Evaluation of Interdiffusion in Liquid Phase during Reactive Diffusion between Cu and Al

Abstract

Using Cu/Al diffusion couples initially composed of pure Cu and Al, the reactive diffusion in the binary Cu–Al system was experimentally examined in a previous study. The diffusion couple was isothermally annealed in the temperature range of T=973–1073 K. Due to annealing, compound layers of the β, γ and ε phases are formed between the Cu-rich solid (α) phase and the Al-rich liquid (L) phase, and the L⁄ε interface migrates towards the ε phase. At each annealing time, the migration distance of the L⁄ε interface is much greater than the total thickness of the compound layers. Furthermore, there exists the parabolic relationship between the migration distance and the annealing time. This means that the migration of the interface is controlled by the volume diffusion in the L phase. The mathematical model for the interface migration controlled by volume diffusion was used in order to analyze quantitatively the migration rate of the interface. Through the analysis, the interdiffusion coefficient D of the L phase was evaluated to be 1.24×10⁻⁹, 2.91×10⁻⁹ and 3.62×10⁻⁹ m²/s at T=973, 1023 and 1073 K, respectively. Expressing the temperature dependence of D as D=D₀exp(−Q⁄RT), values of D₀=1.42×10⁻⁴ m²/s and Q=93.5 kJ/mol were obtained by the least-squares method. According to the analysis, the interdiffusion coefficient is much greater for the L phase than for the solid phases. Consequently, the L⁄ε interface migrates towards the ε phase, and the migration rate of the interface is much greater than the overall growth rate of the compound layers.