Cr-Triggered FCC Ti-Rich Precipitation and Its Effects on the Mechanical and Oxidation Performance of TiVNbTa...

This study investigates the effects of Cr content on the microstructure, room-temperature and 600 °C mechanical properties and high-temperature oxidation behavior of TiVNbTaCr_x (x = 0, 0.25, and 0.5). Cr addition significantly intensified Ti segregation in the interdendritic regions during solidification, inducing the formation of an Face-Centered Cubic (FCC) Ti-rich precipitate phase. As the Cr content increases from 0 to 0.5, the Ti-rich phases evolve from a straw-like morphology to a blocky morphology, and the mechanical properties at room temperature continue to decrease. Fracture analysis reveals that cracks initiate at grain boundaries associated with the FCC Ti-rich phase, leading to a transition from ductile to brittle fracture in the Cr-containing alloys. At 600 °C, all Cr-containing alloys exhibit elongations below 0.20%, indicating that the precipitation of the FCC Ti-rich phase severely degrades the deformation capability of the alloys at 600 °C. Oxidation tests demonstrate that Cr addition provides only a marginal beneficial effect on the mass gain rate during the initial stage (0-10 h at 600 °C), while the Cr-containing alloys continue to gain mass upon prolonged exposure due to the reduced integrity of the oxide film. The oxide scale consists primarily of (Ta, Nb)₉VO₂₅, and no protective Cr₂O₃ scale was observed under the present experimental conditions. In summary, within the composition range studied, the FCC Ti-rich phase precipitates at Cr contents of 5.88 and 11.11 at.%, resulting in the fragmentation of the body-centered cubic lattice (BCC) matrix continuity and a comprehensive deterioration of mechanical properties at both room temperature and 600 °C, while failing to improve the oxidation resistance at 600-700 °C.