Volume 53,Issue 7,2024 Table of Contents
2024, 53(7):1836-1844.
DOI: 10.12442/j.issn.1002-185X.20240084
Abstract:
TC17 titanium alloy was weld under different laser heat input conditions. Optical microscope, scanning electron microscope, transmission electron microscope, tensile and fatigue tests were used to compare the macroscopic morphologies, microstructures, and mechanical properties of the welded joints. The results show that with the increase in heat input, the morphology of weld changes from Y- to X-shaped. The number of pore defects in the weld increases first and then decreases. The pore defects are mainly distributed in the middle and lower part of the weld zone. The weld is composed of coarse columnar grains with strip dendrites inside, and the spacing of dendrite increases gradually with the increase in heat input. The heat affected zone comprises finer equiaxed grains, and the increase in heat input leads to the refinement of α phase and coarsening of β phase. Moreover, the TC17 laser welded joints all fracture at the weld zone in the tensile and fatigue tests. Under the influence of dendrite size, the tensile strength decreases with the increase in heat input. The welding pore is the main reason for the fatigue fracture, and the fatigue life peaks when the number of pore defect is the lowest.
TC17 titanium alloy was weld under different laser heat input conditions. Optical microscope, scanning electron microscope, transmission electron microscope, tensile and fatigue tests were used to compare the macroscopic morphologies, microstructures, and mechanical properties of the welded joints. The results show that with the increase in heat input, the morphology of weld changes from Y- to X-shaped. The number of pore defects in the weld increases first and then decreases. The pore defects are mainly distributed in the middle and lower part of the weld zone. The weld is composed of coarse columnar grains with strip dendrites inside, and the spacing of dendrite increases gradually with the increase in heat input. The heat affected zone comprises finer equiaxed grains, and the increase in heat input leads to the refinement of α phase and coarsening of β phase. Moreover, the TC17 laser welded joints all fracture at the weld zone in the tensile and fatigue tests. Under the influence of dendrite size, the tensile strength decreases with the increase in heat input. The welding pore is the main reason for the fatigue fracture, and the fatigue life peaks when the number of pore defect is the lowest.
2024, 53(7):1845-1854.
DOI: 10.12442/j.issn.1002-185X.20230520
Abstract:
The microstructure of TC18 titanium alloy die forging shows delamination. The brighter microstructure has lower performance and is often called cold die microstructure (CDM). Decreasing the cooling rate can hinder the generation of CDM, but it may also aggravate the die wear. The balance relation between microstructure delamination of TC18 frame forging and the die wear in different parameters was studied by simulation and experiment. The programs to predict the CDM and wear depth were built and realized by secondary development. Continuous forging production process was simulated by DEFORM software and the characteristics of CDM and wear were researched. The balance relationship between the die wear and the CDM content in different parameters was discussed by the response surface method and the optimal parameters. Results show that the preheating temperature of die plays a dominant role in the variation of the wear depth. The most influential factor of CDM content is the contact condition. Applying glass fiber can reduce the CDM content without increasing the wear depth.
The microstructure of TC18 titanium alloy die forging shows delamination. The brighter microstructure has lower performance and is often called cold die microstructure (CDM). Decreasing the cooling rate can hinder the generation of CDM, but it may also aggravate the die wear. The balance relation between microstructure delamination of TC18 frame forging and the die wear in different parameters was studied by simulation and experiment. The programs to predict the CDM and wear depth were built and realized by secondary development. Continuous forging production process was simulated by DEFORM software and the characteristics of CDM and wear were researched. The balance relationship between the die wear and the CDM content in different parameters was discussed by the response surface method and the optimal parameters. Results show that the preheating temperature of die plays a dominant role in the variation of the wear depth. The most influential factor of CDM content is the contact condition. Applying glass fiber can reduce the CDM content without increasing the wear depth.
2024, 53(7):1909-1916.
DOI: 10.12442/j.issn.1002-185X.20230340
Abstract:
The elastic properties of titanium alloys are not only affected by heat treatment processes, but also by their composition and structure. For example, the elastic modulus of high-purity Ti varies depending on its alloy type, ranging from approximately 93 to 120.5 GPa. Based on the constitutive model of multi-scale elastic response, for example, the effective elastic response of alpha+beta titanium alloy with different contents under load was theoretically predicted and the effective elastic properties of titanium alloys were calculated, such as effective elastic modulus E ? , effective bulk modulus K ?, effective shear modulus G ? and effective Poisson"s ratio ν ?, the mechanism of the effect of contents on the effective elastic properties of titanium alloy was also revealed. The comparison with different micromechanical models and experimental measurements were shown that the E ? of titanium alloy was affected by α phase, and approximately decreased from 111.11 GPa to 87.49 GPa as α phase; K ?, G ?, and ν ? were affected by β phase, K ? approximately increased from 104.12 GPa to 117.21 GPa, K ? approximately decreased from 42.02 GPa to 31.81 GPa, and ν ? approximately increased from 0.322 to 0.376, the accuracy of which was confirmed by the consistence with experimental measurements.
The elastic properties of titanium alloys are not only affected by heat treatment processes, but also by their composition and structure. For example, the elastic modulus of high-purity Ti varies depending on its alloy type, ranging from approximately 93 to 120.5 GPa. Based on the constitutive model of multi-scale elastic response, for example, the effective elastic response of alpha+beta titanium alloy with different contents under load was theoretically predicted and the effective elastic properties of titanium alloys were calculated, such as effective elastic modulus E ? , effective bulk modulus K ?, effective shear modulus G ? and effective Poisson"s ratio ν ?, the mechanism of the effect of contents on the effective elastic properties of titanium alloy was also revealed. The comparison with different micromechanical models and experimental measurements were shown that the E ? of titanium alloy was affected by α phase, and approximately decreased from 111.11 GPa to 87.49 GPa as α phase; K ?, G ?, and ν ? were affected by β phase, K ? approximately increased from 104.12 GPa to 117.21 GPa, K ? approximately decreased from 42.02 GPa to 31.81 GPa, and ν ? approximately increased from 0.322 to 0.376, the accuracy of which was confirmed by the consistence with experimental measurements.
2024, 53(7):1917-1927.
DOI: 10.12442/j.issn.1002-185X.20230339
Abstract:
Ti-48Al-2Cr-2Nb alloy reinforced by in-situ Ti2AlC was prepared by vacuum arc melting. The effect of CNTs content on the microstructure evolution and mechanical properties of TiAl alloy was investigated. The results show that with the increase of CNTs, the solidification path of the alloy moves to the direction of high Al and the volume fraction of γ phase increases. Meanwhile, the lamellar structure is gradually refined, and the length-diameter ratio of Ti2AlC gradually decreases. The mechanical properties of the alloy incresase significantly under the action of solid solution strengthening, grain refinement strengthening and Ti2AlC precipitated phase strengthening. With the increase of CNTs content, the Vickers hardness of the alloy increases from 358.4±19.2 HV to 428.5±23.1 HV. The compressive strength at room temperature and high temperature of the alloy first increases and then decreases with the increase of CNTs. When the addition of CNTs is 3.0 at.%, the compressive strength and maximum strain at room temperature reach 1890.61 MPa and 29.09%, respectively, which increase by 54.95% and 28.31%, respectively. At 800 ℃, the hardening and softening effects of the alloy are affected by the CNTs content. The alloy with 3.0 at. % CNTs shows the highest compressive strength, increasing by about 31.42% compared with without CNTs addition, and the alloy with 4.5 at. % CNTs shows better softening effect without sacrificing the compressive strength.
Ti-48Al-2Cr-2Nb alloy reinforced by in-situ Ti2AlC was prepared by vacuum arc melting. The effect of CNTs content on the microstructure evolution and mechanical properties of TiAl alloy was investigated. The results show that with the increase of CNTs, the solidification path of the alloy moves to the direction of high Al and the volume fraction of γ phase increases. Meanwhile, the lamellar structure is gradually refined, and the length-diameter ratio of Ti2AlC gradually decreases. The mechanical properties of the alloy incresase significantly under the action of solid solution strengthening, grain refinement strengthening and Ti2AlC precipitated phase strengthening. With the increase of CNTs content, the Vickers hardness of the alloy increases from 358.4±19.2 HV to 428.5±23.1 HV. The compressive strength at room temperature and high temperature of the alloy first increases and then decreases with the increase of CNTs. When the addition of CNTs is 3.0 at.%, the compressive strength and maximum strain at room temperature reach 1890.61 MPa and 29.09%, respectively, which increase by 54.95% and 28.31%, respectively. At 800 ℃, the hardening and softening effects of the alloy are affected by the CNTs content. The alloy with 3.0 at. % CNTs shows the highest compressive strength, increasing by about 31.42% compared with without CNTs addition, and the alloy with 4.5 at. % CNTs shows better softening effect without sacrificing the compressive strength.
2024, 53(7):1937-1943.
DOI: 10.12442/j.issn.1002-185X.20230282
Abstract:
Metal plastic heat dissipation is still an unsolved problem. For example, the experimental results of the work-heat conversion coefficient and its strain and strain rate correlation in the existing literature are not consistent. In this paper, the heat dissipation characteristics of commercial purity titanium TA2 during tensile process at 0.1 s^(-1)-100 s^(-1) strain rate were studied. DIC and infrared temperature measurement synchronous test system were used to analyze the deformation and temperature field evolution process of plate tensile specimens. The experimental results show that when the strain rate is greater than 1 s^(-1), it can be approximately adiabatic before the necking of specimen. The Taylor-Quinney coefficient β of TA2 is not sensitive to the strain rate effect, however it is not a constant, but evolves with strain. In the initial stage of loading, β increases with the increase of strain, and reaches the maximum value of 0.92 when the tensile strain is about 9%. Then β decreases gradually with the development of strain, and it decreases to about 0.8 at 30% strain. The EBSD microscopic analysis of the specimens at different deformation stages indicates that the variation of Taylor-Quinney coefficient is related to the twinning and microstructure evolution during the deformation process.
Metal plastic heat dissipation is still an unsolved problem. For example, the experimental results of the work-heat conversion coefficient and its strain and strain rate correlation in the existing literature are not consistent. In this paper, the heat dissipation characteristics of commercial purity titanium TA2 during tensile process at 0.1 s^(-1)-100 s^(-1) strain rate were studied. DIC and infrared temperature measurement synchronous test system were used to analyze the deformation and temperature field evolution process of plate tensile specimens. The experimental results show that when the strain rate is greater than 1 s^(-1), it can be approximately adiabatic before the necking of specimen. The Taylor-Quinney coefficient β of TA2 is not sensitive to the strain rate effect, however it is not a constant, but evolves with strain. In the initial stage of loading, β increases with the increase of strain, and reaches the maximum value of 0.92 when the tensile strain is about 9%. Then β decreases gradually with the development of strain, and it decreases to about 0.8 at 30% strain. The EBSD microscopic analysis of the specimens at different deformation stages indicates that the variation of Taylor-Quinney coefficient is related to the twinning and microstructure evolution during the deformation process.
2024, 53(7):1953-1961.
DOI: 10.12442/j.issn.1002-185X.20230359
Abstract:
The uniform and gradient lattice structures of TC4 titanium alloy were fabricated using SLM technology. The study investigated the effects of different rod diameters (ranging from 0.8mm to 1.2mm), cell types (bcc, fcc, fbcc), and adding vertical struts (bccz, fccz, fbccz) on the compressive properties and energy absorption of both uniform and gradient lattice structures. The results indicate that the lattice structure with 1.2mm rod diameters exhibits the best performance. The fccz and fbccz lattice structures respectively exhibit the best performance in terms of both mass and volume efficiency. The presence of vertical struts significantly enhances the performance of lattice structures under specific loading conditions. Compression performance and energy absorption of uniform lattice structures before failure are better than those of gradient lattice structures with the same relative density and strain, due to the layer-by-layer fracture characteristic of gradient lattice structures, they have better performance under 50% and larger strain conditions, and are more suitable for application in energy absorption devices.
The uniform and gradient lattice structures of TC4 titanium alloy were fabricated using SLM technology. The study investigated the effects of different rod diameters (ranging from 0.8mm to 1.2mm), cell types (bcc, fcc, fbcc), and adding vertical struts (bccz, fccz, fbccz) on the compressive properties and energy absorption of both uniform and gradient lattice structures. The results indicate that the lattice structure with 1.2mm rod diameters exhibits the best performance. The fccz and fbccz lattice structures respectively exhibit the best performance in terms of both mass and volume efficiency. The presence of vertical struts significantly enhances the performance of lattice structures under specific loading conditions. Compression performance and energy absorption of uniform lattice structures before failure are better than those of gradient lattice structures with the same relative density and strain, due to the layer-by-layer fracture characteristic of gradient lattice structures, they have better performance under 50% and larger strain conditions, and are more suitable for application in energy absorption devices.
2024, 53(7):1992-1998.
DOI: 10.12442/j.issn.1002-185X.20230279
Abstract:
The key equipment in the reprocessing industry, such as dissolvers and evaporators, have continually serviced in boiling nitric acid with high concentration and high radioactivity. Ensuring the safe and reliable operation of the equipment is the primary goal. This article investigated the effect of heat treatment process on the corrosion behavior of Ti-5Ta-5V-8Cr-1Al alloy (Ti5581) in 6mol/L boiling nitric acid solution using full immersion corrosion and electrochemical corrosion experimental methods. The results indicated that Ti5581 alloy has a lower corrosion rate under solid solution only process and 460 ℃ aging process, the corrosion rate was 0.022mm/a after 240 hours corrosion. Further analysis was conducted using metallographic microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and other analytical methods to analyze the structure and composition of the passivation film in the surface layer of Ti5581 alloy after corrosion. After corrosion, the surface passivation film was smooth and dense, and the surface passivation film was composed of a mixed oxide of Ti and Ta. Formation of passivation film in the surface layer of Ti5581 alloy was related to quantity and morphology of α phases. Compared to 550 ℃ aging process, the size of α phase was smaller and the mass fraction of Ta was higher in 460 ℃ aging process, which resulting in better corrosion uniformity and passivation film stability.
The key equipment in the reprocessing industry, such as dissolvers and evaporators, have continually serviced in boiling nitric acid with high concentration and high radioactivity. Ensuring the safe and reliable operation of the equipment is the primary goal. This article investigated the effect of heat treatment process on the corrosion behavior of Ti-5Ta-5V-8Cr-1Al alloy (Ti5581) in 6mol/L boiling nitric acid solution using full immersion corrosion and electrochemical corrosion experimental methods. The results indicated that Ti5581 alloy has a lower corrosion rate under solid solution only process and 460 ℃ aging process, the corrosion rate was 0.022mm/a after 240 hours corrosion. Further analysis was conducted using metallographic microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and other analytical methods to analyze the structure and composition of the passivation film in the surface layer of Ti5581 alloy after corrosion. After corrosion, the surface passivation film was smooth and dense, and the surface passivation film was composed of a mixed oxide of Ti and Ta. Formation of passivation film in the surface layer of Ti5581 alloy was related to quantity and morphology of α phases. Compared to 550 ℃ aging process, the size of α phase was smaller and the mass fraction of Ta was higher in 460 ℃ aging process, which resulting in better corrosion uniformity and passivation film stability.
2024, 53(7):2035-2041.
DOI: 10.12442/j.issn.1002-185X.20230304
Abstract:
Creep loading has a certain effect on the service performance of structural components. In this paper, the creep preloading on Ti6321 titanium alloy with equiaxed, bimodal and Widmanstatten microstructures were carried out. Dynamic compression tests of the material after creep investigated at a strain rate about 3000s-1. The dynamic behavior of Ti6321 titanium alloy after different creep stress loading was studied. The results show that the yield stress decreases and the compressive strength increases after creep preloading. With the increase of creep stress, the impact absorption energy of titanium alloy with three microstructures after dynamic compression increases and the adiabatic shear sensitivity decreases. Titanium alloys without creep have phase transition bands after dynamic compression, Titanium alloy with equiaxed microstructure and bimodal microstructure after dynamic compression after creep preloading do not fail, only produce deformation band. Titanium alloy with Widmanstatten microstructure fails due to phase transition bands. Adiabatic shear of equiaxed and bimodal microstructure are delayed by creep.
Creep loading has a certain effect on the service performance of structural components. In this paper, the creep preloading on Ti6321 titanium alloy with equiaxed, bimodal and Widmanstatten microstructures were carried out. Dynamic compression tests of the material after creep investigated at a strain rate about 3000s-1. The dynamic behavior of Ti6321 titanium alloy after different creep stress loading was studied. The results show that the yield stress decreases and the compressive strength increases after creep preloading. With the increase of creep stress, the impact absorption energy of titanium alloy with three microstructures after dynamic compression increases and the adiabatic shear sensitivity decreases. Titanium alloys without creep have phase transition bands after dynamic compression, Titanium alloy with equiaxed microstructure and bimodal microstructure after dynamic compression after creep preloading do not fail, only produce deformation band. Titanium alloy with Widmanstatten microstructure fails due to phase transition bands. Adiabatic shear of equiaxed and bimodal microstructure are delayed by creep.
2024, 53(7):2049-2058.
DOI: 10.12442/j.issn.1002-185X.20230742
Abstract:
In order to improve the metallurgical quality of large titanium alloy castings by vertical centrifugal casting, the mold flow analysis method was used to explore the influence of linear and spiral runner systems on the melt filling flow state. The results indicated that there is a phenomenon of melt adhering to the wall distribution in traditional linear runners, and reducing the cross-sectional size of the runner cannot avoid the formation of the suction zone in the transverse runner cavity. In addition, the melt accumulation and backflow exhibited in the transverse runner, and the melt in the filled casting cavity was in a jet flow state. Based on the D"Alembert"s principle, the motion behavior of melt particles in the two-dimensional plane of the runner was analyzed, revealing that the main reason for the above problem is the mismatch between the particle motion trajectory and the linear runner structure. Further exploration was conducted on the effects of centrifugal speed and initial particle velocity on the shape characteristics of trajectory lines. A design method for a spiral shaped runner gating system suitable for large annular titanium alloy castings was proposed. The mold flow analysis results verified that the spiral shaped runner can effectively reduce suction and turbulence tendencies, balance the casting filling flow field, and form a bottom-up filling sequence.
In order to improve the metallurgical quality of large titanium alloy castings by vertical centrifugal casting, the mold flow analysis method was used to explore the influence of linear and spiral runner systems on the melt filling flow state. The results indicated that there is a phenomenon of melt adhering to the wall distribution in traditional linear runners, and reducing the cross-sectional size of the runner cannot avoid the formation of the suction zone in the transverse runner cavity. In addition, the melt accumulation and backflow exhibited in the transverse runner, and the melt in the filled casting cavity was in a jet flow state. Based on the D"Alembert"s principle, the motion behavior of melt particles in the two-dimensional plane of the runner was analyzed, revealing that the main reason for the above problem is the mismatch between the particle motion trajectory and the linear runner structure. Further exploration was conducted on the effects of centrifugal speed and initial particle velocity on the shape characteristics of trajectory lines. A design method for a spiral shaped runner gating system suitable for large annular titanium alloy castings was proposed. The mold flow analysis results verified that the spiral shaped runner can effectively reduce suction and turbulence tendencies, balance the casting filling flow field, and form a bottom-up filling sequence.
Zhang Jianyu
,
Chen Yayu
,
Yang Guoqiang
,
Lü Zheng
,
Liu Hongji
,
Ma Penghui
,
Zeng Hongtao
,
Li Hezong
2024, 53(7):2067-2082.
DOI: 10.12442/j.issn.1002-185X.20240176
Abstract:
The Ti-Al system intermetallic compounds and composites fabricated through Ti and Al，such as TiAl3, γ-TiAl and α2-Ti3Al intermetallic compounds, and Ti/Al, Ti/α2-Ti3Al, Ti/γ-TiAl, Ti/TiAl3,Ti/TiAl3/Al and Al/TiAl3 metal-metal and metal-intermetallic compound composites, have good application prospects in aerospace, automotive and other fields owing to their excellent physical, chemical and mechanical properties. The preparation of the above materials involves a variety of Ti-Al reaction diffusion processes. Therefore, an in-depth understanding of Ti-Al reaction diffusion mechanism and kinetics will help to prepare Ti-Al intermetallic compounds and composites reasonably and efficiently. At present, Ti-Al reaction diffusion mechanism and kinetics have been extensively studied, but there are still many divergences on some conclusions. In part II of this paper, the research progress of Ti-Al reaction diffusion kinetics involved in the preparation of Ti-Al intermetallic compounds and composites is reviewed, and the future research direction of Ti-Al reaction diffusion kinetics is prospected.
The Ti-Al system intermetallic compounds and composites fabricated through Ti and Al，such as TiAl3, γ-TiAl and α2-Ti3Al intermetallic compounds, and Ti/Al, Ti/α2-Ti3Al, Ti/γ-TiAl, Ti/TiAl3,Ti/TiAl3/Al and Al/TiAl3 metal-metal and metal-intermetallic compound composites, have good application prospects in aerospace, automotive and other fields owing to their excellent physical, chemical and mechanical properties. The preparation of the above materials involves a variety of Ti-Al reaction diffusion processes. Therefore, an in-depth understanding of Ti-Al reaction diffusion mechanism and kinetics will help to prepare Ti-Al intermetallic compounds and composites reasonably and efficiently. At present, Ti-Al reaction diffusion mechanism and kinetics have been extensively studied, but there are still many divergences on some conclusions. In part II of this paper, the research progress of Ti-Al reaction diffusion kinetics involved in the preparation of Ti-Al intermetallic compounds and composites is reviewed, and the future research direction of Ti-Al reaction diffusion kinetics is prospected.
11 Effect of Test Temperature on Crack Propagation Behavior of Nickel-Based Single-Crystal Superalloy
2024, 53(7):1874-1881.
DOI: 10.12442/j.issn.1002-185X.20230618
Abstract:
The fatigue crack propagation behavior of DD6 nickel-based single-crystal superalloy was investigated at temperatures ranging from 530 °C to 850 °C. The fatigue properties were assessed along the [001] direction, parallel to the loading axis in tension. After the fatigue crack propagation test, the fracture morphology was examined by scanning electron microscope and classified into four zones, including source zone, prefabricated crack zone, stable extension zone, and rapid extension zone. Electron backscatter diffraction was utilized to observe the profiles of plastic deformation perpendicular to the fracture. Additionally, the dislocation motion mechanism near the fracture was studied by transmission electron microscope. Results show that oxidation occurs at 650 °C under combined influences of the temperature field, stress field, and exposure time. Furthermore, due to weakened γ′ phase, a significant number of consecutive dislocations form in the γ and γ′ phases between 650 and 760 °C, resulting in increased oxidation of alloy. Besides, a notable decrease in fatigue propagation life can be observed at 760 °C.
The fatigue crack propagation behavior of DD6 nickel-based single-crystal superalloy was investigated at temperatures ranging from 530 °C to 850 °C. The fatigue properties were assessed along the [001] direction, parallel to the loading axis in tension. After the fatigue crack propagation test, the fracture morphology was examined by scanning electron microscope and classified into four zones, including source zone, prefabricated crack zone, stable extension zone, and rapid extension zone. Electron backscatter diffraction was utilized to observe the profiles of plastic deformation perpendicular to the fracture. Additionally, the dislocation motion mechanism near the fracture was studied by transmission electron microscope. Results show that oxidation occurs at 650 °C under combined influences of the temperature field, stress field, and exposure time. Furthermore, due to weakened γ′ phase, a significant number of consecutive dislocations form in the γ and γ′ phases between 650 and 760 °C, resulting in increased oxidation of alloy. Besides, a notable decrease in fatigue propagation life can be observed at 760 °C.
2024, 53(7):1882-1886.
DOI: 10.12442/j.issn.1002-185X.E20230040
Abstract:
Regional microstructure characteristic always appears in shear-compression deformed GH4169 superalloy, which is detrimental to subsequent cold-rolling process in engineering. Recrystallization annealing treatments within temperature range of 1000?1080 °C and holding time range of 1?3 h were carried out to investigate the microstructure evolution behavior, and the cold-forming property of GH4169 superalloy was optimized by regulating the grain size. Results show that static recrystallization (SRX) grains are fully nucleated at 1000 °C and the original coarse grains are completely replaced by fine recrystallized grains. Bulges of high angle grain boundaries are the preferred nucleation points of SRX. At 1020?1060 °C, grain annexation takes place among adjacent SRX grains, causing partial grains to increase, while the original dynamic recrystallization (DRX) grains keeps tiny in the strain con-centration region. Recrystallized grains (both SRX and DRX) uniformly grow up, with an average grain size of 87.89 μm at 1080 °C, at which the regional characteristic completely disappears, and the microstructure is significantly homogenized. Step twins appear at 1080 °C due to the SRX growth accidents, and the length fraction of twin boundaries (Σ3) reaches 35.8%, which can effectively improve the high temperature resistance of GH4169 superalloy. Ultimately, the optimal recrystallization annealing of shear-compression deformed GH4169 superalloy is determined as 1080 °C-1 h, followed by water cooling.
Regional microstructure characteristic always appears in shear-compression deformed GH4169 superalloy, which is detrimental to subsequent cold-rolling process in engineering. Recrystallization annealing treatments within temperature range of 1000?1080 °C and holding time range of 1?3 h were carried out to investigate the microstructure evolution behavior, and the cold-forming property of GH4169 superalloy was optimized by regulating the grain size. Results show that static recrystallization (SRX) grains are fully nucleated at 1000 °C and the original coarse grains are completely replaced by fine recrystallized grains. Bulges of high angle grain boundaries are the preferred nucleation points of SRX. At 1020?1060 °C, grain annexation takes place among adjacent SRX grains, causing partial grains to increase, while the original dynamic recrystallization (DRX) grains keeps tiny in the strain con-centration region. Recrystallized grains (both SRX and DRX) uniformly grow up, with an average grain size of 87.89 μm at 1080 °C, at which the regional characteristic completely disappears, and the microstructure is significantly homogenized. Step twins appear at 1080 °C due to the SRX growth accidents, and the length fraction of twin boundaries (Σ3) reaches 35.8%, which can effectively improve the high temperature resistance of GH4169 superalloy. Ultimately, the optimal recrystallization annealing of shear-compression deformed GH4169 superalloy is determined as 1080 °C-1 h, followed by water cooling.
2024, 53(7):1887-1896.
DOI: 10.12442/j.issn.1002-185X.20230637
Abstract:
The forging load of super large turbine disc with a diameter over 2 m may approach or even surpass the limit of 800 MN of the largest press machine in China, which is the extreme manufacturing. Thus, maintaining good mechanical properties and controlling forging load are two key factors during the forging process of super large turbine disc. 25 groups of forging parameters was designed based on Taguchi method. The multi-objective optimization of finite element method simulation results was conducted by SNR and ANOVA methods. Results show that the most uniform and refined recrystallization microstructures are obtained under optimal forging load. The optimal combination of process parameters is determined under extreme manufacturing condition: temperature=1120 °C, strain rate=0.06 s-1, pre-forging size=985/610/475 mm, and die temperature=280 °C. The order of importance of each parameter to the simulation results is as follows: temperature>strain rate>billet shape>>die temperature. The experimental results obtained under the optimal parameters combination show good agreement with the simulated results, which demonstrates that this approach may be used to manage the load and microstructure of super large forgings while avoiding a significant number of experiments and numerical simulations.
The forging load of super large turbine disc with a diameter over 2 m may approach or even surpass the limit of 800 MN of the largest press machine in China, which is the extreme manufacturing. Thus, maintaining good mechanical properties and controlling forging load are two key factors during the forging process of super large turbine disc. 25 groups of forging parameters was designed based on Taguchi method. The multi-objective optimization of finite element method simulation results was conducted by SNR and ANOVA methods. Results show that the most uniform and refined recrystallization microstructures are obtained under optimal forging load. The optimal combination of process parameters is determined under extreme manufacturing condition: temperature=1120 °C, strain rate=0.06 s-1, pre-forging size=985/610/475 mm, and die temperature=280 °C. The order of importance of each parameter to the simulation results is as follows: temperature>strain rate>billet shape>>die temperature. The experimental results obtained under the optimal parameters combination show good agreement with the simulated results, which demonstrates that this approach may be used to manage the load and microstructure of super large forgings while avoiding a significant number of experiments and numerical simulations.
2024, 53(7):1897-1908.
DOI: 10.12442/j.issn.1002-185X.20230649
Abstract:
Ni-based superalloys exhibit exceptional mechanical properties and high-temperature resistance, making them suitable for use in aggressive environments. The oxidation behavior of Ni-based superalloys is primarily influenced by the intrinsic material properties and oxide scale properties, which are largely dependent on the complex composition and content of alloying elements. Various environmental parameters, including atmosphere composition, temperature, stress and molten salts, directly impact the oxidation behavior of materials. The effects of alloying elements and the service environment on the oxidation behavior of Ni-based superalloys were comprehensively reviewed. Aluminium, chromium and cobalt are considered as favorable elements to form compact and adherent scales that protect the matrix. The addition of titanium, molybdenum, niobium, tungsten and tantalum is traditionally believed to be detrimental. However, recent researches have presented different opinions, which were discussed. The oxidation mechanism was also explored and an insight into the future developments of Ni-based superalloys was provided.
Ni-based superalloys exhibit exceptional mechanical properties and high-temperature resistance, making them suitable for use in aggressive environments. The oxidation behavior of Ni-based superalloys is primarily influenced by the intrinsic material properties and oxide scale properties, which are largely dependent on the complex composition and content of alloying elements. Various environmental parameters, including atmosphere composition, temperature, stress and molten salts, directly impact the oxidation behavior of materials. The effects of alloying elements and the service environment on the oxidation behavior of Ni-based superalloys were comprehensively reviewed. Aluminium, chromium and cobalt are considered as favorable elements to form compact and adherent scales that protect the matrix. The addition of titanium, molybdenum, niobium, tungsten and tantalum is traditionally believed to be detrimental. However, recent researches have presented different opinions, which were discussed. The oxidation mechanism was also explored and an insight into the future developments of Ni-based superalloys was provided.
2024, 53(7):1985-1991.
DOI: 10.12442/j.issn.1002-185X.20230295
Abstract:
The sphericity, specific surface area, oxygen content, surface oxygen state, and high temperature oxidation characteristics of nickel-based superalloy powders with various particle sizes were studied. The oxygen absorption characteristics of the alloy powder at room temperature and the oxidation characteristics at high temperature were obtained. The argon atomized powders were sieved into different sizes of <30 mm, 30~49 mm, 50~60 mm, 61~73 mm, and 74-105 mm. The results show that the powders with size of 61~73 μm have the lowest average sphericity, minimum specific surface area, and lowest oxygen content. The powders with size of 30~49 μm have the highest average sphericity and specific surface area. However, the powder less than 30 μm has the highest oxygen content. The high-temperature oxidation process of powders at 950 ℃ can be defined as two stages: the initial stage of oxidation (0~12 h) and the later stage of oxidation (＞12 h). At the initial stage of oxidation, a dense mixed oxide layer of NiO, Cr2O3 and TiO2 was formed on the powder surface. After 12 hours oxidation, the mixed oxide layer peels off and the oxidation resistance begins to fail. After 24 hours oxidation, the mixed oxide layer peels off obviously and exposes the substrate, resulting in complete failure of oxidation resistance. After 100 hours oxidation, the powder was mainly oxidized into NiO and no obvious oxide layer exists on the surface.
The sphericity, specific surface area, oxygen content, surface oxygen state, and high temperature oxidation characteristics of nickel-based superalloy powders with various particle sizes were studied. The oxygen absorption characteristics of the alloy powder at room temperature and the oxidation characteristics at high temperature were obtained. The argon atomized powders were sieved into different sizes of <30 mm, 30~49 mm, 50~60 mm, 61~73 mm, and 74-105 mm. The results show that the powders with size of 61~73 μm have the lowest average sphericity, minimum specific surface area, and lowest oxygen content. The powders with size of 30~49 μm have the highest average sphericity and specific surface area. However, the powder less than 30 μm has the highest oxygen content. The high-temperature oxidation process of powders at 950 ℃ can be defined as two stages: the initial stage of oxidation (0~12 h) and the later stage of oxidation (＞12 h). At the initial stage of oxidation, a dense mixed oxide layer of NiO, Cr2O3 and TiO2 was formed on the powder surface. After 12 hours oxidation, the mixed oxide layer peels off and the oxidation resistance begins to fail. After 24 hours oxidation, the mixed oxide layer peels off obviously and exposes the substrate, resulting in complete failure of oxidation resistance. After 100 hours oxidation, the powder was mainly oxidized into NiO and no obvious oxide layer exists on the surface.
Su Hai
,
Wang Chen
,
Luo Tong
,
Huang Hailiang
,
Zhang Hua
,
Zhang Shangzhou
,
Jiang Liang
,
Zhou Xin
2024, 53(7):2006-2017.
DOI: 10.12442/j.issn.1002-185X.20230286
Abstract:
In this paper, the hot deformation behavior of IN783 low-expansion superalloy was investigated through hot compression experiments at the deformation temperatures of 1000-1120 ℃ and strain rates of 0.01-10 S-1. The microstructure evolution of the alloy under different deformation conditions was studied using electron backscatter diffraction (EBSD). The results indicate that the peak stress of IN783 alloy significantly decreases with the increase of deformation temperature and the decrease of strain rates. Combined with Arrhenius equation and Zener Hollomon parameter model, the constitutive equation of the alloy was established, which can well describe the relationship between peak stress, deformation temperature and strain rate during hot deformation of IN783 alloy. The hot working diagram of IN783 alloy was drawn based on the dynamic material model. According to the hot working diagram and the microstructure observation, the instability zone of IN783 superalloy was determined as: deformation temperature of 1095 ℃ - 1120 ℃, strain rate of 100.39814-101 S-1. In addition, under the condition of high temperature and low strain rates (1060-1120 ℃, 0.01 S-1), mixed crystal and grain coarsening would occur, which makes it not suitable for the hot working of IN783 alloy although the alloy has high power dissipation coefficient in those parameters.
In this paper, the hot deformation behavior of IN783 low-expansion superalloy was investigated through hot compression experiments at the deformation temperatures of 1000-1120 ℃ and strain rates of 0.01-10 S-1. The microstructure evolution of the alloy under different deformation conditions was studied using electron backscatter diffraction (EBSD). The results indicate that the peak stress of IN783 alloy significantly decreases with the increase of deformation temperature and the decrease of strain rates. Combined with Arrhenius equation and Zener Hollomon parameter model, the constitutive equation of the alloy was established, which can well describe the relationship between peak stress, deformation temperature and strain rate during hot deformation of IN783 alloy. The hot working diagram of IN783 alloy was drawn based on the dynamic material model. According to the hot working diagram and the microstructure observation, the instability zone of IN783 superalloy was determined as: deformation temperature of 1095 ℃ - 1120 ℃, strain rate of 100.39814-101 S-1. In addition, under the condition of high temperature and low strain rates (1060-1120 ℃, 0.01 S-1), mixed crystal and grain coarsening would occur, which makes it not suitable for the hot working of IN783 alloy although the alloy has high power dissipation coefficient in those parameters.
2024, 53(7):2025-2034.
DOI: 10.12442/j.issn.1002-185X.20230346
Abstract:
Based on DD98M nickel-based superalloy, four kinds of alloys of A1-Ta /(Ta+Ti)=0, A2-Ta /(Ta+Ti)=0.34, A3-Ta /(Ta+Ti)=0.66 and A4-Ta /(Ta+Ti)=1 were prepared by vacuum induction melting, keeping the total amount of γ" phase forming elements of (Ta+Ti) in the alloys unchanged. The as-cast alloys were subjected to solution aging and long-term aging at 1273k. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe (EPMA) were used to study the microstructure of the four alloys after aging. The effects of long-term aging at a high temperature and the change of Ta/(Ta+Ti) on the as-cast microstructure and properties of the alloys were analyzed. The results show that long-term aging causes partial decomposition of γ" phase, promotes element diffusion and intensifies element segregation. With the extension of long-term aging time, the γ" phase coarsens, the hardness decreases, the absolute value of misfit decreases, and the cubic degree of γ" phase decreases. With the increasing proportion of Ta in (Ta+Ti), the absolute value of misfit decreases, the cubic degree of γ" phase decreases, and the hardness increases. Under the long-term aging condition, the segregation of Cr, Mo, W and Ta is intensified, and the segregation of Ti is alleviated. The addition of Ta will squeeze W into the γ phase. After long-term aging, σ phase and MC carbide precipitated at the grain boundaries of A2 and A3 alloys, while no precipitation was observed at the grain boundaries of A1 and A4 alloys, indicating that the synergistic effect of Ta and Ti promotes the precipitation of σ phase and MC carbide. A2 alloys have relatively high γ" phase volume fraction, γ" phase cubed degree, hardness and strength, the smallest γ" phase size and the highest elongation, so A2 alloys have the best comprehensive mechanical properties of the four alloys.
Based on DD98M nickel-based superalloy, four kinds of alloys of A1-Ta /(Ta+Ti)=0, A2-Ta /(Ta+Ti)=0.34, A3-Ta /(Ta+Ti)=0.66 and A4-Ta /(Ta+Ti)=1 were prepared by vacuum induction melting, keeping the total amount of γ" phase forming elements of (Ta+Ti) in the alloys unchanged. The as-cast alloys were subjected to solution aging and long-term aging at 1273k. X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe (EPMA) were used to study the microstructure of the four alloys after aging. The effects of long-term aging at a high temperature and the change of Ta/(Ta+Ti) on the as-cast microstructure and properties of the alloys were analyzed. The results show that long-term aging causes partial decomposition of γ" phase, promotes element diffusion and intensifies element segregation. With the extension of long-term aging time, the γ" phase coarsens, the hardness decreases, the absolute value of misfit decreases, and the cubic degree of γ" phase decreases. With the increasing proportion of Ta in (Ta+Ti), the absolute value of misfit decreases, the cubic degree of γ" phase decreases, and the hardness increases. Under the long-term aging condition, the segregation of Cr, Mo, W and Ta is intensified, and the segregation of Ti is alleviated. The addition of Ta will squeeze W into the γ phase. After long-term aging, σ phase and MC carbide precipitated at the grain boundaries of A2 and A3 alloys, while no precipitation was observed at the grain boundaries of A1 and A4 alloys, indicating that the synergistic effect of Ta and Ti promotes the precipitation of σ phase and MC carbide. A2 alloys have relatively high γ" phase volume fraction, γ" phase cubed degree, hardness and strength, the smallest γ" phase size and the highest elongation, so A2 alloys have the best comprehensive mechanical properties of the four alloys.
2024, 53(7):2042-2048.
DOI: 10.12442/j.issn.1002-185X.20230343
Abstract:
The single crystal (SC) castings of superalloy DD419 were prepared by using seeds deformed in different degrees. The grain structure on the etched seed surface and on the longitudinal sections was examined, combined with the measurement of the corresponding crystal orientation, in order to identify the origin of the stray grains. On the surface of the light-deformed seeds, only slightly?recrystallized?grains were detected, which had no influence on the SC growth of the superalloy castings. In the moderately and severely deformed seeds, however, recrystallized?grains in different degrees were observed. It was deduced that the recrystallization on the surface of deformed seeds occurred during preheating and holding stage, which was very similar to the recrystallization structure formed during the conventional solution heat treatment. These recrystallized grains were partially melted in preheating and pouring stage. In the subsequent solidification process, stray grains grown epitaxially from the unmelted residual recrystallized grains near the remelting interface. The experimental results show that the origin of the stray grains during seeding process is the recrystallization in the seed surface layer, instead of the nucleation of the new grains ahead of the melt-back interface.
The single crystal (SC) castings of superalloy DD419 were prepared by using seeds deformed in different degrees. The grain structure on the etched seed surface and on the longitudinal sections was examined, combined with the measurement of the corresponding crystal orientation, in order to identify the origin of the stray grains. On the surface of the light-deformed seeds, only slightly?recrystallized?grains were detected, which had no influence on the SC growth of the superalloy castings. In the moderately and severely deformed seeds, however, recrystallized?grains in different degrees were observed. It was deduced that the recrystallization on the surface of deformed seeds occurred during preheating and holding stage, which was very similar to the recrystallization structure formed during the conventional solution heat treatment. These recrystallized grains were partially melted in preheating and pouring stage. In the subsequent solidification process, stray grains grown epitaxially from the unmelted residual recrystallized grains near the remelting interface. The experimental results show that the origin of the stray grains during seeding process is the recrystallization in the seed surface layer, instead of the nucleation of the new grains ahead of the melt-back interface.
2024, 53(7):1817-1825.
DOI: 10.12442/j.issn.1002-185X.20230636
Abstract:
(Fe63.3Mn14Si9.1Cr9.8C3.8)99.5?xCuxAg0.5 (x=1, 2, 3, 4, 5, at%) alloys were prepared by water-cooled copper crucible magnetic levitation vacuum melting furnace. The effects of Cu contents on microstructure, corrosion resistance, and antibacterial performance of the alloys were investigated. The results show that the medium entropy alloys possess fcc phase after solid solution and aging treatment. With the increase in Cu content, the Cu-enriched and Ag-enriched fcc2 phase is precipitated on the fcc1 Fe-rich matrix. The corrosion resistance of the alloys in 3.5wt% NaCl solution is superior to that of AISI304. The corrosion current density first decreases and then increases, and the impedance arc radius first increases and then decreases, indicating an initial enhancement and subsequent weakening of the corrosion resistance as the Cu content increases. Moreover, the corrosion rate of the alloys in Escherichia coli suspension shows a trend of increasing first and then decreasing. When x=2 the alloy exhibits the best corrosion resistance, and there is a trade-off effect between the corrosion resistance and antibacterial performance. The fcc2 phase effectively enhances the antibacterial performance of the alloy, and the alloy of x=5 shows the optimal antibacterial rate of 99.94%.
(Fe63.3Mn14Si9.1Cr9.8C3.8)99.5?xCuxAg0.5 (x=1, 2, 3, 4, 5, at%) alloys were prepared by water-cooled copper crucible magnetic levitation vacuum melting furnace. The effects of Cu contents on microstructure, corrosion resistance, and antibacterial performance of the alloys were investigated. The results show that the medium entropy alloys possess fcc phase after solid solution and aging treatment. With the increase in Cu content, the Cu-enriched and Ag-enriched fcc2 phase is precipitated on the fcc1 Fe-rich matrix. The corrosion resistance of the alloys in 3.5wt% NaCl solution is superior to that of AISI304. The corrosion current density first decreases and then increases, and the impedance arc radius first increases and then decreases, indicating an initial enhancement and subsequent weakening of the corrosion resistance as the Cu content increases. Moreover, the corrosion rate of the alloys in Escherichia coli suspension shows a trend of increasing first and then decreasing. When x=2 the alloy exhibits the best corrosion resistance, and there is a trade-off effect between the corrosion resistance and antibacterial performance. The fcc2 phase effectively enhances the antibacterial performance of the alloy, and the alloy of x=5 shows the optimal antibacterial rate of 99.94%.
2024, 53(7):1826-1835.
DOI: 10.12442/j.issn.1002-185X.20230644
Abstract:
The corrugated cold rolling bonding (CCRB) process, as a new rolling technique, has gained widespread attention in the preparation of metal composite plates. However, the mechanical properties of corrugated composite plates and the microstructure of the interface at different reduction levels are not yet clear. Numerical simulation and experimental methods were employed to investigate the preparation of Cu/Al corrugated composite plates under reduction levels of 55%, 60%, 65%, and 70%. A three-dimensional model was established by finite element simulation software ABAQUS to simulate the normal stress and strain curves during the rolling process. The interface morphology of the composite plate was characterized by scanning electron microscopy, electron backscatter diffraction, and X-ray energy dispersive spectroscopy. Results show that the ultimate tensile strength and shear strength reach the maximum values at a reduction level of 65%, measuring 221.08 and 79 MPa, respectively; while they reach the minimum values at a reduction level of 55%, measuring 169.34 and 45 MPa, respectively. Particularly, at reduction levels of 65% and 70%, the composite plate exhibits elongated grains and fine equiaxed grains due to severe plastic deformation. At a reduction level of 70%, excessive rolling force causes microcracks in the matrix metal, leading to a decrease in tensile performance, which is consistent with the mechanical test results.
The corrugated cold rolling bonding (CCRB) process, as a new rolling technique, has gained widespread attention in the preparation of metal composite plates. However, the mechanical properties of corrugated composite plates and the microstructure of the interface at different reduction levels are not yet clear. Numerical simulation and experimental methods were employed to investigate the preparation of Cu/Al corrugated composite plates under reduction levels of 55%, 60%, 65%, and 70%. A three-dimensional model was established by finite element simulation software ABAQUS to simulate the normal stress and strain curves during the rolling process. The interface morphology of the composite plate was characterized by scanning electron microscopy, electron backscatter diffraction, and X-ray energy dispersive spectroscopy. Results show that the ultimate tensile strength and shear strength reach the maximum values at a reduction level of 65%, measuring 221.08 and 79 MPa, respectively; while they reach the minimum values at a reduction level of 55%, measuring 169.34 and 45 MPa, respectively. Particularly, at reduction levels of 65% and 70%, the composite plate exhibits elongated grains and fine equiaxed grains due to severe plastic deformation. At a reduction level of 70%, excessive rolling force causes microcracks in the matrix metal, leading to a decrease in tensile performance, which is consistent with the mechanical test results.
Xu Yang
,
Liu Gaoshang
,
Liu Chengbao
,
Zheng Leizhi
,
Chen Feng
,
Qian Junchao
,
Qiu Yongbin
,
Meng Xianrong
,
Chen Zhigang
2024, 53(7):1855-1862.
DOI: 10.12442/j.issn.1002-185X.E20230043
Abstract:
With the rapid depletion of fossil fuels and a series of environmental problems, it is urgent to develop and to utilize new electrochemical energy storage devices, and the design, preparation and optimization of electrode materials are key factors to determine the performance of supercapacitors. Hydrothermal method was used to convert hollyhock stalks into porous carbon matrix with MnO and Co nanocrystals anchored on it. Results show that the prepared biocarbon has porous structure and good electron transport properties, and the nanosrystal MnO-Co on it has high capacitance. Due to the unique nanostructure of carbon skeleton and large specific surface area (345.9 m2·g-1), MnO-Co nanocrystal/porous carbon shows excellent electrochemical capacitance (146 F·g-1 at 1 A·g-1) and cycle stability. After 1000 cycles, the specific capacity still remains 99.4%.
With the rapid depletion of fossil fuels and a series of environmental problems, it is urgent to develop and to utilize new electrochemical energy storage devices, and the design, preparation and optimization of electrode materials are key factors to determine the performance of supercapacitors. Hydrothermal method was used to convert hollyhock stalks into porous carbon matrix with MnO and Co nanocrystals anchored on it. Results show that the prepared biocarbon has porous structure and good electron transport properties, and the nanosrystal MnO-Co on it has high capacitance. Due to the unique nanostructure of carbon skeleton and large specific surface area (345.9 m2·g-1), MnO-Co nanocrystal/porous carbon shows excellent electrochemical capacitance (146 F·g-1 at 1 A·g-1) and cycle stability. After 1000 cycles, the specific capacity still remains 99.4%.
2024, 53(7):1863-1873.
DOI: 10.12442/j.issn.1002-185X.20230639
Abstract:
It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for T-lap joints, due to the low heat input and poor plastic flow of the inner corner of the T-joint in friction stir welding (FSW), which leads to easy occurrence of wormholes, tunnel, bonding line defects, etc, and thus further causes stress concentration. Therefore, pre-set welding wires at the fillet were innovatively applied to 6061-T6 aluminum alloy (4 mm in thickness) and pure copper dissimilar plate FSW T-lap joints, in order to improve the internal plastic flow of T-joints, reduce defects, and obtain joints with good microstructure and properties. The effect of three types of pre-set wires on the microstructure and mechanical properties of Al/Cu dissimilar FSW T-lap joints was analyzed. Results reveal that three types of pre-set wire joints exhibit onion ring-like pattern in the large pin stirring zone at a constant travel speed of 35 mm/min and a rotation speed of 700?800 r/min. The progressive tool at all rotation speeds effectively inhibits migration of large amounts of stringer material to the skin and avoids base materials mixing. Small amounts of Cu particles are mechanically stirred and have a long flow path in the large pin stirring regions, which inhibits the formation of brittle Al/Cu intermetallic compound (IMC) phases during welding. Al/Cu forms effective metallurgical bonding, and the IMC thickness of the Al/Cu interface is less than 1 μm. The Al/Cu T-joints with pre-set Cu are similar to butt joints of the same material in the skin direction, showing a typical ductile fracture. In Al/Cu T-joints with pre-set Al, the direction of the bonding line defects is changed, a certain height of Al/Cu mixing zone is obtained in the direction of the stringer, achieving optimal mechanical interlocking bonding, and break mostly occurs at the intersection, with a tensile strength of 157 MPa, showing hybrid fracture. The pre-set welding wire is proved to be a good method for Al/Cu dissimilar FSW T-lap joints.
It is difficult to achieve Al/Cu dissimilar welds with good mechanical properties for T-lap joints, due to the low heat input and poor plastic flow of the inner corner of the T-joint in friction stir welding (FSW), which leads to easy occurrence of wormholes, tunnel, bonding line defects, etc, and thus further causes stress concentration. Therefore, pre-set welding wires at the fillet were innovatively applied to 6061-T6 aluminum alloy (4 mm in thickness) and pure copper dissimilar plate FSW T-lap joints, in order to improve the internal plastic flow of T-joints, reduce defects, and obtain joints with good microstructure and properties. The effect of three types of pre-set wires on the microstructure and mechanical properties of Al/Cu dissimilar FSW T-lap joints was analyzed. Results reveal that three types of pre-set wire joints exhibit onion ring-like pattern in the large pin stirring zone at a constant travel speed of 35 mm/min and a rotation speed of 700?800 r/min. The progressive tool at all rotation speeds effectively inhibits migration of large amounts of stringer material to the skin and avoids base materials mixing. Small amounts of Cu particles are mechanically stirred and have a long flow path in the large pin stirring regions, which inhibits the formation of brittle Al/Cu intermetallic compound (IMC) phases during welding. Al/Cu forms effective metallurgical bonding, and the IMC thickness of the Al/Cu interface is less than 1 μm. The Al/Cu T-joints with pre-set Cu are similar to butt joints of the same material in the skin direction, showing a typical ductile fracture. In Al/Cu T-joints with pre-set Al, the direction of the bonding line defects is changed, a certain height of Al/Cu mixing zone is obtained in the direction of the stringer, achieving optimal mechanical interlocking bonding, and break mostly occurs at the intersection, with a tensile strength of 157 MPa, showing hybrid fracture. The pre-set welding wire is proved to be a good method for Al/Cu dissimilar FSW T-lap joints.
2024, 53(7):1928-1936.
DOI: 10.12442/j.issn.1002-185X.20230306
Abstract:
To investigate the effect of longitudinal wave rolling (LR) on the texture of AZ31B magnesium alloy sheet, the AZ31B magnesium alloy sheet was heat treated at 400℃/20min and 450℃/20min, with amplitude of 0.35mm and period of 4mm, longitudinal-wave roll and flat-roll rolling. XRD was used to characterize the macro texture of the heat-treated and rolled plates, and the texture evolution was analyzed by polar diagram and ODF. Meanwhile, the deformation behavior of the metal in the rolling deformation zone was simulated. The results show that the peak texture intensity of (0002) at 400℃ decreases from 11.21 to 8.41, and at 450℃ to 7.08. The texture intensity at 450℃ is weaker than that at 400℃. After longitudinal-wave rolling, the substrate texture of the plate is weakened significantly, and a large number of grains are deflected towards RD and TD,with a maximum deflection of 30° towards RD and 40° towards TD. The peak texture intensity of (0002) decreases to 4.33 at 400℃ and 5.62 at 450℃. The texture weakening effect is more obvious at 400℃ than at 450℃. After two passes of rolling, the texture intensity of the base surface at 450℃ is weaker than that at 400℃. The analysis shows that: LR makes the C-axis orientation of grains deflect from ND to TD and RD. The reason is that there is a " cross-shear zone" similar to that in the process of induction rolling in the process of p-wave rolling, in which the shear force prompts grains along the RD direction. While there is also metal flow and shear force similar to the hetero-tooth combined deformation process and the bending and flattening combined deformation technology. This results in a deflection of grain orientation along the direction of TD.
To investigate the effect of longitudinal wave rolling (LR) on the texture of AZ31B magnesium alloy sheet, the AZ31B magnesium alloy sheet was heat treated at 400℃/20min and 450℃/20min, with amplitude of 0.35mm and period of 4mm, longitudinal-wave roll and flat-roll rolling. XRD was used to characterize the macro texture of the heat-treated and rolled plates, and the texture evolution was analyzed by polar diagram and ODF. Meanwhile, the deformation behavior of the metal in the rolling deformation zone was simulated. The results show that the peak texture intensity of (0002) at 400℃ decreases from 11.21 to 8.41, and at 450℃ to 7.08. The texture intensity at 450℃ is weaker than that at 400℃. After longitudinal-wave rolling, the substrate texture of the plate is weakened significantly, and a large number of grains are deflected towards RD and TD,with a maximum deflection of 30° towards RD and 40° towards TD. The peak texture intensity of (0002) decreases to 4.33 at 400℃ and 5.62 at 450℃. The texture weakening effect is more obvious at 400℃ than at 450℃. After two passes of rolling, the texture intensity of the base surface at 450℃ is weaker than that at 400℃. The analysis shows that: LR makes the C-axis orientation of grains deflect from ND to TD and RD. The reason is that there is a " cross-shear zone" similar to that in the process of induction rolling in the process of p-wave rolling, in which the shear force prompts grains along the RD direction. While there is also metal flow and shear force similar to the hetero-tooth combined deformation process and the bending and flattening combined deformation technology. This results in a deflection of grain orientation along the direction of TD.
2024, 53(7):1944-1952.
DOI: 10.12442/j.issn.1002-185X.20230344
Abstract:
The compression deformation behavior of as-annealed Mg-Nd alloy sheet along rolling direction at room temperature (RT) and cryogenic temperature (CT) of -150℃ were investigated by in-situ electron backscattering diffraction (EBSD), slip trace method and in-grain misorientation angle method. The results show that the twinning mode is not affected by the deformation temperature, in contrast, the twinning nucleation rate and slip types are dramatically affected. Compared with RT compression, local stresses are obviously increased in the sample under CT compression. As a result, the twinning nucleation rate and total length of twin boundary are increased by about 10% and 8% respectively at CT under the same compression deformation strain (4%). In the meantime, non-basal slips are promoted during CT compression deformation, with the proportion of non-basal slips increasing from 45.5% at RT to 65.9% at CT. In addition, the low temperature inhibits basal slip during compression deformation, and the proportion of basal slip decreases from 54.5% at RT to 34.1% at CT.
The compression deformation behavior of as-annealed Mg-Nd alloy sheet along rolling direction at room temperature (RT) and cryogenic temperature (CT) of -150℃ were investigated by in-situ electron backscattering diffraction (EBSD), slip trace method and in-grain misorientation angle method. The results show that the twinning mode is not affected by the deformation temperature, in contrast, the twinning nucleation rate and slip types are dramatically affected. Compared with RT compression, local stresses are obviously increased in the sample under CT compression. As a result, the twinning nucleation rate and total length of twin boundary are increased by about 10% and 8% respectively at CT under the same compression deformation strain (4%). In the meantime, non-basal slips are promoted during CT compression deformation, with the proportion of non-basal slips increasing from 45.5% at RT to 65.9% at CT. In addition, the low temperature inhibits basal slip during compression deformation, and the proportion of basal slip decreases from 54.5% at RT to 34.1% at CT.
2024, 53(7):1962-1969.
DOI: 10.12442/j.issn.1002-185X.20230332
Abstract:
Cr-coated zirconium alloy cladding is an important method to improve the high temperature oxidation resistance of light water reactor fuel assembly. The purpose of this paper is to study the high-temperature oxidation behavior of Cr-coated Zr-4 alloys in steam environment. The Cr-coated Zr-4 alloy samples were prepared by multi-arc ion plating process. High temperature oxidation experiments were carried out in 1000 °C and 1100 °C steam environment. The oxidation weight gain of the sample was obtained by a high-precision balance, and the surface and cross-section micro-morphology, element distribution, phase and thickness of the Cr-Zr diffusion layer were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The results show that there are a large number of droplets of different sizes on the surface of the Cr-coated Zr-4 alloy samples prepared by multi-arc ion plating, and the Cr coating grows preferentially along the (1 1 0) crystal plane. The oxidation weight gain per unit area and time approximately follows a parabolic law. The steam oxidation rate at 1100 °C is significantly higher than that at 1000 °C. At the same temperature, the steam oxidation rate of the Cr-coated Zr-4 alloy is lower than that of the uncoated Zr-4 alloy. After high-temperature steam oxidation, whisker-like oxides were formed on the surface of the samples, and there were a large number of micro-pores between the oxides. After 3 h and 4 h of high temperature steam oxidation at 1100 °C, the surface of the sample was oxidized to form worm-like agglomerates. The cross section of the sample has a layered structure, from the outside to the inside, there are Cr2O3 layer, Cr coating, Cr-Zr diffusion layer, and Zr-4 alloy layer. However, the thickness of the surface Cr2O3 layer does not increase synchronously with the increase of the oxidation time, while the thickness of the Cr-Zr diffusion layer increases with the increase of the oxidation temperature and oxidation time, and has a linear relationship with the oxidation time. Therefore, the Cr-coated Zr-4 alloy prepared by multi-arc ion plating showed good resistance to high temperature steam oxidation at 1000 °C and 1100 °C.
Cr-coated zirconium alloy cladding is an important method to improve the high temperature oxidation resistance of light water reactor fuel assembly. The purpose of this paper is to study the high-temperature oxidation behavior of Cr-coated Zr-4 alloys in steam environment. The Cr-coated Zr-4 alloy samples were prepared by multi-arc ion plating process. High temperature oxidation experiments were carried out in 1000 °C and 1100 °C steam environment. The oxidation weight gain of the sample was obtained by a high-precision balance, and the surface and cross-section micro-morphology, element distribution, phase and thickness of the Cr-Zr diffusion layer were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffractometer (XRD). The results show that there are a large number of droplets of different sizes on the surface of the Cr-coated Zr-4 alloy samples prepared by multi-arc ion plating, and the Cr coating grows preferentially along the (1 1 0) crystal plane. The oxidation weight gain per unit area and time approximately follows a parabolic law. The steam oxidation rate at 1100 °C is significantly higher than that at 1000 °C. At the same temperature, the steam oxidation rate of the Cr-coated Zr-4 alloy is lower than that of the uncoated Zr-4 alloy. After high-temperature steam oxidation, whisker-like oxides were formed on the surface of the samples, and there were a large number of micro-pores between the oxides. After 3 h and 4 h of high temperature steam oxidation at 1100 °C, the surface of the sample was oxidized to form worm-like agglomerates. The cross section of the sample has a layered structure, from the outside to the inside, there are Cr2O3 layer, Cr coating, Cr-Zr diffusion layer, and Zr-4 alloy layer. However, the thickness of the surface Cr2O3 layer does not increase synchronously with the increase of the oxidation time, while the thickness of the Cr-Zr diffusion layer increases with the increase of the oxidation temperature and oxidation time, and has a linear relationship with the oxidation time. Therefore, the Cr-coated Zr-4 alloy prepared by multi-arc ion plating showed good resistance to high temperature steam oxidation at 1000 °C and 1100 °C.
2024, 53(7):1970-1977.
DOI: 10.12442/j.issn.1002-185X.20230324
Abstract:
In this study, Fe and Al were used as joint variables for fine tuning, and the effects of the common changes of Fe and Al on the phase structure, microstructure, compression properties, hardness and friction properties of Fe(2-x)CrMnAlxCu (x=1.3, 1.4, 1.5, 1.6, 1.7) high entropy alloy were detected and analyzed. The experimental results show that the interdendrite and dendrite structure of Fe(2-x)CrMnAlxCu high entropy alloy are composed of bcc phase, and the ordered BCC phase and FeAl phase precipitates are precipitated inside the dendrite, and the content of precipitates increases slightly with the decrease of Fe content and the increase of Al content. The hardness of Fe(2-x)CrMnAlxCu high entropy alloy keeps increasing. When x=1.6, the comprehensive performance of high entropy alloy reaches the best, with the hardness up to 558.5 HV, the yield strength 1205.43 MPa, the compressive strength 1431.52 MPa and the deformation rate 9.06%. In addition, with the decrease of Fe content and the increase of Al content, the segregation of elements in high entropy alloy is alleviated to a certain extent.
In this study, Fe and Al were used as joint variables for fine tuning, and the effects of the common changes of Fe and Al on the phase structure, microstructure, compression properties, hardness and friction properties of Fe(2-x)CrMnAlxCu (x=1.3, 1.4, 1.5, 1.6, 1.7) high entropy alloy were detected and analyzed. The experimental results show that the interdendrite and dendrite structure of Fe(2-x)CrMnAlxCu high entropy alloy are composed of bcc phase, and the ordered BCC phase and FeAl phase precipitates are precipitated inside the dendrite, and the content of precipitates increases slightly with the decrease of Fe content and the increase of Al content. The hardness of Fe(2-x)CrMnAlxCu high entropy alloy keeps increasing. When x=1.6, the comprehensive performance of high entropy alloy reaches the best, with the hardness up to 558.5 HV, the yield strength 1205.43 MPa, the compressive strength 1431.52 MPa and the deformation rate 9.06%. In addition, with the decrease of Fe content and the increase of Al content, the segregation of elements in high entropy alloy is alleviated to a certain extent.
2024, 53(7):1978-1984.
DOI: 10.12442/j.issn.1002-185X.20230283
Abstract:
An amorphous alloy Zr60Al10Co22Ag8 with high thermal stability was designed by introducing Co-Ag atom pair with positive mixing enthalpy and large atomic size difference and reducing Zr content. The as-spun amorphous alloy ribbons were prepared by vacuum single-roller melt-spinning method. The as-spun amorphous alloy ribbons were annealled at different temperatures. The structural characteristics and crystallization behaviors of the as-spun amorphous alloy ribbons were studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and transmission electron microscope (TEM). The formation of clustered glass phase in Zr60Al10Co22Ag8 amorphous alloy and its effect on the thermal stability of the alloy were discussed. The results show that a fully amorphous phase (am) was formed in Zr60Al10Co22Ag8 as-spun alloy ribbons, and there were two exothermic peaks during heating. Clustered glass phase (C-glass) was formed after annealing at temperature just above Tx1. Even heating for up to 24 hours, the alloy ribbons still exhibited atomic disordered structure. The crystallization behavior was as follows: [am] → [C-glass] → [C-glass’ + Al2CoZr6 + AgZr + Ag2Al] → [Al2CoZr6 + AgZr + AlZr3] (where, C-glass" was the crystalline residual clustered glass phase). The existence of a large number of Co-Ag atom pairs with positive mixing enthalpy and large atomic size difference leaded to the difficulty of long range rearrangement of constituent elements, which induced the extremely high resistant to crystallization of clustered glass phase. This kind of amorphous alloys, which can form in clustered glass phase and resist crystallization at wide annealing condition, provide a new design method for new heat-resistant amorphous alloy.
An amorphous alloy Zr60Al10Co22Ag8 with high thermal stability was designed by introducing Co-Ag atom pair with positive mixing enthalpy and large atomic size difference and reducing Zr content. The as-spun amorphous alloy ribbons were prepared by vacuum single-roller melt-spinning method. The as-spun amorphous alloy ribbons were annealled at different temperatures. The structural characteristics and crystallization behaviors of the as-spun amorphous alloy ribbons were studied by X-ray diffraction (XRD), differential scanning calorimeter (DSC), and transmission electron microscope (TEM). The formation of clustered glass phase in Zr60Al10Co22Ag8 amorphous alloy and its effect on the thermal stability of the alloy were discussed. The results show that a fully amorphous phase (am) was formed in Zr60Al10Co22Ag8 as-spun alloy ribbons, and there were two exothermic peaks during heating. Clustered glass phase (C-glass) was formed after annealing at temperature just above Tx1. Even heating for up to 24 hours, the alloy ribbons still exhibited atomic disordered structure. The crystallization behavior was as follows: [am] → [C-glass] → [C-glass’ + Al2CoZr6 + AgZr + Ag2Al] → [Al2CoZr6 + AgZr + AlZr3] (where, C-glass" was the crystalline residual clustered glass phase). The existence of a large number of Co-Ag atom pairs with positive mixing enthalpy and large atomic size difference leaded to the difficulty of long range rearrangement of constituent elements, which induced the extremely high resistant to crystallization of clustered glass phase. This kind of amorphous alloys, which can form in clustered glass phase and resist crystallization at wide annealing condition, provide a new design method for new heat-resistant amorphous alloy.
2024, 53(7):1999-2005.
DOI: 10.12442/j.issn.1002-185X.20230331
Abstract:
Study on vaporization process of nickel powder particles inside direct current thermal plasma can provide theoretical guidelines for improving preparation process of nickel nanopowder. In this paper, The effects of particle size, working gas flow rate and feeder rate on the nickel particle behavior in thermal plasma are investigated by coupled solution of the magnetohydrodynamic equations and particle thermodynamics equations. The research shows that small particles can be heated to complete vaporization in a shorter time owing to longer residence time in the high temperature region; Decrease of working gas flow rate and powder feeder rate can increase the energy of nickel particle get from plasma, thus Improving the quality of the final prepared nano nickel powder.
Study on vaporization process of nickel powder particles inside direct current thermal plasma can provide theoretical guidelines for improving preparation process of nickel nanopowder. In this paper, The effects of particle size, working gas flow rate and feeder rate on the nickel particle behavior in thermal plasma are investigated by coupled solution of the magnetohydrodynamic equations and particle thermodynamics equations. The research shows that small particles can be heated to complete vaporization in a shorter time owing to longer residence time in the high temperature region; Decrease of working gas flow rate and powder feeder rate can increase the energy of nickel particle get from plasma, thus Improving the quality of the final prepared nano nickel powder.
Ma HaiBin
,
Wang Haoyu
,
Zhang Wenhuai
,
Lin Xiaodong
,
Xue Jiaxiang
,
Ren QIsen
,
Liao Yehong
,
Hu Lijuan
,
Sun Rongrong
,
Liang Xue
,
Li Yifeng
,
YAO Meiyi
2024, 53(7):2018-2024.
DOI: 10.12442/j.issn.1002-185X.20230289
Abstract:
The corrosion behavior of Fe13Cr5Al4Mo alloy in 70 μL/L LiOH aqueous solution at 360 °C,18.6 MPa was studied using a static autoclave to assess its corrosion resistance. The microstructure of the oxide film on the Fe13Cr5Al4Mo alloy after corrosion was investigated by SEM, TEM and EDS. The results show that the Fe13Cr5Al4Mo alloy exhibits corrosion weight loss in lithiated water, which is related to the dissolution-redeposition process of Fe oxide affected by LiOH. The oxide film formed on the alloy during the long-term corrosion in lithiated water is mainly composed of Fe(Cr,Al)2O4, and a small amount of Fe3O4 present near the outer surface. The Fe(Cr,Al)2O4 layer can hinder the diffusion of metal ions and oxygen ions within the oxide film, which in turn retards further corrosion of the alloy.
The corrosion behavior of Fe13Cr5Al4Mo alloy in 70 μL/L LiOH aqueous solution at 360 °C,18.6 MPa was studied using a static autoclave to assess its corrosion resistance. The microstructure of the oxide film on the Fe13Cr5Al4Mo alloy after corrosion was investigated by SEM, TEM and EDS. The results show that the Fe13Cr5Al4Mo alloy exhibits corrosion weight loss in lithiated water, which is related to the dissolution-redeposition process of Fe oxide affected by LiOH. The oxide film formed on the alloy during the long-term corrosion in lithiated water is mainly composed of Fe(Cr,Al)2O4, and a small amount of Fe3O4 present near the outer surface. The Fe(Cr,Al)2O4 layer can hinder the diffusion of metal ions and oxygen ions within the oxide film, which in turn retards further corrosion of the alloy.
Chen Yan
,
Fang Yang
,
Jixing Liu
,
Yixuan He
,
Shengnan Zhang
,
Dayou Wang
,
Guo Yan
,
Pingxiang Zhang
2024, 53(7):2059-2066.
DOI: 10.12442/j.issn.1002-185X.20230351
Abstract:
Iron-based superconductors have attracted extensive attention from scientists due to their high critical current density, low anisotropy and extremely high upper critical magnetic field since it was discovered. It has excellent application prospects and is also one of the keys to study the mechanism of high temperature superconductivity. As the simplest iron-based superconducting material, the 11 system iron-based superconductor has become a research hotspot in the field due to its characteristics of no toxic element As and sensitivity to doping. In this paper, the research progress of the practical application of 11 system iron-based superconducting materials is reviewed from two perspectives: wire and strip, coated conductor and thin film.
Iron-based superconductors have attracted extensive attention from scientists due to their high critical current density, low anisotropy and extremely high upper critical magnetic field since it was discovered. It has excellent application prospects and is also one of the keys to study the mechanism of high temperature superconductivity. As the simplest iron-based superconducting material, the 11 system iron-based superconductor has become a research hotspot in the field due to its characteristics of no toxic element As and sensitivity to doping. In this paper, the research progress of the practical application of 11 system iron-based superconducting materials is reviewed from two perspectives: wire and strip, coated conductor and thin film.
2024, 53(7):2083-2093.
DOI: 10.12442/j.issn.1002-185X.20230321
Abstract:
Eutectic high-entropy alloys have received extensive research in recent years due to their good castability and exceptional combination of strength-ductility balance. However, compositional designation of eutectic high-entropy alloys is still a challenge. Based on this challenge, a variety of methods for compositional designation in eutectic high-entropy alloys have been developed. Each method has its own characteristics and limitations. The methods for compositional designation in eutectic high-entropy alloys are reviewed in this paper.
Eutectic high-entropy alloys have received extensive research in recent years due to their good castability and exceptional combination of strength-ductility balance. However, compositional designation of eutectic high-entropy alloys is still a challenge. Based on this challenge, a variety of methods for compositional designation in eutectic high-entropy alloys have been developed. Each method has its own characteristics and limitations. The methods for compositional designation in eutectic high-entropy alloys are reviewed in this paper.
2024, 53(7):2094-2108.
DOI: 10.12442/j.issn.1002-185X.20230301
Abstract:
Laser selective melting (SLM) technology has been widely used in biomedical, aerospace, automotive and military manufacturing industries because of its short processing cycle and easy to form parts with complex structure.SHowever, due to the complex interaction between laser and powder in the forming process, the defects of laser selective melting parts show diversified characteristics, and it is more difficult to control, which limits the development and application of this technology to a certain extent.SThe research on the formation mechanism and control methods of spatter defects is one of the research hotspots in recent years.SThis paper summarizes the relevant research achievements recently, taking powder, molten pool and forming layer as clues, expounds the spatter formation mechanism and control methods in the SLM process from four parts: the influence of spatter on formed parts, the cause of splash formation, the monitoring and control methods and the future research direction, and looks forward to the future development direction.
Laser selective melting (SLM) technology has been widely used in biomedical, aerospace, automotive and military manufacturing industries because of its short processing cycle and easy to form parts with complex structure.SHowever, due to the complex interaction between laser and powder in the forming process, the defects of laser selective melting parts show diversified characteristics, and it is more difficult to control, which limits the development and application of this technology to a certain extent.SThe research on the formation mechanism and control methods of spatter defects is one of the research hotspots in recent years.SThis paper summarizes the relevant research achievements recently, taking powder, molten pool and forming layer as clues, expounds the spatter formation mechanism and control methods in the SLM process from four parts: the influence of spatter on formed parts, the cause of splash formation, the monitoring and control methods and the future research direction, and looks forward to the future development direction.
