Abstract
The intermetallic compound NiAl is highly ordered at stoichiometry, even at high temperatures. For instance, its point-defect concentration at 900 °C is on the order of 10−3 at this composition. Moreover, its enthalpy of formation is highly negative and exhibits a minimum at stoichiometry. All of these data suggest that the interdiffusion coefficient should exhibit a minimum at this composition. Yet, the literature data show that the minimum interdiffusion coefficient occurred between 48 and 49 at. pct Al. Accordingly, we have carried out diffusion-couple measurements employing single-phase NiAl wafers over the temperature interval from 700 °C to 1000 °C. The measured concentration profiles were analyzed in terms of the lattice mole fraction, yielding interdiffusion coefficients as a function of composition and temperature. For all the temperatures studied, the interdiffusion coefficients were found to exhibit a minimum at the stoichiometric composition, with a corresponding maximum in the activation energies obtained from the temperature dependence of the interdiffusion coefficients.
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Kim, S., Chang, Y.A. An interdiffusion study of a NiAl alloy using single-phase diffusion couples. Metall Mater Trans A 31, 1519–1524 (2000). https://doi.org/10.1007/s11661-000-0162-7
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DOI: https://doi.org/10.1007/s11661-000-0162-7