Influence of chemical composition on coarsening kinetics of coherent L12 precipitates in FCC complex concentrated alloys

In this study, we report the experimental coarsening kinetics at 850, 900 and 950 °C of four complex concentrated alloys in the Al–Ti–Cr–Fe–Co–Ni senary system with different chemical compositions but a similar γ’ (L12) volume fraction (∼35 % at 950 °C) in a face-centered cubic (γ, FCC) matrix. The selected alloys were specifically designed to investigate the influence of Fe additions and Ni–Co substitutions on Ostwald ripening kinetics. Atom Probe tomography (APT) was used to determine the compositions of the FCC and L12 phases, which agree very well with Calphad calculations at thermodynamic equilibrium. Thermo-kinetic modeling of L12 precipitation was carried out using the Prisma module developed by Thermo-Calc and compared with experimental results. Apparent activation energies were determined and discussed in light of diffusion-controlled coarsening models to identify the key parameters affecting Ostwald ripening. We suggest that the abnormally high apparent activation energies results from composition-dependent parameters. When the latter are accounted for, the corrected activation energies for coarsening are in better agreement with available diffusion data.