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1CHALLENGE AND DEVELOPEMENT TRENDS TO FUTURE AERO ENGINE MATERIALS
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2Development of advanced polymer composites
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3Progress on Electrically Conductive Silicone Rubber
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4Damage characterization and failure analysis in fiber reinforced composites
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5Review and prospect on developments of cast superalloys
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6Strengthening mechanisms of metal matrix composites
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7POLYMERS OBTAINED FROM BENZOCYCLOBUTENES
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8Study on In-Plane Anisotropy of 2524 Aluminum Alloy Sheet
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9Investigation on Indentation Creep by Depth Sensing Indentation
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10Control and relief of residual stresses in high-strength aluminum alloy parts for aerospace industry
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11Study on Fatigue Performance of 7075-T651 Aluminum Alloys
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12Development and Application of P/M Superalloy
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13Development of honeycomb cell structure and materials
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14High-temperature polyimide composites and its application in aeronautical engine
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15Progress on Self-Healing Silicon Carbide Ceramic Matrix Composites and Its Applications
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16Progress of Advanced Near Net-Shape Investment Casting Technology of Superalloys
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1Investigation on microstructure and mechanical properties of ultra-high strength TiCp/Mg-1.4Zn-2.6Ca-0.5Mnnanocomposite after hot extrusion
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2Resent development in high-entropy alloys and other high-entropy materials
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3First-principle Calculations of Mechanical Properties of Al2Cu, Al2CuMg and MgZn2 Intermetallics in High Strength Aluminum Alloys
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4Research Process in Plasma Spray Physical Vapor Deposited Thermal Barrier Coatings
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5Research Progress in Preparation and Crystallization Technologies of Amorphous ITO Film
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6Recent Process and Application of Electrochromism
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7Research Progress and Application Perspectives of 4D Printing
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8Effect of Filler Systems on Properties of Fluororubber Vulcanized by Peroxide
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9Additive Manufacture of Metamaterials: a Review
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10Effect of Rare Earth Y on Microstructure and Properties of Sn-58Bi Solder Alloy
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11Research Progress in Cemented Carbide with Co-Ni-Al Composite Binder Phase
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122018-02-Catalog
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13Research Progress of Metal-Intermetallic Laminated Composites
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14Novel Ceramic Materials for Thermal Barrier Coatings
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15Effect of sintering temperature on microstructure and mechanical behavior of alumina-based ceramic shell by SLS
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16Effect of Low Angle Grain Boundaries on Mechanical Properties of DD5 Single Crystal Ni-base Superalloy
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Abstract:
The effect of grain size and crystal orientation on the tensile deformation behavior of Ti-3Al-4.5V-5Mo titanium alloy was studied by using scanning electron scanning electron, X diffraction instrument and theoretical calculation. The results of tensile test of the wires in different states have verified that there are obvious macroscopic yield points on true stress-true strain curves of 720-840 ℃ annealing structures, and then a stress drop occurs. When the crystal orientation of α phase all shows <0001> fiber texture of different wires, the grain size determines the macroscopic yield stress of the wire. The larger the grain size is, the lower macroscopic yield stress is. Compared with <0001> fiber texture, the existence of <\begin{document}$ {10\bar 10} $\end{document} ![]()
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The effect of grain size and crystal orientation on the tensile deformation behavior of Ti-3Al-4.5V-5Mo titanium alloy was studied by using scanning electron scanning electron, X diffraction instrument and theoretical calculation. The results of tensile test of the wires in different states have verified that there are obvious macroscopic yield points on true stress-true strain curves of 720-840 ℃ annealing structures, and then a stress drop occurs. When the crystal orientation of α phase all shows <0001> fiber texture of different wires, the grain size determines the macroscopic yield stress of the wire. The larger the grain size is, the lower macroscopic yield stress is. Compared with <0001> fiber texture, the existence of <
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000087
Abstract:
Metallic-ceramic functionally graded materials have potential application value in the design of thermal barrier systems for aircraft panels due to their ultrahigh temperature resistant and high strength properties. In this article, the FGMs plate was used as the object to study the influence of parameters such as the volume fraction index, the geometric size of the plate and the thermal environment on the modal frequencies of a FGMs plate. Firstly, the power law distribution function was employed to discuss the influence of thermal environment on the physical properties of FGMs plates. Thereafter, the FGMs linear layered model dependent on temperature field was established by using the temperature continuously changing with the spatial position trait in the finite element, and the validity of this model in dynamic analysis was verified. Finally, the effects of ceramic volume fraction index, FGMs plate length-to-width ratio, temperature gradient and other variables on the modal frequencies of a FGMs plate were comprehensively analyzed and discussed. Results indicate that the higher order modes are mostly impacted by the uniform temperature field, while the linear and nonlinear temperature fields have the greatest impact on the first-order modes. In linear and nonlinear temperature fields, the volume fraction index is the most sensitive one to the effects of modal frequency drop ratio, while the modal frequency drop ratio is mainly affected by the coupling effect of the volume fraction index and the temperature gradient in uniform temperature field.
Metallic-ceramic functionally graded materials have potential application value in the design of thermal barrier systems for aircraft panels due to their ultrahigh temperature resistant and high strength properties. In this article, the FGMs plate was used as the object to study the influence of parameters such as the volume fraction index, the geometric size of the plate and the thermal environment on the modal frequencies of a FGMs plate. Firstly, the power law distribution function was employed to discuss the influence of thermal environment on the physical properties of FGMs plates. Thereafter, the FGMs linear layered model dependent on temperature field was established by using the temperature continuously changing with the spatial position trait in the finite element, and the validity of this model in dynamic analysis was verified. Finally, the effects of ceramic volume fraction index, FGMs plate length-to-width ratio, temperature gradient and other variables on the modal frequencies of a FGMs plate were comprehensively analyzed and discussed. Results indicate that the higher order modes are mostly impacted by the uniform temperature field, while the linear and nonlinear temperature fields have the greatest impact on the first-order modes. In linear and nonlinear temperature fields, the volume fraction index is the most sensitive one to the effects of modal frequency drop ratio, while the modal frequency drop ratio is mainly affected by the coupling effect of the volume fraction index and the temperature gradient in uniform temperature field.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000083
Abstract:
A uniform distribution of TiC nanoparticles was realized in the TiCp/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite fabricatedby the method of ultrasonic-assisted semisolid stirring. Microstructure and mechanical properties of the nanocomposite before and after extrusion were investigated. The results show that the grains in the dense area of the second phase was smaller than that in the barren area, and the second phase was Ca2Mg6Zn3. Dynamic recrystallization (DRX) occurred in the nanocomposites after extrusion at different temperatures (350°C, 310 °C and 270 °C). Both the sizes and volume fraction of DRXedgrainsand precipitates size were obviously refined as the extrusion temperature decreased, while the volume fraction of precipitates increased. Ultrafine recrystallized grain structure (~0.34 μm) with a substantial of fine precipitates appeared in the nanocomposite extruded at 270 °C. The refined grain structure was not only due to DRX, but also the synergistic pinning effect of nano-TiCp, precipitated MgZn2 and α-Mn particles. The optimum tensile strength was achieved in the nanocomposites extruded at 270 °C/0.1 mm s-1, and the yield strength (YS), ultimate tensile strength (UTS) andelongation to failure (EL)were ~439.7 MPa、~460.2 MPa and ~1.73%, respectively. The grain refinement strengthening with the contribution ratio over 60% to YS increment was much higher relative to thermal expansion effect, Orowan strengthening and dislocation strengthening.
A uniform distribution of TiC nanoparticles was realized in the TiCp/Mg-1.4Zn-2.6Ca-0.5Mn nanocomposite fabricatedby the method of ultrasonic-assisted semisolid stirring. Microstructure and mechanical properties of the nanocomposite before and after extrusion were investigated. The results show that the grains in the dense area of the second phase was smaller than that in the barren area, and the second phase was Ca2Mg6Zn3. Dynamic recrystallization (DRX) occurred in the nanocomposites after extrusion at different temperatures (350°C, 310 °C and 270 °C). Both the sizes and volume fraction of DRXedgrainsand precipitates size were obviously refined as the extrusion temperature decreased, while the volume fraction of precipitates increased. Ultrafine recrystallized grain structure (~0.34 μm) with a substantial of fine precipitates appeared in the nanocomposite extruded at 270 °C. The refined grain structure was not only due to DRX, but also the synergistic pinning effect of nano-TiCp, precipitated MgZn2 and α-Mn particles. The optimum tensile strength was achieved in the nanocomposites extruded at 270 °C/0.1 mm s-1, and the yield strength (YS), ultimate tensile strength (UTS) andelongation to failure (EL)were ~439.7 MPa、~460.2 MPa and ~1.73%, respectively. The grain refinement strengthening with the contribution ratio over 60% to YS increment was much higher relative to thermal expansion effect, Orowan strengthening and dislocation strengthening.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000016
Abstract:
High cycle fatigue P-S-N curve of aero-engine material is an important foundation for the design of aero-engine strength. Based on the data processing requirement of the high cycle fatigue of aero-engine, a novel data processing method has been developed by proposing the criterion of selecting fitting model and the method for determining the critical stress between the medium and high fatigue cycle regions. Furthermore, the testing data of two common Ti-alloy materials of aero-engine which are used to validate the present batch processing method and the P-S-N curves in various conditions have been obtained. And the comparison of the process time between the present method and the conventional method has been conducted finally. The results show that the present data processing method is suitable not only for the data processing of the traditional high cycle fatigue issues, but also for the data processing of very high cycle fatigue issues. More important that the efficiency of data processing is significantly improved.
High cycle fatigue P-S-N curve of aero-engine material is an important foundation for the design of aero-engine strength. Based on the data processing requirement of the high cycle fatigue of aero-engine, a novel data processing method has been developed by proposing the criterion of selecting fitting model and the method for determining the critical stress between the medium and high fatigue cycle regions. Furthermore, the testing data of two common Ti-alloy materials of aero-engine which are used to validate the present batch processing method and the P-S-N curves in various conditions have been obtained. And the comparison of the process time between the present method and the conventional method has been conducted finally. The results show that the present data processing method is suitable not only for the data processing of the traditional high cycle fatigue issues, but also for the data processing of very high cycle fatigue issues. More important that the efficiency of data processing is significantly improved.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000014
Abstract:
DD15 single crystal superalloys with 9%Co and 12%Co were prepared in a directionally solidified furnace. By keeping the other alloying element contents unchanged, the influence of Co content on the microstructure, phase stability and stress rupture properties of the single crystal superalloy under the condition of 980 ℃/300 MPa was investigated. The results show that the primary dendrite arm spacing increases and the volume fraction of γ/γ′ eutectic decreases with increasing of Co content. The size of γ′ phase has no obvious change, its cubic shape turns a little irregular, its volume fraction decreases with increasing of Co content. The microstructure stability of the alloy increases with increasing of Co content. Increasing Co content decreases the stress rupture properties of the alloy.
DD15 single crystal superalloys with 9%Co and 12%Co were prepared in a directionally solidified furnace. By keeping the other alloying element contents unchanged, the influence of Co content on the microstructure, phase stability and stress rupture properties of the single crystal superalloy under the condition of 980 ℃/300 MPa was investigated. The results show that the primary dendrite arm spacing increases and the volume fraction of γ/γ′ eutectic decreases with increasing of Co content. The size of γ′ phase has no obvious change, its cubic shape turns a little irregular, its volume fraction decreases with increasing of Co content. The microstructure stability of the alloy increases with increasing of Co content. Increasing Co content decreases the stress rupture properties of the alloy.
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Available online
, doi: 10.11868/j.issn.1005-5053.2019.000160
Abstract:
The metal/ceramic laminated composites prepared from the unique "brick + mud" structure of biomimetic shells have been proved to have better strength and toughness, and have gradually become the research focus at domestic and abroad. In this paper, the current research of Al-based, Ti-based, Ni-based and other common metal/ceramic laminated composites is introduced, and the characteristic and process of each method are analyzed. The failure modes such as crack deflection, multiple crack propagation and crack bridging in metal/ceramic laminated composites are commonly summarized. The interface bonding strength of metal/ceramic laminated composites can be improved by controlling interfacial reactions and improving interfacial wettability. Optimizing of the preparation process and understanding the failure mechanism are the basis of engineering application of metal-ceramic layered composite materials. The introduction of the computational science into the research of metal/ceramic interface and damage mechanisms is an effective way to realize the controllability of the whole preparation process, and the realization of large size and diversified shape of products is the key to its large-scale application and promotion.
The metal/ceramic laminated composites prepared from the unique "brick + mud" structure of biomimetic shells have been proved to have better strength and toughness, and have gradually become the research focus at domestic and abroad. In this paper, the current research of Al-based, Ti-based, Ni-based and other common metal/ceramic laminated composites is introduced, and the characteristic and process of each method are analyzed. The failure modes such as crack deflection, multiple crack propagation and crack bridging in metal/ceramic laminated composites are commonly summarized. The interface bonding strength of metal/ceramic laminated composites can be improved by controlling interfacial reactions and improving interfacial wettability. Optimizing of the preparation process and understanding the failure mechanism are the basis of engineering application of metal-ceramic layered composite materials. The introduction of the computational science into the research of metal/ceramic interface and damage mechanisms is an effective way to realize the controllability of the whole preparation process, and the realization of large size and diversified shape of products is the key to its large-scale application and promotion.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000021
Abstract:
CoCrAlYSi-hBN coatings were fabricated using the high-velocity oxygen fuel (HVOF) process under several processing conditions and the effects of process parameters, gas flow and spray distance, on the microstructure and properties of the coating have been investigated in the present paper. The microstructure, hardness, bonding strength and chemical composition of these coatings were researched by using scanning electronmicroscopy (SEM), microhardness tester, adhesivestrength measuring and energy dispersive spectroscopy (EDS). The results showed that with the increasing gas flow, the porosity and h-BN content of the coating were reduced, and the hardness were improved; However, the bonding strength increases first and then decreases due to excessive energy leading serious oxidation. With the increase of spraying distance, the oxide inclusions increase, which results in thehardness of coatings increases and the bonding strength decreases. In addition, when the spraying distance is 225 mm, the hardness and bonding strength of the coating are the highest due to the low porosity and boron nitride content.
CoCrAlYSi-hBN coatings were fabricated using the high-velocity oxygen fuel (HVOF) process under several processing conditions and the effects of process parameters, gas flow and spray distance, on the microstructure and properties of the coating have been investigated in the present paper. The microstructure, hardness, bonding strength and chemical composition of these coatings were researched by using scanning electronmicroscopy (SEM), microhardness tester, adhesivestrength measuring and energy dispersive spectroscopy (EDS). The results showed that with the increasing gas flow, the porosity and h-BN content of the coating were reduced, and the hardness were improved; However, the bonding strength increases first and then decreases due to excessive energy leading serious oxidation. With the increase of spraying distance, the oxide inclusions increase, which results in thehardness of coatings increases and the bonding strength decreases. In addition, when the spraying distance is 225 mm, the hardness and bonding strength of the coating are the highest due to the low porosity and boron nitride content.
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Available online
, doi: 10.11868/j.issn.1005-5053.2020.000015
Abstract:
A Co-free Fe56.5Ni30Al10.5Nb3 (atom fraction/%) alloy was developed. In the preparation, the as-cast alloy was subjected to aging treatment at 650 ℃ following solution treatment directly. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to analyze the microstructure and phases of the alloy. At the same time, the hardness test, compressive strength test, superelasticity test and electron backscatter diffraction (EBSD) test were performed. The results show that, when the aging time ranges from 0 to 95 h, the alloy can exhibit superelasticity at room temperature with the maximum superelastic strain of 10.62%. There are nano-sized γ′ precipitates and fine β precipitates in the alloy. The γ′ phase is formed in the grain interiors and is most densely distributed when the aging time is 70 h. After the aging time exceeds 70 h, the γ′ phase enters the growth stage. By comparison, the β phase can be formed both in the grain interiors and in the grain boundaries, and the amount of β precipitates increases with the aging time. The precipitation of the β phase can improve the hardness, but its formation in the grain boundaries is detrimental to the strength. With the increase of aging time, the hardness of the alloy increases continuously, and the compressive strength and superelastic strain first increase and then decrease reaching the maximum value at 70 h. The nano-sized γ′ precipitates and strong {100}<100> texture in the alloy have a great influence on its superelasticity.
A Co-free Fe56.5Ni30Al10.5Nb3 (atom fraction/%) alloy was developed. In the preparation, the as-cast alloy was subjected to aging treatment at 650 ℃ following solution treatment directly. Scanning electron microscope (SEM) and X-ray diffractometer (XRD) were used to analyze the microstructure and phases of the alloy. At the same time, the hardness test, compressive strength test, superelasticity test and electron backscatter diffraction (EBSD) test were performed. The results show that, when the aging time ranges from 0 to 95 h, the alloy can exhibit superelasticity at room temperature with the maximum superelastic strain of 10.62%. There are nano-sized γ′ precipitates and fine β precipitates in the alloy. The γ′ phase is formed in the grain interiors and is most densely distributed when the aging time is 70 h. After the aging time exceeds 70 h, the γ′ phase enters the growth stage. By comparison, the β phase can be formed both in the grain interiors and in the grain boundaries, and the amount of β precipitates increases with the aging time. The precipitation of the β phase can improve the hardness, but its formation in the grain boundaries is detrimental to the strength. With the increase of aging time, the hardness of the alloy increases continuously, and the compressive strength and superelastic strain first increase and then decrease reaching the maximum value at 70 h. The nano-sized γ′ precipitates and strong {100}<100> texture in the alloy have a great influence on its superelasticity.
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Available online
, doi: 10.11868/j.issn.1005-5053.2019.000143
Abstract:
SiCf/SiC textile composites have enormous development potentials in the field of aerospace hot-end component owing to their strong structural design, low density, excellent mechanical properties, high-temperature resistance and oxidation resistance. However, there are few researches on the preparation technology, performance and meso-structure of SiCf/SiC textile composites. Therefore, an important field of SiCf/SiC textile composites in the future is the employ of advanced apparatus for observation and accurate characterization of the textile microstructure. In this paper, the research status of SiCf/SiC textile composites in recent years is introduced from three aspects: meso-scale structure, mechanical properties and numerical simulation. The problems that need to be paid attention to in the follow-up research work are put forward, and the research prospects are prospected.
SiCf/SiC textile composites have enormous development potentials in the field of aerospace hot-end component owing to their strong structural design, low density, excellent mechanical properties, high-temperature resistance and oxidation resistance. However, there are few researches on the preparation technology, performance and meso-structure of SiCf/SiC textile composites. Therefore, an important field of SiCf/SiC textile composites in the future is the employ of advanced apparatus for observation and accurate characterization of the textile microstructure. In this paper, the research status of SiCf/SiC textile composites in recent years is introduced from three aspects: meso-scale structure, mechanical properties and numerical simulation. The problems that need to be paid attention to in the follow-up research work are put forward, and the research prospects are prospected.
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2020, 40(4): 1 -2
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2020, 40(4): 1 -8
doi: 10.11868/j.issn.1005-5053.2020.000012
Abstract:
Previously, the preparation of graphene often required one or more of strong acid oxidants, reduction temperatures above 1000 ℃,expensive metal catalysts, and accompanied by the problems of low efficiency, high and heavy pollution. Our work provided a novel strategy for low-temperature vacuum preparation of high-quality graphene. Anhydrous AlCl3 and FeCl3 were used as bi-intercalants to prepare stage-1 graphite intercalation compounds (AlCl3-FeCl3-GICs) with accordion-like structure. Vacuum treatment of stage-1 AlCl3-FeCl3-GICs at a relatively low temperature of 180 ℃, low-boiling-point AlCl3 was heated and vaporized to further stretch the graphite sheet to obtain worm-like expanded graphite. The expanded graphite could maintain a loose structure under atmospheric conditions and was not collapsed. The effect of van der Waals force between the sheets of adjacent graphite layers was greatly weakened, which made the expanded graphite easily to be exfoliated. High-quality graphene was obtained by ultrasonic treatment of expanded graphite in solvent using liquid-phase exfoliation method. The preparation process of expanded graphite did not use strong oxidants, and was carried out in an anhydrous and oxygen-free environment. The reaction temperature was also controlled within 180 ℃. The overall preparation conditions were relatively mild and environmentally friendly. The preparation of graphene by the liquid-phase method could avoid the destruction of the graphene lattice structure as much as possible. The scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) were used to observe the microscopic morphology of graphene, and the X-ray powder diffraction (XRD) instrument, ray photoelectron spectroscopy (XPS) instrument and Raman spectrometer were used to characterize the microstructure of graphene. The results show that the prepared graphene has extremely low defects, the sp2 lattice structure still maintains a high degree of regularity, and most graphene layers are within three.
Previously, the preparation of graphene often required one or more of strong acid oxidants, reduction temperatures above 1000 ℃,expensive metal catalysts, and accompanied by the problems of low efficiency, high and heavy pollution. Our work provided a novel strategy for low-temperature vacuum preparation of high-quality graphene. Anhydrous AlCl3 and FeCl3 were used as bi-intercalants to prepare stage-1 graphite intercalation compounds (AlCl3-FeCl3-GICs) with accordion-like structure. Vacuum treatment of stage-1 AlCl3-FeCl3-GICs at a relatively low temperature of 180 ℃, low-boiling-point AlCl3 was heated and vaporized to further stretch the graphite sheet to obtain worm-like expanded graphite. The expanded graphite could maintain a loose structure under atmospheric conditions and was not collapsed. The effect of van der Waals force between the sheets of adjacent graphite layers was greatly weakened, which made the expanded graphite easily to be exfoliated. High-quality graphene was obtained by ultrasonic treatment of expanded graphite in solvent using liquid-phase exfoliation method. The preparation process of expanded graphite did not use strong oxidants, and was carried out in an anhydrous and oxygen-free environment. The reaction temperature was also controlled within 180 ℃. The overall preparation conditions were relatively mild and environmentally friendly. The preparation of graphene by the liquid-phase method could avoid the destruction of the graphene lattice structure as much as possible. The scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) were used to observe the microscopic morphology of graphene, and the X-ray powder diffraction (XRD) instrument, ray photoelectron spectroscopy (XPS) instrument and Raman spectrometer were used to characterize the microstructure of graphene. The results show that the prepared graphene has extremely low defects, the sp2 lattice structure still maintains a high degree of regularity, and most graphene layers are within three.
2020, 40(4): 9 -18
doi: 10.11868/j.issn.1005-5053.2020.000098
Abstract:
4 types of graphene were used to fabricate graphene/polytetrafluoroethylene (PTFE) composites with loadings of 0.5% and 1% respectively. The average size, thickness, specific surface area and carbon/oxygen ratio (C/O ratio) of these graphene were characterized by SEM, AFM, BET and XPS. The friction coefficient was performed on the Controllable Environment Friction and Wear Instrument. The volume wear rate was carried out with the 3D White Light Interferometer. The results show that at the same load, the C/O ratio of graphene is the main factor affecting the friction coefficient of the composites, while the specific surface area of graphene is the main factor affecting the volume wear rate of the composites. With the addition of 1%（mass fraction, the same below） graphene in PTFE, the friction coefficient is reduced by 27.97% when the C/O ratio reaches 45.64 and the carbon content reaches 97.66%. With a specific surface area reaches 466.78 m2/g, graphene can reduce the volume wear rate of the PTFE composite by 76.46%.
4 types of graphene were used to fabricate graphene/polytetrafluoroethylene (PTFE) composites with loadings of 0.5% and 1% respectively. The average size, thickness, specific surface area and carbon/oxygen ratio (C/O ratio) of these graphene were characterized by SEM, AFM, BET and XPS. The friction coefficient was performed on the Controllable Environment Friction and Wear Instrument. The volume wear rate was carried out with the 3D White Light Interferometer. The results show that at the same load, the C/O ratio of graphene is the main factor affecting the friction coefficient of the composites, while the specific surface area of graphene is the main factor affecting the volume wear rate of the composites. With the addition of 1%（mass fraction, the same below） graphene in PTFE, the friction coefficient is reduced by 27.97% when the C/O ratio reaches 45.64 and the carbon content reaches 97.66%. With a specific surface area reaches 466.78 m2/g, graphene can reduce the volume wear rate of the PTFE composite by 76.46%.
2020, 40(4): 19 -24
doi: 10.11868/j.issn.1005-5053.2019.000188
Abstract:
Zr3O-ZrC/graphene composite layer was directly in-situ grown on the surface of Zr foil by plasma heat treatment method. The microstructure and component of the as-prepared sample were systematically characterized by X-ray diffraction (XRD), Raman spectrum and scanning electron microscopy (SEM). The surface hardness was both characterized by micro hardness tester and nanoindentor. The results show that the composite layer was uniformly distributed on the surface of Zr foil. The surface hardness values of pure Zr foil and Zr/Zr3O-ZrC/graphene composite were 195 HV and 639 HV, respectively. The surface hardness of the TiC/graphene layer can be signi?cantly increased 3.2 times as that of the pure Zr foil surface. Nanoindentor results showed the signi?cantly improved surface hardness could be attributed to the Zr3O-ZrC layers. This study provides a particular heat treatment process for significant reinforcement of Zr and its alloys, and showing its great potential application for the future .
Zr3O-ZrC/graphene composite layer was directly in-situ grown on the surface of Zr foil by plasma heat treatment method. The microstructure and component of the as-prepared sample were systematically characterized by X-ray diffraction (XRD), Raman spectrum and scanning electron microscopy (SEM). The surface hardness was both characterized by micro hardness tester and nanoindentor. The results show that the composite layer was uniformly distributed on the surface of Zr foil. The surface hardness values of pure Zr foil and Zr/Zr3O-ZrC/graphene composite were 195 HV and 639 HV, respectively. The surface hardness of the TiC/graphene layer can be signi?cantly increased 3.2 times as that of the pure Zr foil surface. Nanoindentor results showed the signi?cantly improved surface hardness could be attributed to the Zr3O-ZrC layers. This study provides a particular heat treatment process for significant reinforcement of Zr and its alloys, and showing its great potential application for the future .
2020, 40(4): 25 -35
doi: 10.11868/j.issn.1005-5053.2020.000035
Abstract:
Quinary Ti-22Al-23Nb-2(Mo, Zr) alloy has a broad application prospect in the aeroengine field. The temperature ranges of phase regions, β/B2 processing, heat treatment and the corresponding mechanical properties were investigated by SEM, TEM and multi mechanical testing machines. The results show that the alloy goes through B2, B2+α2, B2+α2+O and B2+O four phase regions in the sequence from high temperature to low temperature, the corresponding critical temperatures are 1060 ℃, 950 ℃ and 930 ℃ respectively. The composition and morphology of the grain boundary phase are influenced by the collective effect of distortion degree of B2 grains and heat treatment. Coarse discontinuous α2 phase is easy to form at the boundaries of original B2 grains with high distortion degree, and is converted into α2+Orim structure if heat treated at B2+O phase region; The fine continuous O phase is inclined to form at the boundaries of dynamic recrystallized B2 grains with low distortion degree, which can be completely transformed into α2 if heat treated at B2+α2 phase region; no phase is formed at the boundaries of static recrystallized B2 grains. Precipitates within B2 grains are mainly influenced by heat treatment. α2 and O can directly and independently precipitate from B2, O can also attach α2 to form an α2/Orim core-shell structure. The α2/Orim core-shell structure indicates α2 has good stability at low temperature. After solid solution and aging treated, mixed microstructure with bi-size precipitates emerge within B2 grains, which can be coarse α2/Orim+ fine O or coarse OI+OII with the corresponding solution treatment at B2+α2 and B2+O respectively. The size distribution of B2 precipitated phase in grain is the main factor affecting the mechanical properties . Larger size is favorable for the ductility and toughness of alloy, but unfavorable for strength and creep resistance.
Quinary Ti-22Al-23Nb-2(Mo, Zr) alloy has a broad application prospect in the aeroengine field. The temperature ranges of phase regions, β/B2 processing, heat treatment and the corresponding mechanical properties were investigated by SEM, TEM and multi mechanical testing machines. The results show that the alloy goes through B2, B2+α2, B2+α2+O and B2+O four phase regions in the sequence from high temperature to low temperature, the corresponding critical temperatures are 1060 ℃, 950 ℃ and 930 ℃ respectively. The composition and morphology of the grain boundary phase are influenced by the collective effect of distortion degree of B2 grains and heat treatment. Coarse discontinuous α2 phase is easy to form at the boundaries of original B2 grains with high distortion degree, and is converted into α2+Orim structure if heat treated at B2+O phase region; The fine continuous O phase is inclined to form at the boundaries of dynamic recrystallized B2 grains with low distortion degree, which can be completely transformed into α2 if heat treated at B2+α2 phase region; no phase is formed at the boundaries of static recrystallized B2 grains. Precipitates within B2 grains are mainly influenced by heat treatment. α2 and O can directly and independently precipitate from B2, O can also attach α2 to form an α2/Orim core-shell structure. The α2/Orim core-shell structure indicates α2 has good stability at low temperature. After solid solution and aging treated, mixed microstructure with bi-size precipitates emerge within B2 grains, which can be coarse α2/Orim+ fine O or coarse OI+OII with the corresponding solution treatment at B2+α2 and B2+O respectively. The size distribution of B2 precipitated phase in grain is the main factor affecting the mechanical properties . Larger size is favorable for the ductility and toughness of alloy, but unfavorable for strength and creep resistance.
2020, 40(4): 36 -44
doi: 10.11868/j.issn.1005-5053.2020.000057
Abstract:
The strain controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of a TiAl alloy were conducted at 750 °C in air. The strain ratio, strain amplitude and strain rate were –1, 0.4% and 1 × 10–3 s–1 respectively. The high temperature LCF and CFI stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life were studied and compared in details. Morrow modified method and unified life model developed in the present study were employed to predict the fatigue life for LCF and CFI life of TiAl alloy. Finally, the failure mechanisms between LCF and CFI specimens were compared, and some interesting conclusions were obtained. The results show that: (1) there are obvious differences on stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life between LCF and CFI tests; (2) Morrow modified method is not able to predict the fatigue life for LCF and CFI life for TiAl alloy, however, the predicted fatigue life by the unified life model is located in the scatter band of ± 1.5; (3) the fatigue cracks are initiated from the surface for all of LCF and CFI specimens, and LCF specimens show more transgranular appearance while CFI specimens show obvious mixed appearance of both transgranular and intergranular.
The strain controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of a TiAl alloy were conducted at 750 °C in air. The strain ratio, strain amplitude and strain rate were –1, 0.4% and 1 × 10–3 s–1 respectively. The high temperature LCF and CFI stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life were studied and compared in details. Morrow modified method and unified life model developed in the present study were employed to predict the fatigue life for LCF and CFI life of TiAl alloy. Finally, the failure mechanisms between LCF and CFI specimens were compared, and some interesting conclusions were obtained. The results show that: (1) there are obvious differences on stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life between LCF and CFI tests; (2) Morrow modified method is not able to predict the fatigue life for LCF and CFI life for TiAl alloy, however, the predicted fatigue life by the unified life model is located in the scatter band of ± 1.5; (3) the fatigue cracks are initiated from the surface for all of LCF and CFI specimens, and LCF specimens show more transgranular appearance while CFI specimens show obvious mixed appearance of both transgranular and intergranular.
2020, 40(4): 45 -51
doi: 10.11868/j.issn.1005-5053.2020.000060
Abstract:
Partial block-dropping phenomenon was existed during the precision process of TA15 titanium alloy casting. In view of multiple means of microscopic physical characterization analysis such as OM/SEM/EDS/XRD and by considering the tensile performance results, the microstructure and mechanical properties between block-dropping area and the regular areahad been investigated. This article focused on the impact mechanism on tensile behavior that generated from the abnormal structure of block-dropping area. The results reveal that both the block-dropping area and the regular area show bi-modal microstructure, whereas the β phase concentration of the block-dropping area is far beyond the regular area and emerges as β spot. Microanalysis shows that the segregation of Fe is the major factor causing the abnormal structure and β spot, as well as the sharp plasticity decreases of alloy. The segregated Fe alters the microstructure and properties of the alloy, mainly because the saturation of Fe in α-Ti is only 0.1%, which leads to the formation of brittle TiFe eutectic phase. The increase of strength reduces the plasticity of the alloy casting, and further lead to the block-dropping during the process.
Partial block-dropping phenomenon was existed during the precision process of TA15 titanium alloy casting. In view of multiple means of microscopic physical characterization analysis such as OM/SEM/EDS/XRD and by considering the tensile performance results, the microstructure and mechanical properties between block-dropping area and the regular areahad been investigated. This article focused on the impact mechanism on tensile behavior that generated from the abnormal structure of block-dropping area. The results reveal that both the block-dropping area and the regular area show bi-modal microstructure, whereas the β phase concentration of the block-dropping area is far beyond the regular area and emerges as β spot. Microanalysis shows that the segregation of Fe is the major factor causing the abnormal structure and β spot, as well as the sharp plasticity decreases of alloy. The segregated Fe alters the microstructure and properties of the alloy, mainly because the saturation of Fe in α-Ti is only 0.1%, which leads to the formation of brittle TiFe eutectic phase. The increase of strength reduces the plasticity of the alloy casting, and further lead to the block-dropping during the process.
2020, 40(4): 52 -61
doi: 10.11868/j.issn.1005-5053.2019.000185
Abstract:
TiZrHfNbMo high-entropy alloy and titanium matrix composite were vacuum brazed using carbon nanotubes reinforced AgCuTi composite filler. Microstructure and mechanical properties of the joints were systematically studied by X-ray diffractometer, scanning electron microscopy, energy spectrum and universal testing machine. The results show that the joints brazed at different temperatures from 820 °C to 910 °C for 15 min are successfully connected. The microstructure of the joint is composed of Ag(s,s), Cu(s,s), Ti(s,s), CuTi, ZrCu and CuTi2, the base material elements are fully diffused in the joint. When the brazing holding time is fixed, the shear strength of the joint at room temperature increases first and then decreases with the increase of brazing temperature. The formation of a certain amount of Ti-Cu intermetallic compounds widens the thickness of the reaction layer and improves the strength of the joint, while the formation of excessive Ti-Cu intermetallic compounds weakens the joint ability to relieve stress through plastic deformation, leading to a significant reduction in the joint strength. The best welded joint is obtained when the brazing temperature is 850 ℃ and the holding time is 15 min. The shear strength is up to 146 MPa, and the fracture mode of the shear fracture of the joint is brittle fracture.
TiZrHfNbMo high-entropy alloy and titanium matrix composite were vacuum brazed using carbon nanotubes reinforced AgCuTi composite filler. Microstructure and mechanical properties of the joints were systematically studied by X-ray diffractometer, scanning electron microscopy, energy spectrum and universal testing machine. The results show that the joints brazed at different temperatures from 820 °C to 910 °C for 15 min are successfully connected. The microstructure of the joint is composed of Ag(s,s), Cu(s,s), Ti(s,s), CuTi, ZrCu and CuTi2, the base material elements are fully diffused in the joint. When the brazing holding time is fixed, the shear strength of the joint at room temperature increases first and then decreases with the increase of brazing temperature. The formation of a certain amount of Ti-Cu intermetallic compounds widens the thickness of the reaction layer and improves the strength of the joint, while the formation of excessive Ti-Cu intermetallic compounds weakens the joint ability to relieve stress through plastic deformation, leading to a significant reduction in the joint strength. The best welded joint is obtained when the brazing temperature is 850 ℃ and the holding time is 15 min. The shear strength is up to 146 MPa, and the fracture mode of the shear fracture of the joint is brittle fracture.
2020, 40(4): 62 -70
doi: 10.11868/j.issn.1005-5053.2019.000163
Abstract:
The ultrafine-grained (UFG) CrCoNi medium entropy alloys (MEAs) with excellent mechanical and tribological performances were fabricated by combining rolling deformation and annealing treatment. The microstructures of CrCoNi MEAs were characterized by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that the materials annealed at 650 ℃ for 10 min after cryogenic rolling display a yield strength as high as 1135 MPa and a graceful uniform ductility of 14.1%. Another group of materials rolled at room temperature followed by annealing at 650 ℃ for 20 min exhibit a yield strength of 987 MPa and an improved ductility of 18.6%. In addition, the grains of CrCoNi medium entropy alloys after above treatment are greatly refined to an average grain size of 0.81 μm and 0.92 μm respectively. The ultra-high strength is due to the grain boundary strengthening of high angle boundaries and dislocation strengthening of low angle boundaries. Remarkably, such UFG MEAs exhibit high wear resistance.
The ultrafine-grained (UFG) CrCoNi medium entropy alloys (MEAs) with excellent mechanical and tribological performances were fabricated by combining rolling deformation and annealing treatment. The microstructures of CrCoNi MEAs were characterized by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that the materials annealed at 650 ℃ for 10 min after cryogenic rolling display a yield strength as high as 1135 MPa and a graceful uniform ductility of 14.1%. Another group of materials rolled at room temperature followed by annealing at 650 ℃ for 20 min exhibit a yield strength of 987 MPa and an improved ductility of 18.6%. In addition, the grains of CrCoNi medium entropy alloys after above treatment are greatly refined to an average grain size of 0.81 μm and 0.92 μm respectively. The ultra-high strength is due to the grain boundary strengthening of high angle boundaries and dislocation strengthening of low angle boundaries. Remarkably, such UFG MEAs exhibit high wear resistance.
2020, 40(4): 71 -76
doi: 10.11868/j.issn.1005-5053.2019.000025
Abstract:
Taking the advanced aeroengine compressor blisk as the application object, the development and experimental study on the TC11/TC17 different materials linear friction welding integral blisk was carried out. The microstructure of welded joint was analyzed, the tensile and stress rupture properties of base metal and welded joint were compared, the vibration fatigue test on welded blade test pieces, and the overrunning test and low-cycle fatigue test on welding blisk were developed. The results show that the TC11/TC17 linear friction welding joint consists of five typical zones, they are TC11 base metal zone, TC11 thermal influence zone, weld zone, TC17 thermal influence zone and TC17 base metal zone. The tensile strength of the welded joint is basically equivalent to that of the TC11 base metal, elongation is equivalent to TC17 base metal; endurance strength lower than TC17 base metal, but less higher than TC11 base metal. The median fatigue life of welded blade test pieces with three weld positions is respectively 1.501 × 106, 0.344 × 106, and 0.132 × 106 cycles, the fatigue crack isn’t at welding seam and thermal influence zone. The welding blisk pass the 115% overrunning test and 1000 cycles low-cycle fatigue test, the experiment results meet the requirement.
Taking the advanced aeroengine compressor blisk as the application object, the development and experimental study on the TC11/TC17 different materials linear friction welding integral blisk was carried out. The microstructure of welded joint was analyzed, the tensile and stress rupture properties of base metal and welded joint were compared, the vibration fatigue test on welded blade test pieces, and the overrunning test and low-cycle fatigue test on welding blisk were developed. The results show that the TC11/TC17 linear friction welding joint consists of five typical zones, they are TC11 base metal zone, TC11 thermal influence zone, weld zone, TC17 thermal influence zone and TC17 base metal zone. The tensile strength of the welded joint is basically equivalent to that of the TC11 base metal, elongation is equivalent to TC17 base metal; endurance strength lower than TC17 base metal, but less higher than TC11 base metal. The median fatigue life of welded blade test pieces with three weld positions is respectively 1.501 × 106, 0.344 × 106, and 0.132 × 106 cycles, the fatigue crack isn’t at welding seam and thermal influence zone. The welding blisk pass the 115% overrunning test and 1000 cycles low-cycle fatigue test, the experiment results meet the requirement.
2020, 40(4): 77 -84
doi: 10.11868/j.issn.1005-5053.2017.000128
Abstract:
1.5 mm thick SUS304 austenitic steel sheet was used as the test material to study the spot weld bonding process and fatigue performance. The joint performance was analyzed by the process, strength distribution, fatigue life and F-N curve. The effectiveness of experimental data was analyzed by t distribution, pivot method and Weibull distribution. Results show that under the same parameters, the nugget diameter of the spot weld bonding joint is larger than the resistance spot welding joint. The static strength of the spot weld bonding joint is decreased by 25% compared with the spot weld, and it is increased by 33% compared with the adhesive joint. At the same loading level, the fatigue life of the spot weld bonding joint is increased by 60%-100% compared with the spot weld.
1.5 mm thick SUS304 austenitic steel sheet was used as the test material to study the spot weld bonding process and fatigue performance. The joint performance was analyzed by the process, strength distribution, fatigue life and F-N curve. The effectiveness of experimental data was analyzed by t distribution, pivot method and Weibull distribution. Results show that under the same parameters, the nugget diameter of the spot weld bonding joint is larger than the resistance spot welding joint. The static strength of the spot weld bonding joint is decreased by 25% compared with the spot weld, and it is increased by 33% compared with the adhesive joint. At the same loading level, the fatigue life of the spot weld bonding joint is increased by 60%-100% compared with the spot weld.
2020, 40(4): 85 -91
doi: 10.11868/j.issn.1005-5053.2019.000106
Abstract:
In order to study the uniaxial compression properties of closed-cell metal foam, three different modeling methods were used in this paper to establish 2D random cell, 3D Kelvin and 3D voronoi metal foam model. Based on the LS-DYNA software, the differences of the compressive mechanical properties of the closed-cell metal foam under three different models were analyzed. The deformation mode and the stress strain response of the metal foam under three models were studied. The results show that 2D random cell model is more suitable for the study of the compression regularity of metal foam, and the 3D model is more suitable for the prediction and optimization of the compression response of metal foam. The 2D random cell model is restricted by its plane geometry, it can only simulate the closed-cell metal foam with low porosity in most cases. The Kelvin model and Voronoi model can simulate the closed- cell metal foam with high porosity. Compared with the Kelvin model and 2D random cell model, the voronoi model is more realistic and reasonable, and it is able to better characterize the compressive mechanical properties of closed-cell metal foam.
In order to study the uniaxial compression properties of closed-cell metal foam, three different modeling methods were used in this paper to establish 2D random cell, 3D Kelvin and 3D voronoi metal foam model. Based on the LS-DYNA software, the differences of the compressive mechanical properties of the closed-cell metal foam under three different models were analyzed. The deformation mode and the stress strain response of the metal foam under three models were studied. The results show that 2D random cell model is more suitable for the study of the compression regularity of metal foam, and the 3D model is more suitable for the prediction and optimization of the compression response of metal foam. The 2D random cell model is restricted by its plane geometry, it can only simulate the closed-cell metal foam with low porosity in most cases. The Kelvin model and Voronoi model can simulate the closed- cell metal foam with high porosity. Compared with the Kelvin model and 2D random cell model, the voronoi model is more realistic and reasonable, and it is able to better characterize the compressive mechanical properties of closed-cell metal foam.
2020, 40(4): 92 -98
doi: 10.11868/j.issn.1005-5053.2019.000178
Abstract:
Aperture-type and patch-type frequency selective surfaces (FSS) were prepared by using carbon fiber paper containing carbon fiber. Using honeycomb as the matching dielectric layer, microscopic characterization of carbon fiber distribution in carbon fiber paper was performed by stereo microscope, the reflectivity of the composite FSS structure was tested by a vector network analyzer. The influences of unit shape, carbon fiber content in carbon fibre paper and carbon fiber length on the wave absorbing performance of aperture type FSS and patch type FSS were studied with the same matrix area ratio of carbon fiber paper. The results show that in the range of 2-18 GHz, the absorbing properties of aperture-type FSS and patch-type FSS are related to the content and length of carbon fiber in carbon fiber paper, and has nothing to do with the shape of the unit. At 6-18 GHz, with the same the ratio of the matrix area of carbon fiber paper, the shape of unit, the length and content of carbon fiber in the carbon fiber paper, the absorbing properties of aperture-type FSS are better than that of patch-type FSS.
Aperture-type and patch-type frequency selective surfaces (FSS) were prepared by using carbon fiber paper containing carbon fiber. Using honeycomb as the matching dielectric layer, microscopic characterization of carbon fiber distribution in carbon fiber paper was performed by stereo microscope, the reflectivity of the composite FSS structure was tested by a vector network analyzer. The influences of unit shape, carbon fiber content in carbon fibre paper and carbon fiber length on the wave absorbing performance of aperture type FSS and patch type FSS were studied with the same matrix area ratio of carbon fiber paper. The results show that in the range of 2-18 GHz, the absorbing properties of aperture-type FSS and patch-type FSS are related to the content and length of carbon fiber in carbon fiber paper, and has nothing to do with the shape of the unit. At 6-18 GHz, with the same the ratio of the matrix area of carbon fiber paper, the shape of unit, the length and content of carbon fiber in the carbon fiber paper, the absorbing properties of aperture-type FSS are better than that of patch-type FSS.
2020, 40(4): 99 -108
doi: 10.11868/j.issn.1005-5053.2019.000141
Abstract:
The progressive damage analysis model of stepped adhesive repairing structure was established to study the ultimate load-bearing strength and failure mode of laminates under axial tensile load after stepped adhesive repairing, and the effect of different slope repairing technology on the strength of repaired laminate was further studied. By compiling VUMAT subroutine, failure criteria and stiffness degradation models of laminate and patch were set respectively, and cohesive element was selected to simulate the adhesive layer to complete progressive damage analysis of composite laminates with stepped adhesive repair structure. The results show that the ultimate tensile strength increases with the decrease of slope, but the strength recovery rate does not change much when the slope is 1:20 or less. The adhesive layer at the 0° laminate connection first occurs damage and extends along the direction perpendicular to the loading until failure, and then causes the damage of laminate and patch. The effective adhesive area of the cohesive layer increases with the decrease of the slope, which can effectively alleviate the stress concentration phenomenon; The tensile failure of laminate first occurs at the minimum radius of the damage area, and the tensile failure of fibers first occurs at the 0° laminate and then extends perpendicular to the loading direction.
The progressive damage analysis model of stepped adhesive repairing structure was established to study the ultimate load-bearing strength and failure mode of laminates under axial tensile load after stepped adhesive repairing, and the effect of different slope repairing technology on the strength of repaired laminate was further studied. By compiling VUMAT subroutine, failure criteria and stiffness degradation models of laminate and patch were set respectively, and cohesive element was selected to simulate the adhesive layer to complete progressive damage analysis of composite laminates with stepped adhesive repair structure. The results show that the ultimate tensile strength increases with the decrease of slope, but the strength recovery rate does not change much when the slope is 1:20 or less. The adhesive layer at the 0° laminate connection first occurs damage and extends along the direction perpendicular to the loading until failure, and then causes the damage of laminate and patch. The effective adhesive area of the cohesive layer increases with the decrease of the slope, which can effectively alleviate the stress concentration phenomenon; The tensile failure of laminate first occurs at the minimum radius of the damage area, and the tensile failure of fibers first occurs at the 0° laminate and then extends perpendicular to the loading direction.
2020, 40(4): 109 -115
doi: 10.11868/j.issn.1005-5053.2020.000013
Abstract:
An attractive type of nanofiller-carbon nanofiber (CNF) was used to modify High-density Polyethylene (HDPE) and polymer blends (UH-HDPE) of HDPE and ultra-high molecular weight polyethylene (UHMWPE), and two-phase and three-phase nanocomposites were prepared via a two-step process including melt mixing and hot press. The effects of CNF addition and their dispersion on the dielectric properties of nanocomposites were investigated. The results show that CNFs are well dispersed in HDPE matrix, while they are not permeated into the UHMWPE. It is demonstrated that CNFs are distributed homogenously in two-phase CNF/HDPE composites and heterogeneously in three-phase CNF/UH-HDPE composites. The dielectric constant of nanocomposites is dramatically improved with higher CNF content. The highest dielectric constant in CNF/HDPE composites, 190 at 102 Hz, is achieved with CNFs above 10% (mass fraction, the same as below), which is about 50 times higher than that of pure HDPE. Simultaneously, the dielectric constant of CNF/HDPE composites shows high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The influence of CNFs on the dielectric constant of CNF/UH-HDPE composites is similar to that of CNF/HDPE composites. However, the dielectric constant of three-phase composites is higher than that of two-phase counterparts with the same CNF addition. Additionally, no obvious dielectric loss is exhibited in both nanocomposites with CNF concentration under 5%.
An attractive type of nanofiller-carbon nanofiber (CNF) was used to modify High-density Polyethylene (HDPE) and polymer blends (UH-HDPE) of HDPE and ultra-high molecular weight polyethylene (UHMWPE), and two-phase and three-phase nanocomposites were prepared via a two-step process including melt mixing and hot press. The effects of CNF addition and their dispersion on the dielectric properties of nanocomposites were investigated. The results show that CNFs are well dispersed in HDPE matrix, while they are not permeated into the UHMWPE. It is demonstrated that CNFs are distributed homogenously in two-phase CNF/HDPE composites and heterogeneously in three-phase CNF/UH-HDPE composites. The dielectric constant of nanocomposites is dramatically improved with higher CNF content. The highest dielectric constant in CNF/HDPE composites, 190 at 102 Hz, is achieved with CNFs above 10% (mass fraction, the same as below), which is about 50 times higher than that of pure HDPE. Simultaneously, the dielectric constant of CNF/HDPE composites shows high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The influence of CNFs on the dielectric constant of CNF/UH-HDPE composites is similar to that of CNF/HDPE composites. However, the dielectric constant of three-phase composites is higher than that of two-phase counterparts with the same CNF addition. Additionally, no obvious dielectric loss is exhibited in both nanocomposites with CNF concentration under 5%.
1998, 18(4): 52-61
2006, 26(3): 283-288
2000, 20(2): 55-63
2000, 20(1): 55-61
2002, 22(2): 49-53
2009, 29(1): 1-6
2006, 26(3): 148-151
2010, 30(4): 92-96
2006, 26(3): 244-250
2000, 20(3): 172-177
2001, 21(1): 55-62
2006, 26(3): 226-232
2006, 26(3): 238-243
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京ICP备15058934号-1
Address：P.Q.BOX 81-44,Beijing 100095,China
Telephone：010-62496277 E-mail：hkclxb@biam.ac.cn
Supported by Beijing Renhe Information Technology Co. LtdTechnical support：info@rhhz.net