The ship is the most important equipment of the Navy, is the sea transport, fighting platform for the construction of the ship's materials to be able to withstand seawater, marine atmospheric corrosion, high strength, toughness and toughness of the processing technology. As the overall structure of the ship complex, the use of large quantities of materials, and varieties, specifications and more. Select the performance of excellent material production warships is to make sure the integrity of the Navy equipment and the basis of advanced.

Titanium alloys are used on ships, primarily based on the following characteristics of titanium alloys: very wide range of strength, excellent mechanical properties, unique physical properties (including magnetic properties), higher specific strength and structural effectiveness, excellent Corrosion resistance and erosion resistance, excellent impact resistance, good machinability and weldability, reasonable cost and effectiveness. The experience of requiring a large number of marine piping materials has confirmed that the service life of traditional materials in piping systems is limited. Among them, the steel pipe system will be used for corrosion after 2 to 2 years, and the service life of CuNi piping system is 6 to 8 years , And titanium pipe system in the tube, pump, valve, heat exchanger and other equipment can serve more than 40 years. As the marine titanium alloy in the marine environment in the long service, the design of marine titanium alloy to be taken into account when considering the strength of the alloy, stress corrosion fracture toughness, solderability and so on.

Russia is the world's first country to develop and utilize marine titanium alloy, marine titanium alloy is the most widely used, the largest number of countries. It mainly includes PT-7M, PT-1M, PT-3V, 37,5V titanium alloys and its corresponding welding wire, and formed 490,585,686,785 MPa and other different strength grade marine titanium alloy products. Titanium alloys have been successfully used in the following components and equipment on ships: deep water risers, supply pipes, pumps, filters, sea pipelines, drinking water pipes, drilling pipes and groundwater pipelines, heat exchangers, diesel engines Independent fire pump and fire extinguishing system, deep water equipment shell, outside the well system flexible tube, pressure vessel, platform fastening joints of high strength flexible tensile parts, process solution piping and containers, and in the former Soviet Union series of nuclear power icebreaker "Lenin", "Arctic", "Russian", "Soviet" and other types of ships used on the former Soviet Union nuclear-powered icebreaker on the titanium steam generator, has been safely used for 20 to 40 years, and No serious damage has occurred.

The titanium alloy of the United States is mainly based on the titanium alloy used in the sea, and the titanium alloy for corrosion resistance, weldability and stress corrosion resistance in seawater corrosive environment is selected, including pure titanium, Ti-0. 3Mo-0.8Ni Ti-3Al-4V, Ti-6Al-4V, Ti-3Al-4V, Ti-3Al-4V, Ti-3Al-4V In addition, of the characteristics of marine titanium alloy, Ti-5Al-1Zr-1Sn-1V-0. 8Mo-0. 1Si, Ti-6Al-2Nb-1Ta-0. 8Mo and other marine titanium alloy were developed. The use of high-performance titanium alloy on ships to improve the mobility of the ship, stability, effectiveness, reduce the full quality and so have a significant role. The United States Navy in the 20th century, 90 years had the following ships certification assessment, including: nuclear power aircraft carrier (CVN), missile cruiser (CG-47), missile frigate (FFG-7), detection ship (MCM), amphibious landing (LSD41CV), landing ship, hovercraft (LVCA), amphibious landing vessel (LHD), fast combat munitions supply ship (AOE-6), double shell monitoring vessel (SWATH T-AGOS19) (MHC-51), missile destroyer (DDG-51). The ship's seawater cooling systems, seawater systems and fire extinguishing systems, structural parts, propellers, sewage treatment systems, electrical components, fasteners, etc., have been or are in the process of use high performance titanium alloys.

China's marine titanium alloy research and application began in the 20th century, 60 years, after decades of development, have formed a more complete marine titanium alloy system, to meet the ships, submarines and submersible on the different strength level requirements. Application areas are related to the hull structure, propulsion systems, power systems, electronic information systems, auxiliary systems, special equipment. 490 ~ 790 MPa is medium-strong titanium alloy, higher than 790 MPa for the high strength titanium alloy, mainly used in ship power engineering (including high-strength titanium alloy), the yield strength of 490 MPa below the low strength titanium alloy, with excellent plasticity; Heat-resistant corrosion-resistant parts and ship special machinery.

Japan's marine titanium alloy is mainly pure titanium, Ti-6Al-4V, Ti-6Al-4V ELI, mainly utilized in deep submersible shell and a variety of civilian cruise ships, fishing boats.

There are problems and solutions in use

3. 1 crevice corrosion

Corrosion problems: the use of detachable connectors in ships (flanges, threaded connections, etc.) and other components there is a small gap, there will be corrosive high concentrations of corrosive chloride ions and fluoride ions, which requires titanium in the sea The environment has a good resistance to high temperature crevice corrosion. Titanium alloy heat exchanger and seawater desalination equipment, the working environment is 90 ~ 250, the medium pH value of 1.5 ~ 4.0 (especially in salt and kerosene deposits), the crevice corrosion is very fatal.

Anti-corrosion measures:

(1) the addition of Pd and Ru in the titanium alloy can effectively increase the corrosion resistance of titanium alloy.

(2) Surface treatment with Ru / Pd is carried out on the surface of titanium alloy, for example, Ru / Pd element is infiltrated on the surface of titanium alloy or micro-arc oxidation is used to form oxide containing Ru / Pd element on titanium alloy surface. In order to decrease the cost of surface treatment, it is also possible to prepare a gradient coating containing Ru / Pd on the surface of the titanium alloy.

(3) the use of cathodic protection technology to protect the steel structure, the potential between-800 mV ~ -1050 mV, to avoid hydrogen saturation caused by titanium alloy hydrogen cracking.

3. 2 galvanic corrosion

Titanium and steel, copper connection is prone to galvanic corrosion, protective measures include:

1, the pipe for thermal oxidation, micro-arc oxidation, anodizing, in the metal surface to form oxide or ceramic layer to achieve insulation. The oxidation treatment of titanium tube, the formation of the oxide film can reduce the titanium cathode polarization effect of 80% to 90%, oxide film life is tantamount to titanium tube life.

2, in the pipe, the valve mouth and steel, copper equipment at the interface with asphaltene rubber insulation treatment;

3, in the titanium tube and stainless, steel nozzle connection with the middle flange protection.

3. 3 welding of large structural parts

Protective measures include:

1, the use of ships on the shell, high pressure pressure vessels, stretching parts and other large structural components based on pressure performance requirements need to use high strength titanium alloy, and requires high strength titanium alloy thick-walled welding parts in the sea to have an excellent connection The operability, after welding without heat treatment.

2, the United States and Europe using TC4 titanium alloy and low gap TC4 titanium alloy (oxygen content control within 0. 13%); Russia Prometheus Structural Materials Central Research Institute developed PT-3V, 37,5 V Marine titanium alloys; China developed TA24, TA31 titanium alloy.

3, for large structural parts, after welding cannot be heat treatment, and the existence of tensile stress on the surface, greatly reducing the corrosion resistance of titanium alloy components and anti-fatigue properties. The surface of welding parts can be ultrasonic impact treatment, the welding surface tensile stress into a compressive stress, in order to facilitate the improvement of fatigue performance.

Development Prospect of Marine Titanium Alloy in China

For the material research, the Chinese marine titanium alloy also need to carry out the titanium alloy in the marine environment performance research, including:

(Corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance and so on) of the titanium alloy in air and seawater under the working conditions (temperature, pH, solution composition), force (free state, reverse bending, torsion) Toughness of the study;

(2) Effect of processing technology on the texture type (radial texture, axial texture) and texture type of titanium alloy pipe on pipe processing technology (flaring, crushing and blasting)

(3) Study on the corrosion resistance of Pd, Ru and trace elements on H2S and Cl-environment;

④ Titanium alloy in the irradiation environment of the tensile, fatigue performance evaluation;

⑤ Corrosion control and correction of different welding forms of corrosion resistant titanium alloy;