Titanium alloy is very sensitive to the forging process parameters. The changes of forging temperature, deformation, deformation and cooling rate will cause the changes of microstructure and properties of titanium alloy. In order to better control the microstructure and properties of forgings, advanced forging technologies such as hot die forging and isothermal forging have been widely used in the forging production of titanium alloys in recent years.
The plasticity of titanium alloy increases with the increase of temperature, and reaches the maximum value in the temperature range of 1000-1200 ℃, and the deformation degree is allowed to reach 70%-80%. Titanium alloy forging temperature range is narrow, should be strictly according to the (α+β)/β transition temperature (except ingot billet), otherwise β grain will grow up violently, reduce room temperature plasticity; α titanium alloy is usually forged in the (α+β) two-phase region www.sotai.cn. Due to the high forging temperature above the (α+β)/β phase change line, β brittle phase will be caused. The initial and final forging of β titanium alloy must be higher than the (α+β)/β transition temperature. The deformation resistance of titanium alloy increases rapidly with the increase of the deformation speed, and the forging temperature has a greater influence on the deformation resistance of titanium alloy. Therefore, the conventional forging must be completed under the condition of the least cooling in the forging die. The content of interstitial elements (such as O, N and C) also has a significant effect on the forging property of titanium alloys.
Due to the high chemical activity of titanium and titanium alloy, it is easy to react violently with N, O, N in the air, and it is easy to react with refractory materials commonly used in casting. The casting of titanium and titanium alloy, especially investment casting, is much more difficult than the investment casting of aluminum and steel, and needs special means to achieve. In the early stage of development of casting titanium, since the development of casting technology lags behind the pressure machining technology, medium and strong titanium alloys with certain deformation are firstly selected, such as Ti-6Al-4V, Ti-5Al-2.5Sn, etc., as casting alloy materials. These alloys are still widely used today. However, with the development of titanium casting technology and the improvement of the performance requirements of cast titanium alloys and the increase of the complexity of casting structure, the argument that "all deformed titanium alloys are suitable for casting alloys" in the past should be revised. With the increase of the working temperature and strength of the alloy, the number and amount of added elements in the alloy also increase correspondingly. However, the casting properties, crystalline structure and mechanical properties of the alloy in the fluidity solidification interval must be considered, that is, the chemical composition of the alloy must be adjusted according to the requirements of the casting process.
