Attractive high-temperature strength and thermal processability in an Fe–Nb–B dual-composite alloy

A novel Fe 80 B 17 Nb 3 dual-composite alloy was designed to significantly enhance microstructural stability and strength at room to elevated temperatures, while maintaining excellent thermal processability and mechanical reliability. The introduction of the Nb element based on the Fe 83 B 17 eutectic alloy leads to a stable dual-composite structure, consisting of α-Fe/Fe 2 B and α-Fe/NbFeB eutectic colonies. The alloy demonstrates a remarkable compressive strength exceeding 1000 MPa at 700 °C, which is 68 % higher than that of the Fe 83 B 17 alloy, while maintaining a large plasticity of over 60 %. Additionally, this alloy exhibits excellent mechanical properties at room temperature after thermally pre-processing of 60 %, e.g., high yield strength of 1218 MPa, fracture strength of 1468 MPa, compression strain of 13.8 %, and hardness of over 400 HV, mainly due to the enhanced microstructural stability by Nb-alloying. Moreover, the Fe 80 B 17 Nb 3 alloy exhibits an anomalous discontinuous hardening behavior at intermediate temperatures (500-600 °C), and a pseudoplasticity enabled by crack/void nucleation and self-healing mechanisms. Furthermore, Fe 80 B 17 Nb 3 demonstrates a high fracture toughness of 14.5 ± 0.2 MPa·m 1 / 2 , superior to that of Fe 83 B 17 and Fe 83 C 17 eutectic alloys. This alloy also exhibits excellent wear resistance at room temperature. These results provide valuable insights for enabling Fe-B series alloys toward high-temperature applications.