Papers by Keyword: Ternary Diffusion

Abstract: Selected isothermal diffusion studies in ternary and quaternary systems are reviewed in order to present analytical and experimental approaches adopted for the determination of interdiffusion fluxes of components, interdiffusion coefficients, diffusional interactions among components, and internal consistency in the experimental data. Several interesting phenomena and observations including uphill diffusion, zero-flux planes and flux reversals, and double serpentine diffusion paths are illustrated with selected single phase Cu-Ni-Zn, Fe-Ni-Al and Cu-Ni-Zn-Mn diffusion couples. The main challenges involved in the experimental determination of interdiffusion data from multicomponent diffusion couples and in the application of such data are also addressed.

Abstract: Steel produced in Electric Arc Furnaces (EAF) contain a high amount of copper that causes a detrimental surface cracking phenomenon called hot shortness. Studies have found that nickel can alleviate hot shortness by increasing copper solubility in the Fe phase, decreasing oxidation rate and promoting occlusion [1-3]. Occlusion is a phenomenon whereby the copper-rich phase becomes incorporated into iron oxides. Nickel promotes occlusion by causing an uneven interface and increasing the number of internal oxides. The uneven interface is likely a result of the two concentration fields resulting from ternary diffusion of nickel, copper and iron in the Fe phase. This work is aimed at explaining why nickel causes wavy oxide/liquid-Cu and liquid-Cu/Fe interfaces. Constitutional super-saturation criterion [4] was applied to explain uneven interfaces caused by nickel. A model simulating diffusion behaviors of copper and nickel in Fe was developed by coupling Comsol Multiphysics® and Matlab®. Interface concentrations of copper and nickel and perturbation criterion values were calculated as a function of time. Modeling results show that (i) the nickel interface concentration first increases to a peak value then decreases slowly during oxidation process as a result of the change in oxidation rates, and (ii) the alloys with higher nickel contents have more potential for interface breakdown and this occurs within the initial linear oxidation regime.

Abstract: A new form of diffusion coefficient termed as thermodynamic diffusion coefficient is introduced in this paper. Conventionally, diffusion coefficients are evaluated using concentration gradient as driving force. But truly, chemical potential gradient is the actual driving force that determines the material flow in any part of the system. Thermodynamic diffusion coefficients are based on chemical potential gradient as driving force. The relation between thermodynamic diffusion coefficients and phenomenological coefficients has been established. The advantages of thermodynamic diffusion coefficients have been underlined, especially, in the cases of line compounds where concentration difference across the phase is zero or in case of intermetallic compounds with narrow homogeneity range. The intrinsic thermodynamic diffusion coefficients are equal to tracer diffusion coefficients. This helps in estimating tracer diffusivities in cases where tracers are not easily available. The advantages of thermodynamic diffusion coefficients are shown in binary and ternary systems by illustrating them in Ni-Al and Fe-Ni-Cr systems.