Abstract: A wide range of polycrystalline alloys witness severe intergranular embrittlement in the intermediate temperature regime, setting limits on their safe applications. The heterogeneous columnar-grained structure provides a substantial intergranular toughening effect, contributing to the recovered ductility at elevated temperatures. However, the stored deformation energy could act as the driving force for recrystallization, setting the heterostructure thermodynamically unstable. In this study, we carefully examine the microstructural stability and associated high-temperature mechanical properties of the heterogeneous columnar-grained structure. The precipitation of the intermetallic phase not only consumes the deformation energy and reduces the driving force for recrystallization, but also impedes dislocation rearrangement and exerts a pinning effect on grain boundaries. Therefore, the heterostructure demonstrated exceptional thermal stability at temperatures up to 800 °C (∼ 0.7 melting temperature). These findings not only advance the mechanistic understanding of the intermediate temperature intergranular embrittling behaviors but also provide promising pathways for developing new-generation strong-yet-ductile high-temperature structural materials.

Key words: Embrittlement, High-entropy alloys, Zener pinning, Heterogeneous structure