sion couples of pure aluminum and copper metals.In the aluminum-copper equilibrium phase diagram there are five intermediate phases in this temperature range, namelyIt appears that the layer growth of each phase is controlled by the process of volume diffusion since the rate of layer growth obeys the parabolic law. From the temperature dependency of the rate constants of layer growth, the activation energies of the individual phases were obtained.The interdiffusion coefficient for each intermediate phase was calculated by the method introduced by Heumann, andAluminum oxide powder was used for the measurement of the Kirkendall effect. It is clear from this measurement that diffusion in the multilayer system is controlled by the vacancy mechanism and that aluminum diffuses more rapidly than copper.
Interdiffusion in the aluminum-magnesium system was investigated in the temperature range of diffusion couples of pure aluminum and magnesium.Electron probe micro-line analysis of specimens indicated that two intermediate phases, namely the diffusion zone. It is concluded that the growth of each phase is controlled by the process of volume diffusion since the rate of layer growth obeys the parabolic law.The activation energies for the interdiffusion in phases estimated from the temperature dependence of the interdiffusion coefficients calculated by Heumann's method were 13.6 and 28.1kcal/mol, respectively. The Kirkendall effect was measured with a marker. The marker shifted to the aluminum side with respect to Matano's interface. The result is opposed to that reported by Heumann and Kottmann who stated on the basis of Bungardt's experimental study that the initial interface moves to the magnesium side with respect to Matano's interface. The measurement of the Kirkendall effect showed that the diffusion in this system was controlled by a vacancy mechanism and that aluminum diffuses more rapidly than magnesium.
The purpose of this study was to account for the origin of the difference between activation energies for the layer growth and interdiffusion in an intermediate phase which was formed in a poly-phase diffusion couple. It was shown that this difference between the two activation energies seems to originate from the temperature dependence of the homogeneity range of the phase. Accordingly, the activation energy of the layer growth (QK2) is equal to a sum of the energy of the interdiffusion (QD) and that attributable to the temperature dependence of the homogeneity range of the phase (Qg).which coincides with QK2 within the experimental accuracy.It is also concluded that the activation energy for a layer growth does not coincide with that for an interdiffusion in the phase where the change in the concentration with temperature at that phase boundary is found.
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