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Title:
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The hydrogen solubility and diffusivity in nickel aluminide and developing a hydrogen tolerant nickel aluminide alloy |
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Author:
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Yang, Liu |
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Advisor:
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McLellan, Rex B. |
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Abstract:
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The solubility of H in single crystals and polycrystalline samples of $\rm Ni\sb{3}Al$ has been measured in equilibrium with $\rm H\sb2$ gas at atmosphere. In all cases the solubility exhibits a maximum at 750 K. A structural transformation from $\rm Ll\sb2$ (cubic) to $\rm Ll\sb2$ (tetragonal) in hydrogenated $\rm Ni\sb3Al\ (Ni\sb3Al$-H) was observed. The transformation temperature was found to be between 720 K and 870 K. No enthalpy change during this transformation was detected in the DTA experiment.
The diffusivity of hydrogen in $\rm Ni\sb3Al$ has been measured in the temperature range of 588 K to 1214 K using a method involving the outgassing of hydrogen charged spheres. The diffusivity of hydrogen exhibits discontinuity in the temperature range of 753 K to 793 K.
Finally, the addition of Pd (0.5 wt) is shown to significantly suppress the hydrogen embrittlement of $\rm Ni\sb3Al.$ Microstructure analysis indicates no second phase is formed due to the small amount of Pd. The addition of Pd alters the fractography of $\rm Ni\sb3Al$ charged with hydrogen. It is suggested that Pd may play a role of trapping hydrogen atoms in lattice and result in reducing the hydrogen concentration around crack tips and grain boundaries, thus improving the susceptibility of $\rm Ni\sb3Al$ to hydrogen embrittlement. |
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Citation:
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Yang, Liu. "The hydrogen solubility and diffusivity in nickel aluminide and developing a hydrogen tolerant nickel aluminide alloy." Doctoral Thesis, Rice University, ETD http://hdl.handle.net/1911/16902. |
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Citable link to this page:
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http://hdl.handle.net/1911/16902 |
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Date:
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1995 |
