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Mechanical Properties of Titanium and Titanium Alloy Processing Materials

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The tensile strength of pure titanium is 265-353 MPa, and that of general titanium alloy is 686-1176 MPa, up to 1764 MPa at present. Titanium alloys have the same strength as many steels, but much better strength than titanium alloys. Here, specific strength refers to the strength of a material divided by its apparent density, also known as strength-weight ratio. The international unit of specific strength is (N/m2)/(kg/m3) or N.m/kg. The ratio of tensile strength to apparent density of materials is called specific strength. The ratio of strength (tension) to density at fracture point. The compressive strength of titanium and its alloys is not lower than their tensile strength. The compressive yield strength and tensile yield strength of industrial pure titanium are approximately equal, while the compressive strength of Ti-6Al-4V and Ti-5Al-2.5Sn alloys is slightly higher than the tensile strength. The shear strength is generally 60%-70% of the tensile strength. The compressive yield strength of titanium and titanium alloy sheets is 1.2-2.0 times of the tensile strength. In normal atmosphere, the rupture strength of processed and annealed titanium and titanium alloys is (0.5-0.65) times the tensile strength. The durable strength of annealed Ti-6Al-4V was 0.2 times of tensile strength when 107 fatigue tests were carried out in notch state (Kt=3.9). The hardness of the highest purity processed industrial pure titanium is usually less than 120HB, while the hardness of other purity processed titanium is 200-295HB. The hardness of pure titanium castings is 200-220 HB. The hardness of titanium alloy under annealing is 32-38HRC, which is equivalent to 298-349HB. The hardness of as-cast Ti-5Al-2.5Sn and Ti-6Al-4V alloys is 320HB, and that of low gap impurity Ti-6Al-4V castings is 310HB. Tensile elastic modulus of industrial pure titanium is 105-109 GPa, and that of most titanium alloys is 110-120 GPa under return condition. Age hardening titanium alloy has a slightly higher tensile modulus than annealed titanium alloy, and the compressive modulus is equal to or greater than the tensile modulus. Although the stiffness of titanium and titanium alloys is much higher than that of aluminium and aluminium alloys, it is only 55% of that of iron. The specific modulus of elasticity of titanium alloys is the same as that of aluminium alloys, which is second only to beryllium, molybdenum and some superalloys. The torsional or shear modulus of industrial pure titanium is 46 GPa, and the shear modulus of titanium alloy is 43-51 GPa. In order to improve the strength of titanium alloy and increase the content of interstitial elements, the impact resistance and fracture toughness of the alloy will be harmful. According to the different types and states of titanium alloys, the impact strength of Charles notch of industrial pure titanium is 15-54J/cm2, and the casting state is 4-10J/cm2. The impact strength of titanium alloy under annealing is 13-25.8J/cm2, and the aging state is slightly lower. The impact strength of Cast Ti-5Al-2.5Sn alloy with V-notch is 10J/cm2, and that of Ti-6Al-4V alloy is 20-23J/cm2. The lower the oxygen content is, the higher the value is. Many titanium alloys have high fracture toughness, or good crack propagation resistance. The annealed Ti-6Al-4V alloy is a kind of material with excellent toughness. When notch concentration factor Kt = 25.4mm, the ratio of notch tensile strength to non-notch tensile strength is greater than 1. Titanium alloys can also maintain certain properties at high temperatures. General industrial titanium alloys can maintain their useful properties at 540 C, but they can only be used for a short time. The temperature range for a long time is 450 – 480 C. Titanium alloys for use at 600 C have been developed. Titanium alloys can be used as missile materials for a long time at 540 C and for a short time at 760 C. Titanium and titanium alloys can maintain their original mechanical properties at low and ultra-low temperatures. With the decrease of temperature, the strength and ductility of titanium and titanium alloys increase gradually. Many annealed titanium alloys have sufficient ductility and fracture toughness at – 195.5 C. Ti-5Al-2.5Sn alloy with very few interstitial elements can be used at – 252.7 C. The ratio of notched tensile strength to non-notched tensile strength is 0.95-1.15 at – 25.7 C. Liquid oxygen, liquid hydrogen and liquid fluorine are important propellants for missiles and cosmic devices. The low temperature properties of materials used to make cryogenic gas containers and cryogenic structures are very important. The ductility of titanium alloy is still above 5% when the microstructure is equiaxed and the content of interstitial elements (oxygen, nitrogen, hydrogen, etc.) is very low. Most titanium alloys have poor ductility at – 252.7 C, while the elongation of Ti-6Al-4V alloys can reach 12%.

Forging Method of Titanium Alloy

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The main methods used in titanium alloy forging are free forging, open die forging (with hairy edge forging), closed die forging (without hairy edge forging), extrusion die forging, multi-direction die forging, partial die forging and isothermal die forging.
  1. Free forging
Free forging is usually carried out between two flat dies or dies without cavity. Free forging tools are simple in shape, flexible, short in manufacturing cycle and low in cost. However, the workload is high, the operation is difficult, the productivity is low, the quality of forgings is not high, and the processing margin is large. Therefore, it is only suitable for the case that there is no special requirement for the performance of the parts and the number of parts is small. For large forgings, free forging is mainly used as a blank-making process. In the free forging process, the billet can be forged into step bar, or the billet can be made into simple shapes such as round cake and rectangle by pier thickness or flattening.
  1. Open die forging (die forging with burr edge)
The billet deforms between two die-carved modules, and the forging is confined to the inside of the die cavity. The excess metal flows out of the narrow gap between the two dies, forming a rough edge around the forging. Under the action of the resistance of the die and the surrounding wool edge, the metal is forced to press into the shape of the die cavity.
  1. Closed die forging (no burr edge die forging)
In the process of closed die forging, no transverse edge is formed perpendicular to the direction of die movement. The die cavity of the closed forging die has two functions: one is used to shape the blank, the other is used to guide it.
  1. Extrusion Die Forging
There are two kinds of die forging: forward extrusion die forging and reverse extrusion die forging. Extrusion die forging can produce various hollow and solid parts. Forgings with high geometric accuracy and denser internal structure can be obtained.
  1. Multidirectional Die Forging
It is carried out on a multi-direction die forging machine. In addition to the vertical punching plug, there are two horizontal plungers in the multi-direction die forging machine. Its ejector can also be used for punching. The pressure of the ejector of the multi-direction die forging machine is higher than that of the common hydraulic press. In multi-direction die forging, the slider acts alternately and jointly on the workpiece from the vertical and horizontal directions, and uses one or more punches to make the metal flow outward from the center of the die cavity to achieve the purpose of filling the die cavity. There is no special forging edge on the parting line of the barrel.
  1. Partial die forging
In order to forge large integral forgings on existing hydraulic pressures, subsection die forging and cushion plate die forging can be used. The characteristic of parting method is that the forgings are processed step by step, one part is processed at a time, so the required tonnage of equipment can be very small. Generally speaking, this method can be used to process large forgings on medium-sized hydraulic presses.
  1. Isothermal die forging
Before forging, the die is heated to the forging temperature of the blank, and the temperature of the die and the blank is the same during the whole forging process, so that the large deformation can be obtained under the action of small deformation force. Isothermal die forging and isothermal superplastic die forging are very similar, but the difference is that the blank of the latter needs to be superplastic treated before die forging, so that it has fine equiaxed grains.

What’s the advantage of titanium pot over stainless steel pot?

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Stainless steel pot hazards: stainless steel pot is made of ferrochromium alloy infiltrated into nickel, molybdenum, titanium, cadmium, manganese and other trace metal elements, these trace metal elements are harmful to human body, long-term use will cause cancer! Harm of iron pot: iron pot is easy to rust, the human body absorbs too much iron oxide, that is, rust, will cause harm to the liver! We all know that ordinary iron pots are very easy to rust. Every time we use them, we need to dry the water in the pot. Titanium pots need not worry about these problems at all, because the corrosion resistance of titanium is excellent, even if it is very corrosive liquids such as seawater, Aqua regia, it is difficult to corrode it, and there is no need to worry about rusting. In recent years, with the continuous development and application of new materials, titanium materials have gradually entered the civil market. A series of products related to titanium have been developed. For example: Titanium chopsticks, Titanium bowls, Titanium spoons, Titanium cups, Titanium pots and so on, lead a wave of kitchen utensils revolution with the theme of health, environmental protection, non-toxic and harmless. Titanium pot is a pot made of 99.5% titanium metal as contact layer, pure aluminum as intermediate layer, magnetic conductive 430 stainless steel as bottom layer, three-layer composite structure, and integrated pressing. Why not use pure titanium single layer structure to make pots? That’s because both thermal conductivity (good thermal conductivity of aluminium) and magnetic conductivity (suitable for 430 stainless steel induction cooker) should be considered. Titanium pot boiling: Although titanium pot has no coating and rust-proof film, the boiling process is also essential! The newly purchased titanium pot is cleaned with detergent first, then rinsed with hot water to remove impurities such as oil and floating ash. Then pour water into the pot, add a little white vinegar, put it on the stove to boil, turn off the fire, and rinse with hot water to remove impurities such as metal and oil. The washed titanium pot is placed on the stove again. After drying and removing the water, turn off the fire. Pour a little cooking oil while the pot is warm. Spread the cooking oil evenly on the inner wall of the pot with a soft cloth. Or it is better to apply lard evenly for 1-2 hours or more. Use of titanium pot: Titanium pot has excellent thermal conductivity and energy storage. When used, medium and small fires have the effect of general pots and large fires. Medium and small fires can meet the needs of daily cooking. (Except for the effect of stir-frying). When oil is poured into the medium-hot pot, it turns into a small fire or keeps the medium-heat cooking. Cooking and energy saving save time and less oil fume. In addition, titanium is very active, with the increase of the number of times used, the oxide film on the surface will become thicker, and the more used, the better. Titanium pot maintenance: scientific use of titanium pot is very important. First heat the pan, then pour the oil, then heat the oil and add the food. It’s not so easy to stick to the pan. Uncertain that the pot is not hot enough, you can do a simple test with water: drop a small drop of water (1/8 teaspoon) into the pot, if the water touches the pot, it immediately becomes a drop of water, and slides along the surface of the pot, your pot has been preheated, you can pour oil! Titanium pot has many advantages, making it the most popular health pot. A healthy titanium pot can ensure the safety of a family for a lifetime!  

Foundry, Forging and Heat Treatment of Flanges

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Casting flange has accurate shape and size, small workload and low cost, but it has casting defects (pore, crack, inclusion); poor streamlined internal structure of casting (if it is a cutting piece, the streamlined shape is worse); forging flange generally contains less carbon than casting flange and is not easy to rust; forging flange has better streamlined shape, compact structure and mechanical properties. The properties of the flange are better than those of the casting flange, and the improper forging process will lead to large or uneven grains, hardening cracks and higher forging cost than that of the casting flange.

Forgings can withstand higher shear and tensile forces than castings. The advantages of castings are that they can produce more complex shapes and lower costs; and the internal structure is uniform, and there are no harmful defects such as blowhole and inclusion; casting flange and forging flange can be distinguished from production process, such as centrifugal flange, which belongs to casting flange.

Centrifugal flange belongs to precision casting method. Compared with common sand casting, this casting method has much finer structure and much better quality. It is not easy to have loose structure, pore and trachoma.

Production Process of Forging Flange

Select high quality billet blanking, heating, forming and cooling after forging. The forging process includes free forging, die forging and die forging. In production, different forging methods are selected according to the quality and quantity of forgings.

The basic process of free forging: when forging freely, the shape of forgings is gradually forged by some basic deformation processes. The basic processes of free forging include upsetting, drawing, punching, bending and cutting.

Upsetting is the process of forging the billet along the axis to reduce its height and increase its cross section. This process is often used to forge gear blanks and other disc forgings. Upsetting can be divided into two types: total upsetting and local upsetting.

Drawing is a forging process that increases the length of blank and decreases the cross section. It is usually used to produce axle blanks, such as lathe spindle and connecting rod.

The forging process of punching through hole or non-through hole on blank with punch.

A forging process in which billets are bent to an angle or shape by bending.

A forging process in which a part of the billet rotates at a certain angle relative to another part by torsion.

The forging process of cutting and cutting blank or cutting blank head.

Die forging is called model forging, which is formed by placing the heated billet in the forging die fixed on the die forging equipment. Basic processes: blanking, heating, pre-forging, final forging, punching, trimming, tempering, shot peening. Common processes include upsetting, drawing, bending, punching and forming. Common die forging equipments include die forging hammer, hot die forging press, flat forging press and friction press. Generally speaking, the quality of forged flange is better. It is usually produced by die forging. The crystal structure is fine and the strength is high. Of course, the price is more expensive.

Cutting flange

In the middle plate, the flange is directly cut out of the disc with the inside and outside diameter and thickness of the processing quantity, and then the bolt hole and the water line are processed. The flange thus produced is called cutting flange. The maximum diameter of such flange is limited to the width of the plate.

Rolled flange

The process of cutting strips with medium plates and rolling them into circles is called rolling, which is mostly used in the production of some large flanges. After successful coiling, welding is carried out, then flattening is carried out, and then the process of water line and bolt hole is processed.

Titanium alloy is an ideal armor material

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Titanium alloys are widely used in aircraft, submarines and other fields. Their specific strength even exceeds that of steel. When the specific gravity is slightly higher than that of aluminium, the strength and toughness of titanium alloys are similar to or even better than that of steel. In theory, titanium alloy is the perfect armor material. Titanium alloy is an ideal armor material only in terms of performance. We know that armored steel is mainly used as armor in armored vehicles, while some light vehicles, such as infantry chariots, paratroopers and armored conveyors, use aluminum alloy armor to reduce weight. However, the hardness and specific strength of aluminium alloy armor are much lower than that of steel, and it can not withstand high temperature. When hit by armor-piercing projectiles, it will produce toxic gases locally. But after all, aluminium alloy is very light. When it is used as armor, under the premise of the same protective force for armor-piercing projectiles, the thickness of aluminium alloy is much higher than that of steel, but the weight can be lighter. But titanium alloys also have a fatal defect, which is expensive. This is expensive, on the one hand, the high-performance titanium alloy material itself is very expensive; on the other hand, more importantly, it is difficult to process titanium alloys, especially titanium alloy welding, which is very difficult. Generally speaking, the price of titanium alloy armor with the same protective force is 10-20 times higher than that of steel. So for a long time, the use of titanium alloy armor is generally in the aircraft and individual body armor. The Soviet Union used titanium alloy to make pressure hulls of submarines. As a result, the “Serra” class nuclear submarine is called “goldfish”, and its cost per ton exceeds the price of gold of the same weight. Only three countries in the world, China, the United States and Russia, have carried out special research on marine titanium alloys and established their own marine titanium alloys system. Moreover, titanium alloys have some defects. According to the related papers, under specific load conditions, projectiles only need a very small amount of energy to cause the destruction of titanium alloy armor, so it is not scientific to completely replace steel with titanium alloys even if it is rich. By the 1990s, some changes had taken place in titanium alloy armor. Represented by the United States, many countries began to study low-cost titanium alloys used in armored vehicles related technology. The price of titanium alloy armor has been reduced by about 40% through the use of new technology and new technology, such as electron beam welding, which finally makes it possible to use titanium alloy materials. The U.S. plan to upgrade M1A2 tanks in the 1990s is to use titanium alloy to make hatch covers, top armor decks, etc. instead of its original steel components, M1 tanks using titanium alloy components can reduce the weight by nearly 500 kg, while the protective force remains unchanged. U.S. military research also points out that the same technology can be used in M2 “Bradley” and M13 armored conveyors, which, of course, needs to be further reduced in the cost of titanium alloy manufacturing. In addition, in the development of EFV Marine Expeditionary Vehicle, the U.S. military also considered using titanium alloy armor, or using titanium alloy to manufacture the vehicle’s mobile system components, to reduce weight. China’s new combat vehicles use titanium alloys to make the body structure, which is obviously better in weight and protection than the previous use of aluminum alloy or steel. So what is this kind of chariot? First of all, it is still in the key technological stage, so it will not be the vehicle that has begun to equip the army. Thus, the 15-type lightweight main battle tank, 05-type amphibious assault vehicle, amphibious infantry chariot family and 04A infantry chariot can be excluded. Weapons and Equipment Group has rich experience in using titanium alloy materials in army weapons. A large number of large titanium alloy parts including titanium alloy shelves are used in the AH-4 type 155 mm ultra-light howitzer. This fact can also illustrate from the side that the Armament Group has a deep foundation in casting, welding and machining of large titanium alloy parts. At the Zhuhai Air Show in 2012, a staff member of the factory interviewed us next to the AH-4 ultra-light artillery with a mysterious smile and said, “After mastering this technology, we will have one hundred links, and there will be more new equipment using titanium alloy in the future, you wait and see.” According to the information disclosed by relevant news, the structure frame material and some armor of new type armored vehicles in China are made of titanium alloy material. This first shows that this is an armored vehicle which has decided to use titanium alloy to make a large number of basic structures from the beginning of design, which is the world’s first.  

Characteristics of Titanium and Titanium Alloy Materials and Application of Cutting and Welding Processing Technology

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Titanium alloy has been widely used in aviation, weapon equipment, naval ships and some light artillery because of its high strength, non-magnetic, good medium temperature, good weldability and corrosion resistance. In recent years, great progress has been made in the application of titanium alloy technology in China. At the same time, there are still some problems to be further studied. It is hoped that there will be greater breakthroughs in the field of processing technology in the future.

Titanium alloys have the characteristics of high temperature resistance, good weldability, high specific strength, easy processing and forming, and have been widely used in aerospace and aerospace fields. In addition, because of its unparalleled corrosion resistance of other materials, it has also been widely used in the ocean and industrial atmosphere. However, titanium alloy has some shortcomings, such as poor formability in cutting, which restricts its application to a certain extent.

CHARACTERISTICS OF TITANIUM ALLOY MATERIALS

Titanium alloys are not only steel in strength, but also light in weight, good corrosion resistance and good thermal stability. In addition to being widely used in aerospace and aerospace fields, titanium alloys are also widely used in biopharmaceutical and petrochemical industries. Titanium alloys have different properties and uses because of their different composition and structure.

(1) Characteristics of Titanium Alloys

Some alloying elements are added to titanium. According to the characteristics of the formed titanium alloys, titanium alloys are usually divided into the following categories:

(1) Alpha phase titanium alloy. This kind of titanium alloy is an alloy with close-packed hexagonal lattice structure. It has strong toughness and strength, and has strong oxidation resistance at high temperature. Its disadvantage is that its formability is poor and it can only be used in high temperature environment.

(2) Titanium alloy with beta phase. This kind of titanium alloy is a body-centered cubic structure alloy with good formability, but it is easy to be damaged in the case of contamination, so its application is not much. It needs to reach a certain aging before its strength can be improved.

(3) Alpha+beta phase alloys. This kind of titanium alloy has good room temperature strength and is easy to form, but its thermal strength is not ideal. After heat treatment and strengthening, it is suitable for parts with high strength requirements. It is not only used in large quantities, but also widely used.

Titanium alloys have good properties at both high and low temperatures, so they can be used in a wide range of applications. It has low density and high strength, so its specific strength is higher. At the same time, titanium alloys have good corrosion resistance in sea water, atmosphere or acidity and alkalinity conditions, which makes titanium alloys become the best choice of corrosion resistant materials in many metal materials. However, its thermal conductivity will be low, and it is generally applicable to all kinds of insulation components.

Titanium alloys also have some disadvantages. That is to say, it lacks good wear resistance, so it is impossible to make some moving parts. The modulus of elasticity is relatively low and lower than that of magnesium and aluminium. Its processing and manufacturing process is more complex, and its production cost will be higher.

  1. Cutting of Titanium Alloys

Titanium alloys contain a variety of alloying elements, including some high activation energy elements, which are relatively stable in the alloy, so titanium alloys have great energy in plastic deformation, but also have a certain degree of workability. However, the thermal conductivity of titanium alloys is poor. In cutting process, the cutting heat gathers on the tool, unlike in aluminum cutting process, the cutting heat is taken away by chips. As a result, the thermal load of titanium alloy material is large and the cutting tool is damaged. Therefore, the common method to improve production efficiency by increasing the amount of removal per unit time is not suitable for the processing of titanium alloy materials. Therefore, suitable processing methods should be selected for different titanium alloy materials.

(1) Titanium alloys have high strength, toughness and hardness, so the hardening problem in cutting is serious, which needs to be treated with annealing. Especially when there are scratches or notches on the workpiece surface, because they are very sensitive to deformation speed, they are prone to scratches or cracks in the cutting process, so the processing speed must be controlled in order to proceed at a low speed.

(2) In general, titanium alloys have good thermal stability and high temperature resistance. Compared with aluminium alloys, the strength of titanium alloys is much higher. In cutting process, the thermal conductivity of titanium alloy is very low, which is equivalent to a small part of iron and aluminium materials. Its heat is concentrated on the cutting edge. When the temperature exceeds a certain standard, it will produce high chemical activity and react with oxygen and hydrogen in the air, thus reducing its plasticity, and worsening tool wear when it contacts with the cutter face and chips.

(3) In cutting, because there is a certain friction between titanium alloy and cutting tool, with the increase of friction speed, the temperature will be higher, the power will be higher, the tool wear will be faster, and it is easy to bond, thus greatly shortening the service life of the cutting tool. Therefore, the rational selection of cutting tools is also very important. Usually, some cemented carbide materials such as tungsten cobalt cemented carbide tools are selected. This can effectively prevent the generation of bad stress in the process of processing and ensure the processing accuracy of components.

These characteristics of titanium alloy in the cutting process make it very difficult to cut, resulting in lower production efficiency and higher production cost. Therefore, in order to improve the processing quality of titanium alloy, it is necessary to constantly improve the processing plan and adjust the reasonable processing parameters in the cutting process of titanium alloy.

  1. Welding Processing of Titanium Alloys

In recent years, in addition to some traditional titanium alloy processing technology, there are also some new processing methods, such as low temperature cutting, laser, ultrasonic and electromagnetic cutting. Especially with the development of welding technology, the processing and application of titanium alloys are more extensive. Because of the physical and chemical characteristics of titanium alloy, the weld is easily oxidized and nitrided, which results in pollution, and the joint is sensitive to embrittlement. Therefore, it is a great challenge to weld titanium alloy.

(1) Tungsten Argon Arc Welding

Tungsten Argon Arc Welding is the most common method in Titanium Alloy welding. Under the protection of argon, tungsten pole acts as the electrode and the weld metal is well protected. However, this welding method has low welding production efficiency, large post-weld structural deformation, coarse grain size of welded joint and poor protection, which will seriously affect the welding process. Weld quality. It is only suitable for thin plate welding or bottom welding.

(2) Laser welding is a high energy density welding method. Using this method to weld titanium alloy can not only reduce the defects of traditional processing technology, but also effectively refine the microstructures and grains of the weld and improve the performance of the weld. However, the power of this welding method is small, the laser beam absorbed by the welded workpiece surface is very low, and there are some threshold problems. It is only suitable for special materials or special requirements for processing structure, and is limited to the processing of small and precise parts, so it is more difficult than traditional processing technology.

(3) Friction stir welding (FSW) is a better technology among many new plastic joining processes. When friction stir welding is used, because of the low heating temperature, the defects in the weld zone are the least, and the structure and properties of the joints are good, so the effective welding of titanium alloys can be realized. However, this method has high requirements on the mixer head and its material, and has no good adaptability, and the process is not mature, so it can only be used in the welding of simple components.

(4) Electron beam welding (EBW) is characterized by high welding energy, strong penetration, large depth-width ratio of welds, isolation of atmospheric pollution and good performance of welded joints, which can realize the welding of titanium alloy thick plates. However, this method requires to be carried out in vacuum, limited by the size and shape of the parts processed, can not be produced in batches, and the requirements for equipment are also very high, the production cost is high, which limits its application scope.

(5) Laser-arc hybrid welding is a good welding technology for titanium alloys. It combines the advantages of laser welding and arc welding, with concentrated energy density, stable arc and good weld performance. However, its welding process parameters are too many to be controlled effectively, and its operation process is too complex, so it is only in the research stage at present.

For the welding process of titanium alloy, no matter which new technology or new method, there are some advantages and disadvantages to some extent. With the extensive application of titanium alloy materials in many fields, new welding processes and methods need to be continuously studied to improve the quality of welds and welding production efficiency, to ensure the welding quality of titanium alloy structural parts and meet the requirements of use.

Nowadays, titanium alloys have been widely used for their unique excellent properties, so the processing technology of titanium alloys has become a hot research topic. Compared with some advanced countries, China still has a certain gap in titanium alloy materials and processing technology. With the rapid development of modern technology, the application field of titanium alloy is also expanding year by year. This requires us to strengthen the optimization and innovation of processing technology, and constantly accumulate technical experience. It is of great significance for our country to make full use of titanium alloy materials by high quality products to meet the application requirements in various fields.

New Technology of Titanium Alloy Dyeing

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A Research Institute in Osaka, Japan, has developed a new dyeing technology of titanium alloy, which utilizes the EDM process in water.

Titanium alloys are rapidly used in building materials, bicycles, watches and glasses due to their high strength and excellent corrosion resistance. In order to adapt to this kind of use and increase its added value, experts are studying various dyeing methods of titanium alloys, such as atmospheric oxidation, anodic oxidation, chemical oxidation, etc. These methods require special corrosive solution and other processes for dyeing. According to the processing conditions, various dyed surfaces can be obtained at the same time by EDM in water.

The underwater electrical discharge machining (EDM) process is to cut the rough surface of the workpiece properly and finish it. On the one hand, removing the surface layer, on the other hand, dyeing at the same time, the dyeing process which used to require two processes can be reduced to one process. The principle of dyeing by this process is that the exposed metal surface is discharged and the oxides produced by the electrolysis are dyed. Because the number of oxides ultimately determines the dyeing tone, by controlling the average processing voltage, not only all color phases can be formed, but also the color can be changed in any part.

New Application of Titanium Alloy Products such as Titanium Bar and Titanium Plate in Domestic Industry

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The prominent feature of titanium is its strong corrosion resistance, which is due to its strong affinity to oxygen, which can generate a dense oxide film on its surface, which can protect titanium from medium corrosion. Titanium metal can form passive oxide film on the surface in most aqueous solutions. Therefore, titanium has good stability in acidic, alkaline, neutral saline solution and oxidizing medium. It has better corrosion resistance than existing stainless steel and other non-ferrous metals, and even can be compared with platinum.

  1. Chemical Industry

Titanium is an excellent corrosion-resistant material in chemical industry, and it has been widely used as it gets older. For example, the use of titanium metal anode and titanium wet chlorine cooler in chlor-alkali industry has achieved good economic results and is known as the revolution in chlor-alkali industry.

  1. Petroleum Industry

Titanium has excellent stability in organic compounds except five organic acids (formic acid, acetic acid, oxalic acid, trichloroacetic acid and triacetic acid) at higher temperatures. Therefore, titanium is an excellent structural material in petroleum refining and petrochemical industry. It can be used to make various heat exchangers, reactors, high pressure vessels and distillation towers.

  1. Metallurgical Industry

Titanium is a kind of active metal, which has good gas absorption property. It is an excellent paint remover in steelmaking industry. It can combine oxygen and nitrogen precipitated from steel during cooling. A small amount of titanium can make the steel tough and elastic. Titanium industry is an important alloy additive in steelmaking and aluminium industry. Titanium is widely used in hydrometallurgical gold industry, such as electrolysis of copper, nickel and cobalt, and Namanganese.

  1. Fertilizer Industry

Urea is an important chemical fertilizer. It is corrosive under high temperature and high pressure in the production process. The service life of the equipment is greatly increased and the maintenance time is greatly reduced when titanium is used instead of non-embroidered steel. So Titanium is used in the main equipment of urea production at present.

  1. Seawater desalination and shipbuilding industry

Titanium is an ideal structural material for shipbuilding industry because of its strong corrosion resistance to sea water and sea air, high strength and light weight. It has been widely used in many parts of warships.

  1. Electric Power Industry

Titanium has good stability in many corrosive hot water containing chloride, sulfide and so on. Therefore, titanium has been widely used as the cooling pipe of heat exchanger in thermal power plants, which greatly reduces the overhaul time and has a remarkable economic effect.

  1. Paper and Textile Industry

Titanium has special corrosion resistance to chlorine dioxide, chlorite, chlorite and other bleaching agents. Therefore, titanium has an important application in bleaching equipment of textile printing and dyeing industry and paper industry.

  1. Medical and other aspects

Titanium has good affinity and is harmless to human body. Therefore, it can be widely used in medical and pharmaceutical industries. Titanium has good gas absorption performance and is widely used in electronic vacuum technology and high vacuum technology.

Application of medical titanium alloys as biomedical materials in dentistry

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At present, medical titanium alloys have been widely used in orthodontics, prosthodontics and dental implants. Table 1 shows the dental uses of titanium and titanium alloys studied in Japan.

(1) Orthodontics. Orthodontics refers to the science of correcting tooth dislocation by mechanical or functional instruments. In order to correct tooth dislocation, external force must be applied through different instruments. The detachable device consists of separate acrylic acid (PMMA) sheets, which are fixed to the patient’s teeth by filamentary elements. The acrylic sheet is separated and applied to the teeth by expanding screw (rotating shaft with left and right threads). In fixing technology, the fixed object (bracket and oral tube) is used to exert force on the teeth through the filamentous original part. Now, except stainless steel, pure titanium is used for fixing and fixing components because of its light weight and high corrosion resistance. For dental arch wires and spring elements, titanium alloy is particularly noticeable because of its lower modulus of elasticity than stainless steel and higher strength than pure titanium. The tensile strength of Beta-type titanium alloy can reach 1300 MPa after cold deformation. The processability of Beta-type alloy is better, and it can even be produced into fine filamentary components. The mechanical properties of cold-worked grade 4 pure titanium are similar to that of beta alloy, so it can replace beta alloy. In addition, Ti-Ni alloy wire shape memory alloy wire has been applied because of its pseudoelasticity, which is based on stress-induced martensitic transformation. (2) Repair. Dental prosthetics refers to the replacement of defective teeth or other parts with prostheses to reproduce the masticatory, aesthetic and pronunciation functions of teeth. As a new material in dental laboratory, the problem of titanium early processing has been solved, and the application of titanium in dental restoration has become more and more successful. Titanium is used not only as ordinary castings, but also as crowns and bridges with ceramics and teeth. Dental precision casting is often used to process titanium parts. For the large structure of fixed implants, the electrochemical properties of cast titanium are comparable to those of industrialized intraosseous implants, which reduces the electrochemical properties and the harm of electrochemical and corrosion effects. In addition, compared with gold-based alloys, titanium has the advantages of economy. Therefore, it is considered to be an ideal material for composite, permanent and removable restorations. Compared with other alloys with cladding ceramics, the thermal expansion coefficient of titanium is very low, so suitable ceramics need to be embedded. The oxidation degree of titanium increases at high temperature, the grain size and microstructure coarsen, and the beta transformation occurs at 882 C. Therefore, the highest calcination temperature of cladding ceramics on titanium surface is 800 C. (3) Dental implantation. Dental implantation refers to the implantation of artificial pillars into the periosteum or bone to reconstruct the masticatory function, aesthetic characteristics and pronunciation function. In modern dental surgery, intraosseous implants are recognized as a method to replace teeth, create permanent dental pillars and stabilize removable dentures. Titanium and titanium alloy dental implants have been used for more than 40 years and are manufactured according to the corresponding standards. A1203 shot peening or titanium plasma flame treatment is usually used to coarsen the surface of implants to promote the adhesion between implants and bone. Local use of absorbable alkyl apatite in the surface area (cortex) will also promote the attachment of key parts of the implant to the bone.

How to Deal with the Reaction Layer of Surface Defects of Titanium Alloy Plate and Titanium Alloy Bar

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The surface reaction layer of titanium plate and rod is the main factor affecting the physical and chemical properties of titanium workpiece. Before processing, the surface contamination layer and defect layer must be completely removed. Physical-mechanical polishing of surface polishing process of titanium plate and rod:

  1. Sandblasting:

White corundum is usually used for sand blasting treatment of titanium wire castings, and the pressure of sand blasting is smaller than that of non-precious metals, which is generally controlled below 0.45 MPa. Because, when the injection pressure is too high, the sand particles impact the titanium surface to produce intense sparks, and the temperature rise can react with the titanium surface, resulting in secondary pollution and affecting the surface quality. The time is 15-30 seconds. Only the adhering sand, sintered layer and partial oxide layer on the surface of the castings can be removed. The other surface reaction layer structures should be removed quickly by chemical acid pickling.

  1. pickling:

Acid pickling can quickly and completely remove the surface reaction layer, and the surface will not produce pollution of other elements. HF-HCL and HF-HNO_3 acid pickling solutions can be used for titanium pickling, but HF-HCL acid pickling solution has a large hydrogen absorption capacity, while HF-HNO_3 acid pickling solution has a small hydrogen absorption capacity, which can control the concentration of HNO_3 to reduce hydrogen absorption, and can brighten the surface. Generally, the concentration of HF is about 3%-5%, and the concentration of HNO_3 is about 15%-30%.

The surface reaction layer of titanium plate and rod can be completely removed by acid pickling after sandblasting.

In addition to physical and mechanical polishing, there are two kinds of reaction layers on the surface of titanium plate and rod: 1. chemical polishing and 2. electrolytic polishing.

  1. Chemical polishing:

In chemical polishing, the aim of leveling and polishing is achieved by the oxidation-reduction reaction of metal in chemical medium. Its advantages are that chemical polishing has nothing to do with metal hardness, polishing area and structure shape. All parts contacted with polishing fluid are polished without special complicated equipment. It is easy to operate and suitable for polishing of titanium denture support with complex structure. However, the process parameters of chemical polishing are difficult to control, which requires that the denture can be polished without affecting the accuracy of the denture. The better titanium chemical polishing solution is HF and HNO 3 in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration of HNO 3 is less than 10%. HNO 3 acts as an oxidizing agent to prevent excessive dissolution and hydrogen absorption of titanium, and at the same time it can produce a bright effect. Titanium polishing solution requires high concentration, low temperature and short polishing time (1-2 minutes).

  1. Electropolishing:

Also known as electrochemical polishing or anodic dissolution polishing, because of the low conductivity and strong oxidation performance of titanium alloy tubes, it is almost impossible to polish titanium using aqueous acidic electrolytes such as HF-H3PO4 and HF-H2SO4. When applied with external voltage, the titanium anode immediately oxidizes and the anodic dissolution cannot proceed. However, the anhydrous chloride electrolyte has a good polishing effect on titanium under low voltage. Small specimens can be polished specularly. However, for complex prostheses, the purpose of complete polishing can not be achieved. Maybe the method of changing the shape of cathode and adding cathode can solve this problem, which needs further study.