Cost-effective design of high-performance NiCoCrAlTi high-entropy alloys through Fe-mediated phase competition control: a combined experimental and first-principles study

The development of cost-effective high-entropy alloys (HEAs) through the strategic incorporation of economically advantageous elements represents a critical pathway for advancing industrial applications. This study systematically investigates the role of Fe as an economical alloying element in mediating competitive precipitation behaviors and yielding exceptional strength-ductility synergies in NiCoCrAlTi HEAs. Using comprehensive multimodal characterization combined with first-principles calculations, we demonstrate that Fe addition fundamentally alters the competitive balance between discontinuous precipitation (DP) and continuous precipitation (CP). Simultaneously, this Fe incorporation facilitates the nucleation and stabilization of the B2 phase, thereby establishing a more favorable microstructural evolution pathway. First, Fe preferentially segregates to grain boundaries, decreasing interfacial energy and restricting boundary migration, thereby diminishing the thermodynamic driving force for DP formation while concurrently refining the grain structure. Second, the enhanced thermodynamic stability of B2 phases relative to L12 phases drives a beneficial transition from DP regions to strengthening B2 precipitates. Furthermore, the room-temperature tensile properties exhibit a nonmonotonic relationship with iron content, initially demonstrating a reduction followed by a significant enhancement. The Fe30 composition demonstrates anomalous strengthening behavior, achieving an exceptional yield strength combined with outstanding elongation, attributed to the synergistic activation of multiple deformation mechanisms including the formation of stacking faults, deformation twinning, immobile Lomer-Cottrell locks, and Hall-Petch strengthening derived from grain refinement. This investigation establishes a fundamental framework for economically driven alloy design, demonstrating how strategic Fe incorporation can simultaneously eliminate detrimental microstructural features while enhancing mechanical performance, thereby providing a cost-effective route toward high-performance structural materials for industrial applications.