Spinodal Decomposition of B2-phase and Formation of Cr-Rich Nano-precipitates in AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

Herein, the occurrence of a B2-phase separation and formation of Cr-rich nano-precipitates during the solidification process of AlCoCrFeNi2.1 eutectic high-entropy alloy is addressed. Toward this end, various advanced characterizations, including high-resolution transmission electron microscopy and atom probe tomography combined with thermodynamic calculations, are employed. The as-solidified microstructure is composed of face-centered cubic (FCC) dendrites and interdendritic regions consisting of a eutectic mixture of FCC and body-centered cubic (BCC) phases. The presence of uniformly distributed Cr-rich nano-precipitates is traced through the BCC B2 phase in the interdendritic area. Regarding the occurrence of upward diffusion and Gibbs free energy variation, the formation of Cr-rich nano-precipitates is attributed to the spinodal decomposition where the critical temperature of 800 degrees C is passed behind during the solidification process. The formation of dense dislocation array in the interdendritic region due to thermal stress induced during solidification is introduced as a pathway for diffusion of alloying elements in the course of cooling stage.