As a commonly used orthopedic implant material, titanium alloy has a lower elastic modulus than stainless steel and cobalt alloy, but it is still higher than bone. After implantation, there is still a "stress shielding" effect, which can cause bone density reduction and increase the risk of implant failure. In order to meet the demand for low elastic modulus of implant materials in the field of orthopedics, researchers have carried out a lot of research and development work to prepare titanium alloy materials with excellent comprehensive properties.
Alloying treatment is the main method to improve the mechanical properties of medical titanium alloys. The principles to be observed in selecting the added elements are: the elements are non-toxic, non-sensitive and can improve the mechanical properties of the alloy. In recent years, the new β-titanium alloys developed mainly include Ti-Nb alloy, Ti-Mo alloy, Ti-Zr alloy and Ti-Ta alloy. Compared with other β-titanium alloys, the elastic modulus of β-titanium alloys of these systems is lower, which is closer to the elastic modulus of human bone. They replace aluminium and vanadium with biocompatible, non-toxic elements such as niobium, molybdenum, zirconium, tantalum, etc., and are more suitable as orthopedic implant materials. Some medical titanium alloys have been successfully developed: Ti-13 Nb-13Zr, Ti-20Nb-0.5Ru, Ti-20Nb-1.0Ru, Ti-24Nb-4Zr-8Sn, Ti-25Nb, Ti-25Nb-1SN-2Cr, Ti-29Nb-2Mo-6Zr, Ti-30Nb-32Zr, Ti-32Nb-2Sn, Ti-35Nb-7Zr-5Ta, Ti-35Nb-2Ta-3Zr, Ti-7Mo, Ti-15Zr-15Mo, Ti-15Zr-20Mo, Ti-20Zr-10Mo, Ti-10Fe-10Ta, etc.
For a long time, Ti-Nb alloy has attracted attention as a candidate material for orthopedic implants due to its high biocompatibility and low elastic modulus. The addition of Nb as an alloying element can reduce the elastic modulus of Ti-Nb alloy. Based on Ti-Nb system, ternary and quaternary Ti-niobium alloys were prepared by adding different contents and different kinds of β-phase stable elements. They have different elastic modulus, tensile strength and other mechanical properties. However, Ti-Mo alloys with high tensile strength and low elastic modulus can be prepared by using Mo element as a β-phase stabilizer. In addition, the Ti-10Fe-10Ta alloy with the addition of non-toxic elements Fe and Ta also shows a low elastic modulus due to the addition of Ta element.
The surface of titanium alloy usually generates a stable and firmly bonded oxide film, which is the main reason for the corrosion resistance of titanium alloy. Due to the complex implanted environment in the body, substances such as chloride ions and proteins present in body fluids can cause corrosion to the oxide film, causing dissolution and stripping, thus affecting the corrosion resistance of titanium alloys. Therefore, improving the corrosion resistance of titanium alloys, while avoiding changing the mechanical properties of titanium alloys, surface modification treatment has become a research focus.
