Diffusivity and solubility of hydrogen as a function of composition in Fe-Ni alloys

An electrochemical method has been used to determine the permeability,P, diffusion coefficient,D, and solubility,c, of hydrogen in alloys of the Fe-Ni system. The heats of activation for diffusion and the heats of solution have been derived.D falls from ≃10⁻⁴ sq cm per sec for pure iron to ≃10⁻¹⁰ sq cm per sec for 40 wt pct of Ni in the alloy. Thereafter it rises slightly to that for pure nickel,c rises by about 10³ between pure iron and 40 wt pct Ni, then remains constant up to pure nickel. The resultantP doubles at 5 wt pct Ni and then falls by 10³ times up to 40 wt pct Ni, afterwards rising slightly to that for pure nickel. Between 0 and 40 wt pct Ni the dominant factor in controlling the value ofP is the fall of the mole fraction of the α phase in the alloy. This hypothesis gives a reasonable quantitative calculation of theP-composition relation. Between 40 and 100 wt pct, the crystallographic phase is allγ and the major effect is the bonding of hydrogen in the alloy, the small changes noted being reasonably calculable. The negligible change of solubility in this region reflects the negligible change ind character of the alloy from 40 to 100 wt pct Ni. The hydrogen permeability of Fe-Ni (5 wt pct) is greater than that of palladium atT > 200°C. The corrosion rate and hydrogen permeability (hence, susceptibility to hydrogen embrittlement) pass through a minimum at about 50 wt pct Ni. A remarkable parallelism exists between corrosion rate and hydrogen permeation in Fe-Ni alloys. An interpretation is suggested. Formerly with the University of Pennsylvania Formerly with the University of Pennsylvania Work carried out by P. K. SUBRAMANYAN in partial fulfillment of the requirements for the degree of Doctor of Philosophy, University of Pennsylvania, 1970.     

Liquidus surface and solidification scheme for alloys of the system Ti-Ni-Zr containing up to 50% Ni

Translated from Poroshkovaya Metallurgiya, No. 8(344), pp. 49–54, August, 1991.     

Projection of the solidus surface of the Sc-Ti-Ni system in the region of TiNi-Ni-ScNi alloys

Metallographic, x-ray diffraction, electron probe, and differential thermal analyses are used to study, the interaction of components of TiNi-Ni-ScNi alloys in the Sc-Ti-Ni system at subsolidus temperatures. The vertical section between TiNi and ScNi is shown to be quasibinary. No ternary compounds are observed in the TiNi-Sc-ScNi system. Six single-phase, nine two-phase, and four three-phase fields are found on the solidus of the TiNi-Ni-ScNi system. A characteristic feature of the structure of alloys of the Sc-Ti-Ni system in the region TiNi-Ni-ScNi ε is that the E phase is in equilibrium with the phases based on TiNi(δ), Ni(γ), ScNi₂(λ₂), Sc₂Ni(v), SCNi₅(ξ), and ScNi(δ).     

Solubility and diffusion of hydrogen in vanadium-oxygen alloys

The solubilities and diffusion coefficients of hydrogen have been measured in vanadium-oxygen alloys. A small increase in the isopiestic solubility of hydrogen at 297 and 373 K was caused by the addition of oxygen to vanadium, but Sieverts’ law was obeyed in each alloy in the hydrogen concentration ranges studied. Hydrogen diffusion coefficients as a function of hydrogen concentration were measured at 227, 297, and 373 K by a Boltzmann-Matano method that also allowed a determination of the terminal hydrogen solid solubility. The hydrogen diffusion coefficients decreased with increasing-oxygen concentrations. The solubility and diffusion results do not fit a simple trapping model. The terminal hydrogen solid solubility increased slightly with oxygen concentration