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Journal of Aeronautical Materials
ISSN:1005-5053
Abstract:
2022, 42(5): 1 -14
Abstract:
Owing to novel design concepts and their unique properties, high-entropy alloy (HEA) has become a hot topic in material science. At present, the studies and applications of high-entropy alloy are still mainly limited to the preparation and synthesis of materials. With its wide application in industry, it must involve the research of high-entropy alloy in welding field. This paper describes the welding of high-entropy alloy with the same material, welding between high-entropy alloy and dissimilar material, and welding between dissimilar material with high-entropy alloy as filler material. The paper focuses on analyzing the welding method, high entropy alloy components, the initial state of welding and welding parameters, and other factors on the joint organization and properties. While the high-entropy alloy is mainly applied as filler material, the high entropy effect and hysteresis diffusion effect for interface controlling are particularly important. Finally, the high-entropy alloy coatings under different preparation methods are analyzed in detail, introducing the cladding process, the addition of microelements, the effect of post-heat treatment, and comparing the wear resistance high-entropy alloy coatings under the laser melting process. By summarizing the research and application of high-entropy alloy in the welding field, it is pointed out that the current problems are that the corresponding standard between high-entropy alloy system and welding process has not been established and the formation mechanism of defects has not been clarified. The future research directions of high entropy alloy in welding field are proposed.
Owing to novel design concepts and their unique properties, high-entropy alloy (HEA) has become a hot topic in material science. At present, the studies and applications of high-entropy alloy are still mainly limited to the preparation and synthesis of materials. With its wide application in industry, it must involve the research of high-entropy alloy in welding field. This paper describes the welding of high-entropy alloy with the same material, welding between high-entropy alloy and dissimilar material, and welding between dissimilar material with high-entropy alloy as filler material. The paper focuses on analyzing the welding method, high entropy alloy components, the initial state of welding and welding parameters, and other factors on the joint organization and properties. While the high-entropy alloy is mainly applied as filler material, the high entropy effect and hysteresis diffusion effect for interface controlling are particularly important. Finally, the high-entropy alloy coatings under different preparation methods are analyzed in detail, introducing the cladding process, the addition of microelements, the effect of post-heat treatment, and comparing the wear resistance high-entropy alloy coatings under the laser melting process. By summarizing the research and application of high-entropy alloy in the welding field, it is pointed out that the current problems are that the corresponding standard between high-entropy alloy system and welding process has not been established and the formation mechanism of defects has not been clarified. The future research directions of high entropy alloy in welding field are proposed.
2022, 42(5): 15 -31
Abstract:
Al-Li alloy has been widely used in aerospace field attribute to the advantages of lower density, higher strength, damage tolerance and corrosion resistance. Dynamic recrystallization phenomena exist in Al-Li alloy during hot deformation. This paper overviews the dynamic recrystallization behavior occurring in hot processing of Al-Li alloy. The research history of dynamic recrystallization is summarized, together with the key factors that influencing the dynamic recrystallization processes including stacking fault energy, grain size, hot processing conditions and secondary particles. The nucleation mechanisms and conditions of discontinuous dynamic recrystallization, continuous dynamic recrystallization and geometric dynamic recrystallization are depicted and analyzed respectively, followed by a discussion on the effects of the forward three dynamic recrystallization mechanisms regarding the mechanical properties and microstructure. Ultimately, the unsolved and challenging scientific and technological issues are highlighted with some aspects desiring further exploration. It is feasible to provide ideas and inspiration for scholars to better comprehend dynamic recrystallization mechanisms during the hot deformation of Al-Li alloy with the assistance of electron backscatter diffraction and transmission electron microscopy characterization methods.
Al-Li alloy has been widely used in aerospace field attribute to the advantages of lower density, higher strength, damage tolerance and corrosion resistance. Dynamic recrystallization phenomena exist in Al-Li alloy during hot deformation. This paper overviews the dynamic recrystallization behavior occurring in hot processing of Al-Li alloy. The research history of dynamic recrystallization is summarized, together with the key factors that influencing the dynamic recrystallization processes including stacking fault energy, grain size, hot processing conditions and secondary particles. The nucleation mechanisms and conditions of discontinuous dynamic recrystallization, continuous dynamic recrystallization and geometric dynamic recrystallization are depicted and analyzed respectively, followed by a discussion on the effects of the forward three dynamic recrystallization mechanisms regarding the mechanical properties and microstructure. Ultimately, the unsolved and challenging scientific and technological issues are highlighted with some aspects desiring further exploration. It is feasible to provide ideas and inspiration for scholars to better comprehend dynamic recrystallization mechanisms during the hot deformation of Al-Li alloy with the assistance of electron backscatter diffraction and transmission electron microscopy characterization methods.
2022, 42(5): 32 -51
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.
2022, 42(5): 52 -70
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(5): 71 -80
Abstract:
GH3536 superalloy was fabricated using Selective Laser Melting (SLM) to investigate the effect of process parameters including the laser power and scanning speed on the density, microscopic defects and surface quality of GH3536 samples. According to the measurement of density, it can be found that the density of samples increases rapidly when the laser energy density is less than 57.0 J/mm3, the density of samples fluctuates within the range of 8.30 g/cm3-8.35 g/cm3 as the laser energy density increases from 57.0 J/mm3 to 187.0 J/mm3, while the density of samples decreases slightly when the laser energy further increases. The conclusion is that the inadequate or excessive energy input reduces the density of samples. The metallographic observation shows that there are a large number of lack-of-fusion defects when the laser energy is insufficient. However, when the input laser energy is too much, many evenly distributed microcracks and gas pores appear inside of samples, indicating that defects are the main reason for low density of samples. The optimal process parameters of SLM-processed GH3536 alloy are determined by the statistical analysis of spatter particles which might cause irregular defects. Tensile properties of the sample fabricated under 175 W and 700 mm/s are tested at room temperature and the results show that the SLM-ed GH3536 superalloy has good tensile properties at room temperature.
GH3536 superalloy was fabricated using Selective Laser Melting (SLM) to investigate the effect of process parameters including the laser power and scanning speed on the density, microscopic defects and surface quality of GH3536 samples. According to the measurement of density, it can be found that the density of samples increases rapidly when the laser energy density is less than 57.0 J/mm3, the density of samples fluctuates within the range of 8.30 g/cm3-8.35 g/cm3 as the laser energy density increases from 57.0 J/mm3 to 187.0 J/mm3, while the density of samples decreases slightly when the laser energy further increases. The conclusion is that the inadequate or excessive energy input reduces the density of samples. The metallographic observation shows that there are a large number of lack-of-fusion defects when the laser energy is insufficient. However, when the input laser energy is too much, many evenly distributed microcracks and gas pores appear inside of samples, indicating that defects are the main reason for low density of samples. The optimal process parameters of SLM-processed GH3536 alloy are determined by the statistical analysis of spatter particles which might cause irregular defects. Tensile properties of the sample fabricated under 175 W and 700 mm/s are tested at room temperature and the results show that the SLM-ed GH3536 superalloy has good tensile properties at room temperature.
2022, 42(5): 81 -90
Abstract:
In the process of directional solidification, the degree of element segregation can be changed by altering the drawing rate to affect the phase transformation behavior of the alloy. In this paper, four kinds of MnNi alloy specimens were prepared by directional solidification at different drawing rates. The phase transformation behavior of the alloy was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermal expansion analysis and dynamic mechanical analysis (DMA). The microstructure of the alloy was observed by metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that the microstructure of directionally solidified MnNi alloy has the characteristics of polymorphy. There are multi-scale twins from micron to nanometer in the alloy, and their coordinated movement makes the internal friction of twins 3-6 times than that of rolled alloy. It is found that during heating, the alloy undergoes fct1→fcc phase transformation in the interdendritic spacings of Mn-poor region while fct2→fco→fcc multi-stage phase transformation occurs in Mn-rich dendrite. This multiply phase transformation behavior makes the damping capacity of directionally solidified MnNi alloy 2-6 times than that of rolled MnNi alloy in a wide temperature range.
In the process of directional solidification, the degree of element segregation can be changed by altering the drawing rate to affect the phase transformation behavior of the alloy. In this paper, four kinds of MnNi alloy specimens were prepared by directional solidification at different drawing rates. The phase transformation behavior of the alloy was studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), thermal expansion analysis and dynamic mechanical analysis (DMA). The microstructure of the alloy was observed by metallographic microscope, scanning electron microscope and transmission electron microscope. The results show that the microstructure of directionally solidified MnNi alloy has the characteristics of polymorphy. There are multi-scale twins from micron to nanometer in the alloy, and their coordinated movement makes the internal friction of twins 3-6 times than that of rolled alloy. It is found that during heating, the alloy undergoes fct1→fcc phase transformation in the interdendritic spacings of Mn-poor region while fct2→fco→fcc multi-stage phase transformation occurs in Mn-rich dendrite. This multiply phase transformation behavior makes the damping capacity of directionally solidified MnNi alloy 2-6 times than that of rolled MnNi alloy in a wide temperature range.
2022, 42(5): 91 -99
Abstract:
Selective electron beam melting (SEBM), which is a powder-bed fusion additive manufacturing technology has unique advantages in the preparation of intermetallic materials with low room temperature plasticity. Recently TiAl alloy parts prepared by SEBM have been successfully used in advanced aeroengines. In this study, crack-free TiAl alloy low-pressure turbine blade simulation parts were prepared by SEBM using Ti-48Al-2Cr-2Nb powder. The tensile properties of the samples at room temperature and the thermal shock resistance of the blades were evaluated. The results indicate that the room temperature tensile strength of TiAl alloy prepared by SEBM can reach 515 MPa after heat treatment, and the elongation after failure is 1.13%. No cracks are found after 120 cycles of thermal shocks at 700 °C tested by the water quenching. The crack perpendicular to the radial direction is appeared in the aerofoil position after 6 times of accelerated thermal shocks tested at 900 °C. Combined with the analysis of crack propagation path and crack fracture, it is determined that the main mechanism of blade component failure under thermal shock conditions is due to the stress concentration caused by the large surface roughness.
Selective electron beam melting (SEBM), which is a powder-bed fusion additive manufacturing technology has unique advantages in the preparation of intermetallic materials with low room temperature plasticity. Recently TiAl alloy parts prepared by SEBM have been successfully used in advanced aeroengines. In this study, crack-free TiAl alloy low-pressure turbine blade simulation parts were prepared by SEBM using Ti-48Al-2Cr-2Nb powder. The tensile properties of the samples at room temperature and the thermal shock resistance of the blades were evaluated. The results indicate that the room temperature tensile strength of TiAl alloy prepared by SEBM can reach 515 MPa after heat treatment, and the elongation after failure is 1.13%. No cracks are found after 120 cycles of thermal shocks at 700 °C tested by the water quenching. The crack perpendicular to the radial direction is appeared in the aerofoil position after 6 times of accelerated thermal shocks tested at 900 °C. Combined with the analysis of crack propagation path and crack fracture, it is determined that the main mechanism of blade component failure under thermal shock conditions is due to the stress concentration caused by the large surface roughness.
2022, 42(5): 100 -108
Abstract:
Electrically driven continuous carbon fiber reinforced shape memory composite (CFSMPC) is a kind of shape memory composite driven by electrical signal to realize controllable deformation.The lightweight cellular structure of continuous carbon fiber reinforced composites is a kind of high-performance structure with low density.In this work, an electrically driven continuous carbon fiber reinforced shape memory poly (lactic acid) composite hollow structure was proposed.By controlling the temperature uniformity, the precise control of structural deformation and the improvement of mechanical properties were realized. 3D printing method was used to fabricate hollow composite structures. The effects of geometric parameters on mechanical properties and shape recovery performance of hollow composite structures were investigated by experiments.The results show that the tensile strength of hollow structure is improved compared with that of non-hollow structure, and the smaller the cell width, the more obvious the tensile strength increases.With the carbon fiber reinforced, the strength of hollow structure is significantly improved, and the strength of CP-3 sample is 66% higher than that of non-hollow PLA.Hollow cell width determines the carbon fiber volume fraction of hollow structure, which affects the mechanical properties of CFSMPC.Moreover, the interfacial properties between printing layers of composite materials are higher.The results show that the volume content of single cell fiber is closely related to tensile strength.In addition, the shape memory recovery speed and the maximum recovery force of CFSMPC hollow structure are obviously increased, and the fastest recovery is completed in 11s.The recovery force of samples is significantly improved.The results show that hollow structure can further release the shape memory performance of structure and obtain higher quality structure-function integrated intelligent material.This is because the hollow structure can effectively avoid the low temperature zone caused by the thermal diffusion of carbon fiber, which can ensure the temperature uniformity of the whole structure.Finally, a coupled electro-thermal-mechanical finite element model of CFSMPC hollow structure is proposed based on viscoelastic constitutive model. The predicted temperature distribution and recovery time are in good agreement with the experimental results, and the error is within 15%.The distribution of internal stress during the recovery process of hollow structure deformation can be obtained by simulation analysis, and it proves that cell width affects the stress release of single cell, which is the difference of shape recovery performance at macro level.Therefore, the model can guide the optimization of CFSMPC structure design.
Electrically driven continuous carbon fiber reinforced shape memory composite (CFSMPC) is a kind of shape memory composite driven by electrical signal to realize controllable deformation.The lightweight cellular structure of continuous carbon fiber reinforced composites is a kind of high-performance structure with low density.In this work, an electrically driven continuous carbon fiber reinforced shape memory poly (lactic acid) composite hollow structure was proposed.By controlling the temperature uniformity, the precise control of structural deformation and the improvement of mechanical properties were realized. 3D printing method was used to fabricate hollow composite structures. The effects of geometric parameters on mechanical properties and shape recovery performance of hollow composite structures were investigated by experiments.The results show that the tensile strength of hollow structure is improved compared with that of non-hollow structure, and the smaller the cell width, the more obvious the tensile strength increases.With the carbon fiber reinforced, the strength of hollow structure is significantly improved, and the strength of CP-3 sample is 66% higher than that of non-hollow PLA.Hollow cell width determines the carbon fiber volume fraction of hollow structure, which affects the mechanical properties of CFSMPC.Moreover, the interfacial properties between printing layers of composite materials are higher.The results show that the volume content of single cell fiber is closely related to tensile strength.In addition, the shape memory recovery speed and the maximum recovery force of CFSMPC hollow structure are obviously increased, and the fastest recovery is completed in 11s.The recovery force of samples is significantly improved.The results show that hollow structure can further release the shape memory performance of structure and obtain higher quality structure-function integrated intelligent material.This is because the hollow structure can effectively avoid the low temperature zone caused by the thermal diffusion of carbon fiber, which can ensure the temperature uniformity of the whole structure.Finally, a coupled electro-thermal-mechanical finite element model of CFSMPC hollow structure is proposed based on viscoelastic constitutive model. The predicted temperature distribution and recovery time are in good agreement with the experimental results, and the error is within 15%.The distribution of internal stress during the recovery process of hollow structure deformation can be obtained by simulation analysis, and it proves that cell width affects the stress release of single cell, which is the difference of shape recovery performance at macro level.Therefore, the model can guide the optimization of CFSMPC structure design.
2022, 42(5): 109 -118
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.
2022, 42(5): 119 -126
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.
2022, 42(5): 127 -134
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.
2022, 42(5): 135 -141
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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2016, 36(4): 89-98
2020, 40(3): 77-94
2016, 36(3): 13-19
2015, 35(4): 63-82
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2009, 29(1): 1-6
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2006, 26(3): 226-232
