Titanium alloys are widely used in various fields due to their high strength, good corrosion resistance, and high heat resistance. Many countries in the world have recognized the importance of titanium alloy materials, have successively carried out research and development on them, and have put them into practical applications. Titanium alloys have great potential for development in ship applications. The following is the application of titanium alloys on ships:
1. Application in ship structure
Although titanium and titanium alloys have high yield strength, they require inert gas protection during welding, which is more difficult to form than steel. Therefore, titanium is rarely used in general surface ship structures. Titanium and titanium alloys are mainly used in submarines, submersibles and other ships to cope with occasions that require high yield strength, density and corrosion resistance at the same time.
China developed Ti80 alloy in the 1980s, which is used to manufacture pressure-resistant shells of deep submersibles and submarines. It has excellent properties such as high strength, high toughness, corrosion resistance, and weldability. Under the condition of 785～885MPa, the fracture toughness and stress corrosion resistance are obviously better than those of Ti6Al4VELI alloy. The Ti91 titanium alloy developed in the 1990s has a yield strength of 700MPa.
2. Used for ship coolers
Since titanium and titanium alloys have better corrosion resistance than other alloys in seawater, and have high strength and low density compared with commonly used copper alloys, the heat transfer efficiency can be ensured by reducing the thickness of the tube wall and increasing the flow rate of seawater. In the fields of nuclear submarines and other applications that have high requirements on the safe operation and reliability of equipment, the application of titanium heat exchangers is very important.
At present, the most widely used industrial pure titanium in the United States is industrial pure titanium, which has special resistance to stress corrosion in natural water, seawater, and various chlorides. In desalination equipment with a seawater flow rate of 3-5m/s, the fouling coefficient of the titanium heat exchanger is only 0.95-0.99. my country has also successfully developed some titanium alloys with excellent performance, such as Ti31 titanium alloys, which are used for waste heat discharge coolers, pipelines, etc. The working environment is high-temperature seawater or normal-temperature high-speed seawater, and it is resistant to high-temperature corrosion at 180 °C.
3. For ship pipelines
Due to the direct contact with the seawater and most of the pipelines in the bilge, the working environment is harsh, and corrosion has always been a prominent problem that restricts its maximum efficiency. In the 1970s, my country successfully developed TA5α titanium alloy (Ti-4Al-0.05B), which has high strength, and the yield strength of as-cast ZTiAl4 is not less than 490MPa, which can be used in the manufacture of pumps and valves in ship auxiliary systems. The Ti75 titanium alloy developed in the 1980s, under the premise of good comprehensive properties, has a strength increase of 50MPa, impact toughness and fracture toughness are 1.4 times and 1.2 times that of TA5, respectively, stress corrosion fracture toughness is 2 times that of TA5, and has excellent Excellent cold and hot workability, casting properties and low impurity sensitivity. Ti75 titanium alloy fills the blank of domestic 730MPa marine titanium alloy and reaches the international advanced level. The reciprocating brine pump is made of Ti75 alloy and the valve stem of the side double seat double ball valve has been used normally.
4. For ship propellers
Titanium alloy has high strength, is lightweight, has excellent resistance to cavitation erosion and fatigue resistance, and is an ideal material for manufacturing propellers. The life of the propeller made of ZTi6Al4V is 3 times that of the copper alloy propeller. China started the research on ZTi6Al4V alloy in the late 1960s and successfully applied it to hydrofoil propellers in the 1970s. After 20 years of real boat verification, the performance is good.
In addition, the high-strength cast titanium alloy with better welding performance, higher toughness, and better anti-cavitation erosion performance developed in my country has been successful, and it has been used in the manufacture of a hydrofoil speedboat propeller.
