Titanium and titanium alloys are new materials developed in the 1950s. With the development of naval equipment, the requirements for naval equipment are getting higher and higher, and traditional metals such as steel, iron, aluminum, and magnesium and their alloys can no longer meet the requirements in many fields. Due to its excellent properties, titanium alloys are increasingly attracting the attention of ships and marine engineering equipment, and are called "marine metals". As the core of "navy equipment", submarines are the backbone of strategic nuclear forces and play a pivotal role. Can the manufacture of submarines with titanium alloys bring new breakthroughs in the performance of submarines? Today, the author will briefly analyze the advantages of titanium alloys used in submarines.

The first advantage - high specific strength



Specific strength refers to the ratio of material strength to density. The larger the specific strength, the smaller the structural weight can be obtained with the same strength design, and conversely, the higher strength can be obtained with the same structural quality. The high specific strength can make the equipment design more compact, greatly reduce the structural mass, and improve the safety of the equipment.



Influence of high specific strength on pressure housing



When the submarine structure is timed, the ultimate diving depth of the submarine is proportional to the product of the yield strength of the hull material and the thickness of the hull. The method of thickening the pressure shell to increase the diving depth will reduce the effective carrying capacity of the submarine. If the effective carrying weight of the submarine is maintained, the size of the submarine will be increased to the extent that it cannot actually be used, thereby reducing the overall performance of the submarine. Therefore, higher specific strength materials must be considered.



Table 1. Performance data of several deep submarine pressure hull materials



From the performance data of several deep submarine pressure hull materials in the above table, it can be seen that although the yield strength of titanium alloy is not as good as that of high-strength steel, it has higher specific strength because of its smaller density. It has the best performance among the materials, so it is very advantageous for titanium alloys to be used as pressure-resistant shell materials for submarines and submersibles. In fact, the diving depth of two titanium alloy submarines in Russia can reach 800 to 1000 meters; while the pressure shells of most of the deep submersibles in the world are made of titanium alloys.

Jiaolong submersible

Jiaolong submersible



The effect of high specific strength on the thruster



Modern submarines, in order to pursue quiet performance, mostly use large-diameter, low-speed seven-blade large-sloping propellers, which have a larger structure and a larger weight. The propeller shaft of the submarine itself is in the form of a cantilever beam. When the weight of the free end is large, the propeller shaft will be bent, and the stern bearing load will be large. In addition, when the weight of the drive shaft itself is large, the bending of the shaft system will be aggravated. The use of materials with high specific strength to manufacture the drive shaft and propeller can reduce the uneven bearing load caused by bearing disturbance and the resulting shaft system vibration problem.

submarine propeller

submarine propeller



The second advantage - is excellent corrosion resistance



Titanium has higher corrosion resistance than other commonly used metal materials in neutral and oxidizing environments and many harsh environments, especially with strong corrosion resistance to chloride ions in seawater. A very thin and strong oxide film forms on the surface of titanium, which passivates the titanium from corrosion by seawater. The passivation film of titanium has good self-healing properties and can be quickly and automatically repaired after being damaged or scratched to form a new protective film. It is this oxide film that protects titanium from seawater corrosion, and in the absence of chemical changes and pollution, titanium can completely resist the corrosion of natural seawater.

Corrosion of seawater to ships

Corrosion of seawater to ships



Excellent corrosion resistance for pipes and valves



Seawater is very corrosive to the hull, but with the development of anti-corrosion technology, the hull of the ship can ensure the safety of the hull during its life by using corrosion-resistant steel, anti-corrosion paint, electrochemical anti-corrosion, and other means. However, the pipeline system of the submarine is very complicated, and it is easy for the process to not be handled properly, and the high flow velocity in the pipeline aggravates the corrosion. According to relevant tests, the tin bronze valve and 70/30 copper-nickel alloy pipe have been used for 15 months at a water speed of 4.5m/s, and both the valve and the pipe are perforated; while the all-titanium pipe system is used at a water speed of 6m/s 36 months without any visible change. This means that the use of titanium and titanium alloy materials for submarine seawater piping and valves can reduce the pipe diameter, increase the water speed, and prolong the service life.

inside the submarine

The complicated pipeline inside the submarine



The third advantage - is good sound transmission performance



The sonar is the "eyes" of the submarine, and to protect the sonar, the sonar is placed in an enclosure. Titanium alloy has the characteristics of high specific strength, small thermal expansion coefficient, high resistance, and good sound transmission performance, which makes it used in submarine acoustic devices. For example, the sonar dome of the former Soviet Union's 607A flying missile nuclear submarine uses titanium alloy; and the sonar domes of the "Minsk" and "Kyiv" aircraft carriers purchased by my country are also made of titanium. Made of alloy. According to these actual use cases, the sound transmission performance of titanium alloy is better than that of FRP and stainless steel, which can effectively guarantee the performance of sonar.



In general, the extensive use of titanium and titanium alloys on submarines can greatly reduce the structural weight of the submarine, achieve high mobility, and ensure the high reliability and safety of the submarine; the corrosion resistance can achieve the same service life and reduce the maintenance time of the submarine. and cost, guarantee the combat effectiveness of equipment, and improve some other technical performance. Therefore, titanium alloy is an ideal material to ensure the performance and tactical level of submarine equipment and has important strategic significance for the development of naval submarines.