Papers by Author: Mysore A. Dayananda

Abstract: There exist several interesting phenomena and observations reported in literature for isothermal diffusion in multicomponent systems. Such phenomena include uphill diffusion, development of zero-flux planes and flux reversals for individual components, flux reversals at interfaces, and instability at interfaces and multiphase layer development. In addition, uncommon diffusion structures exhibiting unusual diffusion paths can develop in both single phase and multiphase diffusion assemblies. An overview of such phenomena is presented to highlight the role of interactions among diffusing components with the aid of selected diffusion studies carried out in multicomponent alloy systems, aluminides, silicides, and nuclear fuels.

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: An analysis of multilayered assemblies set up with multicomponent alloys selected in a single phase field has been recently developed on the basis of a matrix of constant interdiffusion coefficients. This analysis employs a transfer matrix method and is applicable to a study of evolution of concentration profiles and diffusion paths as a function of time for multilayered diffusion assemblies (MDAs) where any number of finite layers is sandwiched between two bulk terminal alloys. The analysis is utilized in this study to simulate concentration profiles and diffusion paths for MDAs assembled with (fcc) Cu-Ni-Zn alloys with two terminal alloys, A and B, sandwiching an alloy layer C in the middle. For short diffusion times the diffusion path of the ternary MDA, A/C/B, corresponds to two segments corresponding to the diffusion paths of the infinite diffusion couples, A/C and C/B. At longer times the diffusion zones of the two individual couples overlap and the diffusion path of the MDA varies continuously with time. The evolution of the concentration profiles and diffusion paths is presented and each intermediate path configuration is associated with a unique ratio of the middle layer thickness to the square root of diffusion time. The simulated concentration profiles clearly show the development of uphill diffusion and zero-flux planes (ZFP) for the individual components due to diffusional interactions among the components. At very long times, the diffusion path of the MDA approaches that of the infinite couple A/B between the two terminal alloys.

Abstract: Selected diffusion couples investigated in the Cu-based and Fe-based multicomponent systems are examined for diffusion path development, zero-flux planes, uphill diffusion, and internal constraints for diffusion paths. The couples are analyzed for interdiffusion fluxes and interdiffusion coefficients with the aid of the “MultiDiFlux” program. Eigenvalues and eigenvectors are also determined from the interdiffusion coefficients determined over various ranges of composition in the diffusion zone. Slopes of diffusion paths at selected sections, including the path ends, are related to interdiffusion coefficients, interdiffusion fluxes and/or eigenvectors. These relations are explored with selected single phase diffusion couples in the Cu-Ni-Zn and Fe-Ni-Al systems and the calculated path slopes are compared with those directly determined from the concentration profiles. Relations between the gradient of interdiffusion flux and the concentration gradient are examined for each component in a two-phase Cu-Ni-Zn diffusion couple. The research is supported by the National Science Foundation.