Hydrogen-induced amorphization and embrittlement resistance in Ti-based in situ composite with bcc-phase in an amorphous
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J.P. Ahn Advanced Analysis Center, Korea Institute of Science & Technology (KIST), Cheongryang, Seoul 130-650, Korea
K.B. Kim and E. Fleurya) Advanced Metals Research Center, Korea Institute of Science and Technology (KIST), Cheongryang, Seoul 130-650, Korea (Received 15 June 2006; accepted 9 October 2006)
We report the hydrogenation characteristics and mechanical properties of Ti50Zr25Cu25 in situ composite ribbons, composed of -Ti crystalline phase dispersed in an amorphous matrix. Upon cathodic charging at room temperature, high hydrogen absorption up to ∼60 at.% (H/M ⳱ ∼1.2) is obtained. At such a high concentration, hydrogen-induced amorphization occurs. Mechanical tests conducted on the composite with varying hydrogen concentrations indicate that the Ti50Zr25Cu25 alloy is significantly resistant to hydrogen embrittlement when compared to conventional amorphous alloys. A possible mechanism that would contribute toward hydrogen-induced amorphization and hydrogen embrittlement is discussed.
I. INTRODUCTION
Amorphous metallic alloys, due to their unique structure, are considered advantageous over their crystalline counterparts for various applications.1,2 Considering the increasing prospects of hydrogen in the energy sector, there is a growing interest to study the interaction of hydrogen with crystalline/amorphous alloys,1,3 for applications such as membranes for gaseous hydrogen purifiers, hydrogen storage, and bipolar plates in fuel cells.4–8 In recent years, concerted interest over the development of non-palladium based hydrogen permeation membranes7,8 has made amorphous alloys a viable alternative for these applications, as these alloys have high hydrogen solubility and diffusivity, as well as good corrosion resistance.4–6 Several works reported excellent permeation properties4,5,7,8; however, similar to their crystalline counterparts, amorphous alloys too have a tendency to embrittle in hydrogen environment,5,9–13 and in view of applications, the study on hydrogen embrittlement is of primary concern. Ti-, Zr-, and Ni-based amorphous alloys have been investigated earlier for their hydrogen permeation and a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0045 428
J. Mater. Res., Vol. 22, No. 2, Feb 2007
embrittlement behavior.7–15 Alloy systems containing both Zr and Ni demonstrated high permeability values in the temperature range of 200–400 K, comparable with those of Pd and Pd-alloys. However, these compositions showed some signs of embrittlement.7,8,13 To circumvent the embrittlement behavior, Aoki and coworkers16 investigated hydrogen permeation through multiphase Ni-TiNb crystalline alloys and defined a composition range without any sign of brittleness after permeation tests. It is thus believed that a composite structure composed of an amorphous matrix would show high permeation and high resistance to embrittlement. For the present study, we selected the Ti-Zr-Cu system because of the high affinity of Ti and Zr to hydrogen.4 The Ti-Zr-Cu ternary syst
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