High strength-ductility synergy in refractory multi-principal element alloys via special deformation mechanisms and dislocation behaviors

Ti-Zr–Nb refractory multi-principal element alloys (RMPEAs) have attracted increased attention due to their excellent mechanical properties. In this study, (TiZr)_80-xNb₂₀Mo_x (x = 0, 5 and 10) alloys were designed, and the intrinsic conflicts between strength and ductility were overcome via composition optimization and recrystallization. The causes of the superior strength-ductility synergy were investigated in terms of their deformation mechanism and dislocation behavior. The results show that the strength improvement can be attributed to the deformation mechanism transition caused by local chemical fluctuations and lattice distortion. Specifically, the slip band widths decrease after Mo addition, and the measured slip traces in the fracture samples are associated with high-order {112} and {123} slip planes. Furthermore, the grain refinement achieved via recrystallization promotes multi-slip system activation and shortens the slip-band spacing, which reduces the stress concentration and inhibits crack source formation, thereby allowing the alloy to ensure sufficient ductility. Consequently, the Ti₃₅Zr₃₅Nb₂₀Mo₁₀ alloy annealed at 900 °C exhibits high yield strength and elongation. These findings provide a new strategy for designing high-strength RMPEAs and addressing room-temperature brittleness.