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  • 1
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    Gas-phase hydrogen permeation through alpha-titanium - Surface film and dimensional effects (1982)
    In:  Other Sources
    Details
    Publication Date: 2011-08-18
    Description: The process of hydrogen transport through alpha-Ti involves simultaneous diffusion and phase boundary reactions at both surfaces, with the relative effect on each surface depending on the extent of surface contamination as well as the physical dimensions of the titanium membrane used. It is shown by the present study that hydrogen permeation in commercially pure alpha-Ti increases exponentially with temperature and is dependent on the first power of the input pressure, whether the surface is as-polished, preoxidized or prenitrided. Permeation decreases in the case of the as-polished condition if nitride or oxide films are formed at the surface in contact with source hydrogen, while increasing slightly for the same condition if such films are formed at the hydrogen exit surface.
    Keywords: METALLIC MATERIALS
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Deformation and fracture of a directionally solidified NiAl-28Cr-6Mo eutectic alloy (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A directionally solidified alloy based on the NiAl-(Cr, Mo) eutectic was examined by transmission and scanning electron microscopy to characterize the microstructure and room temperature deformation and fracture behavior. The microstructure consisted of a lamellar morphology with a group of zone axes (111) growth direction for both the NiAl and (Cr, Mo) phases. The interphase boundary between the eutectic phases was semicoherent and composed of a well-defined dislocation network. In addition, a fine array of coherent NiAl precipitates was dispersed throughout the (Cr, Mo) phase. The eutectic morphology was stable at 1300 K with only coarsening of the NiAl precipitates occurring after heat treatment for 1.8 ks (500 h). Fracture of the aligned eutectic is characterized primarily by a crack bridging/renucleation mechanism and is controlled by the strength of the semicoherent interface between the two phases. However, contributions to the toughness of the eutectic may arise from plastic deformation of the NiAl phase and the geometry associated with the fracture surface.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-200016 , NAS 1.26:200016 , NIPS-96-07174
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Gas phase hydrogen permeation in alpha titanium and carbon steels (1980)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Commercially pure titanium and heats of Armco ingot iron and steels containing from 0.008-1.23 w/oC were annealed or normalized and machined into hollow cylinders. Coefficients of diffusion for alpha-Ti and alpha-Fe were determined by the lag-time technique. Steady state permeation experiments yield first power pressure dependence for alpha-Ti and Sievert's law square root dependence for Armco iron and carbon steels. As in the case of diffusion, permeation data confirm that alpha-titanium is subject to at least partial phase boundary reaction control while the steels are purely diffusion controlled. The permeation rate in steels also decreases as the carbon content increases. As a consequence of Sievert's law, the computed hydrogen solubility decreases as the carbon content increases. This decreases in explained in terms of hydrogen trapping at carbide interfaces. Oxidizing and nitriding the surfaces of alpha-titanium membranes result in a decrease in the permeation rate for such treatment on the gas inlet surfaces but resulted in a slight increase in the rate for such treatment on the gas outlet surfaces. This is explained in terms of a discontinuous TiH2 layer.
    Keywords: METALLIC MATERIALS
    Type: NASA-CR-3190
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Gas-phase hydrogen permeation through alpha-titanium - Surface film and dimensional effects (1976)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The two techniques normally used to determine diffusivity and permeability in metals are considered and a description is presented of experiments which had been conducted to determine the direct effect of oxide and nitride films on the membrane surface as a function of location and thickness. The test specimens used in the experiments has been machined from commercially pure titanium rod. The results of the experiments show that hydrogen transport in alpha-titanium is partially or completely controlled by surface reactions depending upon membrane wall thickness and the composition and thickness of the surface film.
    Keywords: METALLIC MATERIALS
    Type: International Conference on Titanium; May 18, 1976 - May 21, 1976; Moscow; USSR
    Format: text
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    NASA TECHNICAL REPORTS
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