Influence of interfacial and strain energies on γ′ coarsening kinetics in complex concentrated alloys

From the technological perspective, the long-term high-temperature application of alloys is dictated by the resistance to coarsening of strengthening precipitates. However, current matrix diffusion-limited coarsening models only consider the role of interfacial energy between the gamma (γ) and gamma prime (γ') phases. This study demonstrates the combined influence of both interfacial and strain energies on coarsening kinetics in two complex concentrated alloys of compositions Co-34.5Ni-12Cr-8Al-3Nb-4Ti-5Fe (5Fe) and Co-31Ni-12Cr-8Al-3Nb-4Ti-10Fe (10Fe), with similar precipitate volume fractions. Despite the 5Fe alloy having a larger interfacial energy value of 22.5 ± 2.3 mJ/m2 compared to 10.2 ± 2.8 mJ/m2 for the 10Fe alloy, both alloys exhibit similar coarsening kinetics at 950°C. The lattice misfit measurements showed a lower misfit value of +0.29 in the 5Fe alloy compared to the value of +0.44 for the 10Fe alloy. These findings highlight the importance of considering interfacial and strain energies in rationalising coarsening kinetics.