| In the multiphase diffusion couple, the moving boundary problem is of importance such as the growth and kinetics of interphase and/or phase transformation. The geometry of interface in the multiphase diffusion couple can be identified as planar, nonplanar or complexities. From the solution of the Fick`s 2nd law, one can extend the solution to the ternary as well as binary diffusion. Based on the assumption of the constant D on each phase in ternary system, the concentration profile may he obtained theoretically with interdiffusion coefficients and interface concentration without diffusion experiments. In this study, the multiphase diffusion couples in the Cu-Ni-Zn alloys were employed for the application of the extended solution to ternary system. The agreement of calculation of the concentrations, C^αand C^β, on each phase in a two-phase β₂/α₁couple was good to the result of the experiment. As simple nonplanar interphase in the diffusion couple, circlar cylinder, sphere, ellipsoid and elliptical paraboloid were assumed for the concentration and growth of the interface with a two-phase β₂/α₄Cu-Ni-Zn diffusion couple. Based on calculation the growth of the nonplanar interface of β₂/α₄couple corresponded with the circular cylinder model. Hence, the moving boundary of nonplanar interface of β/α Cu-Ni-Zn alloy diffusion couple at 775℃ may be grown forming the circular cylinder. |
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