Defects that are prone to occur in ultrasonic flaw detection of titanium alloy forgings

In the application of various titanium alloy products, titanium forging are mostly used in applications requiring high strength, high toughness and high reliability, such as gas turbine compressor disks and medical artificial bone. Therefore, not only high dimensional accuracy is required for titanium forgings, but also materials with excellent characteristics and high stability are required. The following mainly introduces the six problems existing in titanium alloy flaw detection.

Titanium alloy ring

1. Segregation 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.

2. Inclusions

Most of them 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 alloys generally adopts vacuum consumable electrode remelting method), such as tungsten arc welding, leaving high-density inclusions, such as tungsten inclusions, and titanium compound inclusions.

The existence of inclusions can easily lead to the occurrence and expansion of cracks, so it is not allowed to exist defects (for example, the Soviet Union's 1977 data stipulated that high-density inclusions with a diameter of 0.3~0.5mm were found in the X-ray inspection of titanium alloys. Record).

3. Residual shrinkage

In the central area of ​​the acid leaching test piece (in most cases), there are irregular folds, cracks or voids, and there are often serious looseness, inclusions (slag inclusions) and composition segregation on or near it.

4. 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.

5. Cracks

Mainly refers to forging cracks. Titanium alloy has high viscosity, poor fluidity, and poor thermal conductivity. Therefore, in the process of forging deformation, due to the large surface friction, obvious internal deformation unevenness and large temperature difference between inside and outside, it is easy to produce shear bands inside the forging ( Strain line), which can lead to cracking in severe cases, and its orientation is generally in the direction of maximum deformation stress.

6. Overheating

The thermal conductivity of titanium alloy is poor. In addition to overheating of forgings or raw materials caused by improper heating during the hot working process, it is also easy to cause overheating due to the thermal effect of deformation during the forging process, causing changes in the microstructure and producing an overheated Widmandarin structure.

Application of titanium alloy screws in shipbuilding industry

The application of titanium metric screw in the shipbuilding industry mainly uses its excellent corrosion resistance, low density, memory, and non-magnetic properties.

Titanium and titanium alloys are widely used in nuclear submarines, deep submersibles, atomic energy icebreakers, hydrofoils, hovercraft, minesweepers, as well as propeller thrusters, civilian antennas, seepage pipes, condensers, heat exchangers, higher education devices, and fire fighting equipment.

Titanium alloy processing parts occupy an important position in the machinery manufacturing industry!

Titanium alloy has the advantages of low density, high specific strength, good corrosion resistance, and good process performance, and is an ideal aerospace engineering structural material. Titanium and its alloys are replacing traditional aluminum alloys in many aerospace applications. Today, the aerospace industry consumes about 42% of total global production, and demand for titanium is expected to continue growing at a double-digit rate between now and 2010. The need for next-generation aircraft to take full advantage of the properties offered by titanium alloys is driving demand for titanium alloys in both the commercial and military aircraft markets. New models such as the Boeing 787, Airbus A380, F-22 Raptor, and F-35 Joint Strike Fighter (also known as Lightning II) use a lot of titanium alloys. Advantages of titanium alloy materials Titanium alloys have high strength, high fracture toughness, and good corrosion resistance and weldability. With the increasing use of composite structures in aircraft fuselage, the proportion of titanium-based materials used in the fuselage will also increase, because the combination of titanium and composite materials is far better than aluminum alloys. For example: Compared to aluminum alloys, titanium alloys can increase the life of airframe structures by 60%.

Since Grade 3 Pure Titanium Plate are more difficult to machine than ordinary alloy steels, titanium alloys are generally considered to be difficult-to-machine materials. The metal removal rate of a typical titanium alloy is only about 25% of that of most common steel or stainless steel, so machining a titanium alloy workpiece takes about 4 times as long as machining a steel workpiece. To meet the growing demand for titanium machining in the aerospace industry, manufacturers need to increase production capacity and therefore need a better understanding of the effectiveness of titanium machining strategies. The machining of a typical titanium alloy workpiece starts with forging until 80% of the material is removed to obtain the final workpiece shape.

 With the rapid growth of the aviation parts market, manufacturers have felt powerless, and the increased processing demand due to the low processing efficiency of titanium alloy workpieces has led to a significant tension in the processing capacity of titanium alloys. Some leading companies in the aerospace manufacturing industry even openly questioned whether the existing machining capabilities could complete the processing tasks of all new titanium alloy workpieces. Since these workpieces are often made from new alloys, changes in machining methods and tool materials are required. Titanium alloy Ti-6Al-4V titanium alloy has three different structural forms: a titanium alloy, a-b titanium alloy and b titanium alloy. Commercially pure titanium and a titanium alloys cannot be heat treated, but usually have good weldability; a-b titanium alloys can be heat treated, and most of them are also weldable; b and quasi-b titanium alloys can be fully heat treated, and generally also have Solderability.

Uncover the unknown features of titanium coils

The strength of the Titanium Coil Tube is higher than that of high-quality steel. Titanium alloy has good heat resistance, low-temperature toughness, and fracture toughness. Titanium equipment is mostly used for aircraft and other components, rockets, missile structural parts, and titanium equipment.

Titanium gold is bright, light, strong, and has good corrosion resistance. The metal made of titanium material will not be deformed, will not fade, and is easy to maintain. Just wipe it with a cotton cloth, it will restore its luster, and it is easy to operate. The longer the time, the better the brightness.

Titanium has stable chemical properties and good biocompatibility. In the human body, it can resist the erosion of exudates, does not damage people's bodies, and conforms to any sterilization method. Since the titanium in the titanium coil has quite high corrosion resistance and stability, there is no chemical reaction between the material and the drying time, so it is a metal that has no effect on people's body autonomic nerves and taste, and will not cause Excessive reaction.

Titanium in titanium coil has excellent physical and chemical properties, low density, lightweight, high strength, good corrosion resistance, mechanical properties, and weldability, making it used in many fields: chemical equipment, offshore power generation Equipment, seawater desalination equipment, ship parts, electroplating industry, and other industries. The corrosion resistance is 15% stronger than that of stainless steel, and the service life is about 10% longer than that of stainless steel.

How to improve the quality of titanium tube welding?

Due to the strong activity of the titanium tube, the welding temperature control, the protective effect of the shielding gas, the welding environment, and other aspects are strictly required in the welding of the Grade 3 Pure Titanium Tube. In severe cases, the product will be scrapped. The practice has proved that: by analyzing the main factors affecting the welding quality, determining the key welding process, and strengthening the control of the environment, personnel, welding parameters, and methods in the welding process, the welding quality of titanium tube materials can be effectively guaranteed to be further improved. Improve, and prevent the appearance of welding scrap.

In recent years, a new Grade 9 Ti3Al2.5V Titanium Tube material has been widely used. Due to the properties and characteristics of lightweight, high strength, and corrosion resistance, titanium alloys are widely used in the fields of aerospace, petrochemical, and machinery manufacturing, and are also used in the construction of surface ships for the first time. However, since titanium alloy is a highly active metal, it has a great affinity for oxygen, hydrogen, nitrogen, and other gases at high temperatures, that is, it has a strong ability to absorb and dissolve gases, especially in welding process. This ability is particularly strong with increasing soldering temperature. The practice has proved that if the absorption and dissolution of titanium alloy and oxygen, hydrogen, nitrogen, and other gases are not controlled during welding, the product will eventually be scrapped. Therefore, in the welding of titanium pipe joints, effective prevention and control must be carried out to meet the quality requirements of welding.

Causes of black stripe defects in the rolling process of TC4 titanium rods!

TC4 (Ti-6Al-4V) is a martensitic a/3 type two-phase titanium alloy with good comprehensive properties, and the operating temperature can reach 450. It is widely used in important structural parts of the aviation industry, such as wing blades, aero-engine wheel discs, etc. Since the TC4 titanium rod is a two-phase titanium alloy, if the composition of the micro-region is not uniform, it will inevitably lead to abnormal macro-structure and micro-structure, resulting in a significant difference in the hardness between the abnormal region and the normal region, and the overall performance of the material is not uniform. It leads to the source of fatigue cracks, which brings great hidden dangers to the safety of parts and reduces the service life of the alloy. Aiming at the black streak defect found in the low magnification inspection of a TC4 titanium alloy bar product, in order to accurately determine the type of defect, the metallographic structure was observed with a metallographic microscope to determine the abnormal area of ​​the metallographic structure. Then, the chemical composition segregation defects of Mo-rich and Al-poor in the black stripe area were analyzed by scanning electron microscope. The composition segregation in the black streak region was determined to be non-brittle segregation by microhardness testing.

The experimental results show that the composition segregation and types of TC4 titanium alloy can be effectively determined according to the above method. And it is determined that this type of defect will not affect use and can be delivered after removal. Such defects can be reduced or eliminated by controlling the selection of raw materials for titanium alloy ingots, material mixing, electrode preparation and voltage and current during smelting. The segregation of titanium alloys can be divided into hard segregation (hardness higher than normal area, also called brittle segregation) and soft segregation (hardness lower than normal area, also called non-brittle segregation). If there are only non-brittle segregations in the product and all properties meet the product standard requirements, the product can still be delivered for use after the segregation has been eliminated. Brittle segregation is not allowed to be delivered after dismantling and should be discarded in batches.

A. For the black stripe defect of Grade 23 Titanium Bar found by visual inspection, the microstructure was observed by metallographic microscope, and the defect area was not much different from the normal area, so the type of defect could not be judged; in addition, the chemical composition of the defect area of ​​the titanium rod was analyzed by scanning electron microscope, The defect region was found to be a segregation of chemical elements rich in heavy and depleted in aluminum. Finally, combined with the microhardness test, it is determined that the segregation type of the TC4 titanium rod is the non-brittle segregation of aluminum-rich and aluminum-poor. The composition segregation and type of TC4 titanium alloy can be effectively determined by microstructure observation, micro-area composition analysis and micro-hardness test.

The segregation in B.TC4 titanium alloy bar is non-brittle segregation rich in heavy and poor in aluminum, which does not affect the use, and can be continuously transported after cutting; by controlling the selection of raw materials, mixing and electrode preparation parameters, as well as the voltage and current in the smelting process, it can be reduce or eliminate this defect.

What are the precautions for alkaline cleaning of titanium alloy rods?

Titanium alloy rods are prone to fire and burns, especially titanium sheets. The chemical activity of the titanium alloy bar in the alkaline solution, the high temperature of the entire alkaline solution, or the local temperature of the titanium alloy bar when it is washed in an alkaline solution containing an oxidant are the causes of titanium burns. The results show that there is a battery effect due to the potential difference between the titanium alloy tool and the steel tool in the alkaline solution. When titanium is in contact with steel, a current is formed. The smaller the contact point, the greater the current, and the titanium alloy rod is often burned from the contact point of the two metals.

In order to prevent and reduce the ignition of grade 5 titanium round bar during the alkaline cleaning process, the following measures can be taken:

1. Select a qualified alkaline lotion for composition;

2. Strictly manage and control the temperature of lye;

3. Insulate the alkali washing rack with high-temperature resistant paint or high temperature resistant insulating gasket. For example, the stainless steel alkaline washing rack can be padded with ceramic strips or sheets to separate the titanium material from the steel frame to avoid fire.

In the process of alkaline cleaning of 6al4v titanium alloy bar, the lye is continuously taken away or evaporated by the workpiece, so we need the enterprise to supplement the lye, and conduct analysis and adjustment in a timely manner to keep the composition of the lye relatively stable. During the alkaline washing process, insoluble oxide slag precipitates at the bottom of the tank, which affects the good thermal conductivity of the tank. The gap caused by the precipitation makes the steel tank prone to electrochemical corrosion, which greatly shortens its service life. Therefore, the sludge should be cleaned up in time.

Die forging process of AMS4928 titanium rod!

Due to the high pressure, the life of the titanium rectangular bar is reduced, so when the titanium rod is forged by the closed die forging method, the closed die forging must strictly limit the volume of the original blank, which complicates the material preparation process.

Whether to use closed die forging should be considered from the two aspects of interest and process feasibility. During open die forging, the burr loss accounts for 15%-20% of the weight of the blank. The technological waste of the clamping part (if this part must be left according to the die forging conditions) accounts for 10% of the weight of the blank. The relative loss of burr metal usually increases with the blank. The weight decreases and increases. For some forgings with asymmetrical structure, large cross-sectional area difference and difficult filling, the burr consumption can be as high as 50%. Although closed die forging has no burr loss, the billet making process is complex and needs to be added. Multiple transition grooves will undoubtedly increase auxiliary costs.

Only the final blank is then heat treated and machined. The forging temperature and the degree of deformation are the basic factors that determine the structure and properties of the alloy. The heat treatment of titanium rod is different from that of steel, and die forging is usually used to make a shape and size close to scrap. It does not play a decisive role in the structure of the alloy. Therefore, the process specification of the final step of the titanium rod plays a particularly important role. It is necessary to make the overall deformation of the blank not less than 30% and the deformation temperature does not exceed the phase transition temperature. In order to obtain high strength and plasticity of the titanium rod at the same time, and the temperature and deformation degree should be distributed as uniformly as possible in the entire deformed blank.

After recrystallization heat treatment, titanium rods and property uniformity are not as good as steel forgings. In the intense metal flow area, the low magnification is fuzzy crystal, and the high magnification is equiaxed fine grain; in the hard-to-deform area, due to the small amount of deformation or no deformation, the structure is often kept in the state before deformation. Therefore, when forging some important titanium rod parts (such as compressor discs, blades, etc.), in addition to controlling the deformation temperature below TB and the appropriate deformation level, it is very important to control the structure of the original blank. Otherwise, the coarse grain structure or Certain defects will be inherited into the forging, and the subsequent heat treatment cannot be eliminated, which will lead to the scrapping of the forging.

In the rapid deformation area where the thermal effect is locally concentrated, when the hammer is forged with complex titanium bar forgings. Even if the heating temperature is strictly controlled, the temperature of the metal may still exceed the TB of the alloy. For example, when a titanium rod blank with an I-shaped cross-section is forged, the hammering is too heavy, and the local temperature in the middle (web area) is affected by the thermal effect of deformation. The edge is locally about 100°C higher. In addition, in the hard-to-deform region and the region with a critical deformation level, it is easy to form a coarse-grained structure with relatively low plasticity and durability during the heating process after die forging. Therefore, forgings with complex shapes on hammer die forging often have unstable mechanical properties. However, it will lead to a sharp increase in deformation resistance, although reducing the heating temperature of die forging can eliminate the risk of local overheating of the blank. Increased tool wear and power consumption necessitates the use of more powerful equipment.

The local overheating of the blank can also be mitigated by using multiple light strokes. However, it is necessary to increase the number of heating times during die forging on the hammer. to make up for the heat lost from the contact between the blank and the cooler mold. And when the requirements for the plasticity and durability strength of the deformed metal are not too high, the forging shape is relatively simple. It is better to use hammer forging. However, hammer forging is not suitable for beta alloys, because multiple heating in the die forging process will have a favorable effect on the mechanical properties. Compared with the forging hammer, the working speed of the press (hydraulic press, etc.) is greatly reduced, which can reduce the deformation resistance and deformation thermal effect of the alloy. When the titanium rod is forged on the hydraulic press, the unit die forging force of the blank is about 30% lower than that of the hammer die forging, which can improve the life of the die. The reduction in thermal effects also reduces the risk of metal overheating and temperature rise exceeding TB.

Under the same conditions as forging hammer die forging, when die forging with a press. The blank heating temperature can be reduced by 50100℃. In this way, the interaction between the heated metal and the periodic gas and the temperature difference between the blank and the die are correspondingly reduced, thereby improving the uniformity of deformation, the uniformity of the structure of the die forging is also greatly improved, and the consistency of mechanical properties is also improved. . When the deformation speed is reduced, the area shrinkage rate increases most obviously, and the area shrinkage rate is the most sensitive to tissue defects caused by overheating.

The friction with the tool is high and the contact surface of the blank cools too quickly. In order to improve the fluidity of the titanium rod and increase the life of the mold. The usual practice is to increase the die forging slope and fillet radius and use a lubricant: the burr bridge height on the forging die is greater than that of steel, and the deformation of titanium rods is characterized by more difficult flow into deep and narrow die grooves than steel. This is because of the high deformation resistance of titanium. Generally about 2mm larger. Flash grooves with non-uniform bridge dimensions are sometimes used to restrict or accelerate the flow of metal to certain parts of the groove. For example, in order to make the groove easy to fill. A rectangular box-shaped forging (as shown in Figure 12) has thinner front and rear side walls; left and right side walls are thicker. When the burr groove shown in B-B is used around the box-shaped part, due to the small resistance of the metal flowing into the left and right side walls, it is difficult for the metal to flow to the thinner front and rear side walls, and the filling is not satisfied. Later, the front and rear side walls still use the burr grooves shown in BB, while the left and right side walls use the burr grooves shown in AA. Due to the wide size of the bridge and the obstruction of the damping groove, the front and rear thinner side walls are completely filled, and the metal is relatively thin. Use the aforementioned burr groove method to save.

It provides a feasible method for solving the forming of large and complex titanium rod precision forgings. This method has been widely used for titanium rod production. One of the most effective ways to improve the fluidity of titanium rods and reduce the deformation resistance is to increase the preheating temperature of the mold. Isothermal die forging and hot die forging developed in the past 20 to 30 years at home and abroad.

Cutting characteristics of titanium alloy materials:

Some physical and mechanical properties of titanium alloys bring great difficulty to cutting. The deformation coefficient of titanium alloy is small during cutting, which increases the sliding friction distance of chips on the rake face and accelerates tool wear. The thermal conductivity of titanium alloy is small, and the heat generated during cutting is not easy to be transmitted, and is concentrated in a small area near the cutting edge. The elastic modulus of titanium alloy is small, and it is easy to bend and deform under the action of radial force during processing, causing vibration, increasing tool wear and affecting the accuracy of parts. Due to the strong chemical affinity of Grade 3 Pure Titanium Plate for tool materials, under the conditions of high cutting temperature and large cutting force per unit area, the tool is prone to bond wear.

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.