Hydrogen Pulverization in Intermetallic-based Alloys
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Hydrogen Pulverization in Intermetallic-based Alloys Satoshi Semboshi, Naoya Masahashi and Shuji Hanada, Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577l, JAPAN ABSTRACT
Pulverization behavior and microstructure evolution with hydrogenation in hydrogen absorbing Ta-Ni intermetallic-based alloys, such as Ta2Ni with Ta solid solution (Tass), TiMn2 with TiMn and Nb3Al with Nb solid solution (Nbss), are investigated to elucidate the mechanism of the hydrogen pulverization. Ta-10at.%Ni consisting of Ta solid solution (Tass) and Ta2Ni Laves phase is pulverized to coarse powder over 100 µm in hydrogenation. Crack propagation occurs preferentially in the brittle Ta2Ni phase rather than in the ductile Tass phase. When the volume fraction of brittle Ta2Ni increases with increasing Ni content, hydrogen pulverization is enhanced. The lattice parameter of Tass increases by hydrogenation, while it does not change in Ta2Ni. In addition, nano-sized regions with Moiré patterns are produced in Tass and Debye rings corresponding to tantalum hydride β−TaH appear in the diffraction pattern. These features are very similar to those of TiMn2 based alloy and Nb3Al based alloys in the literature. Based on the present results along with those in the literature it is concluded that the hydrogen pulverization is attributable to (1) the absorption of a large amount of hydrogen in constituent phase(s), (2) the large strain introduced by lattice expansion and the hydride formation, and (3) the ease of crack nucleation and propagation in brittle constituent phase(s). Introduction Intermetallic-based alloys as hydrogen absorption materials are pulverized in a hydrogen atmosphere, during cycle hydrogenation [1,2]. From the viewpoint of hydrogen absorption property the pulverization should be avoided, because it causes the degradation of hydrogen absorbing capacity with hydrogenation [2]. It is necessary to suppress the hydrogen pulverization to improve the cyclic property of hydrogen absorbing capacity. On the other hand, the hydrogen pulverization is expected for a new powder fabrication process to produce fine powder with high quality and low cost, especially for refractory metals like Nb and Ta based alloys [3-5]. Therefore, there are different reasons for investigating the mechanism of hydrogen pulverization for intermetallic-based alloy; one is the improvement of the cyclic property in hydrogen absorption material by pulverization suppression, and the other is the application to fine powder fabrication of intermetallic-based alloys. In this paper, hydrogen pulverization behavior and microstructure evolution in hydrogen absorbing Ta-Ni alloys consisting of Ta2Ni and Ta solid solution (Tass) are investigated. Based on N5.16.1
the obtained results the mechanism of hydrogen pulverization is discussed, referring to the results on the hydrogen pulverization in TiMn2 based and Nb3Al based alloys, which has been already reported [2-5]. EXPERIMENTAL PROCEDURE Button ingots of Ta -5at.%Ni, Ta -8at.%Ni, Ta
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