Tritium permeation through clean incoloy 800 and sanicro 31 alloys and through steam oxidized incoloy 800

The tritium permeabilities,DK, of Incoloy 800 and Sanicro 31 have been determined for tube samples that were protected from surface oxidation by electroplated nickel. The permeabilities of these analogous alloys over the 400 to 750°C range were essentially equal;DK = 0.566 exp (-16120/RT) and 0.367 exp (-15610/RT cm³ (T2 · STP) · mm/(cmsu2 · min · torr^1/2), respectively. The effects ofin-situ steam oxidation of Incoloy 800 were observed to reduce tritium permeabilities by factors up to 400 at 150 days. Permeation rates through oxide-coated Incoloy 800 were observed to be 0.5 rather than 1.0 power dependent on the tritium pressure. Permeabilities of the oxides formed at 520, 660 and 725°C were determined to be 5.4 E-11, 4.9 E-10 and 2.4 E-9 cc (T₂,STP) · mm/(cm² · min · torr^1/2), respectively. Severe thermal shock was observed to essentially destroy the permeation barrier characteristics of the oxide coatings while mild temperature cycling had no observable effects on permeation rates through the oxide coated material. H. F. BITTNER formerly on the Research Staff, Oak Ridge National Laboratory.     

Permeation of hydrogen through alpha iron

The permeation rate of hydrogen through two alpha iron specimens was measured by means of a low pressure steady-state permeation technique under conditions such that diffusion was the rate controlling process for permeation. The observed permeation rate in these samples can be described by the equation: J=5.55 ±.52 × 10^-9 p ^1/2 exp - 8095 ± 88/RT mole s^-1 cm^-1 torr^-1/2 over a range of hydrogen pressures from 21 torr to 766 torr and over a temperature range of 342 to 619 K. Variation of permeation rate with the square root of hydrogen pressure was used as evidence that the permeation process was diffusion rather than surface reaction controlled. The permeation data were used in conjunction with the solubility expression of Gonzalez¹ to determine the diffusivity of hydrogen through alpha iron as:D = 1.01 × 10^-3 exp - 1595/RT cm²/s     

Hydrogen trapping in precipitation-hardened alloys

The ingress of hydrogen in three precipitation-hardened alloys (Inconel 718, Incoloy 925, and 18 Ni maraging steel) exposed to an acetate electrolyte (1 mol L⁻¹ HAc/1 mol L⁻¹ NaAc where Ac = acetate) was studied using a potentiostatic pulse technique. The data were shown to fit a diffusion/trapping model under interface control, and values were determined for the irreversible trapping constants (k) and the flux of hydrogen into the alloys. The density of irreversible trap defects in Inconel 718 and Incoloy 925 was calculated from k and found to be in excellent agreement with the concentration of NbTi(CN) and TiC particles, respectively. The maraging steel was characterized by two trapping constants; one is associated with quasi-irreversible traps that saturate, leaving only irreversible traps thought to be TiC/Ti(CN) particles. The irreversible trapping constants for these alloys are consistent with their relative susceptibilities to hydrogen embrittlement. Moreover, a comparison of the trapping constants with those for AISI 4340 steel and two other nickel-base alloys (Monel K-500 and MP35N) indicates that a strong correlation exists between hydrogen embrittlement susceptibility and trapping capability over all the alloys.     

Diffusion in the titanium-nickel system: II. calculations of chemical and intrinsic diffusion coefficients

Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:D ^u (cm²/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:D ^u (cm²/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti₂Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofD _Ni/D _Ti have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface.Diffusion coefficients in the Ti-Ni system have been calculated by the aid of equations given by Sauer and Freise, and Wagner. Values for the TiNi (50 at. pct Ni) phase were found to be:D ^u (cm²/s) = 0.0020 exp - 142,000/R for the temperature range between 650 and 940°C. The heat of activation, expressed in J/mol, has an accuracy of ±6000. For the β-Ti(Ni) phase containing 6 at. pct Ni the temperature dependence of the diffusion coefficient is expressed by:D ^u (cm²/s) = 0.0688 exp - 141,000/RT. The uncertainty in the energy of activation is ±12000 J/mol. No clear variation of the diffusion coefficient with concentration could be detected. It was found that Ni is by far the fastest moving component in β-Ti(Ni), Ti₂Ni and TiNi (at least in the composition range between 50 and 53 at. pct Ni). Values ofD _Ni/D _Ti have been calculated with an equation derived by van Loo. The significance of the calculated values is critically examined. By means of a practical example it is shown that the calculated ratio of the intrinsic diffusion coefficients can be extremely sensitive to slight variations in the position of the marker interface. This paper is based on a Thesis submitted by G. F. BASTIN in fulfillment of requirements for the degree of Doctor in Technological Sciences.     

The nitridation of chromium and Cr-Ti alloys

Reaction zones and growth kinetics were studied after exposing high-purity chromium and alloys containing 0.5, 3.0, and 5.0 wt pct Ti to 1 atm of nitrogen between 1000° and 1400°C. Outer layers of Cr₂N and regions of internal nitridation, containing dispersed TiN particles, grew in a parabolic manner. An exact solution of Maak’s simplified analysis for internal oxidation provided calculations of nitrogen diffusion in the internal-nitride zone of each alloy. Extrapolation gave the relationshipD = 9.6 × 10^-3 exp (-28,500/RT) cm² sec^-1 for nitrogen diffusion in high-purity chromium. Increasing titanium to 5.0 wt. pct gaveD = 2.5 × 10^-3 exp (-24,000/RT) cm² sec^-1.     

Solute diffusion in alpha- and gamma-iron

The diffusion rates of chromium, vanadium, and hafnium in α- and γ-Fe have been determined by radiotracer techniques. The results are (in sq cm sec⁻¹): α-Fe γ-Fe ChromiumD = 8.52 exp (−59,900/RT)D = 10.80 exp(−69,700/RT) VanadiumD = 3.92 exp (−57,600/RT)D = 0.25 exp (−63,100/RT) HafniumD = 1.31 exp (−69,300/RT)D = 3600 exp (−97,300/RT) The differences in diffusion rates are discussed in terms of the compressibility of the diffusing atom. Diffusion of chromium in γ-Fe was also measured by a microprobe analysis technique. The result is:D = 4.08 exp (−68,500/RT) Comparison is made between diffusion analysis by tracer techniques and by electron probe microanalysis. Formerly with Department of Metallurgy, University of Manchester, Manchester, England     

Electrotransport and diffusion of iron and silver in α-yttrium

The electrotransport mobilities and diffusion coefficients were determined for iron and silver impurities in yttrium. The mobility of iron increased from 1.2 x10^-4 cm²/V-s at 900°C to 7.4X10^-4 cm²/V-s at 1330°C. The silver mobility ranged from 8.1X10^-6 cm²/V-s at 905°C to 6.4 x 10^-5 cm²/V-s at 1095°C. The iron movement was anode-directed, and the silver movement was cathode-directed. The diffusion coefficients obtained fit an Arrhenius equationD = D₀e-ΔH/RT with the following values: Fe:D ₀ = 1.8 x 10^-2 cm²/s ΔH = 85 kJ/mol (20 kcal/mol); Ag:D ₀ = 5.4 x 10^-3 cm²/s ΔH = 77 kJ/mol (18 kcal/mol). A substitutional-interstitial mechanism previously proposed for anomalously high diffusion rates of impurities in cerium and lanthanum is also proposed for yttrium.     

The diffusivity and solubility of oxygen in liquid tin and solid silver and the diffusivity

The diffusivity and solubility of oxygen in liquid tin and solid silver in the temperature range of about 750° to 950°C (1023 to 1223 K) and the diffusivity of oxygen in solid nickel at 1393°C (1666 K) were determined using the electrochemical cell arrangement of cylindrical geometry: Liquid or Solid Metal + O (dissolved) | ZrO₂ + (3 to 4%)CaO | Pt, air The diffusivity and solubility of oxygen in liquid tin are given by:D _O(Sn) = 9.9 × 10⁻⁴ exp(−6300/RT) cm²/s (9.9 × 10⁻⁸ exp − 6300/RT m²/s) andN _O ^S (Sn) = 1.3 × 10⁵ exp(−30,000/RT) at. pct The diffusivity and solubility of oxygen in solid silver follow the relations:D _O(Ag) = 4.9 × 10⁻³ exp (−11,600/RT) cm²/s ( 4.9 × 10⁻⁷ exp − 11,600/RT m²/s) andN _O ^S (Ag) = 7.2 exp (−11,500/RT) at. pct The experimental value for the preexponential in the expression forD _O(Ag) is lower than the value calculated according to Zener’s theory of interstitial diffusion by a factor of 11. The diffusivity of oxygen in solid nickel at 1393°C (1666 K) was found to be 1.3 × 10⁻⁶ cm²/s (1.3 × 10⁻¹⁰ m²/s). Formerly Graduate Student, Department Formerly Graduate Student, Department Formerly Graduate Student, Department This paper is based upon a This paper is based upon a This paper is based upon a This paper is based upon a     

Carbon diffusion in Mo2C as determined from carburization of Mo

A diffusion coefficient of C in nonstoichiometric α-Mo2C has been determined from the growth kinetics of the carbide layer. The results conform to the relationship:Dc (in cm²/s) = 68.86 ± 1.51 exp [(-294.77 ± 4.98)/RT] for the temperature range of 1273 to 1673 K, with the activation energy in kJ/mole. The growth rate,Kp, of the carbide thickness can be expressed as:Kp (in cm²/s) = 32.63 ± 1.52 exp [(-319.06 ± 5.12)/RT].     

Diffusion of cobalt,chromium, and titanium in Ni3Al

Diffusion studies of cobalt, chromium, and titanium in Ni₃Al (γ′) at temperatures between 1298 and 1573 K have been performed using diffusion couples of (Ni-24.2 at. pct Al/Ni-24.4 at. pct Al-2.91 at. pct Co), (Ni-24.2 at. pct Al/Ni-23.1 at. pct Al-2.84 at. pct Cr), and (Ni-24.2 at. pct Al/Ni-20.9 at. pct Al-3.17 at. pct Ti). The diffusion profiles were measured by an electron probe microanalyzer, and the diffusion coefficients of cobalt, chromium, and tita-nium in γ′ containing 24.2 at. pct Al were determined from those diffusion profiles by Hall’s method. The temperature dependencies of their diffusion coefficients (m[su2]/s) are as follows: ~D_(Co) = (4.2 ± 1.2) × 1O^-3exp {-325 ± 4 (kJ/mol)/RT} ~D_(Cr) = (1.1 ± 0.3) × 10^-1 exp {-366 ± 3 (kJ/mol)/RT} and D_(Ti) = (5.6 ± 3.1) × 10¹ exp {-468 ± 6 (kJ/mol)/RT} The values of activation energy increase in this order: cobalt, chromium, and titanium. These activation energies are closely related to the substitution behavior of cobalt, chromium, and titanium atoms in the Ll₂ lattice sites of γ′; the cobalt atoms occupying the face-centered sites in the Ll₂ structure diffuse with the normal activation energy, whereas the titanium atoms oc-cupying the cubic corner sites diffuse with a larger activation energy that includes the energy due to local disordering caused by the atomic jumps. The chromium atoms which can occupy both sites diffuse with an activation energy similar to that of cobalt atoms.     

Diffusion of managenese and silicon in liquid iron over the whole range of composition

The measurement of the diffusivities of manganese and silicon in molten binary ferroalloys over the whole range of composition was undertaken to clarify existing but conflicting data at lower concentrations, to present new data at higher concentrations and to indirectly confirm the behavior of both systems observed in thermodynamic studies. The experiments were carried out under argon atmosphere in a Tammann furnace. The diffusion couples were held in 5 mm ID alumina tubes (98 pct Al₂O₃). Electron probe microanalysis of the samples led to a diffusion-penetration curve for the system under consideration. Results obtained over the whole range of composition showed a slight negative deviation for the Fe−Mn system and a very large positive deviation for the Fe−Si system. At lower concentrations (0 to 4 pct Mn), the temperature dependence of managanese diffusivity for the Fe−Mn binary alloy in the temperature range 1550° to 1700°C is as follows:D _Fe−Mn=1.8×10⁻³ exp (−13,000/RT) cm²/sec The concentration dependence of manganese diffusivity for the same system at 1600°C may be expressed asD _Fe−Mn={5.48−0.0137 (%Mn)+0.000276 (%Mn)²}×10⁻⁵ cm²/sec The temperature dependence of silicon diffusivity for the Fe−Si binary system in the temperature range 1550° to 1725°C at various concentrations is as follows:D _Fe−Si=2.8×10⁻³ exp (−11,900/RT) cm²/sec at 20 pct SiD _Fe−Si=2.1×10⁻³ exp (−13,200/RT) cm²/sec at 12.5 pct SiD _Fe−Si=5.1×10⁻⁴ exp (−9,150/RT) cm²/sec at 2.2 pct Si FELIPE P. CALDERON, formerly Graduate Student. University of Tokyo, Tokyo, Japan. This paper is based on a portion of a thesis submitted by FELIPE P. CALDERON in partial fulfillment of the requirements for the degree of Doctor of Engineering at University of Tokyo.     

Diffusion of vanadium,chromium, and manganese in copper

The diffusion coefficients of vanadium, chromium and manaanese in copper have been determined by the residual activity method with radioactive tracers V⁴⁸, Cr⁵¹ and Mn⁵⁴ in the temperature ranges between 955 and 1342 K, between 999 and 1338 K and between 971 and 1253 K, respectively. The temperature dependence of the diffusion coefficients is expressed by the following Arrhenius equations along with the probable errors:D _V/Cu = (2.48 _-0.44 ^+0.53 ) x 10⁻⁴ exp [-(215 ± 2) kJ mol⁻¹/RT] m² per s,D _Cr/Cu = (0.337 _-0.090 ^+0.124 ) x 10⁻⁴ exp [-(195 ± 3) kJ mol⁻¹/RT] m² per s,D _Mn/Cu = (1.02 _-0.18 ^+0.22 ) x 10⁻⁴ exp [-(200 ± 2) kJ mol⁻¹/RT] m² per s. Anomalous penetration profiles for the diffusion of Cr⁵¹ and Mn⁵⁴ in the present results suggest that experimental results onD _Cr/Cu andD _Mn/Cu in the past have been influenced by oxidation and evaporation of the chemically active radiotracers during annealing for diffusion. formerly Graduate Student, Tohoku University     

Tracer diffusion of63Ni in Fe-17 wt pct Cr-12 wt pct Ni

The tracer diffusion of⁶³Ni in Fe-17 Cr-12 Ni by both volume and grain boundary transport has been studied from 600° to 1250°C. The use of an RF sputtering technique for serial sectioning allowed the determination of very small volume diffusion coefficients at the lower temperatures. Volume diffusion of nickel in this alloy was observed to be much slower than in pure iron or austenitic stainless steel at comparable temperatures. The volume diffusion coefficient is described byD _v =8.8 exp (−60,000/RT) cm²/s and grain boundary diffusion is described by σD _gb =3.7×10⁻⁹ exp (−32,000/RT) cm³/s. R. A. PERKINS, formerly Presidential Intern, Metals and Ceramics Division, Oak Ridge National Laboratory, Oak, Ridge, Tenn. 37830, is     

Oxygen solubility in liquid indium and oxygen diffusivity in liquid indium and tin

The solubility of oxygen in liquid indium, C_o, at 973 and 1073 K in equilibrium with its oxide was determined by an isopiestic equilibration technique in order to resolve discrepancies reported in the literature. The present results, C_o = 0.0092 at. pet at 973 K and 0.0377 at. pet at 1073 K, agree with those obtained by Otsuka, Sano, and Kozuka using a modified coulometric titration method. Oxygen diffusivity in liquid indium from 873 to 1073 K and in liquid tin from 973 to 1273 K was measured utilizing a combined potentiostatic and emf method using the following double electrochemical cells: Fe,FeO/ZrO₂(+CaO)/O in Me(I)/ZrO₂(+CaO)/O in Me(II). The present results are D_O(In) = 6.6 ( _-1.6 ^+2.0 ) x 10⁻³ exp[(-3-600 ± 5600)/RT]873 K ≤T ≤ 1073 K and D_O(Sn), = 8.7( _-5.7 ^+13.5 ) x 10⁻⁴ exp[(-18800 ± 6700)/RT]973 K ≤T ≤ 1273 K. The present results are of the same order of magnitude with the self-diffusivity of the liquid metals, and are about two orders of magnitude greater than the oxygen diffusivity reported by Stevenson and co-workers. The ratio of oxygen diffusivity to self-diffusivity of the solvent was found to be correlated to the enthalpy of formation per mole of oxygen of the respective oxide at 298 K.     

The interdiffusivity matrix of Fe2O3-CaO-SiO2 melt at 1693 to 1773 K

The diffusion couple method was used at 1693 to 1773 °K on liquid slags with their average compositon of 20 wt pct Fe₂O −₃−35 wt pct CaO-45 wt pet SiO₂. After diffusion runs for 40 min, the samples have been quenched to glassy state. The samples were sectioned, polished, and analyzed by a X-ray micro analyzer. The diffusivities matrix obtained from the penetration curves can be expressed by the following equations,D ³⁰ ₁₀₋₁₀ = 3.27 exp (−50000―RT)(cm²/s)D ³⁰ ₁₀₋₂₀ = -11.1 exp (−50000―RT)(cm²/s)D ³⁰ ₂₀₋₁₀ = 8.30 exp (−56300―RT)(cm²/s)D ³⁰ ₂₀₋₂₀ = 11.5 exp (−56200―RT)(cm²/s) where 10, 20, and 30 mean Fe₂O₃, CaO and SiO₃, respectively and the activation energies are in Cal per mol. The elements obtained satisfy the restriction derived from the second law of thermodynamics. The diffusion-composition paths obtained are consistent with the Cooper's parallelogram.     

The trapping and transport phenomena of hydrogen in nickel

Hydrogen thermal analysis experiments have been employed to study the trapping and transport phenomena of hydrogen in nickel. Dislocations in nickel act as trapping sites of hydrogen, and the hydrogen trap activation energy at dislocations appears to be lower than the activation energy for the bulk diffusion of hydrogen. It is suggested that both hydrogen trapping at grain boundaries and short-circuit diffusion through grain boundaries in nickel are present. The trap binding energy at grain boundaries is estimated as 20.5 kJ ⋅ mol^-1. Using the hydrogen thermal analysis experiments, the solubility and diffusivity of hydrogen in nickel have been measured. The temperature dependences of those are described by C (H atoms/Ni atom) = 1.57 × 10^-3 exp(-11.76 kJ ⋅ mol^-1/RT) and D (m² s^-1) = 7.5 × 10^-7 exp(-39.1 kJ ⋅ mol^-1/RT), respectively.     

Improvement of Kryukov and Zhukhovitskii method for measurement of diffusion. Application to self-diffusion in alpha iron

Abstract

The method developed by Kryukov and Zhukhovitskii for the measurement of diffusion coefficients has been improved by deriving the exact relation between the measured activities and the diffusion time. The new equation is similar to that of Kryukov and Zhukhovitskii except for an additional term and is linear for all values of time. The method has been used to measure the self-diffusion coefficient of alpha iron between 809 and 889°C. The self-diffusion coefficient (in cm²/sec) is given by

D _a = 5.4 exp (?60.3/RT)

The extrapolation of this result to the delta phase is in good agreement with the value determined experimentally in that phase.

Résumé

Les auteurs ont amélioré la méthode de Kryukov et Zhukhovitskii pour la mesure des coefficients de diffusion en dérivant la relation exacte entre les activités mesurées et le temps de diffusion. La nouvelle relation est semblable à celie de Kryukov et Zhukhovitskii sauf pour un terme additionnel; elie est lineaire pour toute valeur du temps. La methode a ete utilisee pour mesurer le coefficient d'autodiffusion du fer en phase alpha entre 809 et 889°C. Le coefficient d'autodiffusion, exprime en cm²/sec, est donne par

D _a = 5.4 exp (?60.3/RT)

L'extrapolation de ce resultat à la phase delta est en bon accord avec les résultats expérimentaux obtenus dans cette phase.     

Annealing and aging of interstitial C in α-Fe,As measured by internal friction

The diffusion of interstitial C in α-Fe has been studied by the dynamic mechanical relaxation method, and the isothermal aging kinetics of the removal of interstitial C by precipitation from its saturated state has been measured at several temperatures. The height of the Snoek peak is found to decrease according to the relation Q_max ^-1(T,t) = Q_max ^-1(T,t → ∞) + δQ_max ^-1(T) exp {- t/[k₀ exp (E/RT)}], where t is the aging time, k₀ a time constant, and E the activation energy for the precipitation of C atoms. The anelastic relaxation time is independent of the amount of C in α-Fe and varies according to Τ = 3.45 × 10^-15 exp [80.0 (kJ/mol)/RT]. The diffusion coefficient varies according to D = 6.61 × 10^-3 exp [-(80.0/RT) cm² s^-1 over the temperature range 303 to 357 K. The effect of chemical composition on k₀ has been determined and a procedure for determining the constant of proportionality between Q_max ^-1 and the amount of dissolved carbon in steel is described. A concept of accumulated equivalent aging time is introduced and theoretically justified on the bases of time-temperature superposition of aging effects. Calculations and experiments show that a substantial decrease occurs in the C content of steel when it is heated to high temperatures and that this effect alters the shape of the Snoek peak.     

Electrotransport of carbon in molybdenum and uranium

The electrotransport velocity of carbon in molybdenum and uranium was measured over a temperature range slightly below their melting points. Carbon was found to have a positive effective valence of 2.26 to 1.74 in molybdenum over the temperature range of 1890 to 2320°C and a negative value of - 5.0 in γ-uranium between 850 and 1000°C. The effective valences of nitrogen and oxygen were also observed to be positive in molybdenum and negative in uranium but their magnitudes were not determined. The diffusion coefficients for carbon in both metals were determined over the same temperature ranges.¹⁴Carbon was used as a tracer in the molybdenum work. The diffusion coefficient for carbon in molybdenum is described by the equationD = D ₀ exp (-†H/RT) whereD ₀ and †H are 0.033 cm²/s and 153 kJ/mole (36.60 kcal/mole), respectively. The values forD ₀ and †H for carbon in γ-uranium were determined as 0.218 cm₂/s and 123 kJ/mole (29.40 kcal/mole), respectively. Electrotransport was shown to be an effective method of purifying a small amount of each metal with regard to carbon as indicated by resistance ratio measurements and chemical analysis. A correlation is also presented showing the relationship between the atomic size of the solvent metal and the sign of the effective charge of the migrating solute.