Material design of novel TiNbTaHfMo high-entropy alloys for biomedical implants: Exploring an industry-adaptable route via FAST/SPS

Novel non-equiatomic Ti–Nb–Ta-Hf-Mo alloys were designed using β-Ti and high-entropy alloy formulation strategies to develop low-modulus materials for load-bearing biomedical implants. Ti 40-x Nb 25 Ta 25 Hf 10 Mo x (x = 0, 5, 10 at.%) alloys were designed by combining the d -electron method for β-Ti alloys with conventional HEA design parameters, aiming to develop low-modulus materials for load-bearing biomedical implants. Compositions were optimized through CALPHAD thermodynamic modeling and validated using a random forest machine learning approach, with predictions matching phase transformations detected during sintering. Alloys were fabricated via elemental powder blending and spark plasma sintering (FAST/SPS) under varied temperatures and dwell times, achieving densification from ∼90 % at 1250 °C/5 min to 98 % at 1350 °C or 10 min. Higher Mo content promoted and stabilized body-centered cubic (BCC) structures even at lower temperatures or shorter times. Mechanical testing confirmed Young's moduli of 16–74 GPa, tunable through densification control to balance strength and mitigate stress shielding. Despite a heterogeneous microstructure, the mechanical performance was comparable to alloys produced by longer, costlier routes. This work demonstrates FAST/SPS from elemental powders as a rapid, scalable, and industrially attractive method for producing biomedical HEAs.