Titanium is widely distributed, and its content exceeds 0.4% of the mass of the earth's crust. The world's proven reserves are about 3.4 billion tons, ranking the 10th among all elements. Sponge titanium after crushing, into the vacuum arc furnace melting, can be cast into titanium ingots, and then processed into a variety of titanium materials. Although the vacuum melting process requires strict requirements, complex equipment and high cost, it is still the only feasible way to obtain high-quality titanium and titanium alloy ingot, which is also one of the reasons for the high cost of titanium alloy. According to the relevant standards, titanium alloy ingots for aviation use need to be obtained through three times of vacuum smelting to ensure the uniformity of its composition.
Titanium sponge production is the basic link of titanium industry. In recent years, the production of titanium sponge in China has ranked the top in the world, but the production of high-quality titanium sponge is low, and the production proportion of high-quality zero-grade titanium sponge is only 40%. The overall quality of China's titanium alloy products still needs to be improved and the industrial structure still needs to be optimized.
The strength of pure titanium is very low and it has no industrial practical value as an aerospace structural material. Because of its excellent properties such as heat resistance, toughness, weldability, corrosion resistance and fatigue resistance, it has become the most widely used titanium alloy. Since 1970s, a series of corrosion resistant titanium alloys have been developed on the basis of TC4. At present, structural titanium alloys have been gradually developed in the direction of high strength, high toughness, high modulus, fatigue resistance and damage tolerance.
The preparation and processing methods of titanium alloy and its parts mainly include vacuum melting, forging, mechanical processing, heat treatment, net near forming, welding and surface treatment. Because of the high chemical activity of titanium, titanium and its alloys must be smelted by vacuum smelting method. Forging deformation is a key method to change the microstructure of cast titanium and obtain the desired microstructure type. Mechanical processing of titanium alloy mainly includes milling, turning, boring, drilling, tapping and so on. High cutting temperature, chemical reaction with tool and low elastic modulus are the main reasons for difficult machining of titanium alloy. The heat treatment of titanium alloy mainly includes annealing, solution and aging.
