Ultra-slow coarsening in precipitation-strengthened refractory high-entropy alloys

The mechanical behavior of precipitation-strengthened materials is strongly influenced by precipitate morphological characteristics and lattice misfit to the matrix. This study examines the impact of 1 at. % Zr on thermal stability and coarsening kinetics in a refractory high-entropy A2-B2 alloy with the composition 27.3Ta-27.3Mo-27.3Ti-8Cr-10Al (at. %). We demonstrate that this minor Zr addition does not lead to the formation of other intermetallic phases, while the Zr strongly partitions into the B2 phase and induces a pronounced change in the precipitate morphology from cuboidal/elongated to spherical, accompanied by an increased number density. Despite coarsening close to the precipitate solvus temperature, extremely slow coarsening kinetics compared to other alloy systems is obtained mainly attributed to much higher solidus temperature rather than misfit or precipitate morphology alone. Overall, this work underscores the potential of tailoring precipitate characteristics to potentially enhance microstructural stability of B2 precipitates and creep resistance in advanced body centered cubic (BCC) superalloys.