The service environment of the ship is a harsh maritime climate. Due to prolonged exposure to seawater, the hull and its equipment and components (such as high-temperature exhaust pipes, seawater valves and pumps, propellers, etc.) are easily corroded and protective measures are extremely It is cumbersome and difficult, so it puts forward special technical requirements for marine materials: 1 It is resistant to seawater corrosion. 2 Good stability in high and low temperature environments. 3 safe and reliable, large load bearing, less maintenance or convenient maintenance, bending, welding and other processability. 1. Advantages of titanium and titanium alloys as materials for ships Titanium and titanium alloys are almost perfect for marine materials because of their excellent properties and almost meet all the requirements of marine materials. The advantages are as follows: (1) Light weight and high specific strength. The density of titanium is 4.5 g/cm3, which is higher than the density of 2.7 g/cm3 of aluminum, and lower than the density of 7.9 g/cm3 of iron, which is only 57% of iron. Titanium is less than twice as dense as aluminum, but its strength is three times that of aluminum. In industrial engineering applications, titanium alloys are the material of choice when selecting metals with higher specific strength. Under the same conditions, the depth of the submersible made of titanium can reach 10,000 meters, while the depth of the deep submersible of steel is far from reach. In addition, the magnetism of titanium is zero, and it will not be disturbed in any magnetic field of strength. Therefore, when it is used at sea, it uses magnetic thunder and torpedo and other magnetic thunder attack weapons. It has no attack on the hull shell made of titanium alloy. The anti-monitoring role, this feature is favored by military engineering applications. (2) Good corrosion resistance in maritime climates. When titanium alloy is in air and some oxygen-containing medium, due to the strong affinity of titanium and oxygen, the surface energy can quickly form a dense, strong adhesion and stable oxide film, which is not easily destroyed in many media. Thereby protecting the titanium matrix. Studies have shown that the corrosion rate of titanium and titanium alloys in the three waters of the South China Sea, the North Sea and the East China Sea is almost zero in the whole immersion area, tidal zone, splash zone or maritime climate. Therefore, the use of titanium alloy for the ship can extend the service life on the one hand, and reduce the cost of protective treatment due to corrosion of the surface at the later stage on the other hand. (3) Excellent overall performance. Titanium alloy can be processed in various forms such as hot and cold forming, free forging, extrusion and welding, and has good processing adaptability. The data show that the titanium alloy is subjected to the impact toughness test in the range of -60 to 20 °C, and there is no brittle transition point. In addition, titanium alloys have the best heat resistance, low temperature resistance and fracture toughness compared to aluminum alloys and steel. 2. Application status of titanium alloy in ships At present, the countries specializing in the research and formation of marine titanium alloys are mainly Russia, the United States, Japan and China. The attached table shows the titanium parts used on ships at home and abroad and the commonly used alloys. Titanium parts and commonly used alloys on ships at home and abroad Russia is the first country in the world to study the application of titanium alloys on ships. It has a complete set of system documentation for engineering applications (related to design, material selection and process). Former Soviet experts demonstrated the feasibility of using titanium alloys to manufacture attack-type nuclear submarines through the Papa-class all-titanium cruise missile test boat. Since then, Russia has successively researched and manufactured "barracuda" and "Vulture" titanium alloy submarines. The combing of Russian marine titanium alloys found that the Russian marine titanium alloy has many grades and simple composition, and pays more attention to the overall research of alloy series and application design. The United States first researched titanium alloys for aviation. Later on the basis of titanium alloys for aviation, it formed a marine titanium alloy system according to the service environment of the ship, and successfully applied titanium alloy to various power submarines and seawater pipelines. Pressure-resistant casings for systems and deep submersibles, such as the Aivin and Sea-Cliff submersibles. American marine titanium alloy grades are not as good as those in Russia, and more emphasis is placed on applications such as improved corrosion resistance. Japan's research and application of marine titanium alloys has developed rapidly. At present, the main applications are pure titanium, Ti-6Al-4V and Ti-6Al-4VELI, which are mainly used in pressure shells and piping of deep submersibles. China first researched and developed titanium alloys for ships in 1962. After decades of development, the level of research and manufacturing has been greatly improved. From the original imitation of foreign grade alloys to the current research and development of marine titanium alloy systems, such as TA2, TA5, Ti31, TiB19, Ti70 and Ti631. . At present, Ti70 alloy jointly developed by CSIC 725 and Baoji Titanium and 701 has been successfully applied to ship shrouds. It is worth noting that China's high-temperature titanium-aluminum alloy material achieved a major cross-domain breakthrough on June 20, 2016, and its life expectancy is better than that of the US one to two orders of magnitude. 3. The development trend of China's titanium alloy application in ships Compared with developed countries, there is a certain gap between the research and application of marine titanium alloys in China. At present, the proportion of titanium used in China's ships to total mass is less than 1%, while the amount of titanium used in Russian ships is close to 18%. With the introduction of China's blue ocean strategy, marine engineering equipment is bound to be vigorously developed, so the titanium alloy called "marine metal" will also usher in a period of rapid development. The following is a description of the development trend of titanium alloys in ships from five aspects: (1) Although China's marine titanium alloy system has been formed, the effective coordination and cooperation mechanism between marine titanium alloy design, material selection and process is still not perfect, and the material evaluation standards are relatively lacking, resulting in the current application level in a scattered and sporadic state. Therefore, we need to integrate existing resources, improve and optimize the performance of titanium alloys; establish a system of marine titanium alloy evaluation system and database to promote its stable and efficient use on ships. (2) Research and develop new technologies and processes, and gradually promote the application of computer information simulation technology to minimize the manufacturing cycle and increase the yield. Such as 3D printing technology, laser rapid prototyping technology. (3) Various industry personnel change the concept of high cost and high investment in titanium alloy. In the past ten years, from the analysis of raw material prices, the price of titanium sponge is at a lower stage, which provides a guarantee for the expansion of the titanium alloy market. According to the service period of traditional materials, it is calculated from 2 to 10 years. In the harsh maritime climate environment, the traditional materials during service must be treated, repaired and even replaced, and the cost will be greatly increased. Titanium alloys only require simple maintenance. In addition, the production cost of titanium and titanium alloy can be reduced by the following ways to expand its application in the shipbuilding industry: 1 to explore new titanium refining methods, or to achieve secondary utilization of resources by adding a certain amount of residual material in the production process. And reduce the cost of raw materials. 2 When designing new alloys, try to use low-cost alloying elements and develop low-cost alloys. (4) Since the marine structural parts are mostly welded parts, the general size is large, so it is particularly important to develop the welding process technology and welding materials related to the marine structural parts. (5) At present, most of the titanium powder produced in China is medium and low-grade products, which cannot meet the requirements of high-end customers. High-quality titanium powder still needs to be imported, which greatly increases the cost price. A team of experts should be formed to tackle this technology and independently develop high-quality titanium powder. 4. Conclusion With the rapid development of science and technology, the cost of titanium alloys has gradually decreased. Under the promotion of a series of national policies, the application of titanium and titanium alloys in ships has shown many advantages such as light weight, high speed and high safety and reliability. The marine titanium alloy is bound to usher in rapid development. This article was published in Metalworking (Cold Processing) polishing machine，polishing machine，polishing machine Jiangmen Gude Polishing Equipment Co., Ltd , https://www.kokipolishing.com
Author: China Shipbuilding Industry Corporation seventh twenty-five Institute Xiashen Lin, etc.