The microstructure,micro-hardness,and tensile properties of interface between hot isostatic pressing densified low alloy steel and Inconel 690 cladding were investigated during the aging process at 600℃.The results s...The microstructure,micro-hardness,and tensile properties of interface between hot isostatic pressing densified low alloy steel and Inconel 690 cladding were investigated during the aging process at 600℃.The results show that the interface region can be divided into four zones from base metal to deposited metal:carbon-depleted zone(CDZ),partial melting zone(PMZ),planar growth zone(PGZ),and brownish feature zone(BFZ).Dimensions of these zones do not significantly change during aging.However,type I carbides noticeably increase in size in the PMZ,and precipitates clearly occur in the PGZ.The main reason for their growth and occurrence is continuous carbon migration.The highest micro-hardness appears in the PGZ and BFZ regions,which is related to carbon accumulation and precipitates in these regions.Tensile failure occurs on the base metal side due to the high strength mismatch between these two materials.The CDZ,composed of only ferrite,has lower strength and fractures at the boundary between CDZ and base metal.The ultimate tensile strength decreases by only 50 MPa after aging for 1500 h,and the interface region maintains high strength without significant deformation.展开更多
In lead-cooled fast reactor(LFR)systems,the liquid lead-bismuth eutectic(LBE)coolant provides a cor-rosive environment that damages the steel components during high-temperature operation.This study investigated the mi...In lead-cooled fast reactor(LFR)systems,the liquid lead-bismuth eutectic(LBE)coolant provides a cor-rosive environment that damages the steel components during high-temperature operation.This study investigated the microstructural deterioration of 9Cr ferritic/martensitic(F/M)steel under thermal aging at 550℃for 2,000,10,000,or 20,000 h and its effect on oxidation corrosion in an LBE environment using multiscale characterization techniques.The results indicated that the thickness of the internal oxidation zone(IOZ)increased significantly with extended thermal aging,whereas that of the spinel layer remained relatively constant.The abundant subgrain boundaries that emerged during extensive thermal aging facil-itated Fe diffusion,and the enlarged Cr-rich M23C6 carbides contributed to the formation of preferential oxidation regions,accelerating IOZ layer growth.The spinel layer formed from the IOZ was influenced by microstructural defects within the IOZ.A theoretical model describing the accelerated oxide layer growth due to thermal aging was developed.These findings support the advancement of LFR technology.展开更多
This study investigates the long-term thermal-oxidative stability and mechanical properties of phenolcontaining phthalonitrile monomer(PN75)and dicyanate ester of bisphenol-A(DCBA)composites reinforced with short carb...This study investigates the long-term thermal-oxidative stability and mechanical properties of phenolcontaining phthalonitrile monomer(PN75)and dicyanate ester of bisphenol-A(DCBA)composites reinforced with short carbon fibers T700SC(SCF)within a temperature range of 330375℃.The research focuses on the PN75 monomer and DCBA blend reinforced SCF composites with varying SCF content,examining mass loss and changes in flexural strength after thermal aging for 50 h(h).Results show that the SCF-reinforced composites based on the PN75/DCBA blend consistently outperform the neat blend in flexural strength,both at room temperature and after thermal aging.The introduction of the SCF significantly improves the composites'thermal stability and mechanical retention,with higher SCF content correlating to better performance.Notably,after aging at 350℃,the SCF-reinforced composites based(30%(mass)SCF)retained 88.8%of its flexural strength,compared to 61.1%for the neat blend.Morphological analysis reveals that while thermal aging causes degradation of the PN75/DCBA blend layer on SCF surfaces,the overall composite structure maintains good mechanical properties up to 350℃.At 375℃,significant degradation occurs,yet the composites still retain flexural strengths above 78 MPa.This study demonstrates the potential of the SCF-reinforced composites based on PN75/DCBA blend for high-temperature applications,establishing their upper-temperature limit for long-term use in oxidative environments.展开更多
In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure v...In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.展开更多
The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of...The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of high angle grain boundaries(HAGB)increased in the steel after thermal aging process,with the observation of micro-textures.The weight gain rate of the steel after aging process increased,presenting the decreased Cr_(2)O_(3)contain in the oxide layer,which resulted in the increasing diffusion rate of Fe and O ions in oxide layer.The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.展开更多
Introduction: The stability of orthodontic brackets throughout orthodontic treatment plays a critical role in the treatment’s effectiveness. The present in vitro study was designed to assess the impact of various die...Introduction: The stability of orthodontic brackets throughout orthodontic treatment plays a critical role in the treatment’s effectiveness. The present in vitro study was designed to assess the impact of various dietary components on the performance of orthodontic brackets. Methods: Metal orthodontic brackets were bonded to 66 extracted anterior teeth divided into groups based on the solution type: Milk, Gatorade, Cold Coffee, and a control group using water. Each group consisted of 20 teeth except for the control group, which included six teeth. The bracketed teeth were submerged in their respective solutions for 15 minutes three times daily at different intervals to mimic an in vivo environment and were stored in artificial saliva at room temperature (23?C). The specimens underwent artificial aging through 10,000 cycles of thermocycling (representing one clinical year) between 5?C and 55?C. Shade measurements were taken using a VITA Easy Shade device, capturing the classic shade and L*, a*, and b* values. Delta E values were calculated immediately post-bonding and after 7 days, 1 month, 1, and 2 clinical years. The shear bond strength of each bracket was measured using an ultra-tester machine. Results: After two clinical years, significant differences in ΔE color values were observed across all groups, with the most substantial change noted in teeth immersed in cold coffee. Brackets submerged in milk demonstrated lower shear bond strength than other solutions, whereas the control group exhibited the highest shear bond strength (P = 0.01). Conclusion: The study indicates that dietary components significantly influence tooth color stability and the shear bond strength of orthodontic brackets, underscoring the importance of considering these factors in orthodontic treatment planning.展开更多
In this work,the characterizations of Cu-SSZ-13 after hydrothermal aging(HTA)and thermal aging(TA)at different temperatures(750,800,and 850°C)are compared,and the differences between those two serious aged sample...In this work,the characterizations of Cu-SSZ-13 after hydrothermal aging(HTA)and thermal aging(TA)at different temperatures(750,800,and 850°C)are compared,and the differences between those two serious aged samples are analyzed.With this data,the effect of steam on catalysts deactivation during hydrothermal aging is analyzed.The TA at 750 and 800°C causes the dealumination and the agglomeration of Cu^(2+)ions to Cu O,resulting in the activity loss of Cu-SSZ-13.The presence of steam upon HTA at750 and 800°C aggravates the catalyst deactivation by increasing the Al detachment and the Cu^(2+)agglomeration.The structure and cupric state are almost the same in the Cu-SSZ-13 after TA and HTA at 850°C,respectively,indicating that the steam has little influence on the deactivation.The formation of CuAl_(2)O_(4) spinel is the primary reason for the deactivation after both HTA and TA at 850°C,probably attributed to the strong interaction between Cu^(2+)ions and framework Al sites at high temperatures.展开更多
The thermal aging and scaling tests of Butadiene-acrylonitrile rubber （NBR） samples in alkaline solution were done, and after the tests, the surface contact angle of samples was measured and the sample surface was a...The thermal aging and scaling tests of Butadiene-acrylonitrile rubber （NBR） samples in alkaline solution were done, and after the tests, the surface contact angle of samples was measured and the sample surface was analyzed by infrared spectroscopy （IR）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）. The test results shows that after the NBR samples were dipped in pH 11, 70 ℃ alkaline solution for 215 d, many microcracks were observed on the surface and a lot of small sized scales existed near the cracks; element constituents of scale adhering on the surface were： Ca, Fe and A1, of which Ca was from saturated CaCO3, Fe was from rust scale and A1 was from A1203 ceramic existing also in the test environment; IR and XPS inspection indicate that there were outgrowths of carboxy group, acyloxy group, hydroxyl group, CaO and Ca3Si309, which showed that oxidation degradation and hydrolyzation happened on NBR and the scale appeared on the samples＇ surfaces. Dissolution, aging or scale adhesion led to non-uniformity of contact angle and surface energy data.展开更多
In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitr...In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitrides during long-term aging, experiments were performed at 700, 800, 850, and 900℃ for different periods （1, 24, 70, and 100 h）. The precipitation behavior of carbonitrides in specimens subjected to various aging conditions was explored using carbon replicas and transmission electron microscopy （TEM） observations. The corresponding sizes ofMX carbonitrides were measured. The results demonstrates that MX carbonitrides precipitate in type 347H austenitic steel as Nb（C,N）. The coarsening rate constant is time-independent; however, an increase in aging temperature results in an increase in coarsening rate of Nb（C,N）. The coarsening process was analyzed according to the calculated diffusion activation energy of Nb（C,N）. When the aging temperature was 800-900℃, the mean activation energy was 294 kJ·mol -1, and the coarsening behavior was controlled primarily by the diffusion of Nb atoms.展开更多
Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitiz...Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.展开更多
Early water damage of asphalt pavement is one of the major types of destruction,so taking maintenance on asphalt pavement at the proper time is necessary. Many new maintenance materials and methods are in use nowadays...Early water damage of asphalt pavement is one of the major types of destruction,so taking maintenance on asphalt pavement at the proper time is necessary. Many new maintenance materials and methods are in use nowadays to prevent pavement from water damage and skidding. This paper aims to study the effects of the silicone maintenance materials on thermal aging resistance of asphalt mixture. After thermal aging,the asphalt mixture using silicone materials and the control mixture are evaluated through their engineering properties,including indirect tensile modulus,low-temperature performance and fatigue resistance. The results indicate that the silicone materials used as repairing material can improve low-temperature performance and fatigue resistance of asphalt mixture,and decrease the indirect tensile modulus ratio before and after thermal aging. Consequently,the silicone maintenance material has the ability to protect asphalt mixture from thermal aging.展开更多
It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for n...It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for nuclear power plants to consider actual operation of nuclear power plants.Both multiple heat treatments and accelerated thermal aging experiment at the same temperature of 400℃ for different time were successively carried out on centrifugal casting stainless steels Z3CN20.09M in order to examine the metallographic modification and impact properties.Finally,an additional investigation on the related fracture properties was carried out,in which the critical initial fracture toughness Ji was determined by stretch zone width and 0.2 mm offset line methods.These results indicated that the multiple heat treatments led to the dispersed distribution of ferrite phases in austenite matrix and thus microhardness increased,but impact energy exhibited a decreasing tendency significantly.After long-term aging,the metallographic structure remained almost unchanged,but the size of ferrite phases showed a slight increasing trend because of spinodal decomposition in ferrite phases and G-phase precipitation.In addition,centrifugal casting stainless steels Z3CN20.09M with multiple heat treatments exhibited the higher microhardness,Charpy impact toughness,critical initial fracture toughness J_(IC)(J-integral determined by 0.2 mm offset line method),and J_(SZW)(J-integral determined by stretch zone width method)than those with primary heat treatment,while the specific number of the heat treatment had a low influence on fracture toughness.展开更多
The life of shipboard cables will decrease due to the complex aging processes. In terms of the safety perspective, remaining life prediction of the cable is essential to maintain a reliable operation. In this paper, f...The life of shipboard cables will decrease due to the complex aging processes. In terms of the safety perspective, remaining life prediction of the cable is essential to maintain a reliable operation. In this paper, firstly, based on Arrhenius equation, residual life of new styrene-butadiene cable is calculated; result indicates that the degradation rate which changes with time is proportional to thermal temperature. Then second order dynamic model is adopted into the residual life prediction, combined with the time-temperature superposition method(TTSP), and a new residual life model is proposed. According to the accelerated thermal aging experiment data and Arrhenius equation, TTSP method demonstrates to be an efficient way for life prediction, and life at normal temperature can be estimated by this model. In order to monitor the state of styrene-butadiene cable more accurately, an improved residual life model based on equivalent environment temperature of cable is proposed, and life of cable under real operation is analyzed. Result indicates that this model is credible and reliable, and it provides an important theoretical base for residual life of cables.展开更多
The thermal aging behavior of poly （ vinyl alcohol ） （ PVA ） hydrogel was studied at four different temperatures of 40 ℃, 50 ℃, 60 ℃ and 70 ℃ in one year. The samples of PVA hydrogel were closely covered by pl...The thermal aging behavior of poly （ vinyl alcohol ） （ PVA ） hydrogel was studied at four different temperatures of 40 ℃, 50 ℃, 60 ℃ and 70 ℃ in one year. The samples of PVA hydrogel were closely covered by plastic film. The changes of their chemical structures and physical properties during aging were measured through different measurable techniques including tensile testing, gel permeation chromatography （ GPC ）, viscosity analysis, and Fourier transform infrared （FTIR） spec- trum. The results showed that the molecular weight of PVA in hydrogel changed little with time and temperature. FTIR spectra of PVA in all the samples were similar to those of the original samples. The tensile strength of PVA hydrogel didn＇t change until the 330th days.展开更多
： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination wi...： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.展开更多
The degradation of crosslinked polyethylene (XLPE) cable insulation during service, such as thermo-oxidation and water treeing may lead to a premature electrical breakdown of the XLPE insulation cables. Therefore, it ...The degradation of crosslinked polyethylene (XLPE) cable insulation during service, such as thermo-oxidation and water treeing may lead to a premature electrical breakdown of the XLPE insulation cables. Therefore, it is necessary to optimize the period of replacement to evenly distribute the replacement cost by ascertaining the deterioration degree. Estimation of the aging degree is at present the most important task for diagnosis of the residual lifetime of the power cable insulation. This paper presents a study on the changes in the dielectric properties of the thermally aged XLPE cables in the frequency range from 0.07～10 MHz. Based on electrical and physicochemical characterization, some new "dactylograms" for the thermally aged XLPE cable insulation have been proposed.展开更多
The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped i...The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110<span style="white-space:nowrap;">°</span>C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.展开更多
The effect of thermal aging on the fatigue crack growth（FCG） behavior of Z3CN20？09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths wer...The effect of thermal aging on the fatigue crack growth（FCG） behavior of Z3CN20？09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths were analyzed to clarify the FCG mechanisms. The microstructure and micromechanical properties before and after thermal aging were also studied. Spinodal decomposition in the aged ferrite phase led to an increase in the hardness and a decrease in the plastic deformation capacity, whereas the hardness and plastic deformation capacity of the austenite phase were almost unchanged after thermal aging. The aged material exhibited a better FCG resistance than the unaged material in the near-threshold regime because of the increased roughness-induced crack closure associated with the tortuous crack path and rougher fracture surface; however, the tendency was reversed in the Paris regime because of the cleavage fracture in the aged ferrite phases.展开更多
The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric con...The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.展开更多
Previous studies,including ASME and RCC-MR standards,did not consider the influence of environmental factors on the ratcheting boundary of the material,and only a unified ratcheting boundary was proposed.In this paper...Previous studies,including ASME and RCC-MR standards,did not consider the influence of environmental factors on the ratcheting boundary of the material,and only a unified ratcheting boundary was proposed.In this paper,thermal aging was taken into consideration,and the effect of thermal aging time on the ratcheting boundary of 316 LN austenitic stainless steel was characterized by the efficiency diagram rule.The results show that,when the secondary ratio U is small,there is no significant difference in ratcheting boundary between the original material and the thermal aged material.When the secondary ratio U is large,the ratcheting boundary of the material presents a slight upward trend with the increase of thermal aging time.Compared with ASME and RCC-MR standards,it is found that RCC-MR is conservative.Based on the evolution of the efficiency index V with the number of cycles,it is more conservative and reasonable to choose the stage when the efficiency index V develops into a constant.展开更多
基金Major Scientific and Technological Project of Gansu(22ZD6GA008)Excellent Doctorate Project of Gansu(23JRRA806)National Natural Science Foundation of China(52175325,51961024,52071170)。
文摘The microstructure,micro-hardness,and tensile properties of interface between hot isostatic pressing densified low alloy steel and Inconel 690 cladding were investigated during the aging process at 600℃.The results show that the interface region can be divided into four zones from base metal to deposited metal:carbon-depleted zone(CDZ),partial melting zone(PMZ),planar growth zone(PGZ),and brownish feature zone(BFZ).Dimensions of these zones do not significantly change during aging.However,type I carbides noticeably increase in size in the PMZ,and precipitates clearly occur in the PGZ.The main reason for their growth and occurrence is continuous carbon migration.The highest micro-hardness appears in the PGZ and BFZ regions,which is related to carbon accumulation and precipitates in these regions.Tensile failure occurs on the base metal side due to the high strength mismatch between these two materials.The CDZ,composed of only ferrite,has lower strength and fractures at the boundary between CDZ and base metal.The ultimate tensile strength decreases by only 50 MPa after aging for 1500 h,and the interface region maintains high strength without significant deformation.
基金supported by the Natural Science Foundation of Shandong Province with grant No.ZR2023ME196the Science and Technology Support Plan for Young Innovation of Colleges and Universities of Shandong Province with grant No.2022KJ273+1 种基金the Youth Innovation Promotion Association of the Chinese Academy of Sciences with grant No.2017486the Patent Navigation Project of Shandong Province with grant No.D202327.
文摘In lead-cooled fast reactor(LFR)systems,the liquid lead-bismuth eutectic(LBE)coolant provides a cor-rosive environment that damages the steel components during high-temperature operation.This study investigated the microstructural deterioration of 9Cr ferritic/martensitic(F/M)steel under thermal aging at 550℃for 2,000,10,000,or 20,000 h and its effect on oxidation corrosion in an LBE environment using multiscale characterization techniques.The results indicated that the thickness of the internal oxidation zone(IOZ)increased significantly with extended thermal aging,whereas that of the spinel layer remained relatively constant.The abundant subgrain boundaries that emerged during extensive thermal aging facil-itated Fe diffusion,and the enlarged Cr-rich M23C6 carbides contributed to the formation of preferential oxidation regions,accelerating IOZ layer growth.The spinel layer formed from the IOZ was influenced by microstructural defects within the IOZ.A theoretical model describing the accelerated oxide layer growth due to thermal aging was developed.These findings support the advancement of LFR technology.
基金funded by the Innovative Research Group project of the National Natural Science Foundation of China(52373003).
文摘This study investigates the long-term thermal-oxidative stability and mechanical properties of phenolcontaining phthalonitrile monomer(PN75)and dicyanate ester of bisphenol-A(DCBA)composites reinforced with short carbon fibers T700SC(SCF)within a temperature range of 330375℃.The research focuses on the PN75 monomer and DCBA blend reinforced SCF composites with varying SCF content,examining mass loss and changes in flexural strength after thermal aging for 50 h(h).Results show that the SCF-reinforced composites based on the PN75/DCBA blend consistently outperform the neat blend in flexural strength,both at room temperature and after thermal aging.The introduction of the SCF significantly improves the composites'thermal stability and mechanical retention,with higher SCF content correlating to better performance.Notably,after aging at 350℃,the SCF-reinforced composites based(30%(mass)SCF)retained 88.8%of its flexural strength,compared to 61.1%for the neat blend.Morphological analysis reveals that while thermal aging causes degradation of the PN75/DCBA blend layer on SCF surfaces,the overall composite structure maintains good mechanical properties up to 350℃.At 375℃,significant degradation occurs,yet the composites still retain flexural strengths above 78 MPa.This study demonstrates the potential of the SCF-reinforced composites based on PN75/DCBA blend for high-temperature applications,establishing their upper-temperature limit for long-term use in oxidative environments.
基金supported by the National Natural Science Foundation of China(No.52071018).
文摘In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.
基金supported by the Hebei Natural Science Foundation(E2023502105)the China Postdoctoral Science Foundation(2023M741155)the Fundamental Research Funds for the Central Universities(JB2023030).
文摘The oxidation behavior of 316L austenitic steel after thermal aging process at 600℃for 6 h was investigated in the supercritical water(600℃/25 MPa)with 1000 h.Results showed that the grain size and the proportion of high angle grain boundaries(HAGB)increased in the steel after thermal aging process,with the observation of micro-textures.The weight gain rate of the steel after aging process increased,presenting the decreased Cr_(2)O_(3)contain in the oxide layer,which resulted in the increasing diffusion rate of Fe and O ions in oxide layer.The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.
文摘Introduction: The stability of orthodontic brackets throughout orthodontic treatment plays a critical role in the treatment’s effectiveness. The present in vitro study was designed to assess the impact of various dietary components on the performance of orthodontic brackets. Methods: Metal orthodontic brackets were bonded to 66 extracted anterior teeth divided into groups based on the solution type: Milk, Gatorade, Cold Coffee, and a control group using water. Each group consisted of 20 teeth except for the control group, which included six teeth. The bracketed teeth were submerged in their respective solutions for 15 minutes three times daily at different intervals to mimic an in vivo environment and were stored in artificial saliva at room temperature (23?C). The specimens underwent artificial aging through 10,000 cycles of thermocycling (representing one clinical year) between 5?C and 55?C. Shade measurements were taken using a VITA Easy Shade device, capturing the classic shade and L*, a*, and b* values. Delta E values were calculated immediately post-bonding and after 7 days, 1 month, 1, and 2 clinical years. The shear bond strength of each bracket was measured using an ultra-tester machine. Results: After two clinical years, significant differences in ΔE color values were observed across all groups, with the most substantial change noted in teeth immersed in cold coffee. Brackets submerged in milk demonstrated lower shear bond strength than other solutions, whereas the control group exhibited the highest shear bond strength (P = 0.01). Conclusion: The study indicates that dietary components significantly influence tooth color stability and the shear bond strength of orthodontic brackets, underscoring the importance of considering these factors in orthodontic treatment planning.
基金supported by the National Key Research and Development Program of China (2018YFC0214103)the National Natural Science Foundation of China (22006044)the Scientific Research Funds of Huaqiao University (605-50Y200270001)。
文摘In this work,the characterizations of Cu-SSZ-13 after hydrothermal aging(HTA)and thermal aging(TA)at different temperatures(750,800,and 850°C)are compared,and the differences between those two serious aged samples are analyzed.With this data,the effect of steam on catalysts deactivation during hydrothermal aging is analyzed.The TA at 750 and 800°C causes the dealumination and the agglomeration of Cu^(2+)ions to Cu O,resulting in the activity loss of Cu-SSZ-13.The presence of steam upon HTA at750 and 800°C aggravates the catalyst deactivation by increasing the Al detachment and the Cu^(2+)agglomeration.The structure and cupric state are almost the same in the Cu-SSZ-13 after TA and HTA at 850°C,respectively,indicating that the steam has little influence on the deactivation.The formation of CuAl_(2)O_(4) spinel is the primary reason for the deactivation after both HTA and TA at 850°C,probably attributed to the strong interaction between Cu^(2+)ions and framework Al sites at high temperatures.
基金Supported by the Science and Technology Foundation of China National Petroleum Corporation (04B70303).
文摘The thermal aging and scaling tests of Butadiene-acrylonitrile rubber （NBR） samples in alkaline solution were done, and after the tests, the surface contact angle of samples was measured and the sample surface was analyzed by infrared spectroscopy （IR）, X-ray photoelectron spectroscopy （XPS） and scanning electron microscopy （SEM）. The test results shows that after the NBR samples were dipped in pH 11, 70 ℃ alkaline solution for 215 d, many microcracks were observed on the surface and a lot of small sized scales existed near the cracks; element constituents of scale adhering on the surface were： Ca, Fe and A1, of which Ca was from saturated CaCO3, Fe was from rust scale and A1 was from A1203 ceramic existing also in the test environment; IR and XPS inspection indicate that there were outgrowths of carboxy group, acyloxy group, hydroxyl group, CaO and Ca3Si309, which showed that oxidation degradation and hydrolyzation happened on NBR and the scale appeared on the samples＇ surfaces. Dissolution, aging or scale adhesion led to non-uniformity of contact angle and surface energy data.
基金the China National Funds for Distinguished Young Scientists (No.51325401)the National High Technology Research and Development Program of China (No.2015AA042504)the National Natural Science Foundation of China (No.51474156) for financial support
文摘In this work, the growth kinetics of MX （M - metal, X - C/N） nanoprecipitates in type 347H austenitic steel was systematically studied. To investigate the coarsening behavior and the growth mechanism of MX carbonitrides during long-term aging, experiments were performed at 700, 800, 850, and 900℃ for different periods （1, 24, 70, and 100 h）. The precipitation behavior of carbonitrides in specimens subjected to various aging conditions was explored using carbon replicas and transmission electron microscopy （TEM） observations. The corresponding sizes ofMX carbonitrides were measured. The results demonstrates that MX carbonitrides precipitate in type 347H austenitic steel as Nb（C,N）. The coarsening rate constant is time-independent; however, an increase in aging temperature results in an increase in coarsening rate of Nb（C,N）. The coarsening process was analyzed according to the calculated diffusion activation energy of Nb（C,N）. When the aging temperature was 800-900℃, the mean activation energy was 294 kJ·mol -1, and the coarsening behavior was controlled primarily by the diffusion of Nb atoms.
文摘Microstructure evolution in neutron irradiated Reactor Pressure Vessel （RPV） steels was experimentally simulated through an improved degradation procedure in this study. The degradation procedure includes austenitizing at 1 150℃ and water quench, deformation 10% and 30% respectively, and then thermal aging at 500℃ for different period of time. The microstructure of the specimens was analyzed in details using transmission electron microscopy （TEM）. The micro-hardness test results showed that all the hardness curves of undeformed, 10% pre-deformed and 30% pre-deformed specimens have two micro-hardness peaks with the first peak value corresponding to different thermal aging time of 1 hour, 5 hours and 10 hours, respectively. It was revealed that the hardness curves were influenced by the precipitation of Cu-rich precipitates （CRPs） and carbides, deposition of martensite and work hardening.
基金Key Laboratory of Silicate Materials Science and Engineering for its financial support of this project.
文摘Early water damage of asphalt pavement is one of the major types of destruction,so taking maintenance on asphalt pavement at the proper time is necessary. Many new maintenance materials and methods are in use nowadays to prevent pavement from water damage and skidding. This paper aims to study the effects of the silicone maintenance materials on thermal aging resistance of asphalt mixture. After thermal aging,the asphalt mixture using silicone materials and the control mixture are evaluated through their engineering properties,including indirect tensile modulus,low-temperature performance and fatigue resistance. The results indicate that the silicone materials used as repairing material can improve low-temperature performance and fatigue resistance of asphalt mixture,and decrease the indirect tensile modulus ratio before and after thermal aging. Consequently,the silicone maintenance material has the ability to protect asphalt mixture from thermal aging.
基金supported by the National Key Research and Development Program of China(No.2017YFB0702200)the Natural Science Foundation of Jiangsu Province(No.BK20171223 and BK20170383).
文摘It is of great significance to investigate effect of multiple heat treatments on fracture property of centrifugal casting stainless steels Z3CN20.09M cut from pump casing with long-term thermal aging degradation for nuclear power plants to consider actual operation of nuclear power plants.Both multiple heat treatments and accelerated thermal aging experiment at the same temperature of 400℃ for different time were successively carried out on centrifugal casting stainless steels Z3CN20.09M in order to examine the metallographic modification and impact properties.Finally,an additional investigation on the related fracture properties was carried out,in which the critical initial fracture toughness Ji was determined by stretch zone width and 0.2 mm offset line methods.These results indicated that the multiple heat treatments led to the dispersed distribution of ferrite phases in austenite matrix and thus microhardness increased,but impact energy exhibited a decreasing tendency significantly.After long-term aging,the metallographic structure remained almost unchanged,but the size of ferrite phases showed a slight increasing trend because of spinodal decomposition in ferrite phases and G-phase precipitation.In addition,centrifugal casting stainless steels Z3CN20.09M with multiple heat treatments exhibited the higher microhardness,Charpy impact toughness,critical initial fracture toughness J_(IC)(J-integral determined by 0.2 mm offset line method),and J_(SZW)(J-integral determined by stretch zone width method)than those with primary heat treatment,while the specific number of the heat treatment had a low influence on fracture toughness.
文摘The life of shipboard cables will decrease due to the complex aging processes. In terms of the safety perspective, remaining life prediction of the cable is essential to maintain a reliable operation. In this paper, firstly, based on Arrhenius equation, residual life of new styrene-butadiene cable is calculated; result indicates that the degradation rate which changes with time is proportional to thermal temperature. Then second order dynamic model is adopted into the residual life prediction, combined with the time-temperature superposition method(TTSP), and a new residual life model is proposed. According to the accelerated thermal aging experiment data and Arrhenius equation, TTSP method demonstrates to be an efficient way for life prediction, and life at normal temperature can be estimated by this model. In order to monitor the state of styrene-butadiene cable more accurately, an improved residual life model based on equivalent environment temperature of cable is proposed, and life of cable under real operation is analyzed. Result indicates that this model is credible and reliable, and it provides an important theoretical base for residual life of cables.
文摘The thermal aging behavior of poly （ vinyl alcohol ） （ PVA ） hydrogel was studied at four different temperatures of 40 ℃, 50 ℃, 60 ℃ and 70 ℃ in one year. The samples of PVA hydrogel were closely covered by plastic film. The changes of their chemical structures and physical properties during aging were measured through different measurable techniques including tensile testing, gel permeation chromatography （ GPC ）, viscosity analysis, and Fourier transform infrared （FTIR） spec- trum. The results showed that the molecular weight of PVA in hydrogel changed little with time and temperature. FTIR spectra of PVA in all the samples were similar to those of the original samples. The tensile strength of PVA hydrogel didn＇t change until the 330th days.
文摘： The effect of isothermal aging treatment on the mechanical and corrosion properties of 2205 duplex stainless steel was investigated by means of impact toughness test and micro-hardness measurement in combination with the critical pitting temperature （CPT） technique. The corresponding fractography of the steel was then observed after the impact toughness test. The results demonstrated that, at the critical temperature for precipitation of the sigma （σ） phase, e. g., 850 ℃, the impact toughness decreased rapidly and the micro-hardness increased gradually with increasing aging time. The CPT decreased from 61 to 15 ℃ as the aging time increased from 4 rain to 8 h. In addition, optical microscopy, transmission electron microscope （TEM） and X-ray diffraction studies showed that the ferrite in the steel transformed into secondary austenite and σ phase.
基金Major Research Project of Shanghai City(No. 045211024)
文摘The degradation of crosslinked polyethylene (XLPE) cable insulation during service, such as thermo-oxidation and water treeing may lead to a premature electrical breakdown of the XLPE insulation cables. Therefore, it is necessary to optimize the period of replacement to evenly distribute the replacement cost by ascertaining the deterioration degree. Estimation of the aging degree is at present the most important task for diagnosis of the residual lifetime of the power cable insulation. This paper presents a study on the changes in the dielectric properties of the thermally aged XLPE cables in the frequency range from 0.07～10 MHz. Based on electrical and physicochemical characterization, some new "dactylograms" for the thermally aged XLPE cable insulation have been proposed.
文摘The purpose of this work is to determine the impact of thermal aging on the dielectric and physicochemical properties of the oil/paper mixed insulation. We performed a comparative analysis of dielectric paper dipped in two cooling fluids: palm kernel oil methyl ester (MEPKO) and mineral oil (MO). Two types of dielectric paper were used: Thermally Upgraded Kraft paper (TUK) and Nomex-910 paper (NP-910). An accelerated aging test was realized at 110<span style="white-space:nowrap;">°</span>C during a total of 96 hours. Samples of oil and paper were collected after 0, 48, 72 and 96 hours for analyses purposes. The analyses performed included the measurement of the Breakdown voltage (BDV) of the dielectric papers, the Total Acid Number (TAN) and the Decay Dissolved Products (DDP) of the liquid dielectrics. The BDV of NP-910 is greater than the BDV of TUK. Concerning the type of oil, the BDV of dielectric papers impregnated with MEPKO is greater than the BDV of similar papers impregnated with MO, indicating a better preservation of paper when dipped in methyl esters. The analyses of TAN and DDP revealed that Nomex-910 improves the oxidation stability of MO, but reduces the oxidation stability of MEPKO. These results prove that methyl esters can be used as a substitute to replace mineral oils in power transformers. Furthermore, they show that NP can be used mainly in areas of transformer where solid insulation is subjected to high thermal and electrical stress, and TUK other places where solid insulation is required. Such combination could assure money savings and a better preservation of the oil viscosity.
基金financially supported by the National High-Tech Research and Development Program of China (Nos. 2012AA03A507 and 2012AA050901)
文摘The effect of thermal aging on the fatigue crack growth（FCG） behavior of Z3CN20？09M cast duplex stainless steel with low ferrite content was investigated in this study. The crack surfaces and crack growth paths were analyzed to clarify the FCG mechanisms. The microstructure and micromechanical properties before and after thermal aging were also studied. Spinodal decomposition in the aged ferrite phase led to an increase in the hardness and a decrease in the plastic deformation capacity, whereas the hardness and plastic deformation capacity of the austenite phase were almost unchanged after thermal aging. The aged material exhibited a better FCG resistance than the unaged material in the near-threshold regime because of the increased roughness-induced crack closure associated with the tortuous crack path and rougher fracture surface; however, the tendency was reversed in the Paris regime because of the cleavage fracture in the aged ferrite phases.
基金supported by the National Natural Science Foundation of China(Grant No.50977025)
文摘The shortcomings of oil-immersed transformer solid insulation like low high-temperature resistance of the insulation paper and the uneven distribution of electric field caused by the large difference of dielectric constants between insulation paper and transformer oil,restricted the development of transformer with smaller size and larger capacity.In view of this situation and the transformer’s demand for the dielectric physicochemical and mechanical property of insulation material,polycarbonate,polyester film and polyphenylene sulfide with high high-temperature resistance were chosen for the comparison analysis in this paper We did the 300-day thermal aging experiment on four samples in transformer oil under different aging temperatures of90°C,110°C and 130°C,then analyzed the changes of their dielectric properties.The experiment results are as follows;the permittivity and dielectric dissipation factor of the three polymer materials are apparently smaller than those of the paper both before and after 300-day aging;the volume resistivity and partial discharge inception voltage of the three materials are higher than those of the paper both before and after aging;and the breakdown field strength of polycarbonate is higher than that of the paper both before and after aging,while that of polyester film and polyphenylene sulfide are slightly lower than that of the paper.
基金the National Natural Science Foundation of China(Grant No.51435012)。
文摘Previous studies,including ASME and RCC-MR standards,did not consider the influence of environmental factors on the ratcheting boundary of the material,and only a unified ratcheting boundary was proposed.In this paper,thermal aging was taken into consideration,and the effect of thermal aging time on the ratcheting boundary of 316 LN austenitic stainless steel was characterized by the efficiency diagram rule.The results show that,when the secondary ratio U is small,there is no significant difference in ratcheting boundary between the original material and the thermal aged material.When the secondary ratio U is large,the ratcheting boundary of the material presents a slight upward trend with the increase of thermal aging time.Compared with ASME and RCC-MR standards,it is found that RCC-MR is conservative.Based on the evolution of the efficiency index V with the number of cycles,it is more conservative and reasonable to choose the stage when the efficiency index V develops into a constant.
