Cr Alloying Enhanced Strength–Ductility Synergy in TiZrNb Alloys at Intermediate Temperature: A Comparative Study with Al and Cu

A systematic investigation was conducted on the effects of Cr alloying on the tensile behavior and microstructural evolution of TiZrNb medium-entropy alloys at 673 K. For comparison, the influences of Al and Cu alloying on the mechanical properties of TiZrNb were also examined. Although Al and Cu alloying enhanced the ultimate tensile strength at room temperature, their improvements in strength and ductility at 673 K were limited. In contrast, the TiZrNb98.5Cr1.5 alloy retained a single body-centered cubic (BCC) phase without forming the conventionally expected Laves phase. Cr effectively suppressed the formation of Zr-rich precipitates. At a strain rate of 1.67 × 10−3 s−1 and 673 K, TiZrNb98.5Cr1.5 exhibits an increase in the ultimate tensile strength of approximately 408 MPa compared with the base TiZrNb alloy, while the fracture elongation increases from 10% to 25% and the threshold stress rises from 669 MPa to 1196 MPa, achieving a markedly improved strength–ductility synergy. These results indicate that Cr alloying effectively stabilizes the microstructure and enhances the mechanical performance of TiZrNb alloys at 673 K by suppressing precipitate formation and reducing dislocation accumulation, outperforming Al and Cu alloying at the same temperature.