Diffusion Coefficient Of Nickel Research Articles

The effect of δ- ferrite formation on the post-solidification homogenization of alloy steels

The profound influence of the δ-γ transition on the rate of alloy steel homogenization is demonstrated using a controlled unidirectional solidification technique. The effect is related to the high rates of diffusion of substitutional solutes in the γ-phase: As shown in this work, for example, the diffusion coefficient of nickel in 5-ferrite is two orders of magnitude greater than the comparable value for austenite.

An electrochemical study of the equilibria in the nickel—mercury system

The electroreduction of nickel(II) at the HMDE in 6 M aqueous solutions of CaCl2 and 5 M LiCl in glycerine in the temperature range 20–230°C has been investigated by chronoamperometry, stationary electrode voltammetry and potentiometry. The formation of a relatively stable homogeneous supersaturated nickel amalgam for concentrations lower than 10−3 and 10−2 M, at temperatures 20° and 200°C respectively, was found. From the diffusion coefficients of nickel in mercury determined in the temperature range 20–230°C it was concluded that nickel atoms in the homogeneous amalgam are solvated by approximately three mercury atoms. It was found that in the crystallization of the homogeneous amalgam three compounds NiHg2, NiHg3 and NiHg4 are formed. Thermodynamic parameters for the formation of these compounds were determined and a mechanism for the crystallization process was suggested.

An electrochemical study of the equilibria in the nickel-mercury system

Summary The electroreduction of nickel(II) at the HMDE in 6 M aqueous solutions of CaCl2 and 5 M LiCl in glycerine in the temperature range 20–230°C has been investigated by chronoamperometry, stationary electrode voltammetry and potentiometry. The formation of a relatively stable homogeneous supersaturated nickel amalgam for concentrations lower than 10−3 and 10−2 M, at temperatures 20° and 200°C respectively, was found. From the diffusion coefficients of nickel in mercury determined in the temperature range 20–230°C it was concluded that nickel atoms in the homogeneous amalgam are solvated by approximately three mercury atoms. It was found that in the crystallization of the homogeneous amalgam three compounds NiHg2, NiHg3 and NiHg4 are formed. Thermodynamic parameters for the formation of these compounds were determined and a mechanism for the crystallization process was suggested.

The high-temperature creep behavior of nickel-rich Ni-W solid solutions

The steady-state creep behavior of four nickel-rich Ni-W solid solutions (1, 2, 4, and 6 wt pct W) was investigated in the temperature range 850° to 1050°C. Constant stress tensile creep tests were performed in vacuum in the stress range 3000 to 7000 psi. Activation energies for creep were observed to be 71.4 ± 2.0, 74.4 ± 3.0, and 75.8 ±2.0 kcal per mole, after correcting temperature dependence of the elastic modulus, for alloys containing 2,4, and 6 pct W respectively. These values closely approximate the activation energies for the weighted diffusion coefficient, $$\bar D$$ =DNiDW/(XWDNi) whereX Ni andX w are the atom fractions of nickel and tungsten respectively, andD Ni andD w are the diffusion coefficients of nickel and tungsten in the alloy. The steady-state creep rates exhibit a power law stress dependence with an exponent,n, equal to 4.8 ±0.2 for all of the alloys studied. For tests conducted at temperatures and stresses such that both the diffusivity, $$\bar D$$ , and the ratio of the applied stress to the elastic modulus, σ/E, are. held constant, the steady-state creep rate, $$\dot \varepsilon _\mathcal{S} $$ , was found to vary with the stacking fault energy, γ, according to the empirical relation $$\dot \varepsilon _\mathcal{S} $$ ∼ γ4 2±4 over the range of creep rates studied.

Diffusion of Nickel in Niobium

Using a residual activity technique, the diffusion of nickel in niobium was studied in the temperature range of 988 to 1246°C. The temperature dependence of diffusivity can be expressed asD=9.3exp(−80400⁄RT)cm2⁄sec.The diffusion coefficient of nickel was found to be of the same order of magnitude as those of cobalt and iron in niobium.

Rates of dissolution of a vertical nickel cylinder in liquid aluminum under free convection

The rate of dissolution of a vertical nickel cylinder, completely immersed in liquid aluminum in the absence of any forced convection at 675°C, was found to be at steady-state and controlled by the rate of mass transfer in the fluid boundary layer under free convection arising from the mass transfer process itself. The value of the diffusion coefficient of nickel in liquid aluminum at 675°C has been caclulated as 1.79×10−5 sq cm per sec. Atx<0.5 cm, wherex is the distance downwards from the upper end of the cylinder, the local rate of dissolution was found to vary asx−1/4, as expected in free convection. However, the rate decreased more rapidly at larger values ofx, possibly due to the interference in fluid flow caused by the proximity of the crucible bottom.

Diffusion of Nickel in Silver

The diffusion coefficient of nickel in single-crystal of silver has been measured by the lathe-sectioning technique as a function of temperature throughout the range from 750°C to 950°C using radioactive isotope Ni 63 as a tracer. The results are expressed as follows: \begin{aligned} D{=}(21.9)\exp\left(-\frac{54 800}{RT}\right) \text{cm}^{2}/\text{sec}. \end{aligned} The value of activation energy, 54.8 kcal/mole, obtained by the present experiment is in good agreement with the result of the screening theory of impurity diffusion.

鋳鉄および球状黒鉛鋳鉄の溶接(第1報)

The metallographic studies have been performed on the structure of weld heat-affected zone in cast irons. The typical heat-affected zone was obtained by the single-bead test, in which a single bead of about 10 to 12 cm was put on a cast-iron plate of 200×75×20 mm, by using various electrodes under the different conditions. Two layers, ledeburitic and martensitic, are observed in a heat-affected zone, the former varing in its thickness with the melting point of electrode. In martensitic layer, "white" martensite is mainly observed in the case of using cast-iron electrode, whereas in other cases using nickel and low-carbon steel electrodes by the same current, and in a case using cast-iron electrode by a higher current, it shows "dark" martensite. When the carrying speed of electrode is reduced, even in the case of cast iron electrode, primary cementite and troostite acommpanying it are observed in the matrix of dark martensite.The isothermal transformation diagrams were determined for two species of cast iron and a nodular graphite cast steel. In these diagrams, the boundary line between white and dark martensites was determined below Ms temperature. It is deduced that the two types of martensite are corresponding to fast and slow cooling below Ms temperature, the critical cooling velocity being about 1°C/sec.There is practically no difference in hardness between the martensitic layers of nickel electrode and of cast-iron electrode, if the welding conditions are the same. The amount of retained austenite was about 17 to 27%, though it reached about 40% in a few microscopic observations, also indicating no appreciable difference between the electrodes.The diffusion of nickel from deposit metal to the heat-affected zone by the weld thermal cycle is not likely to occur, since the diffusion coefficient of nickel in austenite is relatively low. The superior properties of nickel electrode may be attributed to the high ductility of weld metal, the martensitic heat-affected zone being not essentially different from those of other electrodes.