A Review: Design from Beta Titanium Alloys to Medium-Entropy Alloys for Biomedical Applications

Abstract

β-Ti alloys have long been investigated and applied in the biomedical field due to their exceptional mechanical properties, ductility, and corrosion resistance. Metastable β-Ti alloys have garnered interest in the realm of biomaterials owing to their notably low elastic modulus. Nevertheless, the inherent correlation between a low elastic modulus and relatively reduced strength persists, even in the case of metastable β-Ti alloys. Enhancing the strength of alloys contributes to improving their fatigue resistance, thereby preventing an implant material from failure in clinical usage. Recently, a series of biomedical high-entropy and medium-entropy alloys, composed of biocompatible elements such as Ti, Zr, Nb, Ta, and Mo, have been developed. Leveraging the contributions of the four core effects of high-entropy alloys, both biomedical high-entropy and medium-entropy alloys exhibit excellent mechanical strength, corrosion resistance, and biocompatibility, albeit accompanied by an elevated elastic modulus. To satisfy the demands of biomedical implants, researchers have sought to synthesize the strengths of high-entropy alloys and metastable β-Ti alloys, culminating in the development of metastable high-entropy/medium-entropy alloys that manifest both high strength and a low elastic modulus. Consequently, the design principles for new-generation biomedical medium-entropy alloys and conventional metastable β-Ti alloys can be converged. This review focuses on the design from β-Ti alloys to the novel metastable medium-entropy alloys for biomedical applications.

Effects of Cold Rolling or Precipitation Hardening Treatment on the Microstructure, Mechanical Properties, and Corrosion Resistance of Ti-Rich Metastable Medium-Entropy Alloys

“…The metastable β structure of the Ti 80 -Nb 10 -Mo 5 -Sn 5 (at%) MEA is achieved by adjusting the molybdenum equivalent ([Mo] eq ) to 15 and the valence electron concentration (VEC) to 4.2, which results in the low elastic modulus of the alloy. The thermodynamic parameters detailed in Table 1 were determined using calculations based on the formulas referenced in [9]. These ingots were prepared using a commercial arc-melting vacuum pressure casting system (A-028, DAWNSHINE, Taichung, Taiwan) with pure Ti (99.7 wt%), Nb (99.95 wt%), Mo (99.95 wt%), and Sn (99.9 wt%).…”

“…In recent years, Ti-rich metastable β high-entropy alloys (HEAs) and medium-entropy alloys (MEAs) have garnered significant attention in the field of biomedical materials [1][2][3][4][5][6][7][8][9]. These alloys are known for their high mechanical strength and low elastic moduli.…”

Nanohydroxyapatite/Peptide Composite Coatings on Pure Titanium Surfaces with Nanonetwork Structures Using Oyster Shells

“…Titanium and its alloys are used as biomedical implants owing to their high specific strength, low elastic modulus, and excellent corrosion resistance [1,2]. However, they are bioinert and cannot bond with living bone; thus, surface modification is necessary.…”

Effect of Partial Substitution of Zr for Ti Solvent on Young’s Modulus, Strength, and Biocompatibility in Beta Ti Alloy

“…Metastable β-Ti alloys with low Young's moduli and bcc structures have been extensively studied and developed [1]. There are several guiding principles for the development of Ti alloys with low Young's moduli, one of which is the reduction of the electron-to-atom ratio (e/a) [5]. The lowness of the e/a is an indicator of the instability of the β phase; it has been shown that a reduction in the e/a reduces the Young's modulus of polycrystalline Materials 2024, 17, 2548 2 of 11 materials [6], as estimated by the Hill approximation [7].…”