Titanium alloys show great development potential in naval applications due to their higher specific strength and better corrosion resistance.
1. Application in ship structure.
Although titanium and titanium alloys have high yield strength, they need inert gas protection during welding, and the difficulty of forming is greater than that of steel. Therefore, titanium is rarely used in general surface naval structures. Titanium and titanium alloys are mainly used in ships such as submarines and deep submersibles to cope with occasions that require high yield strength, density and corrosion resistance at the same time. my country developed Ti80 alloy in the 1980s for the manufacture of pressure-resistant shells for deep-diving vehicles and submarines. It has excellent properties such as high strength, high toughness, corrosion resistance, and weldability. It has a tensile strength of 880 to 925 MPa and yields. Under the condition of strength between 785MPa and 885MPa, the fracture toughness and stress corrosion resistance are significantly better than Ti6Al4VELI alloy. The Ti91 titanium alloy developed in the 1990s has a yield strength of 700MPa.
2. Used for ship cooler.
Because titanium and titanium alloys have better corrosion resistance than other alloys in seawater, and have higher strength and lower density than commonly used copper alloys, the heat transfer efficiency can be ensured by reducing the thickness of the pipe wall and increasing the seawater flow rate. In nuclear submarines and other applications that have high requirements for the safe operation and reliability of the equipment, the application of titanium heat exchangers has received great attention. At present, the most widely used in the United States is industrial pure titanium. Industrial pure titanium has special stress corrosion resistance in natural water, seawater and various chlorides. In desalination equipment with a seawater velocity of 3 to 5 m/s, the fouling coefficient of the titanium heat exchanger is only 0.95 to 0.99. Our country has also successfully developed some titanium alloys with excellent properties, such as Ti31 titanium alloy, used for waste heat discharge coolers, pipelines, etc. The working environment is high temperature sea water or normal temperature high speed sea water, and it is resistant to high temperature corrosion at 180 ℃.
3. Used for ship pipeline.
Because of the direct contact with seawater and most of the pipelines in the marine system, the working environment is harsh, and corrosion has always been a prominent problem that restricts its maximum effectiveness. In the 1970s, Chinese 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 marine auxiliary systems. The Ti75 titanium alloy developed in the 1980s, under the premise of good overall performance, has an increase in strength of 50MPa, impact toughness and fracture toughness are 1.4 times and 1.2 times that of TA5, respectively, and stress corrosion fracture toughness is twice that of TA5, and has excellent The cold and hot workability, casting performance and low impurity sensitivity. Ti75 titanium alloy fills the gap in domestic 730MPa marine titanium alloy and reaches the international advanced level. The reciprocating salt water pump made of Ti75 alloy and the side double-seat double-ball valve stem have been in normal use.
4. Used for ship propellers.
Titanium alloy has high strength, light weight, excellent resistance to cavitation erosion and fatigue resistance. It is an ideal material for manufacturing propellers. The service life of propellers made of ZTi6Al4V is three times that of copper alloy propellers. my country started the research of ZTi6Al4V alloy in the late 1960s, and successfully applied it to the propeller of hydrofoil in the 1970s. After 20 years of real boat verification, the performance is good. In addition, the high-strength cast titanium alloy developed by my country with better welding performance, higher toughness and better resistance to cavitation erosion has been successful and has been used in the manufacture of a hydrofoil speedboat propeller.
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