Structure-property relations of lightweight Ti-Sc-Zr-Nb-V high-entropy alloys

Recently, it has been a hot topic to explore lightweight high entropy alloys (HEAs) for their future potential application as engineering materials. In this work, novel lightweight Ti22Sc22Zr22Nb17V17, Ti24Sc20Zr22Nb17V17, Ti24Sc22Zr20Nb17V17, and Ti26Sc20Zr20Nb17V17 HEAs were fabricated by rapid solidification. The phase constituents and microstructures of the HEAs in the cast and annealed states were characterized by X-ray diffraction spectrum (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and energy dispersive spectrum (EDS), while their mechanical properties were also investigated in detail. The microstructures of the cast samples consist of the coarse equiaxed BCC dendrites with extremely heterogeneous chemical distributions and the intergranular structures that are made up of BCC and HCP precipitates. Both precipitates inside the intergranular structures exhibit slightly large worm-shaped and fine lamellar morphology features. After annealing at temperatures below 1273 K, the desolvation reaction occurs due to the strong solute redistribution, leading to the disappearance of the lamellar structures, the coarsening of the large worm-shaped BCC particles, and the solid phase separation of the equiaxed BCC dendrites. At 1273 K, the combined interaction from the eutectoid transformation and phase separation leads to the formation of the TiNbV-rich BCC, ScZr-rich HCP, and transitional BCC+HCP structures. Compared with reported lightweight HEAs (density ≤ 6.5 g/cm3), the present HEAs in the cast and annealed states exhibit excellent comprehensive mechanical properties, which are attributed to the combined effect from the solid-solution strengthening, second phase strengthening, and fine-grained strengthening. The present studies provide potential candidates as lightweight high-temperature structural materials in the future.