The naval vessel is the most important equipment of the Navy. It is the platform of marine transportation and battle, and the material used to construct the ship is capable of corrosion of seawater and ocean atmosphere, and has high specific strength, good plasticity and good processing technology. As the overall structure of the ship is complex, the amount of material used is large. It is the foundation of the integrity and advancement of naval equipment to select warships with excellent performance.
Titanium alloy can be used in the ship, is mainly the following characteristics of titanium alloy based on excellent mechanical properties, high strength, excellent corrosion resistance and erosion corrosion resistance, excellent impact resistance, good processability and weldability, reasonable cost and effectiveness.
Russia is the earliest country in the world to develop and use marine titanium alloys. It is also the most widely used and the largest number of marine titanium alloys. The United States Marine titanium alloys are mainly based on aviation titanium alloys. Titanium alloys with corrosion resistance, weldability and stress corrosion resistance are selected under seawater corrosion. The research and application of China's marine titanium alloys began in 1960s. After decades of development, it meets the requirements of different intensity levels for naval vessels, submarines and submersibles. The titanium alloys used in Japan are mainly pure titanium, Ti-6Al-4V and Ti-6Al-4V ELI. They are mainly used in the submersible pressure hull and all kinds of civilian cruise ships and fishing boats.
Problems in use and Solutions
1. Crevice Corrosion
The corrosion problem: ship used in the detachable connection part and so there is a small gap, there will have the erosion of the high concentration of chloride ion and fluorine ion in the gap, which requires high temperature titanium alloy has good ability of crevice corrosion in marine environment.
(1) adding Pd and Ru elements to the titanium alloy
(2) surface treatment with Ru/Pd on the surface of titanium alloy
(3) when cathodic protection technology is used to protect the steel structure, the potential is between 800 mV and 1050 mV, so as to avoid hydrogen supersaturation and lead to hydrogen induced cracking of titanium alloy.
2. Galvanic Corrosion
When titanium is connected with steel and copper, galvanic corrosion is easy to occur, and protective measures include:
(1) The pipe is oxidized, micro arc oxidized and anodized, and the oxide layer or ceramic layer is formed on the metal surface to realize the insulation.
(2) In the pipe, valve mouth and steel, copper equipment at the interface, the use of asphalt rubber insulation treatment;
(3) Protect the middle flange between the titanium tube and the stainless steel nozzle.
Prospect of development of China's marine titanium alloys
For the study of materials, it is necessary to study the performance of titanium alloys in marine environment, including:
(1) Effects of working condition, force mode and alternating load on corrosion fatigue, fatigue crack propagation rate and stress corrosion fracture toughness of Ti alloy in air and sea water
(2) The influence of processing technology on the texture and texture of the titanium alloy tube and the processing properties of the tube
(3) Study on the mechanism of corrosion resistance of Pd and Ru trace elements to titanium alloys in H2S and Cl- environment
(4) Evaluation of tensile and fatigue properties of titanium alloy under irradiation
(5) Study on welding deformation control and correction of corrosion resistant titanium alloy in different welding forms.
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