Hydrogenation-induced fragmentation in Ta-Ni alloy

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 Ta₂Ni 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 Ta₂Ni increases with increasing Ni content, hydrogen-induced fragmentation is enhanced. The lattice parameter after hydrogenation increases in Ta_ss, but not in Ta₂Ni. 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.