Compositional pathways and capillary effects during isothermal precipitation in a nondilute Ni–Al–Cr alloy

Abstract

For a Ni–5.2Al–14.2Cr at.% alloy with moderate solute supersaturations, the compositional pathways, as measured with atom-probe tomography, during early to later stage γ′(L1 2)-precipitation ( R = 0.45–10 nm), aged at 873 K, are discussed in light of a multi-component coarsening model. Employing nondilute thermodynamics, detailed model analyses during quasi-stationary coarsening of the experimental data establish that the γ/γ′ interfacial free-energy is 22–23 ± 7 mJ m −2. Additionally, solute diffusivities are significantly slower than model estimates. Strong quantitative evidence indicates that an observed γ′-supersaturation of Al results from the Gibbs–Thomson effect, providing the first experimental verification of this phenomenon. The Gibbs–Thomson relationship for a ternary system, as well as differences in measured phase equilibria with CALPHAD assessments, are considered in great detail.