Effects of selected metallic and interstitial elements on the microstructure and mechanical properties of beta titanium alloys for orthopedic applications

Metallic biomaterials are widely used for orthopedic application to resolve pain and improve patients' quality of life. Among these biomaterials, beta (beta)-phase titanium (Ti) alloys have received intense interest over last two decades. Unfortunately, the issue of insufficient mechanical properties of biocompatible beta Ti alloys is still significant, including low tensile strength (UTS) and high Young's modulus (E), which causes the early failure of the implant and degradation of natural bone, respectively. Thus, this article reviews the effects of some commonly used alloying elements on UTS, E and microstructure of Ti alloys for orthopedic application. Niobium is highlighted as the optimum beta-stabilizer addition, with other elements such as tantalum and molybdenum also somewhat suitable. Tin and zirconium, although not beta-stabilizers, are also suggested for their effects on microstructure. Additionally, the effects of four interstitial elements have been discussed; oxygen and nitrogen are noted to show significant effects on microstructure and phase transformations in beta alloys, and so are of interest in developing high-strength novel Ti alloys, though further research is needed. Carbon is less beneficial, but is not harmful if carbide formation is avoided. Hydrogen is solely detrimental, and should be limited as much as possible.