Among the several types of medical implanted titanium alloys, the research on β-type titanium alloys is the latest. The preliminary research in foreign countries is relatively mature, and the domestic is still in the preliminary test stage. This requires more scientific researchers to pay more attention and research to make research early Transform into productivity and benefit mankind. The medical implant metal materials used at home and abroad are: 316, CoCr alloy, titanium and titanium alloy. Compared with the human bone elastic modulus, titanium and titanium alloys are the closest. At present, the most widely used in this category are commercial pure titanium and Ti-6Al-4V, while the new β alloys, because they have the most similar elastic modulus to bones, are currently receiving much attention. The process design is:
- Titanium alloy composition
In the design of titanium alloys, α-stabilizing elements (Al, O, N, etc.) and β-stabilizing elements (V, Mo, Nb, etc.) determine the classification of alloys. The alpha alloy has only the alpha phase; the near alpha alloy contains a small amount of beta stable elements; the alpha + beta alloy contains a higher beta stable element; the beta alloy has only the beta phase. The study believes that: Nb, Zr, Mo, Ta are added elements for medical β titanium alloy. After adding to a certain content, metastable β phase can be obtained by rapid cooling, which can effectively reduce the elastic modulus of the alloy, but the addition of such alloy elements The amount should not be too high. Excessively high will cause the brittle ω phase to precipitate, causing the alloy to become brittle and the elastic modulus to increase. Therefore, a reasonable choice and control of the amount of addition is the key to obtain an ideal low modulus. Typical is the TNZ series titanium alloy (including Ti-13Nb-13Zr, Ti-13Nb-20Zr, etc.).
- Heat treatment
In order to obtain the ideal β-phase structure, the β-type alloy should be fully solution-treated in the β-phase region and then rapidly cooled (such as water quenching). The heat treatment of medical β-phase alloys is as follows:
1) Cold deformation with large deformation + annealing treatment or hot working deformation with large deformation (β phase region or α + β two-phase region);
2) After thermomechanical processing, fully solution in the β-phase region and quickly cool to obtain the full β-structure as much as possible.
- Ultrafine grain
Fine grains are an effective means for metallic materials to obtain excellent comprehensive mechanical properties. The advantages of medical implant β-titanium alloy after ultrafine grain treatment are:
1) Without changing the modulus of elasticity, increase the strength of the alloy, thereby improving service life;
2) Improve wear resistance and reduce wear caused by contact between implant alloy and bone and tissue;
3) From the perspective of material processing and molding, the ultrafine grain alloy has excellent plastic deformation ability, and has superplastic characteristics, and the moldability is very good. The method in the study is: using ultra-fine pipe extrusion method to obtain ultra-fine grains. In addition, there is a dual-state structure of nano-ultrafine matrix and micro-scale dendrite β phase obtained by alloying specific smelting method.
- Surface treatment
In addition to the strength and modulus properties of titanium alloys, the surface wear resistance of medical implant materials also has a great impact on its service life. Poor wear resistance of implanted titanium alloys will cause premature wear and failure. The method of improving the wear resistance of implant materials generally uses surface coating. The traditional coating design mainly considers the biocompatibility, corrosion resistance and surface activity of the alloy, such as Al2O3 and TiO2 coatings. In recent years, techniques such as ion implantation, plasma spray coating, surface nitriding, and surface carburizing have been used to improve the surface hardness and wear resistance of alloys. Especially a diamond-like carbon (Diamond-like carbon) coating, the effect of improving alloy wear resistance is remarkable. In addition, the ultrafine treatment of the near-surface structure of the titanium alloy to obtain submicron or nanophase grains is also an effective way to improve the wear resistance and fatigue resistance of the material. For example, by adopting cyclic induction heating and quenching treatment, the “skin effect” of induction heating can be used to achieve instantaneous induction heating of the titanium alloy near the surface.