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 aluminum 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-13Nb-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-Nb 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. Although researchers have concerns about the biocompatibility of the Mo element, it can be used as a β-phase stabilizer to prepare Ti-Mo alloys with high tensile strength and low elastic modulus. 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 preparation of titanium alloy with excellent comprehensive mechanical properties can be achieved by preparing porous structures in addition to adding different alloying elements. The commonly used methods for preparing porous materials include foaming method, powder metallurgy method, fiber sintering method, plasma spraying method, gel injection molding method, laser drilling technology, 3D printing technology, etc. When preparing porous titanium alloy materials, the elastic modulus of titanium alloy materials should be reduced and the appropriate strength should be ensured. At present, researchers have developed such as Ti-6Al-4V porous alloy, Ti-3Cu porous alloy, Ti-Ag/Ti radial gradient porous composite, Ti-2Cu-4Ca porous alloy, Ti-35Zr-28Nb porous alloy, etc., it is not difficult to see that such materials show lower elastic modulus than alloying treatment.
