As an important functional material, titanium metal is widely used in aerospace, energy industry, medical supplies and other fields due to its advantages of low density, high specific strength and good corrosion resistance. The development of medical titanium and titanium alloys can be roughly divided into three periods: the first period is represented by pure titanium and Ti-6AI-4V; the second period is α+β type alloys, with Ti-5A1-2.5Fe and Ti-6Al -7Nb is the representative; in the third period, the main line of defense is to develop β-type titanium alloys with better biological properties and lower elastic modulus. The application of new titanium alloy materials will be the current development direction of mainstream medical devices. The research on medical titanium alloy materials began in my country in the 1970s. The Northwest Nonferrous Metals Research Institute developed Ti-2.5Al-2.5Mo-2.5Zr (TAMZ), and in the 1990s, it developed Ti-2.5Al-2.5Mo-2.5Zr (TAMZ) successively with independent intellectual property rights. -6Al-4V, Ti-Al-2.5Fe and Ti-6Al-7Nb materials. The Chinese Academy of Sciences has also developed a new beta titanium alloy Ti-24Nb-4Zr-7.6Sn. The current development of titanium alloys in my country is mainly based on breakthrough new materials and active application of titanium alloy materials. 1. Corrosion of titanium Titanium is a thermodynamically unstable metal, and the passive potential is relatively negative, and the standard electrode potential is -1.63V. Therefore, it is easy to form an oxide film with passivation properties in the atmosphere and aqueous solution, and the corrosion resistance is good. 1. Corrosion resistance of titanium in different media It is very important to study the corrosion resistance of medical materials. On the one hand, some metal ions or corrosion products of implanted materials penetrate into biological tissues, which can trigger physiological responses to different degrees; on the other hand, due to the presence of body fluids, the performance of some materials may be severely degraded, causing them to be rapidly damaged or even damaged. invalid. The human environment is relatively complex, which is more likely to cause the dissolution of trace elements and change the stability of the oxide layer. Slight friction can damage the passivation film formed on the titanium surface to varying degrees. For example, in an oxygen-poor environment, the stability of the oxide layer is weakened. When damaged, it cannot be repaired immediately or a new oxide layer can be formed, which is more likely to cause corrosion. This situation is almost unavoidable in the repeated movement of the human body and the use of equipment. Plastic deformation will change the microstructure of the material, which in turn affects the corrosion performance of the material. Different degrees of plastic deformation have different effects on the corrosion performance of materials. In the process of plastic deformation, due to the concentration of internal stress, defects are generated in the interface and grains, therefore, the plastic deformation will weaken the corrosion resistance of the material. 2. Corrosion mechanism of titanium Titanium is a transition element of the IVB group, with active chemical properties and a great affinity with oxygen. In any oxygen-containing medium, a dense passivation film is easily formed on the surface of titanium. This passivation film is extremely thin, and its thickness is usually several nanometers to several tens of nanometers. The existence of titanium alloy passivation film reduces the surface active dissolution area and slows down the dissolution rate, thus resisting the damage caused by dissolution. In addition, the passivation film can also be repaired automatically, and when damaged, a new protective film can be rapidly formed. Therefore, titanium has good corrosion resistance. The corrosion forms of titanium implanted in living organisms can be divided into pitting corrosion, stress corrosion, crevice corrosion, galvanic corrosion and wear corrosion. 2.1 Stress corrosion Stress corrosion refers to the phenomenon that the metal cracks when tensile stress and corrosion act simultaneously. The general process is as follows: the action of tensile stress makes the protective film formed on the metal surface begin to rupture, forming a crack source of pitting or crevice corrosion, which develops in depth. cracks and even breakage. 2.1.1 Factors affecting stress corrosion of titanium alloys The occurrence of SCC in titanium alloys is the result of the combined action of three factors: environment, stress and material. SCC is highly selective, as long as any one of the above three factors is changed, SCC will not occur. 1) Environment (1) Medium Titanium alloys may undergo SCC under the action of many aqueous solutions, distilled water, organic solutions and hot salts. The SCC mechanism is different in different media. (2) pH value There are still considerable differences in the effect of pH value on the SCC of titanium alloys. In general, with the increase of pH value, the SCC sensitivity of titanium alloy decreases, and when the pH value is 13-14, SCC can often be inhibited. However, a strong corrosive environment with a pH value of 2-3 can even be formed in the front section of the local crack where the SCC changes. (3) Potential The effect of potential on the degree of SCC is crucial. The corrosion system composed of alloy and medium is different, and its SCC sensitive potential is different. For example, B-titanium alloy in the aqueous solution containing halide, when the potential is around -600mV, the SCC is aggravated; at the overpassivation potential, cracks also occur; but no cracks appear at the potential lower than -1000mV. In the aqueous solution containing Cl- and Br-, the SCC sensitive potential of Ti8Al1Mo1V is -500mV--600mV. In the aqueous solution containing I-, the sensitive potential region is above 0mV. (4) Temperature Temperature is one of the important factors affecting the production of SCC in titanium alloys. Generally speaking, as the temperature increases, the sensitivity of SCC increases. In the hot salt-air environment of 300-500℃, the stress corrosion of Ti6Al3Mo2Zr0.5Sn alloy is more sensitive to SCC above 450℃. The SCC sensitivity of Ti6Al4V alloy with a certain amount of Pd or Mo added in H2S+CO2+NaCl+S solution at 200℃ is lower than that at 250℃. But materials implanted in the human body have limited sensitivity to temperature. (5) Cl ion concentration The higher the Cl- concentration in the solution, the greater the SCC sensitivity. 2) Stress The SCC accident caused by the residual stress generated during the cold working, forging, welding, heat treatment or assembly process of the alloy accounts for 40% of the entire SCC accident. In addition, the external stress generated during work or the external stress caused by the volume effect of the corrosion product or the unevenness caused by the volume effect of the corrosion product should be