Interdiffusion fluxes and transport coefficients under multiple gradients in selected ternary systems
Abstract
A new analysis is developed for the determination of diffusion coefficients and parameters relevant to various driving forces that give rise to atomic flow in solids. In this analysis, the interdiffusion fluxes of each component are determined directly from the experimental concentration profiles and integrated for the determination of diffusion parameters such as average ternary interdiffusion coefficients and average coefficients of thermotransport. Average ternary interdiffusion coefficients were evaluated from a single diffusion couple experiment over selected regions in the diffusion zone from the experimental concentration profiles of couples in the Cu-Ni-Zn, Ni-Cr-Al and Fe-Ni-Al systems selected from literature. These ternary interdiffusion coefficients were found to be consistent with those determined by the Boltzmann-Matano analysis and employed to successfully model the experimental concentration profiles on the basis of error function solutions. Thermotransport studies carried out in the U-Pu-Zr system at the Argonne National Laboratory were also examined in the framework of the new analysis from the evaluation of average coefficient of thermotransport, effective interdiffusion coefficients and average ternary interdiffusion coefficients for selected composition ranges. These coefficients were employed to identify the flux contributions arising from the gradients of temperature and concentrations, and to evaluate the ternary diffusional interactions during multicomponent thermotransport. Isothermal diffusion in the Fe-Ni-Al system at 1000°C was experimentally investigated by using solid-solid diffusion couples assembled with [special characters omitted], [special characters omitted], [special characters omitted] and [special characters omitted] alloys. Diffusion structures were examined by optical and scanning electron microscopy and concentration profiles and diffusion paths were determined by electron microprobe analysis. The developments of planar and nonplanar interfaces, two-phase layers and demixing of two-phase layers into single phase layers were examined in the light of diffusion paths. A diffusion path that deviates from an s-shaped path by crossing the straight line joining the terminal alloys two times was experimentally observed for the first time. Ternary interdiffusion coefficients were also calculated on the basis of the Boltzmann-Matano analysis and examined as a function of composition. For several couples, average ternary interdiffusion coefficients on the basis of the new analysis were calculated over selected composition ranges and examined to identify the ternary diffusional interactions in the Fe-Ni-Al system.
Degree
Ph.D.
Advisors
Dayananda, Purdue University.
Subject Area
Materials science|Metallurgy|Nuclear physics
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