Temperature Dependence of the γ/γ′ Interfacial Energy in Binary Ni–Al Alloys
A.J. Ardell
Abstract
Abstract Published data on the coarsening kinetics of γ ′ (Ni 3 Al) precipitates in binary Ni–Al alloys aged at 12 temperatures ranging from 773 K to 1073 K are analyzed to provide a comprehensive evaluation of the temperature dependence of the γ / γ ′ interfacial free energy, σ . The data are analyzed using equations of the trans-interface-diffusion-controlled (TIDC) theory of coarsening, with temporal exponent n = 2.4. The results show that σ decreases with increasing temperature, T . A linear empirical equation is fitted to the data on σ vs T ; it extrapolates to σ = 0 in the liquid region of the Ni–Al phase diagram, as it should do. A quantitative temperature-dependent transition radius, r trans , is calculated; it depends on the product of the interface width and the ratio of the chemical diffusion coefficients in the γ phase and interface regions. Applying the TIDC coarsening equations to calculate σ is justified when the average radius, 〈 r 〉, satisfies the condition 〈 r 〉 < r trans , which is valid for all the data used in the fit. The data on σ vs T are compared with theoretical predictions. The results are discussed in the context of previous work, as well as with values of σ obtained through analyses using the equations of traditional LSW coarsening kinetics, n = 3.