Anti-fatigue Surface Modification of Titanium Alloys

While meeting the lightweight requirements of aerospace vehicles, titanium alloy parts also need to meet the requirements of long life and high reliability, which requires titanium alloy parts to have good fatigue resistance. However, medical titanium plate is a typical difficult-to-machine material. Adhesive wear of the tool during machining may cause complex surface stress. In addition, its poor thermal conductivity leads to a local temperature rise. Therefore, it is difficult to control the surface integrity of titanium alloy parts after machining. The industry uses a large number of anti-fatigue surface modifications (or surface deformation strengthening technology, Surfacemechanicaltreatment) to improve the surface integrity of titanium alloy parts, thereby achieving a long life and high-reliability requirements. In the anti-fatigue surface modification, mechanical shot peening (Shotpeening) and laser shock peening (Laser shock peening or Laserpeening) have strong structural adaptability and are widely studied in the industry. A series of researches have also been carried out on some surface strengthening technologies adapted to special structures, such as Cold expansion adapted to pore structures and Ultrasonic impact treatment or Ultrasonic impact peening adapted to welded structures.

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

In addition to physical and mechanical polishing, there are two types of reaction layers on the surface of Grade 3 Pure Titanium Plate and titanium rods: 1. Chemical polishing, 2. Electrolytic polishing.

1. Chemical polishing:

During chemical polishing, the purpose of leveling and polishing is achieved through the redox reaction of metal in the chemical medium. The advantage is that chemical polishing has nothing to do with the hardness of the metal, the polishing area, and the structural shape, and all the parts in contact with the polishing liquid are polished, no special complicated equipment is required, and the operation is simple, and it is more suitable for the polishing of titanium denture brackets with complex structures. However, the process parameters of chemical polishing are difficult to control, and it is required to have a good polishing effect on the denture without affecting the accuracy of the denture. A better titanium chemical polishing solution is prepared by HF and HNO3 in a certain proportion. HF is a reducing agent, which can dissolve titanium metal and play a leveling role. The concentration is less than 10%. HNO3 plays an oxidizing role to prevent excessive dissolution of titanium and hydrogen absorption. , at the same time can produce bright effect. Titanium polishing liquid requires high concentration, low temperature and short polishing time (1-2min).

2. Electrolytic polishing:

Also known as electrochemical polishing or anodic dissolution polishing, due to the low conductivity and strong oxidation performance of titanium alloy tubes, it is almost impossible to polish titanium with aqueous acidic electrolytes such as HF-H3PO4 and HF-H2SO4 electrolytes. After the external voltage, the Grade 12 Titanium Sheet is oxidized immediately, so that the anode dissolution cannot be carried out. However, the use of anhydrous chloride electrolyte at low voltage has a good polishing effect on titanium. Small specimens can be mirror polished, but for complex restorations, the purpose of complete polishing can still not be achieved. It may be possible to change the shape of the cathode and add an additional cathode. The method can solve this problem, and further research is needed.

Application of titanium alloy plate in medical field

Titanium plate is a very common substance, and the purity of sponge titanium can reach 99.9%. The physical and chemical properties of titanium alloy products are very stable, they will not be absorbed by the human body, and they will not react chemically with body fluids and medicines, nor will they be ionized, nor will they react with the musculoskeletal body of the human body. Biophilic Metals". Because titanium is "biophilic", titanium in the human body can resist the corrosion of secretions and is non-toxic, and is suitable for any sterilization method. Therefore, the titanium plates produced by many titanium plate manufacturers are widely used in the manufacture of medical devices, the manufacture of human hip joints, knee joints, shoulder joints, flank joints, skull bones, active heart valves, and bone fixation clips.

Titanium metal materials are the earliest biomedical materials used in clinical medicine. Titanium plates are processed into Grade 23 Ti-6Al-4V ELI Titanium Sheet. The metal materials currently used for surgical implants and orthopedic instruments mainly include three series of stainless steel, cobalt-based alloys, and titanium alloys, which account for three major series. The market share of the entire biomaterial product is about 40%. Among them, titanium alloys have been widely used in the repair, orthopedic and replacement treatment of defects, trauma, and diseases of human hard tissues (including all bones and teeth in the human torso).

 Since the middle of the 20th century, medical metal materials based on titanium alloys have been shown in the surgical implantation of human hard tissues and the interventional treatment of human soft tissues (including cardiovascular and cerebrovascular, peripheral blood vessels, and non-vascular such as liver, biliary tract, urethra, etc.). It has a unique and miraculous curative effect, and titanium alloy artificial joints, dental implants, intravascular stents, and heart valves have the development, production, and application of titanium alloy materials for medical devices in China, and the advent of typical representative medical device products. The development of medicine has an epoch-making significance and revolutionary contribution, which makes the clinical treatment rise from the primary simple "repair and orthopedic" treatment to the higher-level "replacement" treatment of tissues and organs, which greatly improves and improves people's lives. The quality has overcome the deficiency that major diseases can only rely on drug treatment in the past.

Physical phenomena of titanium machining

The cutting force of titanium alloy processing is only slightly higher than that of steel with the same hardness, but the physical phenomenon of processing titanium alloy is much more complicated than that of processing steel, which makes titanium alloy processing face huge difficulties.

Why do we consider titanium alloys to be a difficult material to the machine? Due to the lack of understanding of its processing mechanism

The thermal conductivity of most Titanium Alloy Rectangular Tube is very low, with only 1/7 of steel and 1/16 of aluminum. Therefore, the heat generated in the process of cutting titanium alloys will not be quickly transferred to the workpiece or taken away by the chips but will accumulate in the cutting area, and the temperature generated can be as high as 1 000 °C or more, which will cause the cutting edge of the tool to rapidly wear, chip and crack. A built-up edge is created, which quickly causes a worn edge, which in turn generates more heat in the cutting area, further reducing tool life.

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

The elasticity of AMS 4928 Titanium Alloy Bar may be beneficial for part performance, but during cutting, the elastic deformation of the workpiece is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to move away from the tool and bounce so that the friction between the tool and the workpiece is greater than the cutting action. The friction process also generates heat, aggravating the problem of poor thermal conductivity of titanium alloys.

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

The usefulness of flanges

titanium alloy flange is the parts used to connect pipes, fittings, or equipment, and there are also flanges used for the inlet and outlet of equipment, which are used for the connection between two pieces of equipment, such as reducer flanges. A flange connection is a detachable sealing structure in which flanges, gaskets, and bolts are connected to each other as a group. First, each is fixed on a flange, and then a flange gasket is placed, and bolts are used to fasten them together. This completes the flange connection.

1. The flange plate is mainly used to connect and fasten pipes, pipe fittings, etc., and maintain the sealing performance of the pipe fittings; the flange plate can be disassembled, which is easy to disassemble and check the pipeline condition.

2. The reducing flanges are corrosion-resistant, acid-alkali-resistant, and can be used in water conservancy, electric power, power stations, pipe fittings, industry, pressure vessels, etc.

3. titanium exhaust flange can be used in boiler pressure vessels, petroleum, chemical industry, shipbuilding, pharmaceutical, metallurgy, machinery, food, and other industries, which is convenient for the replacement of a certain section of pipeline.

4. The reducer flange is mainly used for the connection between the motor and the reducer, as well as the connection between the reducer and other equipment. Welding flanges are used to transfer the pressure of the pipeline, thereby reducing the high-stress concentration in the flange base.

Features of Titanium Plates

1. The oxide film on the surface of the titanium seed plate is equivalent to a good long-lasting wear-resistant hair separator. The use of the titanium seed plate saves the separator, makes the plate peeling easy, and eliminates the process of pre-treatment of the seed plate. The board is half lighter than the copper seed board.

2. The service life of the Grade 1 Pure Titanium Plate is more than 3 times that of the copper seed plate, and it can reach 10 to 20 years according to the operating conditions;

3. The electrolytic copper prepared with titanium seed plate has a dense crystal structure, smooth surface, and excellent quality;

4. Since the titanium seed plate does not need to be coated with a separating agent, the pollution of the copper electrolyte can be avoided;

5. Increase the production capacity and reduce the production cost of electrolytic copper, so as to have better economic benefits.

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.