Ductile Lightweight Tix(AlCrZrV)100−x Medium Entropy Alloys with Superior Specific Yield Strength Through Compositional Tuning and Thermomechanical Treatment

In this study, the Nb from the lightweight Ti65(AlCrNbV)35 medium-entropy alloy was replaced with Zr to create lower-density Tix(AlCrZrV)100−x (x = 65, 67, 70, or 75) alloys. All alloy ingots were fabricated through vacuum arc melting and drop casting. X-ray diffraction analysis revealed all as-cast alloys exhibited only a single body-centered cubic structure. As the Ti content increased, the strength of the as-cast alloys decreased from 1247 to 981 MPa, whereas their elongation marginally improved. Moreover, the mechanical properties of these alloys were considerably enhanced through thermomechanical treatment (50% hot rolling and 80% cold rolling) and then rapid annealing at 700 °C, 800 °C, or 900 °C. An increase in the annealing temperature led to a notable decrease in the yield strength of the alloys but a considerable increase in their ductility. Ti65, Ti67, and Ti70 alloys annealed at 700 °C or 800 °C exhibited a yield strength of ≥1200 MPa and a ductility of ≥10%. Of the fabricated alloys, the Ti67 alloy annealed at 700 °C exhibited the optimal mechanical properties (yield strength of 1552 MPa and ductility of 13.6%). It exhibited low density (4.89 g/cm3) and a specific yield strength of 317 MPa·cm3/g, thus demonstrating considerable potential for transportation and energy applications.