Hydrogenation-induced fragmentation in Ta–Ni alloy

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Hydrogen-induced fragmentation behavior of Ta–Ni binary alloys is investigated to understand the mechanism of hydrogen pulverization of refractory metals and alloys and to develop the powder fabrication process by hydrogenation. Single-phase alloy of Ta solid solution (Ta ss) exhibits no change in sample shape by hydrogenation at room temperature, while two-phase alloys of Ta ss and Ta 2Ni Laves phase are broken into fragments. Crack propagation occurs preferentially in the brittle Ta 2Ni phase rather than in the ductile Ta ss phase. When the volume fraction of brittle Ta 2Ni increases with increasing Ni content, hydrogen-induced fragmentation is enhanced. The lattice parameter after hydrogenation increases in Ta ss, but not in Ta 2Ni. Nanosized clusters with Moiré patterns are observed in a HRTEM image of hydrogenated Ta ss, and Debye rings corresponding to tantalum hydride β-TaH appear in the associated diffraction pattern. It is suggested that the hydrogen fragmentation is attributed to the absorption of a large amount of hydrogen, the interfacial strain introduction by lattice expansion and hydride formation, and crack formation at brittle constituent phase(s) and hydride.