_3AI, Nb_2A1 and Nb are not pulverized, although they can absorb a considerable amount of hydrogen. In Nb-Cr binary alloys, only Nb solid solution can absorb hydrogen among constituent phases, Nb, NbCr_2, and Cr. Pulverization takes place only in Nb/NbCr_2 two phase alloys. When NbCr_2 is alloyed with Ti, it can absorb hydrogen. Ti-containing monolithic NbCr_2 is pulverized by hydrogenation. From these results, it is concluded that pulverization is initiated at a crack in an intermetallic compound which is caused by difference in dilatation either of both phases accompanied with hydrogen absorption or of surface and interior generated by a gradient of hydrogen content.