Compared with previous alloy materials, titanium alloy has many advantages such as low density, high specific strength, corrosion resistance, excellent high and low temperature performance, etc. Therefore, it can be more widely used in many fields such as petrochemical industry, marine environment, biomedicine, aerospace, automotive industry, and ships. Cast titanium alloy is obtained by casting titanium alloy into the required shape, among which ZTC4 (Ti-6Al-4V) alloy is the most widely used, with stable process performance, good strength and Fracture toughness (below 350 ℃).

As the main control component of various special environments and special fluid medium pipeline transportation systems, valves have become an important component of many equipment in production, and it can be said that any industry cannot do without valves. Due to different environmental, temperature, and medium requirements in different fields, valve material selection is particularly crucial and widely valued. Valves based on titanium alloys and cast titanium alloys have broad prospects in the field of valves due to their excellent corrosion resistance, high and low temperature performance, and high strength.

1. Commonly used cast titanium alloys

1.1 Types

With the development of technology and production needs, different types of cast titanium alloys have been developed and applied in many fields. From the perspective of photographic composition, cast titanium alloys can be divided into α、β and α+β 3 types; From the perspective of strength, it can be divided into medium strength titanium alloys and high strength titanium alloys; From the perspective of environmental temperature, it can be divided into low-temperature titanium alloys (less than or equal to room temperature), medium temperature titanium alloys (400 ℃), high-temperature titanium alloys (greater than or equal to 500 ℃), and anti combustion titanium alloys. It can be seen that the use of cast titanium alloys is extensive, covering almost all aspects, and has high market value.

1.2 Mechanical properties

There are various types of cast titanium alloys, including ZTA1, ZTA2, ZTA5, and ZTC4, covering α、β and α+β Three types are represented by TA, TC, and TB in China, and their common mechanical properties are shown in Table 1.

Table 1 Mechanical Properties of Common Cast Titanium Alloys

Taking the most widely used ZTC4 cast titanium alloy as an example, its Al content ranges from 5.5% to 6.75%, V content ranges from 3.5% to 4.5%, and the remaining components are all Ti. From Table 1, it can be seen that the tensile strength and yield strength of ZTC4 cast titanium alloy are 895 MPa and 825 MPa, respectively. Its mechanical properties are relatively close to those of medium to high strength steel, which can be used as a good substitute for steel. On the other hand, its density is only 4.4 g/cm3, which is much smaller than that of steel, which is beneficial for equipment weight reduction. At the same time, it also retains the superior corrosion resistance of titanium alloy, which cannot be met by steel.

Therefore, in future industrial production, if it is necessary to reduce weight due to production needs, choosing suitable cast titanium alloys as substitutes can effectively reduce product weight while ensuring product performance, which is a good choice.

2. Application of Cast Titanium Alloy in the Valve Industry

2.1 Marine titanium valves

In recent years, with the rapid development of China's economy, various industries have blossomed everywhere. As an essential universal mechanical equipment, the market demand for valves continues to increase, and China's valve industry has also experienced rapid development.

Valves are usually composed of valve body, valve cover, valve disc, valve stem, hot plate, packing, and driving components. The material selected for the valve body and valve cover is the main material, while the selected materials for valve disc (gate plate), ball, valve seat, valve stem, and sealing seat are called internal material, and there are also fastener materials; Common materials for valves include gray cast iron, ductile iron, alloy steel, and copper alloy, which can be selectively diversified. However, with the further demand for production, researchers have found that in some harsh working environments and complex and special working conditions, conventional valve materials cannot meet production and scientific research needs. At this time, titanium and cast titanium alloys attracted people's attention due to their superior performance, and titanium valves developed to a certain extent.

The working environment of seawater Plumbing is very harsh, and the performance of marine valves directly affects the safety and overall performance of Plumbing. As early as the 1960s, Russia began research on titanium alloys for ships and subsequently developed them for marine use β Titanium alloy is widely used in military ship pipeline systems, including globe valves, check valves, and ball valves, with a wide variety of types and a large number of applications; At the same time, titanium valves have also been used in civil ship Plumbing. Compared to the previously used copper alloys, steel, etc., subsequent drainage tests have also shown that the use of cast titanium alloys has high reliability in many aspects such as structural strength and corrosion resistance, and the service life has been greatly extended, from the original 2-5 years to more than twice, which has attracted widespread attention from everyone. The three eccentric butterfly valve supplied by the China Shipbuilding 725 Research Institute in Luoyang, China for a certain model of ship is a change in the previous material selection and design scheme, using Ti80 and other materials as the main body, extending the service life of the valve to over 25 years, improving the reliability and practicality of valve product applications, and filling the technical gap in China.

2.2 Aerospace Titanium Valves

In the field of aerospace, cast titanium alloys also perform well, thanks to their excellent heat resistance and strength. It was also during the 1960s that American Airlines first tried titanium castings. After a period of research, cast titanium alloys have been formally used in aircraft (Boeing 757, 767, 777, etc, Meanwhile, due to the relatively small density and weight of titanium alloy compared to other alloys, which is only about 60% of the same strength steel, its widespread application can promote aircraft to steadily move towards high strength and lightweight direction.

At present, aerospace valves are mainly used in many control systems such as pneumatic, hydraulic, fuel, and lubrication, and are more suitable for environments with corrosion resistance and high environmental temperatures. They are one of the crucial components of aerospace vehicles, engines, and other departments. Traditional valves often require phased replacement, and may not even meet demand. At the same time, with the rapid expansion of the aerospace valve market, titanium valves are also occupying an increasing share due to their superior performance.

2.3 Titanium valves in the chemical industry

Chemical valves are generally used in harsh environments such as high temperature, high pressure, corrosion resistance, and large pressure difference. Therefore, the selection of appropriate materials is crucial for the application of valve chemical industry. In the early stage, carbon steel, stainless steel, and other materials are mainly selected, and corrosion may occur after use, requiring replacement and maintenance. With the continuous development of casting titanium alloy technology and its superior performance gradually being discovered, titanium valves have also appeared in people's eyes.

Taking PTA production plant in chemical fiber industry as an example, the working medium is mainly acetic acid and Hydrobromic acid, which is highly corrosive. Nearly 8000 valves, including stop valves, ball valves and other valves, need to be used, which are numerous and numerous. Therefore, titanium valves become a good choice, increasing the reliability and safety of use. In general, due to the corrosiveness of urea, the valves at the outlet and inlet of the urea synthesis tower can meet the service life of 1 year and have already reached the usage requirements. Enterprises such as Shanxi Lvliang Fertilizer Plant, Shandong Tengzhou Fertilizer Plant, and Henan Lingbao Fertilizer Plant have made multiple attempts and ultimately chose titanium valve high-pressure check valves H72WA-220ROO-50, H43WA-220ROO-50, 65, 80, and insulation stop valves BJ45WA-25R-100, 125, etc. for the import of urea synthesis towers, with a service life of more than 2 years, demonstrating good corrosion resistance [9], reducing the frequency and cost of valve replacement.

The application of cast titanium alloy in the valve market is not limited to the above-mentioned industries, but there is good development in other aspects. For example, the new cast titanium alloy Ti-33.5Al-1Nb-0.5Cr-0.5Si developed in Japan has many advantages such as low density, high creep strength, and good wear resistance. When used in the rear exhaust valve of automotive engines, it can improve the safety performance of the engine and extend its service life.

3. Application of Cast Titanium Alloy in Other Industries

Compared to the application of cast titanium alloys in the valve industry, other applications of cast titanium alloys are more extensive. Titanium and titanium alloys have excellent corrosion resistance, which is of great significance for industries with corrosive requirements such as petrochemical industry. In these industries, many large equipment that require industrial production such as volumetric pumps, heat exchangers, compressors, and reactors will use corrosion-resistant titanium castings, which have the greatest market demand. In the field of medicine, due to titanium being a globally recognized safe, non-toxic, and heavy metal free metal, many medical assistive devices, human prostheses, and others are made of cast titanium alloys. Especially in dental medicine, almost all dental castings that have been tried out are made of industrial pure titanium and Ti-6Al-4V alloy, which have good biocompatibility, mechanical properties, and corrosion resistance. On the other hand, due to the advantages of low density and good performance of titanium and titanium alloys, they are widely used in golf clubs, ball heads, Tennis racquet, badminton rackets, fishing tackle and many other sports equipment. The products made of them are light in weight, quality guaranteed and very popular with the public. For example, the SP-700 new titanium alloy developed by Japan Steel Pipe Company (N104) is used as a surface material for Taylor brand 300 series golf ball heads, which is best-selling in the global golf market.

Since the late 20th century, cast titanium alloys have gradually formed industrialization and scale in fields such as petrochemical, aerospace, biomedical, automotive industry, and sports and leisure, from initial exploration to current vigorous promotion and development.

4. Limitations of application

However, although valves and other products based on cast titanium alloys, pure titanium, and other titanium materials have broad application prospects in many fields, they also have certain limitations.

Compared to other metal materials, titanium, as an emerging metal, has a very short development time, and the application of titanium alloys is only 70 years ago. Therefore, the technical information available for reference is currently very limited and still in the exploratory stage. On the one hand, due to the high difficulty in smelting titanium metal, the cost remains high; On the other hand, due to the high processing cost and long processing time of titanium and titanium alloys, as well as cast titanium alloys, the processing cost is several times or even tens of times the value of their materials, making them recognized as one of the most difficult to process materials and unable to achieve large-scale promotion and use. Therefore, improving the smelting technology of titanium metal and finding suitable processing methods is currently an urgent task.

5. Conclusion

For titanium and its alloys, on the one hand, they have superior performance and are ideal substitutes for many materials such as steel. On the other hand, they have abundant reserves of titanium resources, which has attracted the attention of many researchers. Although there are still some problems with titanium resource extraction, high difficulty in smelting technology, and processing difficulties, the valve industry and the titanium industry are both vibrant and rapidly developing industries. With the stable mining and production of titanium materials in the future, as well as the introduction and improvement of new processes, the application and development of cast titanium alloys and castings in the valve industry will become more mature and tend to scale up, and there will also be broad application prospects in other industries.