Segregation-assisted yield anomaly in a Co-rich chemically complex intermetallic alloy at high temperatures

Chemically complex intermetallic alloys (CCIMAs) have emerged as promising materials for achieving exceptional softening resistance at elevated temperatures, owing to their unique superlattice structures and elemental synergism. However, the lack of experimental endeavors and understanding regarding their temperature-dependent mechanical behaviors hinders their advancement for high-temperature applications. Here, we conducted a systematic investigation on the mechanical properties and associated deformation mechanisms of an L1₂-type Co-rich CCIMA using transmission electron microscopy. The Co-rich CCIMA exhibits superior strength across a wide temperature range of 700-900°C, with an anomalous peak yield strength (YS) of ∼1.0 GPa at 700°C, which surpasses most previously reported L1₂-type intermetallic alloys. This superior softening resistance can be primarily attributed to a combination of cross-slip hardening and segregation-assisted hardening. Specifically, massive Kear-Wilsdorf (K-W) locks formed by multiple cube cross-slips of screw dislocations prevail at 700-900°C, providing strong barriers for dislocation movements and enhancing the yield strength (YS) accordingly. More interestingly, we revealed a segregation-assisted formation of superlattice stacking faults and nanotwins at the peak yield temperature (700°C). The interlocking of these substructures and the associated element dragging effect further impeded the propagation of dislocations, contributing to the observed yield anomaly. This work provides in-depth insight into the high-temperature performance and deformation behaviors of CCIMAs, which paves the way for the future development of novel heat-resistant structural alloys.