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Chinese Society of Aeronautics and Astronautics
AECC Beijing Instistute of Aeronautical Materials
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000213
Abstract:
The silicone rubber with high strength and high-temperature resistant properties was prepared via a dual-vulcanizer system based on the raw silicone rubber containing of both vinyl group and hydroxyl group. The effect of the dosage of cross-linker KH-CL, the processing way of silicon oxide and the antioxidant on the properties of silicone rubber were investigated. The optimum recipe was confirmed. It’s shown that the optimum dosage of KH-CL is 3phr, which is benefit for the vulcanization and the suppression of the main chain of silicone rubber. The silazane treated silicon oxide and home-made antioxidant are the optimum additives of the silicone rubber. The prepared silicone rubber shows outstanding heat-resistant properties at 350 ℃ for a short time and 300 ℃ for a long time.
The silicone rubber with high strength and high-temperature resistant properties was prepared via a dual-vulcanizer system based on the raw silicone rubber containing of both vinyl group and hydroxyl group. The effect of the dosage of cross-linker KH-CL, the processing way of silicon oxide and the antioxidant on the properties of silicone rubber were investigated. The optimum recipe was confirmed. It’s shown that the optimum dosage of KH-CL is 3phr, which is benefit for the vulcanization and the suppression of the main chain of silicone rubber. The silazane treated silicon oxide and home-made antioxidant are the optimum additives of the silicone rubber. The prepared silicone rubber shows outstanding heat-resistant properties at 350 ℃ for a short time and 300 ℃ for a long time.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000219
Abstract:
According to the flanged structure of composite casing, a typical sample with laminated structure manufactured by RTM process was designed using T800 grade carbon fiber fabrics reinforced polyimide composite. The strength property under the uniaxial tension condition was simulated by finite element method, and the calculated fracture load was 21.7 kN. The maximum strain was appeared at the corner of flanged structure, indicated that the corner area of flanged structure was weak relatively. Ultrasonic C-scan and optical microscope methods were applied to analyze the internal quality of the corner area. The results show that the overall internal quality of the sample corner area is good without obvious delamination defects. However, some micro-pores enriched at near surface and the fill region are still visible. The measured average tensile fracture load is 19.81 kN, and that is very close to the calculated value. After cyclic loading with 25% of the fracture load for 24000 times, the residual tensile fracture load is still 19.94 kN, this result means fatigue test has no effect to the mechanical property of the samples. Little interlayer defects and cracks happened in several samples at the corner area, but no visual damage. It shows that the sample can still bear the load after the delamination defects appear.
According to the flanged structure of composite casing, a typical sample with laminated structure manufactured by RTM process was designed using T800 grade carbon fiber fabrics reinforced polyimide composite. The strength property under the uniaxial tension condition was simulated by finite element method, and the calculated fracture load was 21.7 kN. The maximum strain was appeared at the corner of flanged structure, indicated that the corner area of flanged structure was weak relatively. Ultrasonic C-scan and optical microscope methods were applied to analyze the internal quality of the corner area. The results show that the overall internal quality of the sample corner area is good without obvious delamination defects. However, some micro-pores enriched at near surface and the fill region are still visible. The measured average tensile fracture load is 19.81 kN, and that is very close to the calculated value. After cyclic loading with 25% of the fracture load for 24000 times, the residual tensile fracture load is still 19.94 kN, this result means fatigue test has no effect to the mechanical property of the samples. Little interlayer defects and cracks happened in several samples at the corner area, but no visual damage. It shows that the sample can still bear the load after the delamination defects appear.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000079
Abstract:
The honeycomb core replacement scarf repair method was used to repair the one side face-sheet and honeycomb core damage of aluminum honeycomb sandwich composite plate. The drop hammer impact tests were carried out on the intact honeycomb sandwich panel and the repaired honeycomb sandwich panel, and the influence of honeycomb core replacement scarf repair on the impact resistance properties was compared and analyzed. X-ray digital imaging technology and macroscopic observation were used to investigate the damage forms and internal failure mechanisms of composite repair structure under the low velocity impact. The residual compression property after impact was characterized. The results show that with the increase of impact energy, the damage areas of both intact and repaired honeycomb sandwich panels are increased, the damage area of intact honeycomb sandwich panel is larger than that of repaired ones under the same impact energy. The impact load curve type of repaired honeycomb sandwich panel is changed completely, and the repaired honeycomb sandwich panel shows better impact resistance. Under the same impact energy, the CAI strength of the repaired honeycomb sandwich panel is higher than that of the intact ones. The failure mechanism includes the expansion of impact damage and compression damage. The impact resistance of the honeycomb splicing area is the best.
The honeycomb core replacement scarf repair method was used to repair the one side face-sheet and honeycomb core damage of aluminum honeycomb sandwich composite plate. The drop hammer impact tests were carried out on the intact honeycomb sandwich panel and the repaired honeycomb sandwich panel, and the influence of honeycomb core replacement scarf repair on the impact resistance properties was compared and analyzed. X-ray digital imaging technology and macroscopic observation were used to investigate the damage forms and internal failure mechanisms of composite repair structure under the low velocity impact. The residual compression property after impact was characterized. The results show that with the increase of impact energy, the damage areas of both intact and repaired honeycomb sandwich panels are increased, the damage area of intact honeycomb sandwich panel is larger than that of repaired ones under the same impact energy. The impact load curve type of repaired honeycomb sandwich panel is changed completely, and the repaired honeycomb sandwich panel shows better impact resistance. Under the same impact energy, the CAI strength of the repaired honeycomb sandwich panel is higher than that of the intact ones. The failure mechanism includes the expansion of impact damage and compression damage. The impact resistance of the honeycomb splicing area is the best.
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Available online
, doi: 10.11868/j.issn.1005-5053.2022.000024
Abstract:
Lithium-sulfur battery is a kind of energy storage system with high specific capacity, low production cost and environmental friendliness. It has great development potential and application prospect in portable electronic device energy storage. However, lithium-sulfur batteries still face the problems of low Coulomb efficiency and short lifespan in practical applications. This is mainly attributed to polysulfide shuttle effect, low electrical conductivity of S8 and Li2S and uncontrolled lithium dendrite growth. The inhibition of lithium dendrite growth and the inhibition of the reaction between soluble polysulfide and lithium can not only enhance the safety and electrochemical performance of lithium sulfur batteries, but also play an important role in high-capacity lithium sulfur batteries. In this paper, the development of lithium-sulfur battery is reviewed, and the progress of high-sulfur loaded lithium battery is introduced emphatically. By analyzing the mechanism, we can understand the operation mechanism of lithium sulfur battery and develop improvement methods, including the use of graded porous carbon for cathode and element doping to increase the sulfur loading rate of active substance and reduce the shuttle effect of polysulfide. The development of liquid and solid electrolyte systems and strategies to enhance anode stability are also introduced. In addition, we believe that in-depth understanding of the mechanism of lithium-sulfur batteries can strengthen the cognition of lithium-sulfur batteries and guide the future development of high-sulfur loaded lithium-sulfur batteries. At the same time, improving synergies between components can further advance lithium-sulfur battery technology from button batteries and flexible pack batteries to subsequent commercial scale applications.
Lithium-sulfur battery is a kind of energy storage system with high specific capacity, low production cost and environmental friendliness. It has great development potential and application prospect in portable electronic device energy storage. However, lithium-sulfur batteries still face the problems of low Coulomb efficiency and short lifespan in practical applications. This is mainly attributed to polysulfide shuttle effect, low electrical conductivity of S8 and Li2S and uncontrolled lithium dendrite growth. The inhibition of lithium dendrite growth and the inhibition of the reaction between soluble polysulfide and lithium can not only enhance the safety and electrochemical performance of lithium sulfur batteries, but also play an important role in high-capacity lithium sulfur batteries. In this paper, the development of lithium-sulfur battery is reviewed, and the progress of high-sulfur loaded lithium battery is introduced emphatically. By analyzing the mechanism, we can understand the operation mechanism of lithium sulfur battery and develop improvement methods, including the use of graded porous carbon for cathode and element doping to increase the sulfur loading rate of active substance and reduce the shuttle effect of polysulfide. The development of liquid and solid electrolyte systems and strategies to enhance anode stability are also introduced. In addition, we believe that in-depth understanding of the mechanism of lithium-sulfur batteries can strengthen the cognition of lithium-sulfur batteries and guide the future development of high-sulfur loaded lithium-sulfur batteries. At the same time, improving synergies between components can further advance lithium-sulfur battery technology from button batteries and flexible pack batteries to subsequent commercial scale applications.
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Available online
, doi: 10.11868/j.issn.1005-5053.2022.000022
Abstract:
The influences of aging on the structure and properties of quartz fiber and its polyimide composites (QW280/AC721) were studied by the artificial accelerated thermal-oxidative aging experiments. The results show that after aging at 300 ℃ for 150 h, the tensile strength of quartz fiber is significantly reduced with the retention ratio of only 44%, which is ascribed to the oxidation and decomposition of the surface wetting agent of the quartz fiber. However, due to the protective effect of polyimide resin on the fiber, the mechanical properties of the polyimide composites have a high retention rate. After aging at 300 ℃ for 150 h, the modulus of the composites shows no obvious change, the retention ratios of tensile strength at room temperature and at 300 ℃ are above 75% and 91% respectively, and the retention ratios of bending and interlaminar shear strength are both above 85%. The dielectric properties of the composites are stable upon the high temperature treatment. After the thermal-oxidative aging at 300 ℃ for different time periods (0-150 h), the dielectric constant in the frequency band of 7-18 GHz remains in the range of 3.5-3.8, and the dielectric loss tangent is lower than 5×10−3.
The influences of aging on the structure and properties of quartz fiber and its polyimide composites (QW280/AC721) were studied by the artificial accelerated thermal-oxidative aging experiments. The results show that after aging at 300 ℃ for 150 h, the tensile strength of quartz fiber is significantly reduced with the retention ratio of only 44%, which is ascribed to the oxidation and decomposition of the surface wetting agent of the quartz fiber. However, due to the protective effect of polyimide resin on the fiber, the mechanical properties of the polyimide composites have a high retention rate. After aging at 300 ℃ for 150 h, the modulus of the composites shows no obvious change, the retention ratios of tensile strength at room temperature and at 300 ℃ are above 75% and 91% respectively, and the retention ratios of bending and interlaminar shear strength are both above 85%. The dielectric properties of the composites are stable upon the high temperature treatment. After the thermal-oxidative aging at 300 ℃ for different time periods (0-150 h), the dielectric constant in the frequency band of 7-18 GHz remains in the range of 3.5-3.8, and the dielectric loss tangent is lower than 5×10−3.
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Available online
, doi: 10.11868/j.issn.1005-5053.2021.000163
Abstract:
Thermoplastic composites have excellent mechanical properties and are ideal structure materials for reusable launch vehicles. The research of mechanical behavior has attracted tremendous attention in the fields of solid mechanics and material sciences worldwide. In this paper, the prediction methods of macro-mechanical properties, plastic constitutive relations, damage and fracture mechanical behavior, and analysis of mechanical behavior of typical structures of thermoplastic composite are reviewed. At present, many important key problems need to be solved, such as accurate prediction of macroscopic mechanical properties of thermoplastic composites, reasonable characterization of elastoplastic damage mechanical behavior of thermoplastic composites, and simulation of mechanical behavior of thermoplastic composite structures in complex multi-field coupling environment such as aerodynamic heating, overload and impact. Future research can be carried out from the following aspects: (1) to establish a unified macro and micro mechanical property prediction model of thermoplastic composites, (2) carry out macro and meso-mechanical analysis of carbon nanotubes reinforced thermoplastic composites, (3) study the mechanical behavior of thermoplastic composites under typical multifield coupling environment such as thermodynamic coupling, (4) carry out structure-level experimental research on thermoplastic composites.
Thermoplastic composites have excellent mechanical properties and are ideal structure materials for reusable launch vehicles. The research of mechanical behavior has attracted tremendous attention in the fields of solid mechanics and material sciences worldwide. In this paper, the prediction methods of macro-mechanical properties, plastic constitutive relations, damage and fracture mechanical behavior, and analysis of mechanical behavior of typical structures of thermoplastic composite are reviewed. At present, many important key problems need to be solved, such as accurate prediction of macroscopic mechanical properties of thermoplastic composites, reasonable characterization of elastoplastic damage mechanical behavior of thermoplastic composites, and simulation of mechanical behavior of thermoplastic composite structures in complex multi-field coupling environment such as aerodynamic heating, overload and impact. Future research can be carried out from the following aspects: (1) to establish a unified macro and micro mechanical property prediction model of thermoplastic composites, (2) carry out macro and meso-mechanical analysis of carbon nanotubes reinforced thermoplastic composites, (3) study the mechanical behavior of thermoplastic composites under typical multifield coupling environment such as thermodynamic coupling, (4) carry out structure-level experimental research on thermoplastic composites.
2022, 42(4): 1 -15
doi: 10.11868/j.issn.1005-5053.2020.000053
Abstract:
More rigorous challenge is put forward by the demand on the structure and thermal protection system of super sonic air-crafts with faster flight speed and longer flight time. The integrated design of structure and thermal protection can give consideration to both load and thermal protection functions, which can give full play to the potential high temperature strength , reduce the thermal stress caused by temperature difference of different parts, and reduce the quality of the thermal protection and structure. It has higher structure efficiency than traditional thermal protection, and can be reused at the same time, reducing the cost. This paper briefly described the research status of integrated thermal protection technology at home and abroad.On this basis, the characteristics and shortcomings of integrated thermal protection were summarized, and the development trend of integrated thermal protection was discussed.China is still in a development stage. Widening the technical cognition of integral technology of structure and thermal protection, actively developing low-cost co-cured technology of structure material and thermal protection material, continuously introducing new thermal protective materials, and sparing no effort to strengthen research and development of the active cooling technology of integrated thermal protection systems is a feasible way of domestic integral technology of structure and thermal protection being quickly applied to models.
More rigorous challenge is put forward by the demand on the structure and thermal protection system of super sonic air-crafts with faster flight speed and longer flight time. The integrated design of structure and thermal protection can give consideration to both load and thermal protection functions, which can give full play to the potential high temperature strength , reduce the thermal stress caused by temperature difference of different parts, and reduce the quality of the thermal protection and structure. It has higher structure efficiency than traditional thermal protection, and can be reused at the same time, reducing the cost. This paper briefly described the research status of integrated thermal protection technology at home and abroad.On this basis, the characteristics and shortcomings of integrated thermal protection were summarized, and the development trend of integrated thermal protection was discussed.China is still in a development stage. Widening the technical cognition of integral technology of structure and thermal protection, actively developing low-cost co-cured technology of structure material and thermal protection material, continuously introducing new thermal protective materials, and sparing no effort to strengthen research and development of the active cooling technology of integrated thermal protection systems is a feasible way of domestic integral technology of structure and thermal protection being quickly applied to models.
2022, 42(4): 16 -27
doi: 10.11868/j.issn.1005-5053.2022.000004
Abstract:
As a new type of structural-functional material developed in recent years, steel foam has the advantages of high specific strength and specific stiffness, high specific surface area, light weight, energy absorption and shock absorption, porous filtration, electromagnetic shielding and biocompatibility. It has a broad application prospect in aerospace, automobile, shipbuilding, civil engineering, heat dissipation and heat insulation, catalysis and filtration, electromagnetic shielding, biomedical engineering and other fields. In this paper, the research and development situation and existing problems of new steel foam are reviewed, and the preparation process, structure , performance characteristics and application fields of steel form are introduced, including the advantages and disadvantages of the existing preparation process, cell structure characteristics, mechanical properties （yield strength, elastic modulus, energy absorption value）, physical properties （heat dissipation and insulation, sound absorption and insulation, electromagnetic shielding）, biological properties and application of steel foam. The existing problems of steel foam and the limiting factors of its industrial development and application are analyzed. In general, the existing research has proved the feasibility of steel foam development and application as a light-weight high strength structural material and a special functional material, and pointed out the technical and theoretical research work to be carried out in the future.
As a new type of structural-functional material developed in recent years, steel foam has the advantages of high specific strength and specific stiffness, high specific surface area, light weight, energy absorption and shock absorption, porous filtration, electromagnetic shielding and biocompatibility. It has a broad application prospect in aerospace, automobile, shipbuilding, civil engineering, heat dissipation and heat insulation, catalysis and filtration, electromagnetic shielding, biomedical engineering and other fields. In this paper, the research and development situation and existing problems of new steel foam are reviewed, and the preparation process, structure , performance characteristics and application fields of steel form are introduced, including the advantages and disadvantages of the existing preparation process, cell structure characteristics, mechanical properties （yield strength, elastic modulus, energy absorption value）, physical properties （heat dissipation and insulation, sound absorption and insulation, electromagnetic shielding）, biological properties and application of steel foam. The existing problems of steel foam and the limiting factors of its industrial development and application are analyzed. In general, the existing research has proved the feasibility of steel foam development and application as a light-weight high strength structural material and a special functional material, and pointed out the technical and theoretical research work to be carried out in the future.
2022, 42(4): 28 -38
doi: 10.11868/j.issn.1005-5053.2020.000173
Abstract:
Oxidation tests of direct-sintered SiC were conducted in tube furnace in static air at 1200 ℃, 1300 ℃ and 1400 ℃ for 1 h, 5 h, 12 h and in Thermogravimetric Analyzer (TGA) at the same temperature for 24 h to obtain continuous mass change curves. Grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) were used to characterize the oxidation products and to reveal the underlying mechanisms. And the ReaxFF Reactive Molecular Dynamics (ReaxFF MD) simulation was conducted in open-source LAMMPS code to study the oxidation behaviors of 6H-SiC. The results of Oxidation tests show that the oxidation of direct-sintered SiC obeys parabolic law, indicating the oxidation process is controlled by the diffusion of O2. Besides, it takes on a 3-stages oxidation kinetics. Morphology of oxide layer initially shows a transition from amorphous SiO2 to spherulitic features accompanied by a decreasing oxidation rate. After a long-time oxidation, spherulitic features are transformed to fine grain structure along with an increasing oxidation rate. The transition of SiO2 structure and the variation in oxidation rate are probably associated with the specific diffusion mode of O2 in the oxide layer. In combination with ReaxFF MD simulation, the oxidation mechanism of 6H-SiC is obtained. It reveals that O2 diffusion inwards controls the oxidation reaction of 6H-SiC along with the formation of C element, followed by oxidation into CO and CO2 and escapes in the form of bubbles.
Oxidation tests of direct-sintered SiC were conducted in tube furnace in static air at 1200 ℃, 1300 ℃ and 1400 ℃ for 1 h, 5 h, 12 h and in Thermogravimetric Analyzer (TGA) at the same temperature for 24 h to obtain continuous mass change curves. Grazing incidence X-ray diffraction (GIXRD), field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS) were used to characterize the oxidation products and to reveal the underlying mechanisms. And the ReaxFF Reactive Molecular Dynamics (ReaxFF MD) simulation was conducted in open-source LAMMPS code to study the oxidation behaviors of 6H-SiC. The results of Oxidation tests show that the oxidation of direct-sintered SiC obeys parabolic law, indicating the oxidation process is controlled by the diffusion of O2. Besides, it takes on a 3-stages oxidation kinetics. Morphology of oxide layer initially shows a transition from amorphous SiO2 to spherulitic features accompanied by a decreasing oxidation rate. After a long-time oxidation, spherulitic features are transformed to fine grain structure along with an increasing oxidation rate. The transition of SiO2 structure and the variation in oxidation rate are probably associated with the specific diffusion mode of O2 in the oxide layer. In combination with ReaxFF MD simulation, the oxidation mechanism of 6H-SiC is obtained. It reveals that O2 diffusion inwards controls the oxidation reaction of 6H-SiC along with the formation of C element, followed by oxidation into CO and CO2 and escapes in the form of bubbles.
2022, 42(4): 39 -48
doi: 10.11868/j.issn.1005-5053.2021.000210
Abstract:
Short beam shear (SBS) test combined with digital image correlation (DIC) can quickly identify the multiple mechanical properties of unidirectional fiber reinforced resin matrix composites. In addition, the complete interlaminar shear stress-strain behavior and interlaminar shear strength of composite materials under uniaxial stress state can be obtained, which is very important to establish the strength criterion of three-dimensional stress state of composite materials with thick section. In order to study the influence of experimental design on the identification accuracy of interlaminar shear mechanical parameters of materials, two stereo digital image correlation systems composed of four CCD cameras were developed for the first time in this paper, and the strain distribution in the front and back surface gage regions of the sample during loading in SBS test was measured. The experimental results show that the shear strain distribution on the front and back surfaces of the sample is asymmetrical, and the relative deviation is up to 44%, because of the thread clearance of fixture and insufficient fixture stiffness. On the one hand, a new method is proposed to identify the shear mechanical properties of materials according to the asymmetrical distribution of shear strain on the front and back surfaces of the sample. By using DIC technology and finite element model updating (FEMU), the measured average shear strain in the distance region of the front and back surfaces of the specimen and the variance of the calculated strain data at the corresponding position of the finite element model are used as the objective function to identify the constitutive parameters and off-axis angles. The complete nonlinear shear constitutive parameters can be obtained, and the identification process is not sensitive to the initial parameters. On the other hand, by improving the test fixture to improve the tool stiffness, the phenomenon of asymmetric shear strain distribution is eliminated, and the complete interlaminar shear stress-strain constitutive relationship parameters of unidirectional laminates are accurately identified.
Short beam shear (SBS) test combined with digital image correlation (DIC) can quickly identify the multiple mechanical properties of unidirectional fiber reinforced resin matrix composites. In addition, the complete interlaminar shear stress-strain behavior and interlaminar shear strength of composite materials under uniaxial stress state can be obtained, which is very important to establish the strength criterion of three-dimensional stress state of composite materials with thick section. In order to study the influence of experimental design on the identification accuracy of interlaminar shear mechanical parameters of materials, two stereo digital image correlation systems composed of four CCD cameras were developed for the first time in this paper, and the strain distribution in the front and back surface gage regions of the sample during loading in SBS test was measured. The experimental results show that the shear strain distribution on the front and back surfaces of the sample is asymmetrical, and the relative deviation is up to 44%, because of the thread clearance of fixture and insufficient fixture stiffness. On the one hand, a new method is proposed to identify the shear mechanical properties of materials according to the asymmetrical distribution of shear strain on the front and back surfaces of the sample. By using DIC technology and finite element model updating (FEMU), the measured average shear strain in the distance region of the front and back surfaces of the specimen and the variance of the calculated strain data at the corresponding position of the finite element model are used as the objective function to identify the constitutive parameters and off-axis angles. The complete nonlinear shear constitutive parameters can be obtained, and the identification process is not sensitive to the initial parameters. On the other hand, by improving the test fixture to improve the tool stiffness, the phenomenon of asymmetric shear strain distribution is eliminated, and the complete interlaminar shear stress-strain constitutive relationship parameters of unidirectional laminates are accurately identified.
2022, 42(4): 49 -56
doi: 10.11868/j.issn.1005-5053.2022.000036
Abstract:
The 10Cr13Co13Mo5Ni3W1VE(S280) ultra-high strength stainless steel was subjected to isothermal and constant strain rate compression experiments at deformation temperature of 800-1150 °C, the strain rate of 0.001-10 s–1, and the deformation amount of 70% by using Thermecmaster-Z thermal simulation testing machine. The hot deformation behavior of the steel was analyzed, and the processing maps based on Murty instability criterion were established. The results show that the flow stress of S280 ultra-high strength stainless steel during hot deformation is sensitive to deformation temperature and strain rate. With the increase of strain rate and the decrease of deformation temperature, the flow stress increases significantly. It is determined that the region of instability occurs in the temperature range of 800-1040 °C and strain rate range of 0.06-10 s–1, and the corresponding instability deformation mechanism is mainly flow localization. The desired parameters are 1095-1150 ℃ and 0.001-0.04 s–1 with the plastic deformation mechanism of dynamic recrystallization, and the optimum parameters are around 1125 ℃ and 0.001 s–1.
The 10Cr13Co13Mo5Ni3W1VE(S280) ultra-high strength stainless steel was subjected to isothermal and constant strain rate compression experiments at deformation temperature of 800-1150 °C, the strain rate of 0.001-10 s–1, and the deformation amount of 70% by using Thermecmaster-Z thermal simulation testing machine. The hot deformation behavior of the steel was analyzed, and the processing maps based on Murty instability criterion were established. The results show that the flow stress of S280 ultra-high strength stainless steel during hot deformation is sensitive to deformation temperature and strain rate. With the increase of strain rate and the decrease of deformation temperature, the flow stress increases significantly. It is determined that the region of instability occurs in the temperature range of 800-1040 °C and strain rate range of 0.06-10 s–1, and the corresponding instability deformation mechanism is mainly flow localization. The desired parameters are 1095-1150 ℃ and 0.001-0.04 s–1 with the plastic deformation mechanism of dynamic recrystallization, and the optimum parameters are around 1125 ℃ and 0.001 s–1.
2022, 42(4): 57 -64
doi: 10.11868/j.issn.1005-5053.2021.000170
Abstract:
The different heat transfer conditions in each region of the vacuum arc remelting superalloy ingot lead to significant difference in the morphology and size distribution of carbide in the ingot. Based on industrial vacuum arc remelting GH4742 alloy as a raw material, using metallographic and scanning electron microscopic analysis quantitative analysis method to study the ingot different position distribution of the carbide precipitation behavior and microstructure, supplemented by MeltFlow-VAR simulation software, the solidification process of remelting different cooling rate and local solidification time on the influence of carbide were analyzed. The results show that Nb and Ti elements are enriched in the carbide precipitates of GH4742 alloy, and the segregation degree of Nb element is the largest. The area of the precipitated phase is decreased from the center to the edge, and the morphology is changed from skeleton-like and cursive to interconnected fine strips. As the cooling rate increases, the dendrites become more slender and compact, and the dendrite spacing decreases. The area of precipitated phase is linearly related to the secondary dendrite spacing. Increasing the cooling rate can reduce the dendrite spacing, thus the area of precipitated phase is reduced effectively.
The different heat transfer conditions in each region of the vacuum arc remelting superalloy ingot lead to significant difference in the morphology and size distribution of carbide in the ingot. Based on industrial vacuum arc remelting GH4742 alloy as a raw material, using metallographic and scanning electron microscopic analysis quantitative analysis method to study the ingot different position distribution of the carbide precipitation behavior and microstructure, supplemented by MeltFlow-VAR simulation software, the solidification process of remelting different cooling rate and local solidification time on the influence of carbide were analyzed. The results show that Nb and Ti elements are enriched in the carbide precipitates of GH4742 alloy, and the segregation degree of Nb element is the largest. The area of the precipitated phase is decreased from the center to the edge, and the morphology is changed from skeleton-like and cursive to interconnected fine strips. As the cooling rate increases, the dendrites become more slender and compact, and the dendrite spacing decreases. The area of precipitated phase is linearly related to the secondary dendrite spacing. Increasing the cooling rate can reduce the dendrite spacing, thus the area of precipitated phase is reduced effectively.
2022, 42(4): 65 -74
doi: 10.11868/j.issn.1005-5053.2020.000198
Abstract:
The light-weight and high-stiffness metal lattice sandwich structure formed by selective laser melting has an important application prospect in aerospace, military and other fields. In this study, the response of square lattice sandwich panels with different core spacings under three-point bending was analyzed by finite element analysis, and the results were verified by experimental samples formed by selective laser melting. The results show that there is a linear relationship between the core spacing and cylindrical bending stiffness when the core spacing is within a certain range, the influence of core spacing on cylindrical bending stiffness is very significant and the influence of core spacing on the cylindrical bending stiffness of the square lattice sandwich panel of 45° is greater than that of the square lattice sandwich panel of 0°. The cylindrical bending stiffness of square lattice sandwich panel of 0° and 45° is basically the same under the same relative density when the relative density is within a certain range, which means that they have similar cylindrical bending stiffness under the same weight. When the relative density is less than 5%, the relative density has a significant influence on the cylindrical bending stiffness, and the influence decreases when the relative density exceeds 5%. With the increase of the core spacing, the stress concentration area is transferred from the part of panel under the loading pad to the ends of cores between the support pads due to the reduction of the cylindrical bending resistance of the lattice structure. According to the mechanical analysis, the initial load prediction formula for the yield and plastic stages can be proposed, The comparison between the theoretical results and the FEA results shows that the relative error is less than 13.6%, indicating that the formula is relatively accurate. The experimental results are in good agreement with the FEA results, especially for the cylindrical bending stiffness, the relative error between the FEA value and the experimental value is only less than 6.5%, indicating that the three-point bending deformation and mechanical properties of the lattice sandwich panel can be effectively predicted by FEA.
The light-weight and high-stiffness metal lattice sandwich structure formed by selective laser melting has an important application prospect in aerospace, military and other fields. In this study, the response of square lattice sandwich panels with different core spacings under three-point bending was analyzed by finite element analysis, and the results were verified by experimental samples formed by selective laser melting. The results show that there is a linear relationship between the core spacing and cylindrical bending stiffness when the core spacing is within a certain range, the influence of core spacing on cylindrical bending stiffness is very significant and the influence of core spacing on the cylindrical bending stiffness of the square lattice sandwich panel of 45° is greater than that of the square lattice sandwich panel of 0°. The cylindrical bending stiffness of square lattice sandwich panel of 0° and 45° is basically the same under the same relative density when the relative density is within a certain range, which means that they have similar cylindrical bending stiffness under the same weight. When the relative density is less than 5%, the relative density has a significant influence on the cylindrical bending stiffness, and the influence decreases when the relative density exceeds 5%. With the increase of the core spacing, the stress concentration area is transferred from the part of panel under the loading pad to the ends of cores between the support pads due to the reduction of the cylindrical bending resistance of the lattice structure. According to the mechanical analysis, the initial load prediction formula for the yield and plastic stages can be proposed, The comparison between the theoretical results and the FEA results shows that the relative error is less than 13.6%, indicating that the formula is relatively accurate. The experimental results are in good agreement with the FEA results, especially for the cylindrical bending stiffness, the relative error between the FEA value and the experimental value is only less than 6.5%, indicating that the three-point bending deformation and mechanical properties of the lattice sandwich panel can be effectively predicted by FEA.
2022, 42(4): 75 -82
doi: 10.11868/j.issn.1005-5053.2021.000216
Abstract:
C/C-SiC composites was prepared by “chemical vapor infiltration + precursor impregnation pyrolysis” (CVI+PIP) combined process by needle preform laying separately with 3K twilled carbon cloth and 12K non-latitude cloth. The long-term oxidation resistance and erosion resistance test of composites were realized by using long-term oxyacetylene ablation test and high- temperature particle erosion test, and the main factors affecting their anti-ablation benavior were studied. The results show that the C/C-SiC composites have certain degree of ablation occurred after 600 s acetylene ablation, the linear ablation rates, mass ablation rates and ablation depth of the material formed by the preform of the non-latitude cloth are lower than that of the material prefabricated with the twilled carbon cloth. Using particles erosion test, the results of the two materials are consistent and the specimen flushing surface presents obvious characteristics of mechanical flushing the the depth of the flushing pit can be reached 7.21-7.25 mm after just 10 seconds. While without the particle airflow flushing test, the degree of material erosion decreased significantly. C/C-SiC composites in the actual use of the process is generally subject to air flow pressure, particle impact and high temperature oxidation of the combined effect, among them the mechanical ablation caused by particle impact has a greater impact on the failure of C/C-SiC composites than thermo-chemical ablation caused by long-term high temperature oxidation, which directly affects the performance of the material.
C/C-SiC composites was prepared by “chemical vapor infiltration + precursor impregnation pyrolysis” (CVI+PIP) combined process by needle preform laying separately with 3K twilled carbon cloth and 12K non-latitude cloth. The long-term oxidation resistance and erosion resistance test of composites were realized by using long-term oxyacetylene ablation test and high- temperature particle erosion test, and the main factors affecting their anti-ablation benavior were studied. The results show that the C/C-SiC composites have certain degree of ablation occurred after 600 s acetylene ablation, the linear ablation rates, mass ablation rates and ablation depth of the material formed by the preform of the non-latitude cloth are lower than that of the material prefabricated with the twilled carbon cloth. Using particles erosion test, the results of the two materials are consistent and the specimen flushing surface presents obvious characteristics of mechanical flushing the the depth of the flushing pit can be reached 7.21-7.25 mm after just 10 seconds. While without the particle airflow flushing test, the degree of material erosion decreased significantly. C/C-SiC composites in the actual use of the process is generally subject to air flow pressure, particle impact and high temperature oxidation of the combined effect, among them the mechanical ablation caused by particle impact has a greater impact on the failure of C/C-SiC composites than thermo-chemical ablation caused by long-term high temperature oxidation, which directly affects the performance of the material.
2022, 42(4): 83 -94
doi: 10.11868/j.issn.1005-5053.2021.000195
Abstract:
WC is one of the cladding synthetic materials that effectively improve the surface tribological properties of TC4 alloy, but it is easy to produce residues in the coating, which always plagues the quality and performance of the coating. In this study, TC4+WC titanium wear-resistant coatings with different WC addition ratios (5%, 10% and 15% (mass fraction /%)) were prepared on the surface of TC4 by coaxial powder feeding laser cladding technology, and the macrostructure, microhardness and tribological properties of the coating were analyzed and studied, focusing on the melting and residue mechanism of WC in the molten pool. The results show that the addition of WC does not affect the types of phases formed in the coatings. The precipitated phases mainly include in-situ TiC and matrix phases α-Ti and β-Ti. Among them, TiC and the remaining WC particles in the coating form a coherent package mosaic structure phase. The decomposition of WC in the molten pool is prevented, leading to the remaining WC is prone to residue and agglomeration. The amount of WC added is positively correlated with the microhardness of the coating. As the WC content in the material system gradually increases, the wear resistance of the coating gradually increases, and compared with the TC4 substrate, the wear rate of the coating decreases by about 21.1%, 38.2%, and 56.1%, respectively, but the residual WC leads to local stress concentration in the friction and wear process of the coating, the tribological performance fluctuates significantly.
WC is one of the cladding synthetic materials that effectively improve the surface tribological properties of TC4 alloy, but it is easy to produce residues in the coating, which always plagues the quality and performance of the coating. In this study, TC4+WC titanium wear-resistant coatings with different WC addition ratios (5%, 10% and 15% (mass fraction /%)) were prepared on the surface of TC4 by coaxial powder feeding laser cladding technology, and the macrostructure, microhardness and tribological properties of the coating were analyzed and studied, focusing on the melting and residue mechanism of WC in the molten pool. The results show that the addition of WC does not affect the types of phases formed in the coatings. The precipitated phases mainly include in-situ TiC and matrix phases α-Ti and β-Ti. Among them, TiC and the remaining WC particles in the coating form a coherent package mosaic structure phase. The decomposition of WC in the molten pool is prevented, leading to the remaining WC is prone to residue and agglomeration. The amount of WC added is positively correlated with the microhardness of the coating. As the WC content in the material system gradually increases, the wear resistance of the coating gradually increases, and compared with the TC4 substrate, the wear rate of the coating decreases by about 21.1%, 38.2%, and 56.1%, respectively, but the residual WC leads to local stress concentration in the friction and wear process of the coating, the tribological performance fluctuates significantly.
2022, 42(4): 95 -103
doi: 10.11868/j.issn.1005-5053.2019.000100
Abstract:
Cu-1.3Cr alloys with directional pore structure were fabricated under hydrogen atmosphere. The pore morphology during the solidification is investigated. It is found that the porosity is increased from 18% to 44% and the average pore diameter was decreased from 3.24 mm to 0.44 mm when the hydrogen pressure varies from 0.1 MPa to 0.6 MPa. Theoretical analysis shows the gas pore pressure drops significantly during the growth of pore. For a coarse pore, the drops of pore pressure will result in a backflow of the melt from solidification interface into gas pore, and this will result in a “bamboo” like structure. For small gas pores, the pressure difference between two neighboring gas pores drives the hydrogen gas from the short one to the long one. This is the reason that a short pore more easily coalesce with a long pore.
Cu-1.3Cr alloys with directional pore structure were fabricated under hydrogen atmosphere. The pore morphology during the solidification is investigated. It is found that the porosity is increased from 18% to 44% and the average pore diameter was decreased from 3.24 mm to 0.44 mm when the hydrogen pressure varies from 0.1 MPa to 0.6 MPa. Theoretical analysis shows the gas pore pressure drops significantly during the growth of pore. For a coarse pore, the drops of pore pressure will result in a backflow of the melt from solidification interface into gas pore, and this will result in a “bamboo” like structure. For small gas pores, the pressure difference between two neighboring gas pores drives the hydrogen gas from the short one to the long one. This is the reason that a short pore more easily coalesce with a long pore.
2016, 36(4): 89-98
doi: 10.11868/j.issn.1005-5053.2016.4.013
2020, 40(3): 77-94
doi: 10.11868/j.issn.1005-5053.2020.000061
2016, 36(3): 13-19
doi: 10.11868/j.issn.1005-5053.2016.3.003
2015, 35(4): 63-82
doi: 10.11868/j.issn.1005-5053.2015.4.010
2016, 36(3): 79-91
doi: 10.11868/j.issn.1005-5053.2016.3.009
1998, 18(4): 52-61
2006, 26(3): 283-288
2000, 20(1): 55-61
2000, 20(2): 55-63
2002, 22(2): 49-53
2010, 30(4): 92-96
2006, 26(3): 148-151
2009, 29(1): 1-6
2006, 26(3): 244-250
2019, 39(6): 1-19
doi: 10.11868/j.issn.1005-5053.2019.000170
2000, 20(3): 172-177
2001, 21(1): 55-62
2006, 26(3): 226-232
