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Research and advances in processing, working, microstructure, properties and industrial application of β-solidifying TiAl alloy

Chen Yuyong, Wu Jingxi

2021, 42(6): 1-16. doi: 10.7513/j.issn.1004-7638.2021.06.001

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Abstract:
The third generation TiAl based intermetallic compounds (β-solidifying TiAl alloy) have a wide application in aerospace, automobile manufacturing and other advanced fields due to their excellent hot workability. However, the introduction of high temperature β phase not only improves the hot deformation capacity of the alloy, but also makes the microstructure evolution and performance optimization more complex. Meanwhile, the development of industrialization is relatively slow because of the influence of alloy composition and poor intrinsic brittleness. This paper provides an overview of the processing and working technologies, progress of microstructure, properties and the current industrialization situation of the typical β-solidifying TiAl alloy. The technology and cost advantages of processing and working were analyzed. The effect mechanisms of alloy composition, hot deformation, heat treatment and alloying on microstructure evolution and property optimization were clarified, and the restrictions and future prospects of industrialization were pointed out.

Current research status of advanced forming technology for high-performance titanium alloys

Li Junzhao, Sun Qingjie, Yu Hang

2021, 42(6): 17-27. doi: 10.7513/j.issn.1004-7638.2021.06.002

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Abstract:
In this paper, characteristics of advanced hot forming technology, pulse current assisted forming technology and electromagnetic assisted forming technology, and progress of these technologies application in titanium alloy thin-wall sheet forming had been reviewed. Hot forming is the most widely used forming process in the plastic processing of titanium alloy. The forming of complex titanium alloy parts can be realized by taking advantage of plastic deformation softening of titanium alloy at high temperature. Pulse current and electromagnetic assisted forming technology have not been widely used in industry, but they present potential application prospects in the forming of high strength and hard-deformation materials.

Development of gas element diffusion wear-resistant treatment technology on titanium surface

Li Zhengxian, Zhang Xuefeng, Chen Min, Li Wei, Luo Xiaofeng

2021, 42(6): 28-35. doi: 10.7513/j.issn.1004-7638.2021.06.003

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Abstract:
In this paper, the resent research progress of gas element diffusion wear treatment technology on surface of titanium and titanium alloy is summarized.It is believed that treatment technology of oxidizing, nitriding and carburizing on the surface of titanium alloy, can improve its surface hardness and wear resistance .In addition, the combination of vacuum and plasma technologies can increase the thickness of the diffusion layer, but appropriate parameters need to be selected in combination with the process, otherwise it will have a greater impact on the mechanical properties of the material.Furthermore, because the wear-resistant environment is diverse, the wear-resistant layer is difficult to adapt to all friction environments. Modern development has made the service environment of materials more complex . It requires not only wear resistance, but also corrosion resistance, electrical conductivity and other functional requirements. In this way, the material surface designer is required to design and innovate on the basis of the existing surface technology based on the harsh conditions of service and the interaction of multiple fields.

Research progress on wear resistance of titanium matrix composites

Zhong Liang, Fu Yu, Xu Yongdong, Song Yunkun, Wang Yinyang

2021, 42(6): 36-42. doi: 10.7513/j.issn.1004-7638.2021.06.004

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Abstract:
Titanium alloys are widely used because of their excellent comprehensive properties such as high specific strength, high specific modulus, corrosion resistance, low temperature resistance, and non-magnetism. However, compared with traditional steel materials, titanium alloys have limitations such as low elastic modulus, insufficient heat resistance and poor wear resistance, which hinder their promotion and application in the aerospace, weapon and other industries. Compared with titanium alloys, titanium matrix composites can combine the advantages of high-strength plasticity of the matrix titanium alloy and the high modulus and high wear resistance of the reinforcement. Titanium matrix composites have higher elastic modulus, wear resistance and high-temperature performance than titanium alloys. It meets the requirements of extreme working conditions such as high load, impact resistance, high wear resistance and high temperature oxidation resistance. Starting from the development history of titanium matrix composites, this paper summarized the research progress on wear resistance of titanium matrix composites, and the characterization methods of wear resistance, friction and wear behaviors of titanium matrix composites were also introduced. The good wear resistance mechanism of titanium matrix composites, the design of high wear-resistance titanium matrix composites and wear resistant surface modification technology were also described.

Progress of anti-oxidation protection technology in titanium alloy welding process

Fan Limin, Geng Naitao, Yang Liu, Wu Shaojie, Cheng Fangjie

2021, 42(6): 43-50. doi: 10.7513/j.issn.1004-7638.2021.06.005

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Abstract:
Titanium and titanium alloys have excellent comprehensive properties, but the welding oxidation problem is serious due to the strong high-temperature activity. Especially the problem of absorbing gas at solid-state temperature is significant, which affects the quality of the welding joint. Therefore, strict welding protection measures are needed. Based on the analyses of oxidation mechanism and characteristics of titanium alloy, various anti-oxidation protection measures and specific technologies in welding process are summarized systematically in this paper. Anti-oxidation protection of titanium alloy in four typical processes of long straight weld, circular weld, space irregular weld and additive manufacturing is introduced in detail. The main protective measures include welding gas shielding trailing, closed argon-filled environment and forced cooling. For local gas protection of long straight weld of titanium alloy, the general form is welding gas shielding trailing combined with back protective gas groove and water cooling measures. For the back protection of the circular weld, the back gas shielding or the whole argon filled protection method can be adopted, and the front protection can use the welding gas shielding trailing. However, due to the limitation of the shape of the irregular weld, the method of welding gas shielding trailing is no longer applicable. The simple argon-filled protective box can be used for small size components, while the protection problem of large size components needs to be solved urgently. The heat accumulation in the additive manufacturing process also increases requirements for its protection form. At present, good results have been achieved by the laminar inert gas and followed by forced CO₂ cooling process.

Study on separation of titanium and slag during carbonization of titanium-bearing blast furnace slag

Jian Tingfang, Zhao Lang, Luo Xiangyu, Hu Meilong

2021, 42(6): 51-58. doi: 10.7513/j.issn.1004-7638.2021.06.006

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Abstract:
The technology of high-temperature carbonization and low-temperature chlorination has been successfully developed by Pangang Group Company Limited to recover titanium from a large number of Ti-containing blast furnace slag produced during the application of the BF ironmaking technology to V-bearing titanomagnetite. However, It is also necessary to explore green and economic treatment methods because there are some challenges for this technology, such as grinding of carbide slag and utilization of chlorinated tailings. In view of the dispersion distribution of Ti(C,N) particles in high-temperature carbonization process, the idea of enrichment of Ti(C,N) by adding iron in carbonization process is proposed in this paper, and the effects of factors such as the mass ratio of iron to slag, the batches of adding iron, the holding time for enriching Ti(C,N) and the pre-adding content of iron on the enrichment process were investigated by experiment. The result shows that Ti(C,N) particles in the molten slag can aggregate on the surface of the molten iron which later sinks to the bottom of the crucible, and the lump iron coated by Ti(C,N) can be naturally separated from the residue by water quenching. With a specific iron-slag mass ratio of 1.50, iron added in two steps, i.e. 15%Fe is prepared in the slag and the rest of iron is added in batches within 30 min after holding at 1 600 ℃ for 30 min, shows good enriching effect. The Ti-content in the slag under this enrichment condition can be reduced from 13.79% to 4.59%, the enrichment rate of Ti(C,N) in carbonized slag can reach to 66.72%.

Study on the effect of molten salt electro-deoxidation on the preparation of titanium metal

Xin Xuesong, Zhang Qiang, Zhang Shanshan, Zhang Min

2021, 42(6): 59-65. doi: 10.7513/j.issn.1004-7638.2021.06.007

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Abstract:
Titanium metal was prepared by electrolysis of high titanium slag in CaCl₂ molten salt under a high-purity argon atmosphere. The relationship between forming pressure and porosity of cathode sheet as well as the influence on the electrolysis process were studied. The phases and microstructures of the cathode sheet and that after electrolysis were characterized by XRD and SEM. The results showed that the forming pressure had a direct influence on the porosity of the cathode sheet, which decreased with the increase of the forming pressure. The porosity of the cathode sheet directly affected the electrode deoxidation process, and an appropriate porosity was beneficial to the formation of intermediate product CaTiO₃ and the increase of the electroreduction rate. The porosity of the cathode pressed by 4 MPa is 34.79% when sintered at 1 050 ℃ for 2 h, and the oxygen content of the product is reduced to 1.75% and titanium content is 95.72% when electrolyzed for 12 h, which shows a better electrochemical performance of the cathode sheet.

Influence of solution treatment on microstructure and mechanical properties of Ti6Al4V ELI titanium alloy

Ran Xing, Wang Zhe, Li Haibin, Lv Zhigang, Li Peijie

2021, 42(6): 66-71. doi: 10.7513/j.issn.1004-7638.2021.06.008

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Abstract:
The scanning electron microscope (SEM) and optical microscope (OM) were employed to investigate the influence of solution treatment on microstructure evolution of Ti6Al4V ELI titanium alloy, and the relationship between microstructure and mechanical properties were discussed. The results show that the content of the primary α_p phase of Ti6Al4V ELI titanium alloy decreases, and the thickness of lamellar α phase and β grain size increase with the increase of solution treatment temperature. The strength and plasticity of Ti6Al4V ELI titanium alloy decrease with the increase of solution temperature. When the solution treatment is 952 ℃, the tensile strength, elongation and fracture toughness values of Ti6Al4V ELI titanium alloy are 915 MPa, 16.8% and 84 MPa·m^1/2, respectively. At the solution treatment up to 997℃, the tensile strength and elongation values decrease to 861 MPa and 9.4%, respectively, but the fracture toughness increases to 115 MPa·m^1/2. It shows a ductile fracture with solution treatment at 952 ℃ while ductile-brittle mixed fracture as the temperature increases.

High temperature compression properties of near α type Ti-1100 alloy prepared by titanium hydride based powder metallurgy

Piao Rongxun, Zhu Wenjin, Lv Shunshun

2021, 42(6): 72-77. doi: 10.7513/j.issn.1004-7638.2021.06.009

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Abstract:
The isothermal compression experiments were carried out on high temperature titanium alloy Ti-1100 prepared by powder metallurgy using titanium hydride powder as raw material. The compression deformation behavior was analyzed through the obtained stress-strain curve of compressed samples, and then the thermal compression constitutive equation was established by using Arrhenius hyperbolic sinusoidal constitutive model. Through the analysis of the stress-strain curve, it is found out that when the strain rate is 0.01 s^?1, all samples show steady-state rheological behavior. When the strain rate is 1 s^?1 and the temperature is 900 ℃ or 1 000 ℃, the flow stress increases with deformation after steady-state rheological state. The activation energy of thermal compression deformation for strain rate at 0.01, 0.1 s^?1 and 1 s^?1 are 96, 165 kJ/mol and 232 kJ/mol, respectively. The hardness test results show that microhardness decreases slightly with increase of temperature and strain rate. When the temperature is 950 ℃ and the strain rate is 0.1 s^?1, the hardness of the alloy is generally small and the best hot workability can be achieved.

Effect of hot deformation parameters on the rheological behavior of two-phase region of titanium alloy

Fu Wen, Zhou Xiaofeng, Li Chengning, Cheng Fangjie, Wang Dongpo

2021, 42(6): 78-83. doi: 10.7513/j.issn.1004-7638.2021.06.010

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Abstract:
Hot-rolled Ti80 alloy was used as the substrate, and the high temperature compression test was carried out on the Gleeble-3500 thermal simulation tester. The deformation temperature was 800～1 000 ℃, the strain rate was 0.01～10 s^?1, and the total deformation ratio was 75%. The results show that the phase of Ti80 titanium alloy was in the α+β two-phase region at 800～950 ℃, and its rheological behavior was significantly affected by the deformation temperature and strain rate. The work hardening of Ti80 titanium alloy mainly came from the increase of the dislocation density in the initial α phase. The increase of the deformation temperature led to the decrease of the α phase, and the rheological peak stress continued to decrease. And the excessively high strain rate restrained the movement of the dislocations in the α phase. The initial α phase in Ti80 titanium alloy was more prone to dynamic recovery and dynamic recrystallization. As the deformation temperature increased, the initial α phase continued to decrease, and the dynamic softening degree gradually decreased until it approached zero. In order to ensure the stability of the hot rolling of the titanium tube, the deformation temperature should be appropriately increased for obtaining a higher β phase volume fraction of the hot deformed structure in the Ti80 titanium alloy, and avoiding the excessive rolling load caused by the excessively high strain rate.

Preparation and properties of porous Ti-Nb alloy materials

Zhang Meili, Chi Xiaotong, Zhou Chunsheng, Liu Yanfeng, Fang Chen, Zheng Guogang

2021, 42(6): 84-89. doi: 10.7513/j.issn.1004-7638.2021.06.011

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Abstract:
The porous Ti-Nb alloy was prepared by adding pore-forming agent in powder metallurgy. The effects of Nb content on the phase structure, pore morphology, porosity, compressive strength and corrosion resistance of the alloy were investigated. The results show that the porous Ti-Nb alloy has α and β phase structure. With the increase of Nb content, the content of β phase in the material increases gradually. When the content of Nb is 25% ~ 30%, the pore size and distribution of the material are more uniform, and the average pore size is about 300 μm. With the increase of Nb content, the porosity of the material increases, while the radial shrinkage rate and the compressive strength gradually decrease, and the corrosion resistance increases first and then decreases. When the Nb content is 30%, the corrosion resistance of the material is the strongest, with the porosity of 33.6%, the radial shrinkage rate of 7.3% and the compressive strength of 130 MPa.

Effects of raw powder on NiTi parts fabricated by selective laser melting

Zhang Yawei, Shi Qi, Tan Chong, Liu Xin, Li Guifa, Zheng Haizhong

2021, 42(6): 90-96. doi: 10.7513/j.issn.1004-7638.2021.06.012

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Abstract:
In this study, Ni + Ti mixed powder and NiTi pre-alloyed powder were used to print by selective laser melting process. The effects of raw material powder on the density, phase composition, microstructure and microhardness of formed parts under the identical processing parameters are studied, so as to feedback the effects of raw powder on the properties of formed parts. The results showed that under the identical processing parameters, the density of the formed parts fabricated by NiTi pre-alloyed powder was higher, while the microhardness of Ni + Ti mixed powder formed parts was higher. For the same powder, with increase of energy density, density of the formed parts first increased and then decreased, while microhardness first decreased and then increased. NiTi pre-alloyed powder formed parts had dense microstructure and uniform phase distribution, but there presented several pores. The microstructure of Ni + Ti mixed powder formed parts has through cracks perpendicular to the construction direction and uneven matrix phase, but there are almost no pores in the structure.

Microstructure and mechanical properties of TC4-DT produced by laser wire-feed additive manufacturing

Zhang Dayue, Liu Xuming, Zhang Jian, Li Binzhou, Zhao Yang, Wang Junsheng

2021, 42(6): 97-101. doi: 10.7513/j.issn.1004-7638.2021.06.013

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Abstract:
Laser wire-feed metal additive manufacturing technology has a wide application prospect in aerospace, marine engineering and shipbuilding. In this paper, TC4-DT samples were prepared by the laser wire-feed additive manufacturing technology combined with solution strengthening heat treatment method, based on the initial optimized process parameters. The microstructure, defects and room temperature tensile mechanical properties of the samples at as-deposited state and heat-treated state were respectively studied. It is found that the morphology of as-deposited TC4-DT is composed of columnar grains and acicular α? martensite. After solution strengthening heat treatment, equiaxed and columnar dual phase structure is formed, and α? martensite is decomposed into acicular structure of α+β. The tensile mechanical properties after heat treatment are equivalent to those of forgings.

Research on heat treatment properties of TC4 titanium alloy based on electron beam additive manufacturing

Huang Xingguang, Sun Baofu, Sun Guohui, Zhang Jianfei

2021, 42(6): 102-108. doi: 10.7513/j.issn.1004-7638.2021.06.014

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Abstract:
In this paper, heat treatment was carried out for TC4 titanium alloy specimens prepared by electron beam selective melting. The microstructure characteristics of the TC4 titanium alloy specimens after heat treatment were studied by using scanning electron microscope and metallographic microscope. The mechanical properties of the TC4 titanium alloy specimens were investigated. The influence of heat treatment process on the specimen was revealed. The results show that the tensile strength of the specimens increased via heat treatment below phase transition temperature with the air cooling or furnace cooling, while the tensile strength of the specimens decreased by heat treatment at temperatures higher than the phase transition point. By observing the microstructure and analyzing the tensile fracture, it is found that the tensile strength of TC4 titanium alloy specimens decreased via heat treatment at 950 ℃ and 1 000 ℃, due to the transformation of β phase into Widmanstatten structure. However, at 850 ℃ of heat treatment temperature, the properties of the TC4 titanium alloy specimens were stable, because the microstructure inside was still equiaxed before reaching the phase transition point. Those results suggest the TC4 titanium alloy manufactured by EBSM have good mechanical properties by an appropriate heat treatment process.

Effect of hot-pressing temperature on element diffusion behavior and microstructure of TC4/Ta layered composites

Yu Hao, Jiang Qingwei, Zhang Xiaoqing, Zhang Shoujian, Zhang Fengzhen

2021, 42(6): 109-114. doi: 10.7513/j.issn.1004-7638.2021.06.015

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Abstract:
TC4/Ta/TC4 layered metal composites (LMCs) were prepared by hot-pressing at different temperatures, and the diffusion behavior of interfacial elements and the microstructure at different temperatures were discussed. The results show that obvious diffusion behavior occurs at the interface during the process of hot-pressing and holding, and the two groups achieve good metallurgical bonding. High temperature hot-pressing promotes the diffusion of Al, V, Ti and Ta, and the degree of diffusion significantly affects the microstructure near the interface. The diffusion depth of each element is closely related to the atomic radius. As the atomic radius decreases, the diffusion behavior occurs more intensely. The element diffusion behavior leads to the decrease in the phase transition temperature of the titanium matrix near the interface, and the basketweave structure appears at 950 ℃ below the phase transition temperature of TC4. The microstructure changes with the change of the interface distance.

Controllable preparation of titanium dioxide nanotubes on titanium foil

Fan Xingping, Ma Lan, Yang Cheng, Fan Wei

2021, 42(6): 115-119. doi: 10.7513/j.issn.1004-7638.2021.06.016

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Abstract:
Titanium dioxide nanotubes were prepared on the surface of titanium foil by electrochemical anodization. The diameter and wall size of the nanotubes were controlled by adjusting the anodizing voltage and time. The morphology of TiO₂ nanotube arrays was observed by scanning electron microscope (SEM) under different preparation conditions. The effects of anodizing voltage and time on the morphology of TiO₂ nanotube arrays were investigated. The crystal of TiO₂ nanotubes was adjusted by heat treatment and characterized by X-ray diffraction (XRD). The results showed that the orderly TiO₂ nanotubes were obtained at 40 V for 30 min in glycol aqueous solution containing 0.5% ammonium fluoride as electrolyte. After heat treatment at 450 ℃ for 2 h, the crystal of TiO₂ nanotubes has changed from amorphous into anatase, and a small part of the nanotubes collapsed.

Preparation and anti-corrosion properties of photoresponsive titanium based nano-films

Li Wenjing, Peng Sui, Xin Yanan, Tang Min

2021, 42(6): 120-132. doi: 10.7513/j.issn.1004-7638.2021.06.017

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Abstract:
Based on the research background and advantages of enterprise production, cheap and easily available titanium sources (such as TiOSO₄) were used as raw materials to prepare one or more nano-titanium-based films on the substrate surface by sol-gel method with simple reaction and convenient operation. The corrosion resistance of substrate after coating was studied under ultraviolet light and dark state conditions, with the intention of greatly improving the corrosion resistance of the substrate through the coating. The preparation process of hydrosol was optimized by selecting titanium source, precipitant, titanium concentration of hydrosol, proportion of complexing agent and reaction temperature. At the same time, the viscosity and temperature characteristics of hydrosol at different concentrations were studied, and the size and morphology of the particles were observed by the sol-gel method. The particle size of the sol was less than 50 nm. In the later stage, the films with different layers were prepared on the substrate surface by uniform pulling method, the nano titanium based films were obtained by corresponding heat treatment, and the morphology of the nano films was studied. Finally, the substrate was made into an electrode and immersed in a 3.5% sodium chloride solution to test its anti-corrosion performance. The particle size on the surface of the nano-film was less than 50 nm, and the thickness of the five layers of film was 1 μm. The results show that the corrosion resistance of the substrate can be improved by anti-corrosive film on the substrate surface. The protection efficiency is up to 99.73% and 99.14% respectively in dark state and under ultraviolet light, compared with that of the substrate. Meanwhile, through the analysis of the open circuit potential of the substrate under dark state and ultraviolet light, the negative shift of the open circuit potential of the substrate under ultraviolet light is different from that of the dark state, which shows the light response of the film.

Research on corrosion of TC4 titanium alloy in concentrated high-salt wastewater environment

Han Xu, Li Qiang, Jiang Xunyong, Xu Ke

2021, 42(6): 133-137. doi: 10.7513/j.issn.1004-7638.2021.06.018

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Abstract:
In this paper, the corrosion resistance of TC4 material was studied by simulating the concentrated solution of high salt wastewater from the perspective of mechanical vapor recompression (MVR) corrosion environment. The corrosion tests were carried out through microstructure characterization, corrosion weight loss, crevice corrosion, electrochemical test (open circuit, electrochemical impedance and potentiodynamic polarization curve test). The properties of TC4 alloy were confirmed (α+β) biphase titanium alloy has strong resistance to crevice corrosion in various high chloride ion environments. There is no local pitting corrosion in 14 day full immersion test, and the maximum corrosion rate is only 1 mg/(cm²·a). The results of electrochemical test also show that the inert passivation layer formed on the surface of TC4 titanium alloy in high chloride ion solution is generated rapidly and remains stable, which also plays an obvious role in inhibiting material surface corrosion and crevice corrosion. TC4 alloy has high temperature corrosion resistance and is suitable for high-salt wastewater environment. For MVR technology, it has potential application value in the treatment of industrial wastewater with high chlorine content.

Preparation of Ti60 high temperature titanium alloy ingot for aerospace

Guo Jie, Yue Ke, Hu Zhaohua, Zhang Tianxin, Geng Naitao

2021, 42(6): 138-141. doi: 10.7513/j.issn.1004-7638.2021.06.019

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Abstract:
Aiming at the key technology of Ti60 high temperature titanium alloy preparation by smelting process, 0A grade military granulated sponge titanium and appropriate master alloy were selected to prepare Φ310 mm large Ti60 high temperature titanium alloy ingot, via vacuum consumable arc furnace smelting. The prepared ingot has a well surface quality without defects such as cold isolation and missing edge. The alloy elements are evenly distributed in the ingot, and the impurities content and distribution are well controlled. The effects of the mixing mode of high melting point elements such as Nb, Ta, Mo and low melting point elements such as Sn, melting current and voltage on composition uniformity and defect control of the alloy ingot were systematically studied. The forgings made from the ingot through subsequent processes have met the industrial and technical requirements through mechanical properties test and ultrasonic flaw detection.

Effect of oxygen content on microstructure and mechanical properties of TC4 ELI titanium alloy bar

Ma Lan, Yang Shaoli, Li Junhan, Zou Xinyi, Wan Xin

2021, 42(6): 142-146. doi: 10.7513/j.issn.1004-7638.2021.06.020

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Abstract:
By using two self-prepared TC4 alloy ingots with different oxygen content, the high-performance TC4 ELI titanium alloy bars are prepared by the processes of cogging-forging-annealing for interstitial impurities well below GB/T 13810—2017 and UNS R56401 requirements. The properties are investigated via chemical analysis, metallurgical microscopy, tensile tests and scanning electron microscopy (SEM). The results show that after process of blooming-forging-annealing, the contents of interstitial elements such as oxygen, nitrogen and hydrogen in titanium alloy bar are significantly lower than these in ingot, and the oxygen contents for two kinds of bar are less than 0.07%. The mechanical properties of the resulted bar are not affected by oxygen content, showing high strength and plasticity. The static tension shows plastic fracture. The microstructure of the bar is mainly composed of equiaxed, bimodal and basket-weave microstructure.

Effect of heat treatment on microstructure and properties of TC6 titanium alloy

Li Guangde, Wang Ying, Li Weilun

2021, 42(6): 147-152. doi: 10.7513/j.issn.1004-7638.2021.06.021

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Abstract:
TC6 titanium alloy bars were annealed by four different heat treatment processes. The microstructure, wear resistance and corrosion resistance of the samples were tested and analyzed. The results show that under the heat treatment at 870 ℃ for 1.5 h, furnace cooling to 600 ℃ and insulation for 2 h followed by air cooling, the wear resistance and corrosion resistance of the alloy (sample 1^#) are the worst. The sample under the heat treatment at 900 ℃ for 1.5 h, furnace cooling to 600 ℃ and insulation for 2 h followed by air cooling shows the best wear resistance and corrosion resistance (sample 2^#). The corrosion potential and corrosion resistance of the samples respectively under the heat treatment processes of 920 ℃ for 1.5 h furnace cooling to 600 ℃ and insulation for 2 h air cooling(sample 3^#), and 900 ℃ for 1.5 h furnace cooling to 620 ℃ and insulation for 2 h air cooling (sample 4^#), are between those of the sample 1^# and sample 2^#. Compared with sample 1^#, the wear volume of sample 2^# decreases by 8×10^?3 mm³, and the corrosion potential shifts by +53 mV.

Study on TiC/SiC reinforcement material by spark plasma sintering

Liu Xiaohong, Wang Yanfeng, Cao Yongdi, Liu Jianxiu, Wang Bingwei

2021, 42(6): 153-157. doi: 10.7513/j.issn.1004-7638.2021.06.022

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Abstract:
Mechanical reinforcement materials were prepared by spark plasma sintering (SPS), using SiC nanopowder and TiC particles as raw materials. The composite samples with different SiC content were characterized by SEM, and the composite sample with 10% SiC was tested by XRD. The effects of SiC content on the fracture toughness, conductivity, density and hardness of the composites were discussed. The results show that the grains are refined in the TiC/SiC reinforcement samples with lower structural defects and excellent compatibility between SiC and TiC. The component content in the sample with 10% SiC coincides well with the XRD analysis result. Compared with those of the pure TiC material, the fracture strength of the sample with 30% SiC is increased by about 116% and the average conductivity is enhanced by about 100 times. At the TiC/SiC ratio of 1.3∶1, the maximum value of density (4.3 g/cm³) and hardness (68.3HRA) can be obtained. The experimental results is consistent with the expected goals.

Research on TIG welding process of high strength titanium alloy

Feng Jing, Fan Limin, Geng Naitao, Yang Liu, Wu Shaojie, Cheng Fangjie

2021, 42(6): 158-163. doi: 10.7513/j.issn.1004-7638.2021.06.023

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Abstract:
A new type of high strength Ti-V-Mo titanium alloy was used as raw material. Welding test was carried out respectively by TIG automatic wire feeding and manual wire filling. The microstructure, forming, and mechanical properties of the joint were analyzed. The results show that the weld appearance shape is very smooth with no splash and edge defects. The base material has a duplex microstructure with higher content of equiaxed α phase. The grain size of the heat affected zone of Ti-V-Mo titanium alloy is very rough with needlelike α' phase inside the alloy. The grain size of weld area is very bulky, made up of a large number of layer α transitional phase structure and a small amount of needlelike α' phase structure. The tensile strength of the joint by TIG automatic and manual wire filling is 822 MPa and 612 MPa, respectively. And the impact absorbing energy of heat affected zone by TIG automatic and manual wire filling is 72.2 J and 84.9 J respectively. It shows good toughness characteristics in heat affected zone through the TIG welding process.

Research on microstructure and properties of TC4 titanium alloy MIG welded joints after heat treatment

He Yifan, Chen Donggao, Zhang Long, Wang Dafeng, Shao Zhiwen, Ma Liangchao

2021, 42(6): 164-170. doi: 10.7513/j.issn.1004-7638.2021.06.024

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Abstract:
Post heat treatment processes had been carried out on TC4 titanium alloy MIG welded joints. The effects of different heat treatment processes on residual stress, microstructure and mechanical properties on resulting TC4 titanium alloy MIG welded joints had been investigated through the blind-hole method, mechanical test and microstructure observation. The results show that average transverse residual stress and longitudinal residual stress of the welded joint after post heat treatment are reduced down to 74.2 MPa and 70.1 MPa, respectively. The base material is α+β lamellar structure, and the weld joint is α' needle shape martensite structure, the heat-affected zone is a mixed structure of α and α'. After heat treatment, with increasing heat treatment temperature and prolonging time, the acicular α' martensite in the weld structure becomes coarser, and grain size increases. For unheated-treatment joint, tensile fracture position locates at base metal, indicating higher joint strength compared with the base material. When the weld joint is subjected to a heat treatment process of 650 ℃+2 h, the elongation of the joint is higher than that in the unheated state, and the fracture mode is a ductile fracture. When the holding time is extended to 3 h, the grain becomes coarse, and the elongation decreases. The impact energy of the welding joint after post heat treatment at room temperature can reach 95% of that of base metal. The post-weld heat treatment can soften the welding joint, resulting in lower room temperature impact energy than the as-welding joint.

Microstructure and properties of electron beam welded TA1 medium plate and analysis of joint strengthening

Bai Wei, Li Dadong, Dong Xuejiao, Chen Rong

2021, 42(6): 171-177. doi: 10.7513/j.issn.1004-7638.2021.06.025

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Abstract:
Electron beam welding was used to weld 30 mm thick TA1 pure titanium plates. Combined with optical microscope (OM) and electron backscatter diffraction (EBSD), the microstructure, Vickers hardness and tensile test of the joint were carried out. The influence of welding process on microstructure and mechanical properties of TA1 material and the strengthening reason of the joint were analyzed. The results show that the microstructure from TA1 base metal to weld metal changes from equiaxed α to serrated α. The strength and hardness of welding seam and the heat affected zone are higher than the base metal. The strengthening of the joint properties is related to the increasing effect of serrated α and acicular α martensite on the hardness, the existence of a large number of serrated α lower than the grain size of the base metal in the weld seam and heat-affected zone, and the refining effect of micro-twinning on the welding microstructure.

Research on microstructure and properties of TC4/ 6061 dissimilar metal resistance spot welding joint

Chen Jinliang, Ma Wei, Li Xiaobing

2021, 42(6): 178-183. doi: 10.7513/j.issn.1004-7638.2021.06.026

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Abstract:
Using 2 mm thick TC4 titanium alloy and 1.5 mm thick 6061 aluminum alloy as raw materials for resistance spot welding, the effects of heat and time on the tensile-shear force and nugget diameter of the joint were studied. The fracture characteristics of the joint were observed, and the microstructure of the joint was analyzed. The results show that the grain size of the heat affected zone and nugget zone become larger than the base material zone, the grain size of the heat affected zone for the 6061 aluminum alloy grows. The fine α' martensite structure of the TC4 side appears, and present directional distribution. With the increase of welding heat, the tensile shear and core diameter of the joint gradually increase. With the welding time prolonged, both of the tensile-shear force and core diameter of the joint increase first and then decrease. When Q=600 J, the highest tensile shear of the joint delivers is 1.17 kN. The microhardness of the 6061 aluminum alloy side of the joint has no obvious change, and the hardness distribution of the nugget zone and the heat affected zone of the TC4 alloy side is nonuniform. When Q =550 J and t =10 s, the ideal hardness distribution is obtained. These experimental data provide theoretical guidance for Ti/Al dissimilar metal spot welding.

Microstructure and properties of architectural TiAl alloy with heat treatment after welding

Liao Chenya, Li Shuxun

2021, 42(6): 184-190. doi: 10.7513/j.issn.1004-7638.2021.06.027

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Abstract:
In this paper, two kinds of heat treatment were carried out on the electron beam welded joints of architectural TiAl alloy. The microstructure of different areas of the joints was analyzed with metallographic microscope (OM), and the microhardness of the welded joints was tested. The influences of the heat treatment processes on the microstructure and hardness of the welded joints of the architectural TiAl alloy were analyzed. The results show that the weld structure of TiAl alloy is composed of α₂ phase, B phase and O phase. The area with higher hardness of the joint increases, but the overall trend is down after the local heat treatment. After heat treatment, the B2 phase size of TiAl alloy reduces, while the O phase plate decomposed from B2 phase becomes large. The overall microhardness of the welded joint is reduced after integral heat treatment. The microhardness of the weld zone can be reduced by two heat treatment methods, and it presents a stable distribution.

Study on temperature field of titanium slab heating process based on walking-beam-type furnace

Xiang Guojin, Luo Xu, Geng Naitao, Zhang Ankang, Li Junhong, Yu Hui

2021, 42(6): 191-198. doi: 10.7513/j.issn.1004-7638.2021.06.028

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Abstract:
Based on the walking-beam-type reheating furnace in a certain steel plant, the TA1 titanium billet in the furnace was taken as the research object, and the mathematical model of heat transfer and the finite element model of heating process were established to study the temperature distribution of titanium billet in the heating process. The effects of furnace temperature and inlet temperature of titanium billet on the maximum temperature difference of cross section in the heating process of titanium billet were studied, and the effects of preheating zone temperature and heating zone (I) temperature on the heating time to meet the requirement of tapping temperature of titanium billet core were studied. The results show that the maximum temperature of the titanium billet is always at the corner of the end face and the minimum temperature is at the core of the titanium billet when the titanium billet is heated by the preheating zone and the heating zone (I), while the corner temperature is the lowest after the soaking zone. When the preheating temperature increases by 5 ℃, the maximum section temperature difference increases by 1～2 ℃, and when the titanium billet temperature increases by 50 ℃, the maximum section temperature difference decreases by 3～8 ℃. When the temperature of preheating zone increases by 10 ℃, the time for the core to meet the requirement of furnace discharge reduces by 1～2 min. When the temperature of heating zone (I) increases by 10 ℃, the time for the core to meet the requirement of furnace discharge reduces by 4～6 min.

Numerical investigation on the solidification process and the theoretical reduction amount of high titanium steel continuous casting slab

Wu Chenhui, Xie Xin, Li Yang, Zhang Min, Wu Guorong, Zeng Jianhua, He Wei

2021, 42(6): 199-205. doi: 10.7513/j.issn.1004-7638.2021.06.029

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Abstract:
High titanium steel has high wear resistance, toughness, strength and intergranular corrosion resistance, and has been widely applied to many fields. In present work, the solidification process and the theoretical reduction amount of the high titanium steel continuous casting slab were numerically investigated. The results indicate that the shell thickness at the exit of crystallizer is 15 mm, and the solidification end is located at 20.4 m from the meniscus with the mushy region length of 10.8 m, at the casting speed of 1.0 m/min. With the casting speed increased by 0.1 m/min, the shell thickness at the exit of crystallizer decreases by 0.2 mm, and the solidification end moves backwards by about 1.7 m, with the mushy region length increased by 0.9 m. The required theoretical reduction amount for compensating the solidification shrinkage of the mushy region keeps at about 2.2 mm under different casting speeds.

Research on damage failure of TA18 titanium alloy based on stress triaxiality

Zhang Tianwen, Wang Ying, Li Wei, Jiang Jian, Peng Li, Yu Hui

2021, 42(6): 206-212. doi: 10.7513/j.issn.1004-7638.2021.06.030

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Abstract:
Tensile specimens made of TA18 titanium alloy with different notch sizes were designed to carry out tensile tests under different stress states at room temperature, and fracture morphology observation had been done. The ductile fracture characteristics of TA18 titanium alloy were studied through the combination of experiment and numerical calculation. The influence law of stress state on microscopic fracture mechanism had been analyzed. The Bridgman forward calculation method was used to correct the stress data after necking instability. The Johnson-Cook (JC) constitutive model of TA18 titanium alloy was established, and the average stress triaxiality and fracture strain of the tensile specimen were calculated and determined by the regression method. The damage failure model of TA18 titanium alloy is presented. The results show that the fracture strain of TA18 titanium alloy under different stress states is different. The fracture strain decreases with the increase of stress triaxiality, and the fracture dimple size is positively correlated with the stress triaxiality. The established damage failure model can explain the fracture characteristics of the material.

2021 Vol. 42, No. 6