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Chinese Society of Aeronautics and Astronautics
AECC Beijing Instistute of Aeronautical Materials
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2023, 43(2): 1 -8
doi: 10.11868/j.issn.1005-5053.2023.000006
Abstract:
The effect of thermal exposure at 1000 ℃ to 1200 ℃ on the properties of porous matrix Al2O3/Al2O3 ceramic matrix composites was studied. The results show that the thermal exposure at 1000 ℃ for 100 h has no effect on the tensile strength of the composites. After 100 h at 1100 ℃, the tensile strength of the composites decreases slightly, and after 100 h at 1200 ℃, the tensile strength of the composites decreases obviously. The effects of different thermal exposure durations at 1200 ℃ on the properties of Al2O3/Al2O3 composites, alumina fibers and alumina matrix are further studied, and the micro morphologies of the samples are characterized by optical microscopy and SEM. The results show that the thermal exposure at 1200 ℃ for 100 h has little effect on the performance of alumina fiber, but has a great effect on the alumina matrix. After the thermal exposure at 1200 ℃ for only 10 h, the porosity of alumina matrix is significantly reduced and the density is significantly increased. It can be seen from the SEM morphology of the matrix fracture that with the increase of thermal exposure time at 1200 ℃, the alumina grain size of the matrix gradually increases and the matrix is further sintered. Correspondingly, it can be seen from the fracture morphology of the Al2O3/Al2O3 composite that the length and number of fibers pulled out also decrease significantly. The degradation of the properties of the composites after high temperature thermal exposure is mainly due to the further sintering of alumina matrix, and the densification of porous matrix reduces the toughening effect of the composites.
The effect of thermal exposure at 1000 ℃ to 1200 ℃ on the properties of porous matrix Al2O3/Al2O3 ceramic matrix composites was studied. The results show that the thermal exposure at 1000 ℃ for 100 h has no effect on the tensile strength of the composites. After 100 h at 1100 ℃, the tensile strength of the composites decreases slightly, and after 100 h at 1200 ℃, the tensile strength of the composites decreases obviously. The effects of different thermal exposure durations at 1200 ℃ on the properties of Al2O3/Al2O3 composites, alumina fibers and alumina matrix are further studied, and the micro morphologies of the samples are characterized by optical microscopy and SEM. The results show that the thermal exposure at 1200 ℃ for 100 h has little effect on the performance of alumina fiber, but has a great effect on the alumina matrix. After the thermal exposure at 1200 ℃ for only 10 h, the porosity of alumina matrix is significantly reduced and the density is significantly increased. It can be seen from the SEM morphology of the matrix fracture that with the increase of thermal exposure time at 1200 ℃, the alumina grain size of the matrix gradually increases and the matrix is further sintered. Correspondingly, it can be seen from the fracture morphology of the Al2O3/Al2O3 composite that the length and number of fibers pulled out also decrease significantly. The degradation of the properties of the composites after high temperature thermal exposure is mainly due to the further sintering of alumina matrix, and the densification of porous matrix reduces the toughening effect of the composites.
2023, 43(2): 9 -16
doi: 10.11868/j.issn.1005-5053.2022.000141
Abstract:
Turbine blades are the most demanding components in aircraft engines, and their performance is related to the safety of the whole engine. Due to the complex service environment and harsh service conditions of blades, various types of damage cannot be prevented in service. Therefore, it is of great engineering and economic significance to study the service damage of blades. In this paper, the directional solidification alloy turbine blade after actual service was selected as the research object. The cross section position of 80% upper height of the blade was intercepted, and the qualitative and quantitative microstructure analysis was carried out by SEM and EDS analysis. The results show that there are two different types of γ' phases in this leaf. One kind of γ' phase has small size and regular shape, the other has large size and irregular shape. The degree of microscopic damage among different parts of the blade is characterized with the help of dimensional distribution characterization of the γ' phase of each part, combined with the analysis of hardness testing of each part of the cross-section.The results show that the service conditions of different parts are different, and the degree of microstructure damage is different. In addition, matrix crack and coating crack in some parts of blade are summarized and analyzed.
Turbine blades are the most demanding components in aircraft engines, and their performance is related to the safety of the whole engine. Due to the complex service environment and harsh service conditions of blades, various types of damage cannot be prevented in service. Therefore, it is of great engineering and economic significance to study the service damage of blades. In this paper, the directional solidification alloy turbine blade after actual service was selected as the research object. The cross section position of 80% upper height of the blade was intercepted, and the qualitative and quantitative microstructure analysis was carried out by SEM and EDS analysis. The results show that there are two different types of γ' phases in this leaf. One kind of γ' phase has small size and regular shape, the other has large size and irregular shape. The degree of microscopic damage among different parts of the blade is characterized with the help of dimensional distribution characterization of the γ' phase of each part, combined with the analysis of hardness testing of each part of the cross-section.The results show that the service conditions of different parts are different, and the degree of microstructure damage is different. In addition, matrix crack and coating crack in some parts of blade are summarized and analyzed.
2023, 43(2): 17 -24
doi: 10.11868/j.issn.1005-5053.2022.000006
Abstract:
In order to investigate the distribution of temperature field in directionally solidified DZ4125 columnar superalloy, and to study the effects of different withdrawl rates on the changes of temperature gradient and mushy zone, the directional solidification processes with withdrawal rates of 3, 5 and 7 mm/min were simulated by ProCAST software. The results show that when the test rod is located in the heating zone, the isotherm is inclined distribution with low outside and high inside. And when the test rod is located in the cooling zone, the isotherm is inclined distribution with high outside and low inside. With the increase of withdrawal rate, the temperature gradient decreases gradually. The shape of the mushy zone depends on the withdrawal rate and the distance from the water-cooled plate. When the withdrawl rate is 5 mm/min, the horizontal state of the solidification front is maintained for a longest time. On this basis, the precision casting experiment of directional solidification test rod is carried out, and the relationship between the shape of liquidus and grain structure is found for castings withdrawn at 3 and 7 mm/min. It is found that when the liquidus is concave and convex, the grain grows towards the center and the surface of the test rod, and the horizontal liquidus can promote the grain growth along the axis of the test rod.
In order to investigate the distribution of temperature field in directionally solidified DZ4125 columnar superalloy, and to study the effects of different withdrawl rates on the changes of temperature gradient and mushy zone, the directional solidification processes with withdrawal rates of 3, 5 and 7 mm/min were simulated by ProCAST software. The results show that when the test rod is located in the heating zone, the isotherm is inclined distribution with low outside and high inside. And when the test rod is located in the cooling zone, the isotherm is inclined distribution with high outside and low inside. With the increase of withdrawal rate, the temperature gradient decreases gradually. The shape of the mushy zone depends on the withdrawal rate and the distance from the water-cooled plate. When the withdrawl rate is 5 mm/min, the horizontal state of the solidification front is maintained for a longest time. On this basis, the precision casting experiment of directional solidification test rod is carried out, and the relationship between the shape of liquidus and grain structure is found for castings withdrawn at 3 and 7 mm/min. It is found that when the liquidus is concave and convex, the grain grows towards the center and the surface of the test rod, and the horizontal liquidus can promote the grain growth along the axis of the test rod.
2023, 43(2): 25 -32
doi: 10.11868/j.issn.1005-5053.2022.000117
Abstract:
By means of short-term aged treated （STA）, standard heat treated （ST）, long-term aged treated （LTA） and microstructure observation, the effect of heat treatment regimes on microstructure of forged GH4169 alloy is investigated. The results show that after short-term aged treated, standard heat treated and long-term aged treated, the microstructure of forged GH4169 alloy consists of γ, γ′, γ", needle-like δ-Ni3Nb phase and particle-like （Nb,Ti）C, M23C6 carbides, therein, the P element is enriched in （Nb,Ti）C phase in which the elements Cr and Mo is poor. And after STA treated, no precipitated phases are identified in the boundary regions. After standard heat treated （ST） and long-term aged treated （LTA）, there are needle-like δ phase precipitated along the grain boundaries, and the quantity and size of the one increase as the aged time prolongs. After LTA treated, the parameters of γ、γ′ and γ" phases in the alloy diminishes slightly, so that the misfits between the phases in alloy are diminished to δγ/γ′= 0.361% and δγ/γ′′= 0.128% respectively, and the misfit between γ′ and γ" phases increases to δγ′/γ′′= 0.233%. And after LTA treated, the crystallography relation between the δ and γ matrix in the alloy is maintained to be （200）γ//（110）δ and [011]γ//[001]δ, therein, the （020）δ, （\begin{document}$1\bar10 $\end{document} ![]()
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By means of short-term aged treated （STA）, standard heat treated （ST）, long-term aged treated （LTA） and microstructure observation, the effect of heat treatment regimes on microstructure of forged GH4169 alloy is investigated. The results show that after short-term aged treated, standard heat treated and long-term aged treated, the microstructure of forged GH4169 alloy consists of γ, γ′, γ", needle-like δ-Ni3Nb phase and particle-like （Nb,Ti）C, M23C6 carbides, therein, the P element is enriched in （Nb,Ti）C phase in which the elements Cr and Mo is poor. And after STA treated, no precipitated phases are identified in the boundary regions. After standard heat treated （ST） and long-term aged treated （LTA）, there are needle-like δ phase precipitated along the grain boundaries, and the quantity and size of the one increase as the aged time prolongs. After LTA treated, the parameters of γ、γ′ and γ" phases in the alloy diminishes slightly, so that the misfits between the phases in alloy are diminished to δγ/γ′= 0.361% and δγ/γ′′= 0.128% respectively, and the misfit between γ′ and γ" phases increases to δγ′/γ′′= 0.233%. And after LTA treated, the crystallography relation between the δ and γ matrix in the alloy is maintained to be （200）γ//（110）δ and [011]γ//[001]δ, therein, the （020）δ, （
2023, 43(2): 33 -41
doi: 10.11868/j.issn.1005-5053.2022.000070
Abstract:
Cold rolling and heat treatment experiments of GH4169 alloy with different deformation were carried out. Effect of different cold rolling deformation and heat treatment state on microstructure and hardness of plate was analyzed. Cold rolling experimental results show that dislocation density is increased, dislocations are cross slipped, deformation texture are enhanced, twins boundaries are decreased and hardness is improved with the increasing of deformation. Different heat treatment experimental results show that when the cold rolling deformation within 0%-20%, after 980 ℃×10 min solution treatment, the recrystallization is incepted, grains are refined, deformed grains and dislocation are remained in the plate. When the deformation within 0%-20%, deformed grains are remained and recrystallized grain size is refined with the increasing of deformation, thus the hardness of solution treated plate is increased with the increasing of deformation. The recrystallization finished and work hardening is eliminated,thus the hardness of solution treated plate decline to undeformed level and remains unchanged when the deformation larger than 25%. The γ' and γ'' phases are precipitated in the plate after aging heat treatment, and the hardness of the plate is significantly higher than that of the cold rolled and solid solution treatment states, and the hardness is basically not affected by the deformation amount of cold rolling. The threshold value of cold rolling deformation for recrystallization inception of GH4169 alloy is within 5%-10% during 980 ℃ solution treatment. And the cold rolling deformation threshold value of complete recrystallization is about 25%. According to actual production condition, the optimal cold rolling deformation is larger than 25%, and the matched solution treatment is 980 ℃×10 min.
Cold rolling and heat treatment experiments of GH4169 alloy with different deformation were carried out. Effect of different cold rolling deformation and heat treatment state on microstructure and hardness of plate was analyzed. Cold rolling experimental results show that dislocation density is increased, dislocations are cross slipped, deformation texture are enhanced, twins boundaries are decreased and hardness is improved with the increasing of deformation. Different heat treatment experimental results show that when the cold rolling deformation within 0%-20%, after 980 ℃×10 min solution treatment, the recrystallization is incepted, grains are refined, deformed grains and dislocation are remained in the plate. When the deformation within 0%-20%, deformed grains are remained and recrystallized grain size is refined with the increasing of deformation, thus the hardness of solution treated plate is increased with the increasing of deformation. The recrystallization finished and work hardening is eliminated,thus the hardness of solution treated plate decline to undeformed level and remains unchanged when the deformation larger than 25%. The γ' and γ'' phases are precipitated in the plate after aging heat treatment, and the hardness of the plate is significantly higher than that of the cold rolled and solid solution treatment states, and the hardness is basically not affected by the deformation amount of cold rolling. The threshold value of cold rolling deformation for recrystallization inception of GH4169 alloy is within 5%-10% during 980 ℃ solution treatment. And the cold rolling deformation threshold value of complete recrystallization is about 25%. According to actual production condition, the optimal cold rolling deformation is larger than 25%, and the matched solution treatment is 980 ℃×10 min.
2023, 43(2): 42 -50
doi: 10.11868/j.issn.1005-5053.2022.000071
Abstract:
Aiming at improving the strength-plasticity match in the as-cast state of the most widely used Ti-6Al-4V the present work designs Ti-Al-V-Zr alloys on the basis of the dual-cluster formula of Ti-6Al-4V, α-{[Al-Ti12]（AlTi2）}12 +β-{[Al-Ti14]（V2Ti）}5: first, the alloys are more biased towards α-Ti by decreasing the number of β unit to 2, then, the stability of β-Ti is improved by increasing the number of V atoms in β unit to 3, and finally, Zr （x=1-5） replaces Ti in the β unit. Finally α-{[Al-Ti12]（AlTi2）}15-β-{[AlTi14-xZrx]V3）}2 is obtained, Ti-（6.64-6.82）Al-（2.42-2.35）V-（1.44-7.02）Zr （mass fraction,%） alloy is designed. The alloy ingots are prepared by melting in a non-consuming vacuum are furnace, and the alloy bars are suction-cast in copper mould. The results show that the alloys are all in α' martensite structure, showing morphologies changing from acicular Widmannstatten structure at lower Zr contents to net-basket structure at higher Zr contents. Among the designed alloys, Ti-6.64Al-2.35V-7.02Zr （x=5） with a net-basket structure, has the best mechanical properties: yield strength of 806 MPa, tensile strength of 963 MPa, and elongation of 5.9%, which are respectively 23%, 19% and 51% higher than those of Ti-6Al-4V alloy under the same preparation condition. In particular, the specific strength and specific hardness are 217kN•m/kg and 0.71 GPa•cm3/g, which are 18% and 10% higher than Ti-6Al-4V alloy.
Aiming at improving the strength-plasticity match in the as-cast state of the most widely used Ti-6Al-4V the present work designs Ti-Al-V-Zr alloys on the basis of the dual-cluster formula of Ti-6Al-4V, α-{[Al-Ti12]（AlTi2）}12 +β-{[Al-Ti14]（V2Ti）}5: first, the alloys are more biased towards α-Ti by decreasing the number of β unit to 2, then, the stability of β-Ti is improved by increasing the number of V atoms in β unit to 3, and finally, Zr （x=1-5） replaces Ti in the β unit. Finally α-{[Al-Ti12]（AlTi2）}15-β-{[AlTi14-xZrx]V3）}2 is obtained, Ti-（6.64-6.82）Al-（2.42-2.35）V-（1.44-7.02）Zr （mass fraction,%） alloy is designed. The alloy ingots are prepared by melting in a non-consuming vacuum are furnace, and the alloy bars are suction-cast in copper mould. The results show that the alloys are all in α' martensite structure, showing morphologies changing from acicular Widmannstatten structure at lower Zr contents to net-basket structure at higher Zr contents. Among the designed alloys, Ti-6.64Al-2.35V-7.02Zr （x=5） with a net-basket structure, has the best mechanical properties: yield strength of 806 MPa, tensile strength of 963 MPa, and elongation of 5.9%, which are respectively 23%, 19% and 51% higher than those of Ti-6Al-4V alloy under the same preparation condition. In particular, the specific strength and specific hardness are 217kN•m/kg and 0.71 GPa•cm3/g, which are 18% and 10% higher than Ti-6Al-4V alloy.
2023, 43(2): 51 -58
doi: 10.11868/j.issn.1005-5053.2022.000162
Abstract:
Direct solid diffusion bonding of Ti2AlNb alloy was carried out, and the effect of pressure on the microstructure and mechanical properties of the bonded joints was studied. Scanning electron microscopy was used to analyze the microstructure of the welded joint under different pressures. The tensile property of the joints with different pressures was tested and the variation trend of the tensile property with pressure was analyzed. The results show that with the increase of pressure, the deformation within the sample surface layer increased, and the dynamic recovery and recrystallization occurred in the deformed area at high temperature, which promotes the closing of voids on the bonding interface and the rise of well-bonded areas. A diffusion bonded joint of Ti2AlNb alloy can be divided into three parts: recrystallization zone, deformation zone and base metal. The recrystallization zone is mainly composed of equiaxed B2 phase and α2 phase. With the increase of pressure, the width of the recrystallization zone becomes wider obviously, and the strength of the bonded joint increases first and then decreases. When the welding parameters are 960 ℃-60 MPa-120 min, the welded joint had the best performance, and its tensile strength is 972 MPa, reaching 98% of the base metal. An excessive pressure coarsened the recrystallization grains, and cracks appeared at the interface of the recrystallized zone and the deformation zone, which deteriorated the performance of the bonded joint.
Direct solid diffusion bonding of Ti2AlNb alloy was carried out, and the effect of pressure on the microstructure and mechanical properties of the bonded joints was studied. Scanning electron microscopy was used to analyze the microstructure of the welded joint under different pressures. The tensile property of the joints with different pressures was tested and the variation trend of the tensile property with pressure was analyzed. The results show that with the increase of pressure, the deformation within the sample surface layer increased, and the dynamic recovery and recrystallization occurred in the deformed area at high temperature, which promotes the closing of voids on the bonding interface and the rise of well-bonded areas. A diffusion bonded joint of Ti2AlNb alloy can be divided into three parts: recrystallization zone, deformation zone and base metal. The recrystallization zone is mainly composed of equiaxed B2 phase and α2 phase. With the increase of pressure, the width of the recrystallization zone becomes wider obviously, and the strength of the bonded joint increases first and then decreases. When the welding parameters are 960 ℃-60 MPa-120 min, the welded joint had the best performance, and its tensile strength is 972 MPa, reaching 98% of the base metal. An excessive pressure coarsened the recrystallization grains, and cracks appeared at the interface of the recrystallized zone and the deformation zone, which deteriorated the performance of the bonded joint.
2023, 43(2): 59 -65
doi: 10.11868/j.issn.1005-5053.2021.000200
Abstract:
The effects of heat extrusion processing of spray forming TiCp/ZA35 composites on extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate had been studied by artificial neural network (ANN). The artificial neural network model was created for heat extrusion processing. The input parameters of the ANN model were extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate. The output of the ANN model was ultimate tensile strength. The model can be used for the prediction of properties of spray forming TiCp/ZA35 composites as functions of processing parameters. It can also be used for the optimization of the processing parameters. The ANN results are in good agreement with experimental phenomena, the biggest relative error and coincidence rate is less than 1.8% and 0.986. The optimized heat extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate are 22415 MPa, 315 ℃ and 8 mm·s−1 respectively, and the tensile strength of spray forming TiCp/ZA35 composites is 486.7 MPa. The reinforcement phase MnAl6 whisker or particle is precipitated in the grains due to the indirect aging treatment of composites by hot extrusion. Dispersion strengthen and dislocation strengthen contribute a combination factor to increase the room temperature mechanical properties of the hot extruded TiCp/ZA35 composites, which is 38.3% higher than that of TiCp/ZA35 composites without heat extrusion.
The effects of heat extrusion processing of spray forming TiCp/ZA35 composites on extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate had been studied by artificial neural network (ANN). The artificial neural network model was created for heat extrusion processing. The input parameters of the ANN model were extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate. The output of the ANN model was ultimate tensile strength. The model can be used for the prediction of properties of spray forming TiCp/ZA35 composites as functions of processing parameters. It can also be used for the optimization of the processing parameters. The ANN results are in good agreement with experimental phenomena, the biggest relative error and coincidence rate is less than 1.8% and 0.986. The optimized heat extrusion ratio, extrusion specific pressure, extrusion temperature and extrusion rate are 22415 MPa, 315 ℃ and 8 mm·s−1 respectively, and the tensile strength of spray forming TiCp/ZA35 composites is 486.7 MPa. The reinforcement phase MnAl6 whisker or particle is precipitated in the grains due to the indirect aging treatment of composites by hot extrusion. Dispersion strengthen and dislocation strengthen contribute a combination factor to increase the room temperature mechanical properties of the hot extruded TiCp/ZA35 composites, which is 38.3% higher than that of TiCp/ZA35 composites without heat extrusion.
2023, 43(2): 66 -74
doi: 10.11868/j.issn.1005-5053.2022.000067
Abstract:
With the development of aerospace technology, protective materials for hot-end components have reached higher requirements. In this paper, a （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O（x=0.2, 0.544, 0.672, 0.796和0.92）quintuple element ceramic system composite is studied based on the solid-phase reaction method and molecular dynamics simulation. By experimental means, ZrO2 （99.99%）, Y2O3 （99.99%）, Ta2O5 （99.99%）, Er2O3 （99.99%） and TiO2 （99%） powder was used as raw material to prepare （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O composite by the solid-phase reaction method. The thermal conductivity of （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O ceramic material was investigated computationally using the LAMMPS program. The study result shows that a consistent trend in the variation of the thermal conductivity is obtained by experiments and simulations at the interval of 200-900 °C. The thermal conductivity reaches a minimum value at x = 0.796, which proves the feasibility of molecular dynamics simulation of the thermal conductivity of multi-ceramic materials. Meanwhile, the effect of porosity on thermal conductivity was investigated, and it is found that there was a competitive relationship between the elemental ratios and the effect of porosity on thermal conductivity. When the porosity is larger than 6.67%, the effect of the porosity is the main influencing factor. when the porosity is smaller than 6.67%, the elemental ratios are the dominant factors in the thermal conductivity.
With the development of aerospace technology, protective materials for hot-end components have reached higher requirements. In this paper, a （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O（x=0.2, 0.544, 0.672, 0.796和0.92）quintuple element ceramic system composite is studied based on the solid-phase reaction method and molecular dynamics simulation. By experimental means, ZrO2 （99.99%）, Y2O3 （99.99%）, Ta2O5 （99.99%）, Er2O3 （99.99%） and TiO2 （99%） powder was used as raw material to prepare （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O composite by the solid-phase reaction method. The thermal conductivity of （ZrxY（1-x/4）Ta（1-x/4）Ti（1-x/4）Er（1-x/4））O ceramic material was investigated computationally using the LAMMPS program. The study result shows that a consistent trend in the variation of the thermal conductivity is obtained by experiments and simulations at the interval of 200-900 °C. The thermal conductivity reaches a minimum value at x = 0.796, which proves the feasibility of molecular dynamics simulation of the thermal conductivity of multi-ceramic materials. Meanwhile, the effect of porosity on thermal conductivity was investigated, and it is found that there was a competitive relationship between the elemental ratios and the effect of porosity on thermal conductivity. When the porosity is larger than 6.67%, the effect of the porosity is the main influencing factor. when the porosity is smaller than 6.67%, the elemental ratios are the dominant factors in the thermal conductivity.
2023, 43(2): 75 -82
doi: 10.11868/j.issn.1005-5053.2022.000072
Abstract:
Based on the theory of micromechanics, the thermal conductivity of poly（lactic acid）（PLA）composites filled with graphene（GR）sheets was studied by representative volume element method. According to the micrographs, the microstructure characteristics of the composite were analyzed, and a two-dimensional random model was established. The equivalent thermal conductivity of GR composite was calculated by finite element method, and the accuracy of the model was verified by experimental results. The influences of the microstructure parameters to the thermal conductivity of the composite were studied by parametric analysis, and its heat transfer mechanism was analyzed. The results show that the numerical results of the random model are in good agreement with the experimental results. With the increase of graphene mass fraction, the heat transfer performance of the composite is enhanced. The aspect ratio and orientation of graphene in the composites have great influence on the overall thermal conductivity of the GR composite. At the same time, the interfacial contact thermal resistance between graphene and matrix also has great influence on the overall thermal conductivity of the composites. The present model and the parametric analysis results can provide reference for optimal design of the absorbing materials.
Based on the theory of micromechanics, the thermal conductivity of poly（lactic acid）（PLA）composites filled with graphene（GR）sheets was studied by representative volume element method. According to the micrographs, the microstructure characteristics of the composite were analyzed, and a two-dimensional random model was established. The equivalent thermal conductivity of GR composite was calculated by finite element method, and the accuracy of the model was verified by experimental results. The influences of the microstructure parameters to the thermal conductivity of the composite were studied by parametric analysis, and its heat transfer mechanism was analyzed. The results show that the numerical results of the random model are in good agreement with the experimental results. With the increase of graphene mass fraction, the heat transfer performance of the composite is enhanced. The aspect ratio and orientation of graphene in the composites have great influence on the overall thermal conductivity of the GR composite. At the same time, the interfacial contact thermal resistance between graphene and matrix also has great influence on the overall thermal conductivity of the composites. The present model and the parametric analysis results can provide reference for optimal design of the absorbing materials.
2023, 43(2): 83 -89
doi: 10.11868/j.issn.1005-5053.2022.000116
Abstract:
ZnO is currently the main coating material for piezoelectric bolt sensors, which exhibits excellent acoustic-electric signal conversion because of its unique piezoelectric effect, but its high-temperature structure and performance stability have been less studied. In this paper, ZnO piezoelectric coating that could generate ultrasonic longitudinal waves was prepared on （100）Si and industrial titanium bolts by RF magnetron sputtering, and annealed at different temperatures and different time durations to investigate the effects of high-temperature annealing treatment on the structure and properties of the coating. The results of scanning electron microscopy show that the annealing treatment below 600 °C does not affect the microscopic morphology of the coating surface, and the cross-sectional morphology of the coating shows a columnar crystal structure, and the columnar crystals tend to merge with the temperature increased. The results of atomic force microscopy show that the surface roughness of the coating varies by ±4 nm, and the X-ray diffraction results show that different annealing temperatures do not affect the crystal structure of the coating significantly. The acoustic signals of the bolt samples after annealing treatment at different temperatures and durations are examined, and the results show that the coating surface is intact after annealing treatment at 500 °C and below, and the bolt coating is completely peeled off after annealing treatment at 600 °C. The ultrasonic signals characterize that the structure of coating is stable after annealing at 500 °C or below; at 300 °C, after a long annealing treatment, none of the excitable ultrasonic properties of the bolt samples are destroyed, indicating that the ZnO coating can serve in the temperature range of 300 ℃ for a long time.
ZnO is currently the main coating material for piezoelectric bolt sensors, which exhibits excellent acoustic-electric signal conversion because of its unique piezoelectric effect, but its high-temperature structure and performance stability have been less studied. In this paper, ZnO piezoelectric coating that could generate ultrasonic longitudinal waves was prepared on （100）Si and industrial titanium bolts by RF magnetron sputtering, and annealed at different temperatures and different time durations to investigate the effects of high-temperature annealing treatment on the structure and properties of the coating. The results of scanning electron microscopy show that the annealing treatment below 600 °C does not affect the microscopic morphology of the coating surface, and the cross-sectional morphology of the coating shows a columnar crystal structure, and the columnar crystals tend to merge with the temperature increased. The results of atomic force microscopy show that the surface roughness of the coating varies by ±4 nm, and the X-ray diffraction results show that different annealing temperatures do not affect the crystal structure of the coating significantly. The acoustic signals of the bolt samples after annealing treatment at different temperatures and durations are examined, and the results show that the coating surface is intact after annealing treatment at 500 °C and below, and the bolt coating is completely peeled off after annealing treatment at 600 °C. The ultrasonic signals characterize that the structure of coating is stable after annealing at 500 °C or below; at 300 °C, after a long annealing treatment, none of the excitable ultrasonic properties of the bolt samples are destroyed, indicating that the ZnO coating can serve in the temperature range of 300 ℃ for a long time.
2023, 43(2): 90 -97
doi: 10.11868/j.issn.1005-5053.2022.000125
Abstract:
Three-dimensional braided Cf/Al composites prepared by vacuum pressure infiltration method have good mechanical properties and great potential in aerospace applications. In this paper, the three-dimensional braided Cf/Al composites were taken as the research object, and the vibration fatigue tests were carried out under different loading stresses, and the microstructure of the fracture was observed after the fatigue tests. The test results show that the greater the loading stress is, the greater the percentage of natural frequency decrease is when T-shaped part reaches reach the fatigue stability stage, that is, the more significant the damage to the internal structure of T-shaped part is. By fitting the fatigue data under different loading stresses and drawing the S-N curve, the mathematical model of vibration fatigue damage evolution law of T-shaped part is obtained, which can be used to predict the life of three-dimensional braided Cf/Al composites. It is found that T-shaped part after the experiment shows typical brittle fracture characteristics through the macroscopic and microscopic analysis of the fracture .
Three-dimensional braided Cf/Al composites prepared by vacuum pressure infiltration method have good mechanical properties and great potential in aerospace applications. In this paper, the three-dimensional braided Cf/Al composites were taken as the research object, and the vibration fatigue tests were carried out under different loading stresses, and the microstructure of the fracture was observed after the fatigue tests. The test results show that the greater the loading stress is, the greater the percentage of natural frequency decrease is when T-shaped part reaches reach the fatigue stability stage, that is, the more significant the damage to the internal structure of T-shaped part is. By fitting the fatigue data under different loading stresses and drawing the S-N curve, the mathematical model of vibration fatigue damage evolution law of T-shaped part is obtained, which can be used to predict the life of three-dimensional braided Cf/Al composites. It is found that T-shaped part after the experiment shows typical brittle fracture characteristics through the macroscopic and microscopic analysis of the fracture .
2023, 43(2): 98 -106
doi: 10.11868/j.issn.1005-5053.2022.000096
Abstract:
The effect of specimen thickness on the very high cycle fatigue （VHCF） properties of DD6 nickel-based single crystal superalloys for turbine blades with hollow air-cooled structure was investigated. Based on the finite element method （FEM）, a thin-walled vibration fatigue specimen with a thickness of 0.5 mm was designed with a natural frequency of 1425 Hz, which was a suitable test efficiency for VHCF test. The VHCF test was carried out by electrodynamic shaker at room temperature, and a VHCF S-N curve up to 109 cycles was obtained. Comparing with the rotational bending fatigue and vibration fatigue test data of conventional size specimens, the results show that the fatigue strength of DD6 single crystal superalloy continues to decrease after 107 cycles and the fatigue strength is decreased about 25%, from 107 to 109 cycles; The high cycle fatigue strength of the thin-walled specimen is basically the same as the standard rotary bending fatigue strength of the same material, and slightly lower than the conventional vibration fatigue strength. The cracks in the thin-walled specimen initiate on the surface of the dangerous section, showing the characteristics of line source. There are two propagation planes in the fatigue growth zone, showing the characteristics of cleavage like.
The effect of specimen thickness on the very high cycle fatigue （VHCF） properties of DD6 nickel-based single crystal superalloys for turbine blades with hollow air-cooled structure was investigated. Based on the finite element method （FEM）, a thin-walled vibration fatigue specimen with a thickness of 0.5 mm was designed with a natural frequency of 1425 Hz, which was a suitable test efficiency for VHCF test. The VHCF test was carried out by electrodynamic shaker at room temperature, and a VHCF S-N curve up to 109 cycles was obtained. Comparing with the rotational bending fatigue and vibration fatigue test data of conventional size specimens, the results show that the fatigue strength of DD6 single crystal superalloy continues to decrease after 107 cycles and the fatigue strength is decreased about 25%, from 107 to 109 cycles; The high cycle fatigue strength of the thin-walled specimen is basically the same as the standard rotary bending fatigue strength of the same material, and slightly lower than the conventional vibration fatigue strength. The cracks in the thin-walled specimen initiate on the surface of the dangerous section, showing the characteristics of line source. There are two propagation planes in the fatigue growth zone, showing the characteristics of cleavage like.
2023, 43(2): 107 -117
doi: 10.11868/j.issn.1005-5053.2022.000066
Abstract:
Aluminum foam sandwich structure （aluminum foam sandwich, AFS） not only has the excellent characteristics of aluminum foam lightweight, damping and shock absorption, energy absorption and protection, but also can solve the problems of low strength and easy damage of single aluminum foam, so it has a broad application prospect in aerospace, automobile manufacturing, rail transportation, precision machine tools and other industrial fields. In this paper, based on the melt foaming method, an aluminum foam sandwich structure with the size of 80 mm×80 mm×18 mm was successfully prepared using pure TA2 as the panel and Al-2Ca alloy as the foaming base material, and a large number of uniform pores were observed in the foam core, of which the polyhedral pores occupied a large area. A binding interface with an average thickness of 7.5 μm was observed between the panel and the core layer, where the elements diffused at the binding layer and existed in the form of intermetallic compounds. The bending test results show that the load curves of sandwich structures with different densities show three distinct areas: linear elastic zone, rapid load drop zone and flatform zone. The maximum peak load and yield strength of the sandwich structure are 1120.5 N and 15.64 MPa respectively. The bending strength of AFS materials increases with the increase of density and the decrease of core porosity. When the bending degree is 15 mm and the AFS density increases by 15.9%, the bending energy absorption WEA and WSEA increase by 3.59 and 3.22 times respectively. In the process of bending test, the failure modes are composed of compressive compaction deformation of aluminum foam core layer, shear and cracking of core material, bending deformation and peeling failure of TA2 panel, and various failure modes of AFS material are formed under the joint action of different stresses at different positions of the sample.
Aluminum foam sandwich structure （aluminum foam sandwich, AFS） not only has the excellent characteristics of aluminum foam lightweight, damping and shock absorption, energy absorption and protection, but also can solve the problems of low strength and easy damage of single aluminum foam, so it has a broad application prospect in aerospace, automobile manufacturing, rail transportation, precision machine tools and other industrial fields. In this paper, based on the melt foaming method, an aluminum foam sandwich structure with the size of 80 mm×80 mm×18 mm was successfully prepared using pure TA2 as the panel and Al-2Ca alloy as the foaming base material, and a large number of uniform pores were observed in the foam core, of which the polyhedral pores occupied a large area. A binding interface with an average thickness of 7.5 μm was observed between the panel and the core layer, where the elements diffused at the binding layer and existed in the form of intermetallic compounds. The bending test results show that the load curves of sandwich structures with different densities show three distinct areas: linear elastic zone, rapid load drop zone and flatform zone. The maximum peak load and yield strength of the sandwich structure are 1120.5 N and 15.64 MPa respectively. The bending strength of AFS materials increases with the increase of density and the decrease of core porosity. When the bending degree is 15 mm and the AFS density increases by 15.9%, the bending energy absorption WEA and WSEA increase by 3.59 and 3.22 times respectively. In the process of bending test, the failure modes are composed of compressive compaction deformation of aluminum foam core layer, shear and cracking of core material, bending deformation and peeling failure of TA2 panel, and various failure modes of AFS material are formed under the joint action of different stresses at different positions of the sample.
2016, 36(4): 89-98
doi: 10.11868/j.issn.1005-5053.2016.4.013
2020, 40(3): 77-94
doi: 10.11868/j.issn.1005-5053.2020.000061
2016, 36(3): 13-19
doi: 10.11868/j.issn.1005-5053.2016.3.003
2015, 35(4): 63-82
doi: 10.11868/j.issn.1005-5053.2015.4.010
2016, 36(3): 79-91
doi: 10.11868/j.issn.1005-5053.2016.3.009
1998, 18(4): 52-61
2006, 26(3): 283-288
2000, 20(1): 55-61
2000, 20(2): 55-63
2002, 22(2): 49-53
2019, 39(6): 1-19
doi: 10.11868/j.issn.1005-5053.2019.000170
2010, 30(4): 92-96
2006, 26(3): 148-151
2009, 29(1): 1-6
2006, 26(3): 244-250
2000, 20(3): 172-177
2001, 21(1): 55-62
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