Titanium alloy has the characteristics of low density, high specific strength, corrosion resistance, high and low temperature resistance. Its forming technology was originally developed to meet the needs of aerospace industry, therefore has the heavy quality, the light cost characteristic. In recent years, China’s high-tech field has developed rapidly, in order to meet the needs of lightweight structural components, major aerospace projects such as the “Manned space project”, the “Lunar Exploration Project”, the “Large aircraft”and the “High-scoring satellite”, as well as new types of weaponry and equipment, have increased the demand for high-quality titanium alloy components. At the same time, titanium alloys have been widely used in civil fields such as ship, chemical industry, medical treatment, nuclear power and fire fighting. However, at present, the production cost of high quality titanium alloy parts is still high, which is mainly caused by two aspects: First, the smelting process is demanding, titanium is extremely active at high temperature, and it is easy to react with oxygen, nitrogen, silicon, carbon and other elements, the melting and heat treatment process needs to be carried out under the protection of vacuum or inert gas, and it is difficult to control the purity and uniformity of components, conventional cold/hot forming is more difficult. It is estimated that in the whole production process of titanium alloy components, the raw material cost of sponge titanium accounts for about 14% , the processing cost of titanium alloy ingot and plate accounts for about 36% , and the final product cost of titanium alloy accounts for about 50% (Fig. 1) , the cost of titanium alloy products mainly comes from the process of casting slab, plate preparation and forging, casting, machining and so on. For example, the production cost of high-end military titanium investment castings is 1500 ~ 2500 yuan/kg, the production cost of ordinary civilian titanium investment castings is 500 ~ 800 yuan/kg, and the production cost of stainless steel investment castings is 50 ~ 200 yuan/kg

At present, there are three main ways to realize the low cost of titanium alloy material and its forming technology, cheap elements such as FE, SI, AL and Sn are used to replace expensive elements such as V, Mo, Zr, NB and TA in the design of Titanium Alloy materials, which can reduce the cost of alloying while maintaining the mechanical properties of titanium alloy, the cost of Titanium Scrap (titanium scrap) is only 20% ~ 30% of that of sponge titanium. Adding recharging material in the process of titanium alloy melting can greatly reduce the cost of slab production, but there are some problems such as the segregation of alloy elements and the high content of impurity elements in the recycled materials. Thirdly, the research on low-cost processing and forming technology is carried out, and the high cost of titanium alloy component forming is the main reason for its high price, the optimization and innovation of forming process is an important way to realize low cost. For Titanium Alloy Ingots, the integrated control of melting and refining can be carried out to reduce the smelting times of titanium alloy ingots, and for titanium alloy deformation processing, the mold can be made by using low cost Refractory instead of yttrium rare earth oxide for the casting of titanium alloy. 1. Development of low-cost titanium alloy materials in order to reduce the production cost of titanium alloy materials, the world has carried out research on new titanium alloy materials, the main approach is to replace the expensive elements such as V, MO, Zr, NB, Ta with the cheap intermediate alloys such as Fe, SI, AL and SN.

1.1 Timetal 62S alloy Timetal 62S (ti-6al-2fe-0.1 SI) is a new low-cost titanium alloy designed and developed by American Timetal company for non-aerospace applications, which belongs to α + β Alloy. The alloy is designed to replace the Ti-6Al-4V Alloy, The v Element in the Ti-6Al-4V alloy is replaced by the FE element, and the microstructure can be refined by adding proper amount of SI. The properties of the alloy are not inferior to that of Ti-6Al-4V alloy, and the cost is reduced by 15% ~ 20% , and has excellent cold and hot processing. This alloy is mainly used in high strength and anti-damage civil domain titanium alloy sheet metal structural parts, has replaced Ti-6Al-4V alloy in the production of valve seat ring. 1.21.2 Timetal LCB alloy Timetal LCB (ti-4.5 Fe-6.8 mo-1.5 AL) is a high strength β alloy developed by American Timetal company. The alloy is designed to replace Ti-10-2-3(Ti10V2Fe3Al) by adding Fe element in the form of Fe-Mo master alloy to replace v Element. The TIMETALLCB alloy has high strength and good formability. It can be cold-worked or warm-worked like steel. Its properties are equivalent to that of Ti-10-2-3. The cost is 78% of TI-6AL-4V. The alloy has high tensile strength after aging hardening. It has been used in automobile parts, springs and suspension springs in Japan and America.

1.31.3ati425 Alloy ATI425 Alloy (Ti-4Al-2.5V-1.5Fe-0.25O) is a Beta-type low-cost titanium alloy developed by Ati Wah Chang Company in the United States. Some v elements are replaced by FE elements, which reduces the cost and has good mechanical properties and corrosion resistance, the tensile strength can reach 827 ~ 965MPA, the yield strength can reach 758 ~ 896MPA, the elongation can reach 6% ~ 16% , and the ballistic resistance is equivalent to that of Ti6Al4V, has Been used in the field of weapons armor plate and military vehicle parts. 1.41.4 Ti-Fe-O-N series alloys Ti-Fe-O-N series alloys are β alloys developed by Japan Iron and Steel Corporation and Toho Titanium Corporation. The V elements in Ti-6Al-4V alloys are replaced by FE, O and n elements, among them, 0.5% ー1.5% fe, 0.2% ー0.5% o, 0.05% ー0.1% N. The room temperature strength of the alloy can reach 700 ~ 1000MPA, but its high temperature properties are poor. The representative of this alloy system is ti-1% fe-0.35% o-0.01% n. the tensile strength of this alloy is about 800 MPA, which is mainly used in the alloy designed for non-aviation applications. 1.51.5SP700 alloy SP700(Ti-4.5Al-3V-2Mo-2Fe) is a kind of superplastic titanium alloy developed in Japan. The superplastic forming and diffusion bonding can be realized at 775 °C. The superplastic forming temperature is lower than that of Ti-6Al-4V alloy, the tensile strength and fatigue strength are better than those of Ti-6Al-4V alloy, which can be used to manufacture thin plate aerospace structural parts. Since the defects of high deformation resistance and poor plasticity of titanium at normal temperature are avoided, thus the deformation processing cost of titanium material is greatly reduced, Japan has applied the alloy to the connecting rod of Honda NSX motorcycle, the US company RMI Titanium makes this titanium alloy into aircraft structural parts and rotating parts.

1.61.6TI8LC and TI12LC alloys low cost titanium alloys of near α type TI8LC and TI12LC, which are Ti-Al-Mo-Fe alloys, have been developed by Northwest Institute of non-ferrous metals, low-cost Fe-Mo master alloy was added to replace V and Zr in Ti-6Al-4V alloy, and pure titanium scrap (such as titanium scrap) was added in smelting process to reduce the amount of sponge titanium, the raw material cost can be reduced by more than 10% , and the preparation cost of small size bar can be reduced by about 30% . After solution and aging treatment, the two alloys have good strength, plasticity and fatigue strength. The tensile strength at room temperature can reach more than 1100MPA, and the strength and plasticity are higher than those of Ti-6Al-4V alloy in GB/T2965, tI12LC alloy has higher strength and plastic matching, strength up to 1200MPA, plastic up to 20% , better than Timetal 62S and Timetal LCB alloy. TI8LC and TI12LC can be used to make automobile inlet and exhaust valves, bicycle Torque Lever, etc. . TI12LC can also be used to make tail nozzle of aerospace solid rocket motor. 1.71.7ti-5322 alloy Ti-5322 is a Ti-Fe-V-Cr-Al system α + β two-phase Titanium Alloy developed by Northwest Institute of non-ferrous Metals for non-aeronautical applications. The cost of the alloy is lower than that of the Ti-6Al-4V alloy when 2% Fe is added instead of V, and the strength and toughness of the alloy after heat treatment match well. The strength of the alloy reaches 1100ー1300mpa at room temperature, the elongation is 7% ~ 14% . At present, the alloy has been applied to the development of tank armor, and its ballistic performance is better than that of TC4 alloy.

1.71.81.81.8ti-35421 alloy Ti-35421 is a new type of high strength titanium alloy developed by the Nanjing University of Technology to meet the requirements of high strength, impact resistance, corrosion resistance and weldability of titanium alloys for marine engineering, the tensile strength is 1313MPA, the yield strength is 1240mpa, the elongation is 8.62% , the section shrinkage is 17.58% , the fracture toughness KIC is 75.8MPA m1/2, the stress corrosion sensitivity is small in 3.5% NACL solution, and the corrosion resistance is good. This alloy consummates the domestic 1000mpa strength grade marine low cost titanium alloy material system, has the vital significance to the equipment in the design and the construction process selection. 2. Low-cost melting technology of titanium alloy low-cost control in melting process of titanium alloy is mainly considered from two aspects. One is to increase the application of residual titanium, instead of titanium sponge. Residual titanium mainly refers to the riser, scrap and scrap produced in the process of melting and machining. The discarded castings produced in the process of melting, testing and machining also belong to residual titanium, and the amount of residual titanium is large, the primary residual titanium can reach 30% ~ 50% , and the secondary residual titanium can reach 20% ~ 80% . The cost of titanium products can be greatly reduced by fully utilizing the residual titanium. Second, improve smelting efficiency and smelting quality, melting, refining integrated control. Low density oxide inclusions and high density TiW inclusions are easily introduced in the process of electrode preparation by Argon Arc welding, which is the most widely used vacuum consumable arc melting technology in China, at the same time, because of the poor composition uniformity in melting process, 2 ~ 3 remelting times are needed to reduce the production efficiency. At present, the Melting technologies that can realize the integrated control of Melting and refining and the recovery of residual titanium mainly include Cold Hearth Melting (CHR) and Cold Crucible Induction Melting (CCIM) .

2.1 Cold bed furnace smelting technology Cold bed furnace smelting technology mainly includes Electron Beam Cold Hearth Melting (EBCHR) and Plasma Cold Hearth Melting (Pachm) . Electron Beam cold-bed melting is the melting, refining and remelting of metals by using the concentrated and controllable stable electron beam emitted by electron gun as a heat source, the vacuum electron beam is replaced by a stabilized plasma arc fired by a plasma gun, which is used as a heating source to melt and refine metals. The melting process of the cold bed furnace is divided into three zones: raw material melting zone, refining zone and solidification zone. In turn, the residual titanium scrap on the transfer equipment is heated and melted by the heating source in the melting zone, and the molten titanium liquid flows into the refining zone to be refined. The cold bed furnace melting technology has the following characteristics: 1 The high density and low density inclusions can be eliminated well in the melting process, and the ingot or casting with fine grain and uniform structure can be obtained. In the refining zone, the high-density inclusions fall into the low-temperature Shell zone due to gravity. After being removed by deposition, the low-density inclusions float to the surface of the molten pool and are melted away by high temperature heating, the intermediate density inclusions are melted and removed gradually by continuous heating in the complex flow field during the flow process in the cold bed. 2 The low requirement of the raw material state does not require the preparation of electrodes, and the 100% recycled titanium residue can be used as raw material, compared with vacuum consumable arc melting, vacuum consumable arc melting can improve melting efficiency greatly, has good composition uniformity, and can save 20% ~ 40% of processing cost

2.2 Cold Crucible Induction Melting (CCIM) is a special Melting method by Induction heating combined with split water-cooled copper Crucible, a split water-cooled crucible is placed in an alternating electromagnetic field, and the eddy current hot melting metal is produced by the electromagnetic field. As a result, a layer of solidified shell is formed at the bottom of the crucible when the metal is melted by this method, also known as Induction Skull Melting (ISM) . The most important feature of this method is that the side wall of the water-cooled crucible is divided into more than 20 lobes. Under the alternating magnetic field, the gap between two adjacent crucible lobes will produce the magnetic field enhancement effect, and strong agitation will be caused by the magnetic compression effect, the alloy composition and melt temperature are balanced to realize the uniform melting of refractory metals. At the same time, the magnetic field produced by the induced current of the side lobes of the crucible and the induced current on the surface of the material produce the electromagnetic repulsion force, which makes the material and the side wall of the crucible keep soft contact or non-contact state. The technology can be used to melt titanium alloy scrap continuously without using Refractory as crucible or welding electrode, so the theoretical utilization rate of titanium remains is 100% , high Quality Titanium and titanium alloy ingots can be obtained without pollution. CCIM equipment has been developed in the United States, Germany, Russia, France and other countries for several decades. At present, the melting capacity of the equipment has exceeded 200 kg (in titanium terms) , the diameter of the crucible has reached over 500 mm, and the melting temperature has reached over 3000 °C, foreign major equipment manufacturers including the United States CONSARC company, the United States RETECH company, Germany ALD company, and has been commercialized applications, the domestic development of the equipment is mostly less than 50 kg capacity.

In recent years, the cold crucible induction melting technology has been gradually combined with other material preparation technologies, such as the cold crucible electromagnetic continuous casting technology, the cold crucible directional solidification technology and the spray deposition technology using the cold crucible as an auxiliary device. The biggest problem of induction melting with cold crucible is that the solidified Shell is thick, because the bottom of the crucible is connected with the whole structure, although the strength of the crucible is ensured, however, the melt contacts with the crucible at the bottom of the crucible and causes a large heat loss. The solidified Shell is often more than 1/3 of the total volume, which greatly reduces the melting efficiency and melting uniformity, especially, it is difficult for alloying of many elements and melting of high melting point materials. The Cold Crucible Levitation Melting (CCLM) technique increases the electromagnetic repulsion force of the bottom of the melt, cancels the connected structure of the bottom of the Crucible, and adopts the cone-shaped bottom Crucible which is completely separated from the bottom of the Crucible, at the same time, changing the structure of the external coil, increasing the frequency of the electromagnetic field, the number of slits and the power input, the semi-suspension or full-suspension of the melt is realized. Compared with cold crucible induction melting, the melting process has better overall stirring effect and composition uniformity, is more suitable for the preparation of high active metals, multi-component alloys and refractory metals, and has high material utilization ratio, the high purity of the leftover material can reduce the preparation cost of the material to a greater extent

3. Low-cost casting technology of titanium alloy the casting technology of titanium alloy itself is a production technology to improve the utilization ratio of titanium alloy materials and control the production cost. Based on experience, the production cost of titanium alloy investment casting process is estimated to be more than 20% as shown in Fig. 3. In recent years, in order to meet the development needs of large-scale complex thin-walled titanium alloy investment casting, the precision casting technology such as graphite mold, metal mold and ceramic mold has been continuously improved and developed, it also provides the development foundation and space for the progress of low-cost and high-efficiency titanium alloy casting technology.

3.1 the moulding materials for titanium and titanium alloy casting in graphite mould process must have good high temperature stability. Graphite is one of the earliest and most stable moulding materials. At present, the most widely used graphite molding method is machining graphite molding process, which has the advantages of simple operation and high internal quality of castings. But since 2017, the price of graphite electrode has soared, and the production cost of titanium alloy casting has risen sharply. The problems mentioned above can be effectively overcome by ramming or pressing graphite sand casting, in which graphite powder is used to prepare graphite mold by a method similar to sand mold casting. Zhu Guang used the residual graphite powder from the mechanical processing of the graphite mould as the Refractory, and used the mixture of Phenol formaldehyde resin and anhydrous ethanol as the binder to prepare the graphite mould by ramming, the Titanium Alloy Globe Valve and centrifugal pump castings were poured. The surface of the castings was free of sand, cold insulation and cracks. The thickness of the surface contamination layer was about 0.1 mm. The mechanical properties and chemical composition of the castings met the requirements of relevant national standards. The military torpedo ejection pump, large sea water pump, ball valve, butterfly valve and other products have been prepared by this process abroad. Compared with the machine-added graphite type, the tamped graphite type has good permeability and concession, can save 30% ~ 40% of graphite material, and the graphite fragment can be used again after being crushed, which greatly reduces the production cost.

3.2 ceramic casting process currently, the most widely used ceramic casting process for titanium alloy in investment casting is the inert oxide process represented by yttrium oxide, such as PCC corporation of the United States, Howmet Corporation of the United States and TITAL corporation of Germany, in China, such as Shenyang Foundry Research Institute Co. , Ltd. , Beijing Institute of Aeronautical Materials, Guizhou Anji foundry, etc. , yttrium oxide is widely used as a surface-layer shell material, although the cost of the inert oxide coating process is significantly lower than that of the tungsten coating process, the price of the yttrium oxide is still more than 30 times higher than that of other conventional Refractory, for the titanium alloy investment castings produced with inert oxide surface materials, the cost of molding materials accounts for more than 30% of the casting cost, and the high cost of molding materials has become an important factor restricting the rapid development of titanium investment casting technology, the replacement of yttrium oxide with cheap Refractory oxide has become an important research direction. Al2O3 as Refractory has been widely used in investment casting. Ordinary Al2O3 needs to be calcined at high temperature or fused to form stable corundum powder. However, when the surface layer is made of corundum powder and conventional binder, the quality of cast titanium alloy is poor. Die Application.

4. Titanium alloy short process preparation forming technology the traditional ingot metallurgy process preparation titanium alloy technology route is: Sponge titanium-multi-times vacuum melting-casting blank-multi-times modified forging-forging blank-forming-deep processing-titanium finished products, the production cost is increased greatly because of the complicated and complicated procedure in the preparation process. Therefore, the development of titanium alloy short-flow preparation technology can effectively reduce the cost and improve the efficiency.

4.1 continuous casting and continuous rolling (CC + HDR) technology has been widely used in the production of steel and aluminum plates. It connects melting, solidification and deformation, and realizes the integrated control of structure-performance-shape, it has significant effect on reducing production energy consumption, improving production efficiency and finished product rate, and improving product uniformity. Ti-15-3, Ti-6242, Ti-10-2-3 and Niti have been studied by the basic process test of continuous casting and rolling. The results show that Ti has good hot plasticity and low thermal strength at above 1200K, the high-temperature workability is better than that of steel. The titanium alloy sheet can be prepared by traditional continuous casting and rolling process as long as the bending deformation does not occur above the temperature t β. The continuous casting and rolling technology based on electron beam cold bed melting was developed by the US Army, and the application of Ti-6Al-4V alloy was verified. It was found that only c content in the prepared plate was slightly higher than that of conventional melting process, and the remaining components were basically similar, the mechanical properties of the three thickness plates (24.6 mm, 38.2 mm and 63.6 mm) tested are all higher than Mil-t-9046j military standard, and have excellent anti-ballistic performance, which fully meet the requirements of tank armor. Chang Hui and his colleagues at the Nanjing University of Technology have carried out continuous casting and rolling of titanium alloy to produce 30 mm diameter billets and 10 mm diameter bars. Further research is being carried out on this technology.

4.2 powder near-net forming is a method of powder forming by injection, extrusion, hot isostatic pressing, cold pressing and laser additive manufacturing, the technology, which can realize the final forming of products with little or no processing, has the advantages of high utilization ratio of raw materials and simple technological process. The near-net-shape forming technology of titanium alloy powder, which solves the melting problem of titanium alloy and avoids the ingot preparation and forging process, is the most rapid development technology of titanium alloy in recent years. Generally, the material utilization rate of forgings is only 10% ~ 15% , that of castings is 45% ~ 60% , and that of powder near net forming is almost 100% , which greatly improves the material utilization rate. Table 2 compares the advantages and disadvantages of the common powder near-net shape forming technology. In view of these technologies, researchers at home and abroad are constantly improving and optimizing the technology. Table 2 advantages and disadvantages of titanium and titanium alloy powder forming technology

At present, the near-net-shape parts of titanium alloy powder have not been used to replace forgings and castings on a large scale except in high-end equipments such as aeronautics and Astronautics, on the one hand, because the internal quality and mechanical properties of the products have not yet been fully recognized by the industry, on the other hand, because of the high cost, the main factor affecting its cost is the high preparation technology and forming technology of high-performance titanium powder. At present, high-quality titanium powders are mainly prepared by means of gas atomization and rotating electrode, which are spherical or nearly spherical in shape, but the sintering property of spherical powders is poor. high-density titanium alloy components can only be obtained by pressure sintering or laser sintering, the cost of producing the Powder metallurgy has been greatly increased. The preparation process of titanium powder with irregular shape by hydrogenating-crushing-dehydrogenation of sponge titanium is simple, low cost and easy to produce on a large scale, liquidity and Poisson’s ratio are relatively poor. Guo Zhimeng and others developed the preparation technology of ultra-fine low-oxygen HDH titanium powder, and realized the low-cost compaction of the powder by cold isostatic pressing and vacuum sintering technology, the relative density of TC4 with different sizes ≥99% was obtained by vacuum sintering.

5. Prospect (1) the research of low-cost titanium alloys at home and abroad is mainly focused on using cheap Fe, O, N and other elements to replace the precious metals in the alloys, but the comprehensive properties of the materials are thus limited, it is difficult to meet the needs of the increasingly developing aerospace high-end titanium alloy equipment, especially in the anti-fatigue strength, high damage tolerance performance there are still problems, so, further research on high-end, high-performance and low-cost titanium alloy materials is needed to expand its application in aerospace high-end products. (2) the recovery rate of titanium alloy scrap is still low, the recovery method is single, the surface pollution layer is serious, the impurity content is high, the control of composition is difficult, the composition uniformity is poor, so more systematic and in-depth research on relevant melting process is needed, a complete set of Operability titanium scrap recycling process method, the establishment of a complete titanium alloy scrap recycling processing line. (3) developing large-capacity induction suspension melting technology. At present, the induction levitation melting technology of titanium alloy at home and abroad is limited by the technical capacity of the equipment, and the melting quantity is too small to meet the practical needs of engineering, so it is necessary to develop new high-capacity induction levitation melting technology, high Clean Recovery and precision forming of large capacity titanium alloy. (4) to develop stable low-cost preparation technology of ceramic mold shell. At present, low-cost ceramic mold shell materials such as Al2O3 and CAZRO3 are still in the laboratory research stage, and have not been used in the investment casting of titanium alloys in large quantities, the preparation of high inertia, high density and high stability surface-layer Shell with complex structure is realized to meet the actual production requirement. 

Source: Titanium Net

Disclaimer: Some pictures and texts on this site are collected from the Internet and are only for learning and communication. The copyright belongs to the original author and does not represent the views of our site. This site will not bear any legal responsibility. If your rights are violated, please contact us to delete it in time.