Corrosion resistance of titanium forgings and TA9 titanium alloy in atmospheric seawater environment

Titanium is a very active metal, its equilibrium potential is very low, and the thermodynamic corrosion tendency in the medium is high. But in fact, titanium is very stable in many media. This is because titanium has a high affinity for oxygen. In an oxygen-containing environment, a dense, strong adhesion and inert oxide film will be formed on the surface of Molybdenum Sputtering Target, thereby protecting the titanium matrix from Corroded; even if it is mechanically worn, it will quickly regenerate, which shows that titanium is a metal with a strong tendency to passivation. The outstanding performance of titanium is that it has extremely high corrosion resistance in fresh water and seawater. The corrosion resistance in seawater is better than aluminum alloy, stainless steel and nickel-based alloys. The dense oxide protective film with high chemical stability formed by titanium and oxygen ensures its high corrosion resistance in low and high temperature gases. At room temperature, titanium does not interact with chlorine, dilute sulfuric acid, dilute hydrochloric acid, nitric acid and chromic acid. It has high corrosion resistance in alkaline solutions and most organic acids and compounds, but it can be affected by hydrofluoric acid, phosphoric acid, Molten alkali erosion.

Seawater contains more than 10 kinds of ions such as Na+, K+, Mg²+, Cl-, etc., which is highly corrosive. The materials used in the ocean should generally be able to withstand the corrosion of the ocean atmosphere, seawater, tides (atmosphere and seawater alternately) and sea creatures, and also withstand seawater erosion and periodic impact of waves, so the material should have good corrosion resistance And better comprehensive mechanical properties. In addition, if the equipment is to float in water, low density and high strength are also very important. Experiments show that steel, stainless steel, copper, and aluminum are all non-corrosive materials in the marine environment, and coatings or other protective measures must be used when using them. Only titanium is a structure that is very corrosion-resistant and does not need coating protection. Material. Seamless Titanium Tube Grade 2 is also a material conducive to obtaining the most buoyant structure. The static pressure of sea water increases by 10.1kPa for every increase of 1m of water depth. In order to make the shell strong enough at a given water depth, the wall thickness of the shell must be increased.

Although titanium is a thermodynamically unstable metal, its standard potential is -1.63V (SHE), but due to the passivation effect of the oxide film, its corrosion potential is largely positively shifted. The self-corrosion potential of drinking in natural water at 25°C is about 0.1V (SCE). The titanium film has very good self-healing properties. When the film is damaged, it can be quickly repaired and replaced into a new protective film. Therefore, titanium can maintain its state in oxygen-containing liquids and non-ion-containing solutions.

In the marine environment, the drink is resistant to both uniform corrosion and local corrosion. Laboratory and engineering practices have shown that titanium has not been tested for significant corrosion after many years of exposure to seawater at different depths. Even if there are encroachments on the surface of the drink, crevice corrosion and pitting corrosion will not occur. The presence of sulfides in seawater does not affect the corrosiveness of the drink. Grade 9 Ti-3Al-2.5V Titanium Sheet does not have corrosion problems in the ocean atmosphere, flying test area and tidal range. Titanium can resist the erosion of high-speed seawater. The suspended friction particles in the seawater are very harmful to copper or aluminum alloy, but have little effect on titanium. Titanium has been recognized as one of the best anti-cavitation corrosion metal materials in seawater. Because titanium is not toxic to marine organisms, marine organisms attach to the surface of titanium more commonly, the titanium under the marine organisms does not undergo crevice corrosion and pitting corrosion, and the surface still maintains the integrity of the corrosion-resistant oxide film. Titanium hardly occurs in seawater pitting corrosion and crevice corrosion, so titanium is the most suitable material for seawater. Therefore, whether it is in still seawater or high-speed flowing seawater, whether it is clean seawater or polluted seawater, or even seawater containing a lot of mud and sand, titanium can maintain its state of transformation and exhibit excellent corrosion resistance.

Application of Titanium Alloy Material in Standard Parts of Aviation Titanium Alloy Screw

Titanium and titanium alloys have a series of outstanding advantages such as high specific strength, good corrosion resistance, and high-temperature resistance. They have developed into a promising metal structure material 121 in the modern aerospace industry. Since the United States first applied Ti-6AI-4V titanium alloy bolts to the B-52 bomber in the 1950s and achieved very good weight-reduction effects, various developed countries in the aviation industry have launched titanium alloy fasteners. Research and engineering applications.

The positive potential performance of the titanium alloy matches the carbon fiber composite material, which effectively prevents the galvanic corrosion of the fastener. It makes the titanium alloy the best connection material for the composite material. Therefore, with the continuous increase in the amount of Gr23 Ti-6Al-4V ELI Titanium Pipe and composite materials used in advanced military and civilian aircraft, the demand for titanium alloy fasteners is increasing. The use temperature of titanium alloy is 150-200C higher than that of aluminum alloy. For parts where aluminum alloy fasteners cannot be used due to the high operating temperature in the aircraft structure, titanium alloy will be a better choice. In addition, the inherent good elasticity and non-magnetism of titanium alloys also play a very important role in preventing the loosening of fastening bolts and preventing magnetic field interference.

In the US military and civilian aircraft, Gr7 Ti-0.2Pd Titanium Sheet has basically replaced alloy steel fasteners. The application of titanium alloy fasteners abroad has been very common. The amount of single titanium alloy fasteners for large civil aircraft has reached hundreds of thousands. At the same time, various new types of titanium alloy fasteners have also been continuously developed. In the late 1990s, with the introduction of foreign third-generation heavy fighter production lines and the development of domestic third-generation fighters, as well as the development of Dazu aviation subcontracting production, some titanium alloy fasteners began to be used in China's aviation industry. In recent years, with the development of China's aerospace industry, relevant domestic units have carried out a large number of research and development work on basic materials and fastener manufacturing technology. At present, the titanium alloy fasteners independently developed and produced in China have been in China. A large number of engineering applications have been obtained in modified aircraft and newly designed aircraft.

The main grades and common products of titanium alloy forgings for aviation

titanium forged discs are mainly used in aircraft engine parts because of their good corrosion resistance and high heat resistance. Specifically, the titanium alloy forgings used on the space shuttle mainly include: high-pressure vessels, wing leading edges, oil pressure pipelines, engine thrust brackets, etc. As a professional manufacturer of titanium alloy forgings, HST TITANIUM provides gr2, gr5 and other grades all year round. The executive standards are GB/T16598, ASTM B381, AMS4928 titanium forgings.

Application function of titanium alloy plate in the petrochemical industry

Titanium alloy plates and titanium plates are mainly used to manufacture various containers, reactors, heat exchangers, distillation towers, pipes, pumps, and valves in the petrochemical machinery manufacturing industry. Titanium can be used as a titanium cathode and condenser in power stations, as well as environmental pollution control devices. The hardness of steel is higher than that of titanium plate, but the specific strength or tensile strength of Grade 5 Ti-6Al-4V Titanium Foil is higher than that of high-quality steel. Titanium alloy has good heat resistance, low-temperature toughness, and fracture toughness, so it is mostly used as aircraft engine parts and rocket and missile structural parts. Titanium alloy can also be used as fuel and oxidant storage tanks and high-pressure vessels. There are already automatic rifles, mortar seat plates, and recoilless gun launch tubes made of titanium alloy.

1. Memory function

Titanium-nickel alloy has one-way, two-way, and omnidirectional memory effects at a certain ambient temperature, and is recognized as the best memory Titanium Flat Washer DIN 125. Pipe joints used in engineering for the hydraulic system of fighter jets; oil pipeline systems for oil complexes; 500mm diameter parabolic mesh antennas made of 0.5mm diameter wires for aerospace vehicles; used in medical engineering for snoring Treatment; Titanium plates are made into screws for fracture healing and so on. The above applications have achieved obvious results.

2. Superconducting function

The niobium-titanium plate exhibits a zero-resistance superconducting function when the temperature is lower than the critical temperature.

3. Hydrogen storage function

6al4v titanium alloy bar-iron alloy has the characteristic of absorbing hydrogen, which can store a large amount of hydrogen safely, and release the hydrogen in a certain environment. This is very promising in hydrogen separation, hydrogen purification, hydrogen storage and transportation, and the manufacture of heat pumps and batteries that use hydrogen as energy.

Titanium dioxide, the oxide of the titanium plate, is a white powder and a better white pigment, commonly known as titanium white. In the past, the main purpose of mining titanium ore was to obtain titanium dioxide. Titanium white has strong adhesion, is not easy to undergo chemical changes, and is always white. Especially valuable is that titanium dioxide is non-toxic. It has a high melting point and is used to make refractory glass, glaze, enamel, clay, high-temperature resistant laboratory utensils, etc.

Titanium consumption of aero engine

The amount of titanium used in advanced foreign engines is usually kept at 20% to 35%. The early turbojet engines produced in my country did not use titanium. The turbojet 13 engine, which was developed in 1978 and was designed and finalized in early 1988, used 13% of titanium. For aero engines with intellectual property rights, the amount of titanium has been increased to 15%, and my country’s first turbofan engine with independent intellectual property rights, which is about to be designed and finalized, has further increased the amount of titanium to 25%.

In the design of airplanes or engines, the alloy grades are mainly selected according to the working temperature and stress level of the parts, and the corresponding molding and welding performances are considered in conjunction with the manufacturing process plan of the parts. The characteristics of different types of Titanium Welding Rods are different, and the specific parts used are also different: α-type alloys cannot be strengthened by heat treatment, and have only moderate room temperature strength, but the structure is stable, the creep resistance is good, and it can work stably at higher temperatures for a long time. It is the basis for the creation of new heat-resistant titanium heat exchanger pipe, and is generally used as sheet metal parts and forgings with greater bearing capacity; β-type alloys have good process plasticity in the solid solution state, which is convenient for processing and forming, and can obtain high strength after aging treatment Performance, but high sensitivity to impurity elements, unstable structure, low heat resistance, not suitable for use at high temperatures, generally used as fasteners and aircraft structural parts; α + β type alloy has good thermal strength and cold Formability, good overall performance, and can be quenched and aging strengthened, generally used as turbine engine body components.

What are the physical phenomena of titanium processing?

The cutting force during titanium alloy processing is only slightly higher than that of steel with the same hardness, but the physical phenomenon of processing titanium alloy is much more complicated than processing steel, which makes titanium alloy processing face huge difficulties. The thermal conductivity of most titanium alloys is very low, only 1/7 that of steel and 1/16 that of aluminum.

Therefore, the heat generated in the process of cutting 6al4v titanium round bar will not be quickly transferred to the workpiece or taken away by the chips, but will be concentrated in the cutting area. The temperature generated can be as high as 1,000 ℃, causing the cutting edge of the tool to wear, crack and quickly. Generate built-up edge, wear blades quickly appear, and generate more heat in the cutting area, further shortening the life of the tool.

The high temperature generated during the cutting process also destroys the surface integrity of the titanium alloy parts, resulting in a decrease in the geometric accuracy of the parts and a work hardening phenomenon that severely reduces its fatigue strength.

The elasticity of titanium alloy may be beneficial to the performance of parts, but during the cutting process, the elastic deformation of the workpiece is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to leave the tool and rebound, so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, which aggravates the problem of poor thermal conductivity of titanium bicycle pipe.

This problem is even more serious when processing thin-walled or ring-shaped parts that are easily deformed. It is not an easy task to process thin-walled titanium alloy parts to the expected dimensional accuracy. Because when the workpiece material is pushed away by the tool, the local deformation of the thin wall has exceeded the elastic range and plastic deformation occurs, and the material strength and hardness of the cutting point increase significantly. At this time, machining according to the originally determined cutting speed becomes too high, which further leads to sharp tool wear.

The demand for aerospace titanium materials drives the demand for high-end titanium materials, and the demand structure for titanium materials continues to be optimized

Titanium has the characteristics of high melting point, small specific gravity, high specific strength, good toughness, fatigue resistance, corrosion resistance, low thermal conductivity, good high and low temperature tolerance, and low stress under rapid cold and hot conditions. Its commercial value in the 20th century It has been recognized since the 1950s that titanium and other elements such as iron, aluminum, vanadium or molybdenum have formed high-strength light alloys, which are used in high-tech fields such as aviation, aerospace, and military industry. With the continuous promotion of titanium to the chemical, petroleum, electric power, seawater desalination, construction, agricultural food, medicine, daily necessities and other industries, titanium metal is increasingly being valued by people and is known as the "third metal", "space metal", "Marine metals" and "universal metals" are also called "modern metals" and "strategic metals" because they are important strategic materials indispensable for improving the level of national defense equipment.

Titanium alloys can be classified:

According to the structure and composition, Gr2 Pure Titanium Sheet alloys can be divided into α titanium alloys, β titanium alloys and α + β titanium alloys. In China, the prefixes TA, TB, and TC of the metal material brands represent α, β, and α+β titanium alloys, respectively.

According to the state of physical form, titanium alloys can be divided into plates, strips, bars, pipes, wires (wires), profiles, castings, and forgings.

The production process of titanium material is mainly to first melt and cast sponge titanium to prepare titanium ingots, and then to forge, extrude, roll or stretch the titanium ingots to obtain titanium or titanium alloy bars, pipes, and tubes for downstream use. Plate, cake, ring and other products. Titanium material has a low yield rate, and a large amount of waste residues are generated during the processing process, resulting in higher production costs. At present, about 1.7 tons of sponge titanium raw materials are needed for 1 ton of titanium material in China.

The production of titanium alloy pipe processed materials is mainly concentrated in China, the United States, Russia, Japan and other countries. In 2010, my country surpassed the United States to become the world's largest producer of titanium materials, but most of my country's titanium materials are used in industrial fields with relatively low technical content, while the United States is mainly high-end titanium materials such as aviation titanium materials. In 2018, my country's titanium output reached 63,400 tons, a year-on-year increase of 14.42%.