Design strategy of Ti-Zr-Hf-Nb high-entropy alloys based on first principles computations

High-entropy alloys (HEAs) have emerged as promising biomaterials owing to their favorable properties. The propensity of Ti-Zr and Hf-Nb atomic pairs within the Ti-Zr-Hf-Nb system was exploited to generate predictive design strategy utilizing the CALPHAD and first-principles calculations. The Ti₃₀Zr₃₀Hf₂₀Nb₂₀ (TZ6) and Ti₃₅Zr₃₅Hf₁₅Nb₁₅ (TZ7) alloys exhibited an optimal balance between strength, ductility, and Young’s modulus. TZ6 alloy possessed a yield strength of 694.5 ± 5.6 MPa and an elongation of 20.7 ± 1.7% in tensile test, with Young’s modulus of 79.8 ± 1.9 GPa. TZ7 alloy was characterized by a yield strength of 676.3 ± 5.6 MPa and an elongation of 19.0 ± 1.7%, with Young’s modulus of 70.3 ± 1.5 GPa. Due to the increased proportion of Ti-Zr pair in the alloy, which destabilized the electronic structure, the Young’s modulus was subsequently diminished. Concurrently, the reduction in dislocation nucleation energy significantly enhanced the ductility. Notably, the Young’s modulus of the TZ6 and TZ7 alloy is reduced by 11.1% and 21.7 %, respectively, compared to equimolar TiZrHfNb (TZ5) HEA. Additionally, TZ6 and TZ7 can be classified as a Class 0 non-cytotoxic material, demonstrating superior cell compatibility compared to Ti6Al4V and TZ5 alloys. The theoretical predictions were in well agreement with the experimental results, which provided a paradigm for the design of comprehensive balanced performance in biomedical HEAs.