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

为了开发氢粉化金属间化合物粉末生产工艺，提高吸氢金属间化合物吸放氢循环寿命，研究了Nb3Al和NbCr2基金属间化合物的氢粉化机理。由于吸氢能力对覆盖金属间化合物的表面氧化膜很敏感，所有样品都是在特殊设计的封闭系统中不暴露在空气中制备的。在这个系统中，手套箱与真空炉相连。测定了氢化前后的吸放氢曲线，计算了氢化前后的晶格常数，并用光学显微镜和扫描电子显微镜观察了粉末的形状和大小。在Nb-Al二元合金中，Nb_3Al/Nb和Nb_3Al/Nb_2Al两相合金中只有Nb_3Al/Nb和Nb_3Al/Nb_2Al两相合金发生粉化。在Nb-Cr二元合金中，只有Nb固溶体能在Nb、NbCr2和Cr3个相中吸氢。只有Nb/NbCr2两相合金发生粉化。当NbCr2与钛合金化时，NbCr2可以吸氢。含钛整体式NbCr2经加氢粉碎。结果表明，粉化起始于金属间化合物中的裂纹，这是由于两相的膨胀差异伴随着氢的吸收，或者是氢含量的梯度引起的表面和内部的膨胀。

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.