The effects of the synergistic addition of Er and Sc on the aging and interfacial segregation behaviors of alloys were systematically studied using transmission electron microscopy(TEM)and high-angle annular dark fiel...The effects of the synergistic addition of Er and Sc on the aging and interfacial segregation behaviors of alloys were systematically studied using transmission electron microscopy(TEM)and high-angle annular dark field(HAADF)imaging.The TEM results show that Al3(Sc,Zr)with a core-shell structure can act as nucleation particles forθ′to promote uniform and fine precipitation.The STEM results show that Er solute atoms were preferentially enriched inside theθ′precipitate during thermal exposure at 225℃for 150 h.However,Sc and Mn solute atoms segregated at theθ′/α-Al matrix interface were observed at 300℃.Due to the early enrichment of Er in theθ′precipitate,the slowly diffusing Sc and Mn were segregated to the interface of theθ′precipitate before the severe coarsening of theθ′precipitate,thus further stabilizing theθ′precipitate at higher temperatures.展开更多
The ageing behavior of as-extruded Ti_(P)/VW94 composites was investigated.The peak hardness of the composites increases compared to the matrix alloy and the 5%Ti_(P)/VW94 composite presents the highest peak hardness ...The ageing behavior of as-extruded Ti_(P)/VW94 composites was investigated.The peak hardness of the composites increases compared to the matrix alloy and the 5%Ti_(P)/VW94 composite presents the highest peak hardness of 148.7 HV after aging for about 50 h.However,the hardness increments first decrease and then slightly increase with increasing Ti particle content due to the introduction of high-density dislocations by Ti particles.展开更多
The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical viewpoints.The obvious changes o...The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical viewpoints.The obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of FKM-A.Meanwhile,much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is found.Three-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of network.FTIR results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C=C bonds in the backbone.The coupling effect of oil medium and high temperature could accelerate the scission of C=C bonds and generate a series of fragments with different molecular sizes.The TGA results,crosslinking density Ve,and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final stage.The newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability.展开更多
A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al...A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.展开更多
The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperat...The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.展开更多
2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 um diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temper...2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 um diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.展开更多
The mechanical properties of magnesium matrix composties can be further improved by aging treatment. To study the aging behavior of SiC particles reinforced AZ61 magnesium matrix composites fabricated by ultrasonic me...The mechanical properties of magnesium matrix composties can be further improved by aging treatment. To study the aging behavior of SiC particles reinforced AZ61 magnesium matrix composites fabricated by ultrasonic method, an investigation has been undertaken by means of Vickers hardness measurement, scanning electron microscopy （SEM） and energy spectrum analyzing apparatus. The box-type heat treatment furnace was used in the study. The results showed that no discontinuous cellular precipitation is observed at the grain boundaries in the magnesium matrix of the composite while the MglTAI12 preferentially precipitates in the matrix. The time to reach the peak hardness for AZ61 alloy or SiCp/AZ61 magnesium matrix composites is reduced with the increase of aging temperature. At the same temperature, the composite exhibit an accelerated aging manner but lower aging efficiency, compared with the unreinforced matrix alloy. The microhardness of the composite is higher than that of the unreinforced matrix alloy, because that the SiC particles distributes homogeneously in the matrix alloy under the ultrasonic processing condition.展开更多
The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA （ZnO-Pr6O11-CoO- Cr203-A1203） ceramics were investigated with various contents of Er203. The ceramic phases consisted o...The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA （ZnO-Pr6O11-CoO- Cr203-A1203） ceramics were investigated with various contents of Er203. The ceramic phases consisted of a bulk phase of ZnO grains, and a minor secondary phase of mixture of Pr6O11 and Er203. The increase of the content of doped Er203 increased the densities of sintered pellet from 5.66 to 5.85 g/cm3, and decreased the average grain size from 9.6 to 6.3 μm. With the increase of the content of doped Er203, the breakdown field increased from 2390 to 4530 V/cm, and the nonlinear coefficient increased from 28.4 to 39.1. The sample doped with 0.25 mol.% Er203 exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA/cm2, and for the non-ohmic coefficient were -3.4% and -23,8%, respectively, after application of a stress of 0.95 Eu/125 ℃/24 h.展开更多
Four Zn-rich Al-Zn-Mg-Cu alloys with different Mg and Cu contents were fabricated by spray deposition.The effects of Mg and Cu contents on the aging behaviors of the whole precipitation process of the alloys were syst...Four Zn-rich Al-Zn-Mg-Cu alloys with different Mg and Cu contents were fabricated by spray deposition.The effects of Mg and Cu contents on the aging behaviors of the whole precipitation process of the alloys were systematically investigated.The results show that the primary precipitates in the under-aged and peak-aged alloys are GPⅡ and η'phases;no GPⅠ zones were observed.During aging,the dissolution driving force of the precipitates increases with increasing Mg content;therefore,the volume fraction of precipitates in the grain interior and the area fraction of precipitates at the grain boundary increase obviously,which contributes to a considerable improvement in yield strength and decrease in plasticity of the high Mg content alloys.Cu content has no apparent effect on the size and volume fraction of precipitates.However,a higher Cu content can effectively prevent coarsening and transformation of precipitates,which is beneficial to maintain the peak aging state of the alloys.This research provides a basis for the composition optimization of the rapid-solidified highly alloying Al-Zn-Mg-Cu alloys.展开更多
Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy ...Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy dispersive spectrum(EDS),and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).The results show that the higher fracture elongation(14±1%)and ultimate tensile strength(275±6 MPa)were simultaneously obtained in the peak-aged AlN/AZ91 composites.Comparied with AZ91 matrix alloy,the strength was increased by about 44%and the elongation was approximately five times higher,which mainly attributed to the precipitation of nano-sizedγ-Mg_(17)Al_(12)phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature.However,the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy,which resulted into the volume fraction decreasing ofγ-Mg_(17)Al_(12)precipitates,and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites.On the other hand,the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles,which promoted the precipitation ofγ-Mg_(17)Al_(12)phase,and then the peak aging time and temperature were decreased.展开更多
Effect of trace rare earth Er addition on the aging behavior of 1420 alloys was studied using hardness testing. Precipitation behavior during aging was investigated by electron microscopy transmission. It is found tha...Effect of trace rare earth Er addition on the aging behavior of 1420 alloys was studied using hardness testing. Precipitation behavior during aging was investigated by electron microscopy transmission. It is found that small amounts of Er can modify the aging behavior of 1420 alloy, for example, improve the hardness and shift peak aging time. All those results may be attributed to the increase of diffusion coefficient of Li atom in the Al matrix added with Er. As a consequence, rate of nucleation and growth of δ′ (Al_3Li) was promoted; the Al_3Er particles act as preferential sites for the nucleation and growth of δ′, which in turn results in the presentation of more composite particles.展开更多
We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chrom...We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes（hexamethyl cyclotrisiloxane） only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.展开更多
The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging tempe...The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3%.The calculation indicates that the mixed precipitation structure containing theβprecipitate band provides a 35%higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.展开更多
In this work,the aging response and mechanism of dual-phase Mg-Li-Al-Zn alloy at various temperatures are investigated.The results show that the strengthening after quenching is primarily attributed to the immediate p...In this work,the aging response and mechanism of dual-phase Mg-Li-Al-Zn alloy at various temperatures are investigated.The results show that the strengthening after quenching is primarily attributed to the immediate precipitation of the semi-coherent~Mg_(3)Zn phase.The aging softening of the studied alloy is mainly caused by the rapid transformation of the strengthening~Mg_(3)Zn phase to the softening MgLi(Al,Zn)phase,along with the coarsening of theα-Mg matrix and precipitates withinβ-Li matrix.Further analysis indicates that the quick precipitation and transformation of~Mg_(3)Zn is a consequence of the high diffusion rate of solute atoms,resulting from dense vacancy concentration in theβ-Li matrix.This research bridges a critical gap in the study of aging mechanism in the dual-phase Mg-Li-Al-Zn alloy,providing a theoretical basis for the development and application of high-performance and thermal-stable Mg-Li alloys.展开更多
Gradient nano-grained structure is frequently engineered into metallic materials,including Mg alloys,to achieve superior combination of strength and ductility.Nevertheless,the influence of this microstructural feature...Gradient nano-grained structure is frequently engineered into metallic materials,including Mg alloys,to achieve superior combination of strength and ductility.Nevertheless,the influence of this microstructural feature on aging precipitation behavior remains inadequately understood.In this study,the age-precipitation behavior of a gradient nano-grained Mg-Gd-Ag-Zr alloy prepared via ultrasonic severe surface rolling was investigated.The result indicates that the aging precipitation behavior exhibits a depth-dependent variation within this alloy.In the nano-grained surface layer,hierarchicalβnano-precipitates are predominant,while at greater depths,the precipitates consist ofβnanoparticles located at grain boundaries,along with intragranularβ′andγ″nano-plates.The formation ofβnano-precipitates deviates from the conventional precipitation behavior observed in Mg-Gd-Ag alloys,and is attributed to the high density of defects induced by the surface nano-grained structure.This finding advances our understanding of the precipitation behavior in the alloys with heterogeneous microstructure.展开更多
The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）...The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.展开更多
The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM...The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the ST condition of 18Cr-16Mn-2Mo-1.1N HNS with wN above 1% is identified as 1100 ℃ for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial time-temperature-precipitation (TTP) curve of aged 18Cr-16Mn-2Mo-1.1N HNS which starts with precipitation of 0.05% in volume fraction is defined and the 'nose' temperature of precipitation is found to be 850 ℃ with an incubation period of 1 min. Hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness, and the increment of cellular Cr2N causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks.展开更多
The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties...The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties,local corrosion properties,and slow strain rate tensile stress corrosion tests.Microstructure characterization techniques such as metallographic microscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were also employed.The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging,and it even exceeds 700 MPa.Furthermore,the yield strength increases by 52.7 MPa,reaching 654.8 MPa after T6I6 aging treatment.The maximum depths of intergranular corrosion(IGC)and exfoliation corrosion(EXCO)decrease from 116.3 and 468.5μm to 89.5 and 324.3μm,respectively.The stress corrosion factor also decreases from 2.1%to 1.6%.These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance.Similarly,when the alloy is treated with T6I4,T6I6 and T6I7 aging,the sizes of grain boundary precipitates(GBPs)are found to be 5.2,18.4,and 32.8 nm,respectively.The sizes of matrix precipitates are 4.8,5.7 and 15.7 nm,respectively.The atomic fractions of Zn in GBPs are 9.92 at.%,8.23 at.%and 6.87 at.%,respectively,while the atomic fractions of Mg are 12.66 at.%,8.43 at.%and 7.00 at.%,respectively.Additionally,the atomic fractions of Cu are 1.83 at.%,2.47 at.%and 3.41 at.%,respectively.展开更多
The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing t...The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing this dilemma via the balance between grain refinement and weakening of dynamic precipitation is proposed and applied on a Mg-10.95Gd-2.06Ag(wt%)alloy treated by sequential processing of equalchannel angular pressing(ECAP),hot rolling and aging.The hot rolling leads to a noticeable dissolution of the dynamic precipitates intensively formed during prior ECAP,together with a tolerable grain growth.Meanwhile,numerous multi-twinning-induced lamellar bands(LBs)demarcated by coaxial grain boundaries(CGBs)subdivide the grains.For the first time,a quadruple twinning pattern for the formation of CGB with a misorientation of~135°is raised.During post-rolling aging,besides the commonβ’andγ”precipitates and theβnano-particles whose Gd/Ag ratio is much lower than that of dynamically precipitatedβparticles,theβ”/βT precipitates,CGB segregation,and stacking fault(SF)-associated segregation/γ’precipitates within LBs,are also involved with the precipitation structure.Benefiting from this complex precipitation structure,a good age-hardening ability manifested by the aging-induced tensile yield strength(TYS)increment reaching 115 MPa is attained.Combining with the strengthening from grain boundaries,dislocations,solutes,and basal texture,a high TYS of 447 MPa is achieved.展开更多
The effect of aging on microstructure of Mg-Zn-Er alloys at 473 K was investigated using hardness measurement,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results indicated that both...The effect of aging on microstructure of Mg-Zn-Er alloys at 473 K was investigated using hardness measurement,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results indicated that both Mg3.8Zn1.5Er and Mg5Zn2.0Er alloys exhibited visible age-hardening effect,especially the latter alloy.Microstructure analysis showed that,after being aged,lots of fine MgZn2 phases with hexagonal structure were found in the α-Mg matrix.Comparing with Mg3.8Zn1.5Er alloy,the accelerated hardenin...展开更多
基金supported by the National Key Research and Development Program of China(Nos.2021YFB3700902,2021YFB3704204,2021YFB3704205)Innovative Research Group Project of the National Natural Science Foundation of China(No.51621003)+3 种基金Beijing Natural Science Foundation,China(No.2202009)Basic Research Program of Jiangsu Province,China(No.BK20191148)Beijing Lab Project for Modern Transportation Metallic Materials and Processing Technology,ChinaJiangsu Key Laboratory for Clad Materials,China(No.BM2014006)。
文摘The effects of the synergistic addition of Er and Sc on the aging and interfacial segregation behaviors of alloys were systematically studied using transmission electron microscopy(TEM)and high-angle annular dark field(HAADF)imaging.The TEM results show that Al3(Sc,Zr)with a core-shell structure can act as nucleation particles forθ′to promote uniform and fine precipitation.The STEM results show that Er solute atoms were preferentially enriched inside theθ′precipitate during thermal exposure at 225℃for 150 h.However,Sc and Mn solute atoms segregated at theθ′/α-Al matrix interface were observed at 300℃.Due to the early enrichment of Er in theθ′precipitate,the slowly diffusing Sc and Mn were segregated to the interface of theθ′precipitate before the severe coarsening of theθ′precipitate,thus further stabilizing theθ′precipitate at higher temperatures.
基金supported by the Guangdong Major Project of Basic and Applied Basic Research (No.2020B0301030006)the National Natural Science Foundation of China (No.52225101)+1 种基金the Graduate Research and Innovation Foundation of Chongqing,China (Grant No.CYB21001)the GDAS'Project of Science and Technology Development (No.2020GDASYL-20200101001).
文摘The ageing behavior of as-extruded Ti_(P)/VW94 composites was investigated.The peak hardness of the composites increases compared to the matrix alloy and the 5%Ti_(P)/VW94 composite presents the highest peak hardness of 148.7 HV after aging for about 50 h.However,the hardness increments first decrease and then slightly increase with increasing Ti particle content due to the introduction of high-density dislocations by Ti particles.
基金This work was financially supported by the Joint Foundation from Ministry of Education and Advanced Research of Equipment(No.6141A02022201)the National Natural Science Foundation of China(Nos.U19A2096,51721091)Department of Science and Technology of Sichuan Province(No.2019YFH0027).
文摘The aging behaviors and mechanism of fluoroelastomer(FKM)under lubricating oil(FKM-O)and air(FKM-A,as a comparison)at elevated temperatures were studied from both physical and chemical viewpoints.The obvious changes of mechanical and swelling performances indicate that the coupling effect of lubricating oil and temperature causes more serious deterioration of FKM-O compared to that of FKM-A.Meanwhile,much stronger temperature dependence of both bulk properties and micro-structures for FKM-O is found.Three-stage physical diffusion process is defined in FKM-O due to the competition between oil diffusion and elastic retraction of network.FTIR results reveal that the dehydrofluorination reaction causes the fracture of C-F bonds and produces a large number of C=C bonds in the backbone.The coupling effect of oil medium and high temperature could accelerate the scission of C=C bonds and generate a series of fragments with different molecular sizes.The TGA results,crosslinking density Ve,and glass transition temperature Tg derived from different measurements coherently demonstrate the network destruction in the initial stage and the simultaneous reconstruction occurring at the final stage.The newly formed local network induced by reconstruction cannot compensate the break of the original rubber network and thus only provides lower tensile strength and thermal stability.
基金Project(2017YFB0306300) supported by the National key R&D Program of ChinaProjects(51675538, 51905551)supported by the National Natural Science Foundation of ChinaProject(ZZYJKT2019-11) supported by Free Exploration Project of State Key Laboratory of High performance Complex Manufacturing,China。
文摘A study was conducted to better understand how different parameters, namely, regression aging time and regression aging temperature, affect the creep aging properties, i.e., the creep deformation and performance of Al-Zn-MgCu alloy during regressive reaging. The corresponding creep strain and mechanical properties of samples were studied by conducting creep tests and uniaxial tensile tests. The electrical conductivity was measured using an eddy-current conductivity meter. The microstructures were observed by transmission electron microscopy(TEM). With the increase in regression aging time, the steady creep strain first increased and then decreased, and reached the maximum at 45 min.The steady creep strain increased with the increase in regression aging temperature, and reached the maximum at 200 ℃.The level of steady creep strain was determined by precipitation and dislocation recovery. Creep aging strengthens 7B50-RRA treated with regression aging time at 190 ℃ for 10 min, and the difference in the mechanical properties of alloy becomes smaller. The diffusion of solute atoms reduces the scattering of electrons, leading to a significant improvement in electrical conductivity and stress corrosion cracking(SCC) resistance after creep aging. The findings of this study could help in the application of creep aging forming(CAF) technology in Al-Zn-Mg-Cu alloy under RRA treatment.
文摘The effect of sintering temperature on microstructure, electrical properties, and pulse aging behavior of （V2O5-Mn3O4-Er2O3）-doped zinc oxide varistor ceramics was systematically studied. When the sintering temperature increased, the average grain size increased from 6.1 to 8.7μm and the sintered density decreased from 5.52 to 5.43 g/cm3. The breakdown field decreased from 3856 to 922 V/cm with an increase in the sintering temperature up to 900 °C, whereas a further increase to 2352 V/cm at 925 °C. The nonlinear coefficient increased pronouncedly from 4.6 to 30.0 with an increase in the sintering temperature. The varistor ceramics sintered at 850 °C exhibited the best clamping characteristics, with the clamp voltage ratio of the range of 2.22-2.88 for pulse current of 1-25 A. The varistor ceramics sintered at 925 °C exhibited the strongest stability, with %ΔE1 mA/cm2=-8.8% after applying the multi-pulse current of 25 A.
文摘2024 Al matrix composite reinforced by SiC particles with 45% volume fraction and 1 um diameter was successfully fabricated by squeeze-exhaust casting method. The aging behavior of SiCp/2024AI composite at four temperatures was investigated and compared to 2024 alloy. It was found that the addition of high volume fraction SiC particles does not alter the aging sequence, but it significantly accelerates the kinetics of precipitation in the composite matrices. Therefore, the aging peak of the composite appears earlier than that of 2024AI alloy. This is attributed to the decrease in the activation energy for the precipitate formation and the increase in the precipitate growth rate due to the high density dislocations in the composite with high volume fraction particles. The high density dislocations, as preferential nucleation sites for precipitates, bring about the tiny and dense precipitates in the composite.
基金financially supported by the National Natural Science Foundation of China(Grant No.50765005)supported by the Innovative Group of Science and Technology of Colleges,Jiangxi Province,China(00008713)
文摘The mechanical properties of magnesium matrix composties can be further improved by aging treatment. To study the aging behavior of SiC particles reinforced AZ61 magnesium matrix composites fabricated by ultrasonic method, an investigation has been undertaken by means of Vickers hardness measurement, scanning electron microscopy （SEM） and energy spectrum analyzing apparatus. The box-type heat treatment furnace was used in the study. The results showed that no discontinuous cellular precipitation is observed at the grain boundaries in the magnesium matrix of the composite while the MglTAI12 preferentially precipitates in the matrix. The time to reach the peak hardness for AZ61 alloy or SiCp/AZ61 magnesium matrix composites is reduced with the increase of aging temperature. At the same temperature, the composite exhibit an accelerated aging manner but lower aging efficiency, compared with the unreinforced matrix alloy. The microhardness of the composite is higher than that of the unreinforced matrix alloy, because that the SiC particles distributes homogeneously in the matrix alloy under the ultrasonic processing condition.
文摘The microstructure, electrical and dielectric properties, and DC-accelerated aging of the ZPCCA （ZnO-Pr6O11-CoO- Cr203-A1203） ceramics were investigated with various contents of Er203. The ceramic phases consisted of a bulk phase of ZnO grains, and a minor secondary phase of mixture of Pr6O11 and Er203. The increase of the content of doped Er203 increased the densities of sintered pellet from 5.66 to 5.85 g/cm3, and decreased the average grain size from 9.6 to 6.3 μm. With the increase of the content of doped Er203, the breakdown field increased from 2390 to 4530 V/cm, and the nonlinear coefficient increased from 28.4 to 39.1. The sample doped with 0.25 mol.% Er203 exhibited the strongest electrical stability; variation rates for the breakdown field measured at 1.0 mA/cm2, and for the non-ohmic coefficient were -3.4% and -23,8%, respectively, after application of a stress of 0.95 Eu/125 ℃/24 h.
基金supported by the National Defense Pre-Research Foundation of China(Grant No.9140C500108140C50225)Shanghai Science and Technology Committee Innovation(Grant Nos.17JC1400600 and 17JC1400601)Open Foundation of Jiangsu Province Key Laboratory of High-end Structure Materials(Grant No.hsm1905).
文摘Four Zn-rich Al-Zn-Mg-Cu alloys with different Mg and Cu contents were fabricated by spray deposition.The effects of Mg and Cu contents on the aging behaviors of the whole precipitation process of the alloys were systematically investigated.The results show that the primary precipitates in the under-aged and peak-aged alloys are GPⅡ and η'phases;no GPⅠ zones were observed.During aging,the dissolution driving force of the precipitates increases with increasing Mg content;therefore,the volume fraction of precipitates in the grain interior and the area fraction of precipitates at the grain boundary increase obviously,which contributes to a considerable improvement in yield strength and decrease in plasticity of the high Mg content alloys.Cu content has no apparent effect on the size and volume fraction of precipitates.However,a higher Cu content can effectively prevent coarsening and transformation of precipitates,which is beneficial to maintain the peak aging state of the alloys.This research provides a basis for the composition optimization of the rapid-solidified highly alloying Al-Zn-Mg-Cu alloys.
基金support for this research by the National Natural Science Foundation of China(Grant Nos.52071268,51771151)Key Laboratory of Interface Science and Engineering in Advanced Materials,Ministry of Education,Taiyuan University of Technology,Taiyuan 030024,China(Grant No.KLISEAM201603)+1 种基金State Key Laboratory of Advanced Metals and Materials(Grant No.2019-Z06)the Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University,China(Grant No.CX201905).
文摘Microstructure evolution and mechanical properties of the aging treated AlN/AZ91 composites were systematically investigated by optical microscopy(OM),high resolution scanning electron microscopy(HRSEM)with an energy dispersive spectrum(EDS),and high-angle annular dark field scanning transmission electron microscopy(HAADF-STEM).The results show that the higher fracture elongation(14±1%)and ultimate tensile strength(275±6 MPa)were simultaneously obtained in the peak-aged AlN/AZ91 composites.Comparied with AZ91 matrix alloy,the strength was increased by about 44%and the elongation was approximately five times higher,which mainly attributed to the precipitation of nano-sizedγ-Mg_(17)Al_(12)phase and the activation of non-basal slip systems induced by in-situ AlN particles at room temperature.However,the in-situ formation of AlN reinforcements consumed part of Al element in the matrix alloy,which resulted into the volume fraction decreasing ofγ-Mg_(17)Al_(12)precipitates,and then the age hardening and strengthening efficiency were reduced in the AlN/AZ91 composites.On the other hand,the mismatch of thermal expansion coefficient between AlN particles and AZ91 matrix generated high density dislocations around AlN particles,which promoted the precipitation ofγ-Mg_(17)Al_(12)phase,and then the peak aging time and temperature were decreased.
文摘Effect of trace rare earth Er addition on the aging behavior of 1420 alloys was studied using hardness testing. Precipitation behavior during aging was investigated by electron microscopy transmission. It is found that small amounts of Er can modify the aging behavior of 1420 alloy, for example, improve the hardness and shift peak aging time. All those results may be attributed to the increase of diffusion coefficient of Li atom in the Al matrix added with Er. As a consequence, rate of nucleation and growth of δ′ (Al_3Li) was promoted; the Al_3Er particles act as preferential sites for the nucleation and growth of δ′, which in turn results in the presentation of more composite particles.
基金Funded by the National Natural Science Foundation of China(21174108)the Science and Technology Project of China Southern Power Grid Co.,Ltd.(K-GD2014-185)
文摘We investigated the aging effect on the chemical structure of silicone rubber composite materials under outdoor environment. The variations of low molecular weight siloxanes in silicone rubber were probed by gas chromatography-mass spectrometry during the degradation process. The experimental results indicate that a series of cyclic siloxanes exist in both the virgin and aged silicone rubber samples, while the additional low molecular weight siloxanes（hexamethyl cyclotrisiloxane） only appear in the aged samples. Meanwhile, the total amounts of low molecular weight siloxanes in the aged samples are much less than those in the virgin ones. The loss of low molecular weight siloxanes is induced by the chain scission and depolymerization.
基金supported by the National Key R&D Program of China(No.2021YFB3701100).
文摘The deformation mechanism,microstructure evolution,and precipitation behavior of a Mg-8.9Gd-1.8Y-0.5Zr-0.2Ag(wt.%)alloy multi-directionally forged at three different temperatures were investigated.As the forging temperature increases,the particle-stimulated nucleation(PSN)effect diminishes as the num-ber of dynamic precipitates decreases,pyramidal slip is activated,grain boundary migration accelerates,and continuous dynamic recrystallization(CDRX)dominates.The microstructures varied greatly,although fine-grained structures were formed at all different forging temperatures.Competitive precipitation be-tween dynamic precipitate growth,dislocation-induced precipitation,and homogeneous precipitation was observed after aging treatment.Among them,the medium temperature(748 K)forged and aged alloy ex-hibits the best mechanical performance,with an ultimate tensile strength of 436 MPa,and elongation of 16.3%.The calculation indicates that the mixed precipitation structure containing theβprecipitate band provides a 35%higher strengthening contribution than the typical homogeneously distributed precipi-tates.The formation of precipitation-free zones(PFZs)ensures that aging will not cause a dramatic de-crease in ductility,which provides a reference for the industrial preparation of high-performance wrought Mg-Gd series alloys.
基金supported by the Foundation Strengthening Plan Technical Field Fund(No.2021-JJ-0112)Major Scientific and Technological Innovation Project of Luoyang(No.2201029A)+1 种基金National Science and Technology Innovation Special Zone(No.02-14-01)National Natural Science Foundation of China(No.U2037601).
文摘In this work,the aging response and mechanism of dual-phase Mg-Li-Al-Zn alloy at various temperatures are investigated.The results show that the strengthening after quenching is primarily attributed to the immediate precipitation of the semi-coherent~Mg_(3)Zn phase.The aging softening of the studied alloy is mainly caused by the rapid transformation of the strengthening~Mg_(3)Zn phase to the softening MgLi(Al,Zn)phase,along with the coarsening of theα-Mg matrix and precipitates withinβ-Li matrix.Further analysis indicates that the quick precipitation and transformation of~Mg_(3)Zn is a consequence of the high diffusion rate of solute atoms,resulting from dense vacancy concentration in theβ-Li matrix.This research bridges a critical gap in the study of aging mechanism in the dual-phase Mg-Li-Al-Zn alloy,providing a theoretical basis for the development and application of high-performance and thermal-stable Mg-Li alloys.
基金supported by the Changzhou Sci&Tech Program(Grant No.20240764)Key Laboratory of Advanced Structural Materials(Changchun University of Technology),Ministry of Education,China(Grant No.ASM-202207).
文摘Gradient nano-grained structure is frequently engineered into metallic materials,including Mg alloys,to achieve superior combination of strength and ductility.Nevertheless,the influence of this microstructural feature on aging precipitation behavior remains inadequately understood.In this study,the age-precipitation behavior of a gradient nano-grained Mg-Gd-Ag-Zr alloy prepared via ultrasonic severe surface rolling was investigated.The result indicates that the aging precipitation behavior exhibits a depth-dependent variation within this alloy.In the nano-grained surface layer,hierarchicalβnano-precipitates are predominant,while at greater depths,the precipitates consist ofβnanoparticles located at grain boundaries,along with intragranularβ′andγ″nano-plates.The formation ofβnano-precipitates deviates from the conventional precipitation behavior observed in Mg-Gd-Ag alloys,and is attributed to the high density of defects induced by the surface nano-grained structure.This finding advances our understanding of the precipitation behavior in the alloys with heterogeneous microstructure.
基金Projects (2010CB731700,2012CB619500) supported by the National Basic Research Program of China
文摘The influence of Li addition on mechanical property and aging precipitation behavior of Al-3.5Cu-1.5Mg alloy was investigated by tensile test,scanning electron microscopy（SEM）,transmission electron microscopy（TEM） and high resolution transmission electron microscopy（HRTEM）.The results show that the tensile strength can be significantly improved with the slightly decreased ductility and the form of fracture morphology is converted from ductile fracture into ductile/britde mixed fracture by adding 1.0%Li.Besides,the peak aging time at 185 ℃ is delayed from 12 to 24 h and the main precipitation phase S（Al2CuMg） is converted into S＇（Al2CuMg）＋δ（Al3Li）,while the formation of S＇（Al2CuMg） is delayed.
基金Item Sponsored by Key Program of National Science Foundation of China(50534010)Fundamental Research Funds for Central Universities of China(N100402015)
文摘The solution-treated (ST) condition and aging precipitation behavior of 18Cr-16Mn-2Mo-1.1N high nitrogen austenitic stainless steel (HNS) were investigated by optical microscope (OM), scanning electron microscope (SEM), and transmission electron microscope (TEM). The results show that the ST condition of 18Cr-16Mn-2Mo-1.1N HNS with wN above 1% is identified as 1100 ℃ for 90 min, followed by water quenching to make sure the secondary phases completely dissolve into austenitic matrix and prevent the grains coarsening too much. Initial time-temperature-precipitation (TTP) curve of aged 18Cr-16Mn-2Mo-1.1N HNS which starts with precipitation of 0.05% in volume fraction is defined and the 'nose' temperature of precipitation is found to be 850 ℃ with an incubation period of 1 min. Hexagonal intergranular and cellular Cr2N with a=0.478 nm and c=0.444 nm precipitates gradually increase in the isothermal aging treatment. The matrix nitrogen depletion due to the intergranular and a few cellular Cr2N precipitates induces the decay of Vickers hardness, and the increment of cellular Cr2N causes the increase in the values. Impact toughness presents a monotonic decrease and SEM morphologies show the leading brittle intergranular fracture. The ultimate tensile strength (UTS), yield strength (YS) and elongation (El) deteriorate obviously. Stress concentration occurs when the matrix dislocations pile up at the interfaces of precipitation and matrix, and the interfacial dislocations may become precursors to the misfit dislocations, which can form small cleavage facets and accelerate the formation of cracks.
基金the Tianjin Key Laboratory of Fastening and Connection Technology Enterprises 2022—2023,China(No.TKLF2022-02-C-02)the technical support from the School of Materials Science and Engineering,Central South University,China.
文摘The effects of interrupted aging on mechanical properties and corrosion resistance of 7A75 aluminum alloy extruded bar were investigated through various analyses,including electrical conductivity,mechanical properties,local corrosion properties,and slow strain rate tensile stress corrosion tests.Microstructure characterization techniques such as metallographic microscopy,scanning electron microscopy(SEM),and transmission electron microscopy(TEM)were also employed.The results indicate that the tensile strength of the alloy produced by T6I6 aging is similar to that produced by T6I4 aging,and it even exceeds 700 MPa.Furthermore,the yield strength increases by 52.7 MPa,reaching 654.8 MPa after T6I6 aging treatment.The maximum depths of intergranular corrosion(IGC)and exfoliation corrosion(EXCO)decrease from 116.3 and 468.5μm to 89.5 and 324.3μm,respectively.The stress corrosion factor also decreases from 2.1%to 1.6%.These findings suggest that the alloy treated with T6I6 aging exhibits both high strength and excellent stress corrosion cracking resistance.Similarly,when the alloy is treated with T6I4,T6I6 and T6I7 aging,the sizes of grain boundary precipitates(GBPs)are found to be 5.2,18.4,and 32.8 nm,respectively.The sizes of matrix precipitates are 4.8,5.7 and 15.7 nm,respectively.The atomic fractions of Zn in GBPs are 9.92 at.%,8.23 at.%and 6.87 at.%,respectively,while the atomic fractions of Mg are 12.66 at.%,8.43 at.%and 7.00 at.%,respectively.Additionally,the atomic fractions of Cu are 1.83 at.%,2.47 at.%and 3.41 at.%,respectively.
基金supported by the National Natural Science Foundation of China(Grant Nos.51979099&51774109)Natural Science Foundation of Jiangsu Province of China(Grant No.BK 20191303)+2 种基金Key Research and Development Project of Jiangsu Province of China(Grant No.BE2017148)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX22_0632)Suqian Sci&Tech Program(Grant No.K202113).
文摘The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing this dilemma via the balance between grain refinement and weakening of dynamic precipitation is proposed and applied on a Mg-10.95Gd-2.06Ag(wt%)alloy treated by sequential processing of equalchannel angular pressing(ECAP),hot rolling and aging.The hot rolling leads to a noticeable dissolution of the dynamic precipitates intensively formed during prior ECAP,together with a tolerable grain growth.Meanwhile,numerous multi-twinning-induced lamellar bands(LBs)demarcated by coaxial grain boundaries(CGBs)subdivide the grains.For the first time,a quadruple twinning pattern for the formation of CGB with a misorientation of~135°is raised.During post-rolling aging,besides the commonβ’andγ”precipitates and theβnano-particles whose Gd/Ag ratio is much lower than that of dynamically precipitatedβparticles,theβ”/βT precipitates,CGB segregation,and stacking fault(SF)-associated segregation/γ’precipitates within LBs,are also involved with the precipitation structure.Benefiting from this complex precipitation structure,a good age-hardening ability manifested by the aging-induced tensile yield strength(TYS)increment reaching 115 MPa is attained.Combining with the strengthening from grain boundaries,dislocations,solutes,and basal texture,a high TYS of 447 MPa is achieved.
基金supported by National Major Fundamental Research Program of China (2007CB613706)
文摘The effect of aging on microstructure of Mg-Zn-Er alloys at 473 K was investigated using hardness measurement,scanning electron microscopy(SEM) and transmission electron microscopy(TEM).The results indicated that both Mg3.8Zn1.5Er and Mg5Zn2.0Er alloys exhibited visible age-hardening effect,especially the latter alloy.Microstructure analysis showed that,after being aged,lots of fine MgZn2 phases with hexagonal structure were found in the α-Mg matrix.Comparing with Mg3.8Zn1.5Er alloy,the accelerated hardenin...
