Metallographic and Morphological Characteristics of TC4

The ratio, properties, and morphology of basic phases α and β are very different in TC4 alloy under different heat treatment and hot working conditions. The β-transformation temperature of Gr5 Ti-6Al-4V Titanium Bar is around 1000 °C. If TC4 is heated to 950 °C, the obtained microstructure is a primary α+β-transformed structure after air cooling; called Weiss organization. If heating and deformation act at the same time, the effect is more obvious. The TC4 alloy is heated above the β-transition temperature, but the deformation is small, that is, the Widmandarin structure is formed. Its organizational characteristics are low plasticity and impact toughness, but good creep resistance. If the initial deformation temperature is above the β transformation, but the deformation degree is large enough, the obtained microstructure is characterized by: the β grain boundary delineated by the α phase is crushed, and the strip-shaped α phase is distorted, which is called a basket-like structure. Its characteristics are that the plasticity and impact toughness is better than Widmancers structure, similar to the equiaxed fine-grained structure, and the high-temperature durability and creep performance are better. If the heating temperature is lower than the β transition temperature and the deformation degree is sufficient, the equiaxed structure is obtained. It is characterized by good comprehensive properties, especially high plasticity, and impact toughness. If it is partially deformed at high temperature in the α+β phase region and then annealed at high temperature, the mixed microstructure will be obtained, and its comprehensive properties will be good.

The advantages of titanium tube:

1. Titanium tube has high specific strength. The density of titanium alloy is generally around 4.5g/cm3, which is only 60% of steel. The strength of pure titanium is close to that of ordinary steel. Some high-strength titanium alloys exceed the strength of many alloy structural steels. Therefore, the specific strength (strength/density) of titanium alloy is much greater than that of other metal structural materials, and parts and components with high unit strength, good rigidity and light weight can be produced. At present, titanium alloys are used in aircraft engine components, skeletons, skins, fasteners and landing gear.

2. The thermal strength of the titanium heat exchanger pipe is high. The operating temperature is several hundred degrees higher than that of aluminum alloys, and the required strength can still be maintained at moderate temperatures, and it can work for a long time at a temperature of 450 to 500 °C. The specific strength of aluminum alloy decreases significantly at 150 °C. The working temperature of titanium alloy can reach 500 ℃, and the working temperature of aluminum alloy is below 200 ℃.

3. Titanium tube has good corrosion resistance. Titanium alloy works in humid atmosphere and seawater medium, and its corrosion resistance is much better than stainless steel; it is particularly resistant to pitting corrosion, acid corrosion, and stress corrosion; it is resistant to alkali, chloride, chlorine, organic substances, nitric acid, sulfuric acid etc. have excellent corrosion resistance. However, titanium has poor corrosion resistance to media with reducing oxygen and chromium salts.

4. The low temperature performance of titanium alloy pipe is good. Titanium alloys can still maintain their mechanical properties at low and ultra-low temperatures. Titanium alloys with good low temperature performance and extremely low interstitial elements, such as TA7, can maintain a certain plasticity at -253 °C. Therefore, titanium alloy is also an important low-temperature structural material.

5. The chemical activity of titanium tube is large. Titanium has great chemical activity and produces strong chemical reactions with O, N, H, CO, CO2, water vapor, ammonia, etc. in the atmosphere. When the carbon content is more than 0.2%, hard TiC will be formed in the titanium alloy; when the temperature is high, a hard surface layer of TiN will also be formed when it interacts with N; when the temperature is above 600 ℃, titanium absorbs oxygen to form a hardened layer with high hardness ; Increased hydrogen content will also form an embrittlement layer. The chemical affinity of titanium is also large, and it is easy to adhere to the friction surface.

6. The thermal conductivity of the titanium tube is small and the elastic modulus is small. The thermal conductivity of titanium is small and the elastic modulus is small. The elastic modulus of titanium alloy is about 1/2 of that of steel, so its rigidity is poor and it is easy to deform. It is not suitable to make slender rods and thin-walled parts. It is very large, about 2 to 3 times that of stainless steel, causing severe friction, adhesion, and bonding wear on the flank of the tool.

Application prospect of titanium alloy in the biomedical field

With the development of the national economy and the improvement of people's living standards, the trend of population aging has become increasingly prominent, and diseases and accidental injuries have increased year by year. As an important branch of human tissue and organ regeneration and repair materials, biomedical titanium alloy materials have huge market prospects.

It should be clearly understood that my country's titanium alloy manufacturers still have a certain gap with the world's advanced level in terms of biomedical grade 7 titanium alloy plate material design, preparation, and processing, surface treatment, product design, and manufacturing. Low cost, safety, and effectiveness will be an important direction for the application of biomedical titanium alloys. The following issues are worthy of attention in future applications.

1. Optimize the composition design of medical titanium alloys

By improving the existing alloy system and creating a new alloy system, the development of low elastic modulus, reasonable matching of strength and toughness, wear resistance, corrosion resistance, fatigue resistance, excellent biological and mechanical compatibility, can meet the needs of human soft and hard tissue repair and replacement New medical titanium alloy material for clinical application.

2. Innovative preparation method of medical titanium alloy materials

Establish and improve advanced theories and methods for the processing and preparation of medical titanium alloy materials, continuously deepen or innovate the preparation methods of porosity, micro-nano, amorphization, and ultra-fine crystallization of materials, and obtain special structures and structures through new preparation methods. Endow the material with biological functionalization and intelligence, and realize the optimization and upgrading of medical titanium alloy materials.

3. Expand research on surface modification of medical titanium alloys

Through the study of the mechanism of action between the titanium alloy and the base metal and the dual interface between the Grade 23 Ti-6Al-4V ELI Titanium Bar and human tissues or body fluids, find and screen various inorganic materials, polymer materials and cytokines to modify the surface of titanium alloys to improve their surface properties and structure. Structure, improve wear and corrosion resistance, biocompatibility and bioactivity, and other performance.

4. Improve the technical level of material production and processing

At present, domestic processing technologies such as medical titanium alloy thick-walled tubes and titanium-nickel alloy capillaries are not very mature, and most of them need to be imported from abroad. Therefore, we especially need to master the core key technologies of titanium alloy material processing, strengthen the construction of a quality control system, and improve the consistency of product performance. properties, reduce processing and manufacturing costs and further meet the manufacturing needs of medical titanium alloy products.

5. Strengthen product design and processing

It is the general trend to use advanced processing technologies such as precision casting, precision CNC machining, and micro-machining for the processing of medical devices. In particular, digital 3D reconstruction technology has become a hot spot in recent years. According to the patient's defect, the technology uses 3D CT. The examination results simulate the natural form, and rely on CT data processing for medical 3D reconstruction. Through the surface drawing of natural curved surfaces, computer graphics and image-aided design, and digital manufacturing of titanium alloys, the patient can be accurately designed and prefabricated with laser forming technology. Personalized instruments , has the advantages of customizability, strong consistency, less process and short cycle. This is a revolutionary progress, marking the entry of titanium alloy instruments into the digital age, and will become one of the key development directions in the field of titanium alloy biomedicine.

Magnetron Sputtering Gold-Based Alloy Target

The magnetron sputtering technology uses an electron source to generate electrons, which are accelerated and focused in a vacuum to form a high-speed energy particle beam to bombard the solid surface (target), and the excited atoms are deposited on the surface of the substrate to form a coating. This technology has many advantages such as high film density, good adhesion, green environmental protection, etc., and has become a hot spot of research and development and attention in the field of new materials at home and abroad. Gold-based alloy is a new type of functional material developed to adapt to the development of modern microelectronics technology and jewelry industry. It not only maintains the original excellent properties of pure gold such as oxidation resistance and corrosion resistance, but also greatly improves its recrystallization temperature. Gold-based alloys are plated on the surface of various base parts by vacuum magnetron Tantalum Sputtering Target technology. The gold-plated parts are widely used in the electronic industry and cutting-edge technology fields due to their high temperature resistance and acid medium corrosion resistance. Such gold-plated materials are often used in various instrument parts on aerospace vehicles, astronaut equipment, jet engines, heat reflectors, infrared devices, etc. As the source material in the magnetron sputtering process, the quality of gold-based alloy targets plays a crucial role in the performance of sputtered gold-plated films. Therefore, how to improve the target preparation technology to improve the target quality and research and development to meet market demand The new high value-added magnetron sputtering gold-based alloy target is of great significance.

6 major factors affecting metal flow during extrusion of titanium alloy materials

The thermal conductivity of titanium rod and titanium alloy rod blank is low, which will cause a great temperature difference between the surface layer and the inner layer during hot extrusion. When the temperature of the extrusion cylinder is 400 degrees, the temperature difference can reach 200~250 degrees. Under the combined influence of inhalation strengthening and the large temperature difference of the billet section, the metal on the surface and the center of the billet has very different strength properties and plastic properties, which will cause very uneven deformation during the extrusion process. A large additional tensile stress is generated in the extruded product, which becomes the source of cracks and cracks formed on the surface of the extruded product. The hot extrusion process of titanium rods and titanium alloy rods is more complicated than that of aluminum alloys, copper alloys, and even steel, which is determined by the special physical and chemical properties of titanium rods and titanium alloy rods.

The metal flow dynamics study of industrial Titanium Alloy Threaded Rods shows that in the temperature region corresponding to the different phase states of each alloy, the flow behavior of the metal is very different. Therefore, one of the main factors affecting the extrusion flow characteristics of titanium rods and titanium alloy rods is the heating temperature of the billet that determines the state of metal transformation. The metal flow is more uniform when extruding at the temperature of the a or a+P phase compared to the extrusion at the temperature of the p phase. It is very difficult to obtain high surface quality of extruded products. Until now, the extrusion process of titanium alloy rods had to use lubricants. The main reason is that titanium will form a fusible eutectic with iron-based or nickel-based alloy mold materials at temperatures of 980 degrees and 1030 degrees, which will cause strong wear of the mold.

The main factors affecting metal flow during extrusion:

1) Extrusion method. The reverse extrusion is more uniform than the forward extrusion, the cold extrusion is more uniform than the hot extrusion, and the lubricated extrusion is more uniform than the non-lubricated extrusion. The effect of the extrusion method is achieved by changing the friction conditions.

2) Extrusion speed. As the extrusion speed increases, the inhomogeneity of the metal flow increases.

3) Extrusion temperature. When the extrusion temperature increases and the deformation resistance of the billet decreases, the uneven flow of the metal intensifies. During the extrusion process, if the heating temperature of the extrusion cylinder and the mold is too low, and the metal temperature difference between the outer layer and the center layer is large, the unevenness of the metal flow will increase. The better the thermal conductivity of the metal, the more uniform the temperature distribution on the end face of the ingot.

4) Metal strength. When other conditions are the same, the higher the metal strength, the more uniform the metal flow.

5) Die angle. The larger the die angle < (that is, the angle between the end face of the die and the central axis), the more uneven the metal fluidity is. When the porous die is used for extrusion, the die holes are arranged reasonably, and the metal flow tends to be uniform.

6) Degree of deformation. If the degree of deformation is too large or too small, the metal flow is uneven.

How to distinguish between aluminum alloy and titanium alloy?

1. If you have two materials on hand, one is aluminum and the other is titanium alloy, as long as the two materials are drawn on each other. The scratched one is aluminum. Because titanium is harder than aluminum.

2. Compared with acid resistance, aluminum reacts immediately with acid, and titanium has good acid resistance.

3. Measure the weight. Aluminum doors of the same size are the lightest, titanium doors are slightly heavier, and steel doors are the heaviest. But if the manufacturer deliberately deceives people, it is possible to make a door that is as heavy as titanium alloy by mixing aluminum and steel. It's easy to tell if there's steel in the door, though. Take a magnet to see if it will attract to the door. grade 7 titanium alloy plates are not magnetic and will not attract magnets.

4. Look at the color. Find an inconspicuous small corner and sand off a layer of oxide film or paint on the surface to fully expose the metal underneath. Then take a closer look at the color of the metal. Take an empty Coke can (aluminum), sand off the paint on the surface, and compare it to the door. Aluminum alloys are light gray, titanium alloys are dark gray, and they look glossier than aluminum.

5. If possible, you can also measure the resistance. The resistance of titanium alloy is much larger than that of aluminum alloy.

Classification of welding materials for titanium and titanium alloys

The welding method of titanium and titanium alloys is best to use tungsten electrode inert gas shielded welding and molten electrode inert gas shielded welding, collectively referred to as hydrogen arc welding. The welding materials used are mainly titanium and titanium alloy welding wires, argon gas and tungsten electrodes.

The composition of titanium and titanium alloy argon arc welding wire should be the same as that of the base metal, that is, the filler wire should generally be made of homogeneous material. In order to improve the plasticity of the joint, a medium wire with a slightly lower alloying degree than the base metal can be used, such as TA1 welding wire when welding TA2. The impurity content of the wire should be much lower than that of the base metal. The titanium welding wire is supplied in vacuum annealed state, and the surface shall not have defects such as burnt skin, crack, oxidation color, metallic or non-metallic inclusions, etc.

Titanium alloys need to be protected with inert gas during welding. Argon, helium or a mixture of argon and nitrogen can be used as protective gas. In my country, only hydrogen is usually used as the shielding gas, so it is called argon arc welding.

Argon is denser than air, has lower specific heat capacity and thermal conductivity than air, and hardly has any chemical interaction with any metal, nor does it melt into metal. These physical and chemical properties enable it to play a good protective role in titanium argon arc welding and to stabilize the welding arc.

The argon gas used for welding titanium and titanium alloys is first-grade argon gas, and the technical requirements of argon gas for welding are stipulated in the national standards GB/T4842-2006 and GB/T10624-1995. The main technical requirements for argon are: purity, argon ≥99.99%; moisture <0.002mg/L; relative humidity not greater than 5%; residual pressure in the hydrogen bottle should not be less than 0.2MPa.

If the purity of argon is unqualified, it means that there are excess impurities such as oxygen, nitrogen and hydrogen in it. Among them, oxygen and nitrogen will melt into the welding pool to make the weld metal brittle, and excess hydrogen will form weld porosity defects. Other impurities will reduce the breaking length of the welding arc,

The purity of argon can be easily identified by observing the color of the weld surface. The specific method is to first use a tungsten electrode to ignite the arc on the titanium plate, and keep it fixed. When a melting zone is formed on the titanium plate, immediately extinguish the arc (still argon gas at this time) to observe. If the solder joint shows bright white dots, it means that the argon gas is of high purity. You can also observe the color of the heated tungsten wire to determine the purity of argon. If the tungsten wire is oxidized under the protection of argon after heating, that is, it is not silver-white, it means that the purity of the bottle of argon is not enough.

Treatment method of center deviation of titanium screw

When the diameter of the titanium metric screw is less than 30mm and the center line is offset within 30mm, you can first use oxyacetylene to bake the bolt red, and then use a sledgehammer to bend the bolt (or bend it with a jack). Prevents recovery when the bolt is tightened.

If the spacing of the titanium bolts is not correct, you can use a sledgehammer to bend them after being baked with an oxyacetylene flame and weld a steel plate in the middle to reinforce it, and then fill it to death in the subsequent grouting.

For large displacement of large bolts (diameter above 30mm), the bolts should be cut off first, and a steel plate should be welded in the middle of the bolts. If the bolt strength is not enough, two reinforcing steel plates can be welded on both sides of the bolt. 3 to 4 times smaller than the diameter of the bolt.

Titanium is a new type of metal. The properties of titanium are related to the content of impurities such as carbon, nitrogen, hydrogen, and oxygen. The purest titanium iodide has an impurity content of no more than 0.1%, but it has low strength and high plasticity. The properties of 99.5% industrial pure titanium are: density ρ=4.5g/cm3, melting point 1725℃, thermal conductivity λ=15.24W/(mK), tensile strength σb=539MPa, elongation δ=25%, section shrinkage Rate ψ=25%, elastic modulus E=1.078×105MPa, hardness HB195.

What are the treatment methods of titanium alloy screw reaction layer?

Titanium alloy screws do not need any surface treatment, the color of the whole screw is silver-gray, sometimes there are many titanium alloy screws of different colors on bicycles and cars, these colored titanium alloy screws will be so bright and colorful after certain surface treatment, titanium screws What do manufacturers think about the treatment methods of titanium alloy screw reaction layer?

1. Sandblasting: The screw maker impacts the sand on the surface of the titanium screw, producing strong sparks. The temperature increase reacts with the surface of the titanium alloy screw, causing secondary pollution and affecting the surface quality. Fifteen to thirty seconds is sufficient to remove adhesive, sintered layers, and partial oxide layers from the casting surface. Chemical pickling is used to quickly remove reactive layers on other surfaces.​​

2. Pickling: Pickling can quickly and effectively remove the reaction layer on the surface of titanium metric screw without contaminating other metal elements. The screws look like steel and have a silvery-white sheen. It is a transition metal. Pure titanium screws have the characteristics of high strength, low density, high hardness, high melting point, and strong corrosion resistance, and can be used in various fields.

The surface corrosion treatment of titanium alloy screws refers to the metallic appearance of the maintenance layer applied by various methods. Its function is to isolate the metal from the corrosive environment to inhibit the corrosion process or reduce the contact of the corrosive medium with the metal surface, so as to prevent or slow down the corrosion.

Defects that are prone to occur in titanium alloy forgings:

1. Segregation type [i] defects

In addition to β segregation, β spot, titanium-rich segregation and strip α segregation, the most dangerous is interstitial α stable segregation (type I α segregation), which is often accompanied by small holes and cracks around it, containing oxygen, nitrogen and other gases , is more brittle. There is also aluminum-rich α stable segregation (type II α segregation), which also constitutes a dangerous defect due to cracks and brittleness, and also reduces the thermal stability and other properties of the alloy.

2. Inclusions

There are inclusions on the surface of the billet, and cracks are often formed along the inclusions during forging, or obvious foreign bodies appear after the forging is corroded, most of which are metal inclusions with high melting point and high density. It is formed by the high melting point and high density elements in the titanium alloy composition that are not fully melted and left in the matrix (such as molybdenum inclusions), and there are also carbide tool chippings or inappropriate electrode welding processes mixed in smelting raw materials (especially recycled materials). The smelting of Titanium Industrial Rod generally adopts the vacuum consumable electrode remelting method [ii]), such as high-density inclusions left by tungsten arc welding [iii], such as tungsten inclusions, and titanium compound inclusions. Titanium alloy forgings with inclusions are not allowed to be put into use.

3. Holes

The holes do not necessarily exist alone, but may also exist in a plurality of clusters, which will accelerate the growth of low-cycle fatigue cracks and cause premature fatigue failure.

4. Cracks

Mainly refers to forging cracks. Titanium alloys have high viscosity, poor fluidity, and poor thermal conductivity. Therefore, in the process of forging deformation, due to large surface friction, obvious internal deformation unevenness, and large temperature difference between inside and outside, it is easy to get inside the forging. A shear band (strain line) is generated, and cracking occurs in the direction of the maximum deformation stress in severe cases.

5. Overheating

The thermal conductivity of titanium alloys is poor. In addition to overheating of forgings or raw materials caused by improper heating during hot working, it is also easy to cause overheating due to thermal effects during deformation during forging, causing changes in microstructure and overheating Widmanderin [iv] ].

In order to ensure the quality of titanium alloy forgings, in addition to strictly controlling the quality of raw materials, attention should also be paid to the ultrasonic flaw detection of forging blanks and semi-finished products to prevent some deformation and physical properties during subsequent heating and processing.

Development in the field of titanium and titanium alloy products

Titanium alloys were widely used in the aerospace field in the early days, mainly in the production of aircraft engines or pneumatic components. Later, with the continuous and in-depth development of technology, titanium alloys have entered the lives of ordinary people, and titanium alloys are also used in factories or household devices. Now countries and institutions are scrambling to develop new titanium alloys, which have the characteristics of low cost and high performance. In recent years, the new development of titanium alloys is mainly concentrated in the following aspects.

(1) Medical titanium alloy.

Titanium alloys have low density and good biocompatibility. They are ideal medical materials and can even be implanted into the human body. Titanium alloys previously used in the medical field contain vanadium and aluminum, which can cause harm to the human body. However, recently, Japanese scholars have developed a new type of titanium alloy with good biocompatibility, but this alloy has not yet been mass-produced. It is believed that such high-quality alloys can be widely used in daily life in the near future.

  (2) Flame retardant titanium alloy.

Titanium-based alloys that can resist combustion under certain pressure, temperature and air flow rate are resistive titanium alloys. The United States, Russia and China have successively developed new resistance titanium alloys. The United States applies these resistance titanium alloys to engines. Because these titanium alloys are not sensitive to combustion, the stability of the engine can be greatly improved.

  (3) High temperature titanium alloy.

Combining the rapid solidification method and the powder metallurgy method, the titanium alloy prepared by the fiber or particle reinforced composite material has excellent high temperature mechanical characteristics. The service temperature limit of high temperature titanium alloy is much higher than that of ordinary titanium alloy. At present, a new type of high-temperature Grade 3 Pure Titanium Sheet has been prepared in the United States.

Problems in CNC titanium machining!

Because the thermal conductivity of titanium processing is small, the heat generated during cutting cannot be dissipated and will be stored in the tool, so the wear on the tool will increase.

Because of the large chemical activity, when the cutting speed increases, cutting heat will occur, and the temperature of the cutting part will increase, so the activity will increase and the wear on the tool will increase.

Because the continuous deformation causes chips to be generated, the cutting resistance of the cutting edge increases, and the tip is prone to chipping and wear.

Because the elastic modulus is small, the machining material is prone to great deformation during cutting, especially when machining thin workpieces, 6al4v titanium round bar the machining accuracy will be reduced and chattering will occur.

Cold Rolling Properties of TC6 Titanium Alloy Sheet

TC6 titanium alloy plate is a martensitic Ti-Al-Mo-Cr-Fe-Si series α+β two-phase thermally strong titanium alloy with good comprehensive properties. Its nominal composition is Ti-6Al-2.5Mo-1.5Cr -0.5Fe-0.3Si, the α/β transition temperature is between 960 and 1000 °C. In addition to the advantages of high specific strength and good corrosion resistance of ordinary titanium alloys, this alloy also has good comprehensive mechanical properties at room temperature and high temperature, and the operating temperature can be as high as 450 °C. Parts, can also be used to manufacture aircraft bulkheads, joints and other parts. In China, a lot of work has been done on the processing technology and performance optimization of TC6 titanium alloy forgings, castings, pipes and bars, etc., but there is less research on TC6 alloy sheets. The basic process parameters of cold rolling processing of TC6 sheet were studied, and the cold rolling processing performance of TC6 sheet was studied.

The TC6 titanium alloy ingot used in the experiment is obtained by three times of smelting in a vacuum consumable electric arc furnace, and its β transition temperature is 975-985 °C. , Fe0.41, Si0.29, O0.10, Zr<0.01, C<0.01, N<0.01, and the remainder of Ti. The TC6 ingot used in the experiment was opened in the β phase region, and the α+β two-phase region was forged into a slab. The slab is hot rolled and opened at the β transformation temperature, and rolled to 3.5mm in the α+β two-phase region. After intermediate annealing and pickling, the cold rolling work hardening experiment is carried out. When the processing rate increases by 5%, a piece of 200mm long test material is cut from the head of the plate, and the remaining plate continues to be rolled. Repeated rolling and sampling until the Grade 3 Pure Titanium Plate has edge cracks or surface cracks. Then the cut 200mm experimental materials with different processing deformations were tested, and the thickness, width, edge cracks, microstructure and mechanical properties of the experimental plates were tested respectively.