The high-temperature mechanical properties and microstructure of forging billets of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo ultra-high-strength cold-rolled steels（tensile strength≥1000 MPa,elongation≥10%） were studied.Throug...The high-temperature mechanical properties and microstructure of forging billets of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo ultra-high-strength cold-rolled steels（tensile strength≥1000 MPa,elongation≥10%） were studied.Through the comparison of reduction in area and hot deformation resistance at 600-1300°C,the Mo-containing steel was found to possess a higher strength and a better plasticity than the Mo-free one.The equilibrium phase diagram and atom fraction of Mo in different phases at different temperatures were calculated by Thermo-Calc software（TCW）.The results analyzed by using transmission electron microscopy and TCW show that precipitates in the Mo-containing steel are primarily M23C6,which promote pearlite formation.The experimental data also show that a lower ductility point existing in the Mo-free steel at 850°C is eliminated in the Mo-containing one.This is mainly due to the segregation of Mo at grain boundaries investigated by electron probe microanalysis（EPMA）,which improves the strength of grain boundaries.展开更多
Two contents(1.5%and3%)of TiB2nanoparticles were introduced in Al?Mn?Mg3004alloy to study their effects on theelevated-temperature properties.Results show that TiB2nanoparticles were mainly distributed at the interden...Two contents(1.5%and3%)of TiB2nanoparticles were introduced in Al?Mn?Mg3004alloy to study their effects on theelevated-temperature properties.Results show that TiB2nanoparticles were mainly distributed at the interdendritic grain boundarieswith a size range of20?80nm,which is confirmed by transmission electron microscopy(TEM)and X-ray diffraction(XRD).Therefore,the volume fraction of the dispersoid free zones is greatly reduced and the motion of grain boundaries and dislocations isinhibited more effectively at elevated temperature.After peak precipitation heat treatment,the yield strengths in the alloy with3%TiB2addition at room temperature and300°C were increased by20%and13%respectively,while the minimum creep rate at300°Cwas reduced to only1/5of the base alloy free of TiB2,exhibiting a considerable improvement of elevated-temperature properties inAl?Mn?Mg alloys.展开更多
Further improvement on high temperature durability is one of the most important aims except for high specific strength, high specific stiffness, and excellent wear resistance, to design and fabricate discontinuously r...Further improvement on high temperature durability is one of the most important aims except for high specific strength, high specific stiffness, and excellent wear resistance, to design and fabricate discontinuously reinforced titanium matrix composites （DRTMCs）. Their superior properties render them extensive application potential in aerospace and military industries due to the urgent demand for the materials with characteristics of lightweight, high strength, high stiffness and high temperature durability. With development on fabrication methods and room temperature properties, testing, characterizing, evaluating and further increasing high temperature properties of DRTMCs are becoming more and more important to promote their applications. This review provides insights and comprehensions on the high temperature tensile properties, superplastic tensile properties, creep behaviors, and high temperature oxidation behaviors of DRTMCs,展开更多
1.Introduction Titanium alloys are widely used in aerospace and weaponry manufacturing due to their high specific strength,low density,heat and corrosion resistance[1,2].However,new titanium alloys with excellent room...1.Introduction Titanium alloys are widely used in aerospace and weaponry manufacturing due to their high specific strength,low density,heat and corrosion resistance[1,2].However,new titanium alloys with excellent room-temperature and high-temperature mechani-cal properties remain rare and hard to obtain in industries such as aerospace,marine engineering and equipment manufacturing[3,4].展开更多
Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of...Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi＇acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy （SEM） on the fracture surfaces of the tested specimens. The ductility indices （percentage elongation aider frac- ture and percentage reduction of area） and the toughness indices （Charpy impact energy Ak and plane-strain fracture toughness Kic） of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.展开更多
High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated tempera...High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.展开更多
The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ult...The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy （SEM）. The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150 C and 240 C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio （NSR） coefficient is in the range of 1.119 to 1.423 from 150 C to 240 C. The creep test results show that, as the test temperature increases from 150 C to 240 C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.展开更多
The effects of Y addition on microstructures and properties of as-cast and solid solutioning and aging treated Mg-0.8Zr-0.35Zn alloys at elevated temperature (250 ℃) were investigated by the use of XJG-04 optical mic...The effects of Y addition on microstructures and properties of as-cast and solid solutioning and aging treated Mg-0.8Zr-0.35Zn alloys at elevated temperature (250 ℃) were investigated by the use of XJG-04 optical microscopy, JCXA-733 electron probe, D/max-rB X-ray diffractometer (XRD) and WDW-200 electronic universal material testing machine. The results show that the microstructures of as-cast and heat treated Mg-0.8Zr-0.35Zn alloys with Y addition are refined and a new phase, Mg_(24)Y_5, is formed. At 250 ℃, the strength at elevated temperature of the alloys increases with increasing amount of Y addition, but relative elongation and area reduction decreases. The tendency of brittle fracture of fractured surface at elevated temperature is enlarged and fracture is changed from ductile into cleavage.展开更多
The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, an...The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, and strength curves were measured. Two brittle zones and one plastic zone were found in the temperature range from the melting point to 600℃. Embrittlement in zone I is caused by the existence of liquid film along dendritic interfaces. Ductility loss in zone Ⅲ mainly results from precipitates and inclusions as well as S segregation along grain boundaries. Pearlite transformation also accounts for ductility deterioration in the temperature range of 700-600℃. Moreover, the straightening temperature of the test steel should be higher than 925℃ for avoiding the initiation and propagation of surface cracks in billets.展开更多
MoSi 2 and rare earths/MoSi 2 materials were prepared by mechanical alloying, IP and high temperature sintering techniques. Their room temperature properties such as bending strength, fracture toughness and elect...MoSi 2 and rare earths/MoSi 2 materials were prepared by mechanical alloying, IP and high temperature sintering techniques. Their room temperature properties such as bending strength, fracture toughness and electric conductivity were measured. The results show that rare earths have better strengthening and toughening effects on the MoSi 2 matrix than SiC does. The room temperature bending strength and fracture toughness of 0 9% rare earths/MoSi 2 material are 419 41 MPa and 5 81 MPa·m 1/2 , which have increased by 46% and 81% than the matrix, respectively. The strengthening mechanisms of rare earths/MoSi 2 are fine grain and dispersion strengthening. The toughening mechanisms are fine grain toughening, crack deflection and bowing toughening. Moreover, the effect of rare earths on the electric conductivity of MoSi 2 is much weaker than that of SiC whiskers. With the addition of 0 9% rare earths, the resistivity of MoSi 2 is only raised by about 13 9%.展开更多
In this study,the microstructure and tensile properties of selective laser melted AlSilOMg at elevated temperature were investigated with focus on the interfacial region.In-situ SEM and in-situ EBSD analysis were prop...In this study,the microstructure and tensile properties of selective laser melted AlSilOMg at elevated temperature were investigated with focus on the interfacial region.In-situ SEM and in-situ EBSD analysis were proposed to characterize the microstructural evolution with temperature.The as-fabricated AlSilOMg sample presents high tensile strength with the ultimate tensile strength(UTS)of~450 MPa and yield strength(YS)of~300 MPa,which results from the mixed strengthening mechanism among grain boundary,solid solution,dislocation and Orowan looping mechanism.When holding at the temperature below 200℃for 30 min,the micro structure presents little change,and only a slight decrement of yield strength appears due to the relief of the residual stress.However,when the holding temperature further increases to 300℃and 400℃,the coarsening and precipitation of Si particles inα-Al matrix occur obviously,which leads to an obvious decrease of solid solution strength.At the same time,matrix softening and the weakness of dislocation strengthening also play important roles.When the holding temperature reaches to 400℃,the yield strength decreases significantly to about 25 MPa which is very similar to the as-cast Al alloy.This might be concluded that the YS is dominated by the matrix materials.Because the softening mechanism counteracts work hardening,the extremely high elongation occurs.展开更多
The tempering behavior was experimentally studied in lath martensitic wear-resistant steels with various Mo/Ni contents after tempering at different temperatures from 200to 600℃.It is shown that a good combination of...The tempering behavior was experimentally studied in lath martensitic wear-resistant steels with various Mo/Ni contents after tempering at different temperatures from 200to 600℃.It is shown that a good combination of hardness（HV）（420-450）and-20℃impact toughness（38-70J）can be obtained after quenching and tempering at 200-250 ℃.The microstructure at this temperature is lath structure with rod-like and/or flake-likeε-carbide with about 10nm in width and 100nm in length in the matrix,and the fracture mechanism is quasi-cleavage fracture combining with ductile fracture.Tempering at temperature from 300to 400℃results in the primary quasi-cleavagefracture due to the carbide transformation from resolved retained austenite and impurity segregation between laths or blocks.However,when the tempering temperature is higher than 500℃,the hardness（HV）is lower than 330 and the fracture mechanism changes to ductile fracture due to the spheroidization and coarsening of cementite.Additions of Mo and Ni have no significant effects on the carbides morphologies at low tempering temperatures,but improve the resistance to softening and embrittling for steels when tempered at above 350℃.展开更多
A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out f...A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.展开更多
This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of ...This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of steel properties.The decrease of the non-uniformity of the transversal profile of sheet heating as effect of the magnetic or electromagnetic screening of the sheet lateral sides was proved.展开更多
The current study investigates the influence of temperature on a one-dimensional piezoelectric phononic crystal using tunable resonant frequencies. Analytical and numerical examples are introduced to emphasize the inf...The current study investigates the influence of temperature on a one-dimensional piezoelectric phononic crystal using tunable resonant frequencies. Analytical and numerical examples are introduced to emphasize the influence of temperature on the piezoelectric phononic crystals. It was observed that the transmission spectrum of a one-dimensional phononic crystal containing a piezoelectric material（0.7 PMN-0.3 PT） can be changed drastically by an increase in temperature.The resonant peak can be shifted toward high or low frequencies by an increase or decrease in temperature, respectively.Therefore, we deduced that temperature can exhibit a large tuning in the phononic band gaps and in the local resonant frequencies depending on the presence of a piezoelectric material. Such result can enhance the harvesting energy from piezoelectric materials, especially those that are confined in a phononic crystal.展开更多
With a high energy efficiency,low geometric limitation,and low cracking susceptivity to cracks,wire arc additive manufacturing(WAAM)has become an ideal substitute for casting in the manufacturing of load-bearing high ...With a high energy efficiency,low geometric limitation,and low cracking susceptivity to cracks,wire arc additive manufacturing(WAAM)has become an ideal substitute for casting in the manufacturing of load-bearing high strength aluminum components in aerospace industry.Recently,in scientific researches,the room temperature mechanical performance of additive manufactured high strength aluminum alloys has been continuously broken through,and proves these alloys can achieve comparable or even higher properties than the forged counterpart.Since the aluminum components for aerospace usage experience high-low temperature cycling due to the absence of atmosphere protection,the high temperature performances of additive manufactured high strength aluminum alloys are also important.However,few research focuses on that.A special 2319Ag Sc with 0.4 wt.%Ag and 0.2 wt.%Sc addition designed for high temperature application is deposited successfully via cold metal transfer(CMT)based on WAAM.The microstructures and high temperature tensile properties are investigated.The results show that the as-deposited 2319Ag Sc alloy presents an alternate distribution of columnar grains and equiaxed grains with no significant textures.Main second phases are Al_(2)Cu and Al3Sc,while co-growth of Al_(2)Cu and bulk Al_(3)Sc is found on the grain boundary.During manufacturing,nanoscale Al_(2)Cu can precipitate out from the matrix.Ag and Mg form nano-scaleΩphase on the Al_(2)Cu precipitates.At 260℃,average yield strengths in the horizontal direction and vertical direction are 87 MPa±2 MPa,87 MPa±4 MPa,while average ultimate tensile strengths are 140 MPa±7 MPa,141 MPa±11 MPa,and average elongations are 11.0%±2.5%,13.5%±3.0%.Anisotropy in different directions is weak.展开更多
The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- cont...The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.展开更多
Effects of lanthanum on microstructure and mechanical properties of ZL702 alloy at room and high temperature conditions are studied. The experiment shows that high temperature intermetallics reticularly distributing ...Effects of lanthanum on microstructure and mechanical properties of ZL702 alloy at room and high temperature conditions are studied. The experiment shows that high temperature intermetallics reticularly distributing at grain boundary are formed with La and Al, Si, Fe etc. elements of alloy, which enhances the thermal stability of the alloy. With appropriate content of La (0.10%～ 0.15%), the mechanical properties of the alloy, such as strength, at room temperature and high temperature can be improved.展开更多
High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resisti...High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resistivity p and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m. cm and 202 V/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application has high temperature thin film thermoelectric devices,展开更多
With the rapid development of deepwater drilling operations,more and more complex technical challenges have to be faced due to the rigorous conditions encountered.One of these challenges is that the drilling fluid use...With the rapid development of deepwater drilling operations,more and more complex technical challenges have to be faced due to the rigorous conditions encountered.One of these challenges is that the drilling fluid used must had good rheological properties at low temperatures and high ability to inhibit hydrate formation.Synthetic drilling fluid has been widely applied to deepwater drilling operations due to its high penetration rate,excellent rheological properties,good ability to prevent hydrate formation,and high biodegradability.A synthetic drilling fluid formulation was developed in our laboratory.The rheological properties of this drilling fluid at low temperatures （0-20 °C） were tested with a 6-speed viscometer and its ability to inhibit hydrate formation was evaluated at 20 MPa CH 4 gas and 0 °C by differential scanning calorimetry （DSC）.Several factors influencing the low temperature rheological properties of this synthetic drilling fluid were studied in this paper.These included the viscosity of the base fluid,the amount of CEMU and organic clay,and the water volume fraction.展开更多
基金supported by the National High-tech Research and Development Program of China (No.2009AA03Z518)
文摘The high-temperature mechanical properties and microstructure of forging billets of C-Si-Mn-Cr and C-Si-Mn-Cr-Mo ultra-high-strength cold-rolled steels（tensile strength≥1000 MPa,elongation≥10%） were studied.Through the comparison of reduction in area and hot deformation resistance at 600-1300°C,the Mo-containing steel was found to possess a higher strength and a better plasticity than the Mo-free one.The equilibrium phase diagram and atom fraction of Mo in different phases at different temperatures were calculated by Thermo-Calc software（TCW）.The results analyzed by using transmission electron microscopy and TCW show that precipitates in the Mo-containing steel are primarily M23C6,which promote pearlite formation.The experimental data also show that a lower ductility point existing in the Mo-free steel at 850°C is eliminated in the Mo-containing one.This is mainly due to the segregation of Mo at grain boundaries investigated by electron probe microanalysis（EPMA）,which improves the strength of grain boundaries.
基金support from the Natural Sciences and Engineering Research Council of Canada(NSERC)and Rio Tinto,through the NSERC Industry Research Chair in Metallurgy of Aluminum Transformation at University of Quebec at Chicoutimi
文摘Two contents(1.5%and3%)of TiB2nanoparticles were introduced in Al?Mn?Mg3004alloy to study their effects on theelevated-temperature properties.Results show that TiB2nanoparticles were mainly distributed at the interdendritic grain boundarieswith a size range of20?80nm,which is confirmed by transmission electron microscopy(TEM)and X-ray diffraction(XRD).Therefore,the volume fraction of the dispersoid free zones is greatly reduced and the motion of grain boundaries and dislocations isinhibited more effectively at elevated temperature.After peak precipitation heat treatment,the yield strengths in the alloy with3%TiB2addition at room temperature and300°C were increased by20%and13%respectively,while the minimum creep rate at300°Cwas reduced to only1/5of the base alloy free of TiB2,exhibiting a considerable improvement of elevated-temperature properties inAl?Mn?Mg alloys.
基金financially supported by the National Natural Science Foundation of China (Nos.51101042,51271064 and 51471063)the High Technology Research and Development Program of China (No.2013AA031202)the Fundamental Research Funds for the Central Universities (No.HIT.BRETIII.201401)
文摘Further improvement on high temperature durability is one of the most important aims except for high specific strength, high specific stiffness, and excellent wear resistance, to design and fabricate discontinuously reinforced titanium matrix composites （DRTMCs）. Their superior properties render them extensive application potential in aerospace and military industries due to the urgent demand for the materials with characteristics of lightweight, high strength, high stiffness and high temperature durability. With development on fabrication methods and room temperature properties, testing, characterizing, evaluating and further increasing high temperature properties of DRTMCs are becoming more and more important to promote their applications. This review provides insights and comprehensions on the high temperature tensile properties, superplastic tensile properties, creep behaviors, and high temperature oxidation behaviors of DRTMCs,
基金supported by the National Natural Science Foundation of China(Nos.52125405,52171122,52371117 and 52271118)the Program for the Innovative Talents of Higher Education Institutions of Shanxi(2024Q005).
文摘1.Introduction Titanium alloys are widely used in aerospace and weaponry manufacturing due to their high specific strength,low density,heat and corrosion resistance[1,2].However,new titanium alloys with excellent room-temperature and high-temperature mechani-cal properties remain rare and hard to obtain in industries such as aerospace,marine engineering and equipment manufacturing[3,4].
基金supported by the Research Foundation of the Ministry of Railways and Tsinghua University (No.T200410)the National Natural Science Foundation of China (Nos.50778102 and 51178244)
文摘Brittle fracture occurs frequently in rails and thermite welded joints, which intimidates the security and reliability of railway ser- vice. Railways in cold regions, such as Qinghai-Tibet Railway, make the problem of brittle fi＇acture in rails even worse. A series of tests such as uniaxial tensile tests, Charpy impact tests, and three-point bending tests were carried out at low temperature to investigate the mechanical properties and fracture toughness of U71Mn and U75V rail steels and their thermite welds. Fracture micromechanisms were analyzed by scanning electron microscopy （SEM） on the fracture surfaces of the tested specimens. The ductility indices （percentage elongation aider frac- ture and percentage reduction of area） and the toughness indices （Charpy impact energy Ak and plane-strain fracture toughness Kic） of the two kinds of rail steels and the corresponding thermite welds all decrease as the temperature decreases. The thermite welds are more critical to fracture than the rail steel base metals, as indicated by a higher yield-to-ultimate ratio and a much lower Charpy impact energy. U71Mn rail steel is relatively higher in toughness than U75V, as demonstrated by larger Ak and Klc values. Therefore, U71Mn rail steel and the corresponding thermite weld are recommended in railway construction and maintenance in cold regions.
基金financially supported by the National Key Research and Development Program of China(Grant No.2018YFC1902400)the National Natural Science Foundation of China(Grant No.51975582)。
文摘High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.
基金support from the National Key Technology Research and Development Program of China (No.2007BAE38B06)Heilongjiang Province Science Fund for Distinguished Young Scholars(No. JC201013)
文摘The elevated temperature performances of 2D70 Al alloy hot extrusion rods after two-stage homogenization and intensive deformation were studied by measuring the elevated temperature enduring strength and the creep ultimate strength. The fracture morphology of some selected samples after testing at different elevated temperatures was observed by scanning electron microscopy （SEM）. The results indicate that, as the test temperature increases, the elevated temperature enduring strength of 2D70 Al alloy decreases gradually. In a comparison between 150 C and 240 C, the notch enduring strength drops from 375 to 185 MPa and the smooth enduring strength drops from 337 to 130 MPa. Enduring strength is not sensitive to the notch. The notch sensitivity ratio （NSR） coefficient is in the range of 1.119 to 1.423 from 150 C to 240 C. The creep test results show that, as the test temperature increases from 150 C to 240 C, the creep ultimate strength of 2D70 Al alloy rods drops gradually from 312 to 117 MPa.
文摘The effects of Y addition on microstructures and properties of as-cast and solid solutioning and aging treated Mg-0.8Zr-0.35Zn alloys at elevated temperature (250 ℃) were investigated by the use of XJG-04 optical microscopy, JCXA-733 electron probe, D/max-rB X-ray diffractometer (XRD) and WDW-200 electronic universal material testing machine. The results show that the microstructures of as-cast and heat treated Mg-0.8Zr-0.35Zn alloys with Y addition are refined and a new phase, Mg_(24)Y_5, is formed. At 250 ℃, the strength at elevated temperature of the alloys increases with increasing amount of Y addition, but relative elongation and area reduction decreases. The tendency of brittle fracture of fractured surface at elevated temperature is enlarged and fracture is changed from ductile into cleavage.
基金financially supported by the National High Technology Research and Development Program of China(No.2013AA031601)
文摘The high-temperature mechanical properties of near-eutectoid steel were studied with a Cleeble-1500 simu- lation machine. Zero strength temperature （ZST）, zero ductility temperature （ZDT）, hot ductility curves, and strength curves were measured. Two brittle zones and one plastic zone were found in the temperature range from the melting point to 600℃. Embrittlement in zone I is caused by the existence of liquid film along dendritic interfaces. Ductility loss in zone Ⅲ mainly results from precipitates and inclusions as well as S segregation along grain boundaries. Pearlite transformation also accounts for ductility deterioration in the temperature range of 700-600℃. Moreover, the straightening temperature of the test steel should be higher than 925℃ for avoiding the initiation and propagation of surface cracks in billets.
文摘MoSi 2 and rare earths/MoSi 2 materials were prepared by mechanical alloying, IP and high temperature sintering techniques. Their room temperature properties such as bending strength, fracture toughness and electric conductivity were measured. The results show that rare earths have better strengthening and toughening effects on the MoSi 2 matrix than SiC does. The room temperature bending strength and fracture toughness of 0 9% rare earths/MoSi 2 material are 419 41 MPa and 5 81 MPa·m 1/2 , which have increased by 46% and 81% than the matrix, respectively. The strengthening mechanisms of rare earths/MoSi 2 are fine grain and dispersion strengthening. The toughening mechanisms are fine grain toughening, crack deflection and bowing toughening. Moreover, the effect of rare earths on the electric conductivity of MoSi 2 is much weaker than that of SiC whiskers. With the addition of 0 9% rare earths, the resistivity of MoSi 2 is only raised by about 13 9%.
基金supported financially by the National Key Research and Development Programme of China(Nos.2016YFB1100602 and 2016YFB1100100)。
文摘In this study,the microstructure and tensile properties of selective laser melted AlSilOMg at elevated temperature were investigated with focus on the interfacial region.In-situ SEM and in-situ EBSD analysis were proposed to characterize the microstructural evolution with temperature.The as-fabricated AlSilOMg sample presents high tensile strength with the ultimate tensile strength(UTS)of~450 MPa and yield strength(YS)of~300 MPa,which results from the mixed strengthening mechanism among grain boundary,solid solution,dislocation and Orowan looping mechanism.When holding at the temperature below 200℃for 30 min,the micro structure presents little change,and only a slight decrement of yield strength appears due to the relief of the residual stress.However,when the holding temperature further increases to 300℃and 400℃,the coarsening and precipitation of Si particles inα-Al matrix occur obviously,which leads to an obvious decrease of solid solution strength.At the same time,matrix softening and the weakness of dislocation strengthening also play important roles.When the holding temperature reaches to 400℃,the yield strength decreases significantly to about 25 MPa which is very similar to the as-cast Al alloy.This might be concluded that the YS is dominated by the matrix materials.Because the softening mechanism counteracts work hardening,the extremely high elongation occurs.
基金Sponsored by National Basic Research Program(973Program)of China(2010CB630800)
文摘The tempering behavior was experimentally studied in lath martensitic wear-resistant steels with various Mo/Ni contents after tempering at different temperatures from 200to 600℃.It is shown that a good combination of hardness（HV）（420-450）and-20℃impact toughness（38-70J）can be obtained after quenching and tempering at 200-250 ℃.The microstructure at this temperature is lath structure with rod-like and/or flake-likeε-carbide with about 10nm in width and 100nm in length in the matrix,and the fracture mechanism is quasi-cleavage fracture combining with ductile fracture.Tempering at temperature from 300to 400℃results in the primary quasi-cleavagefracture due to the carbide transformation from resolved retained austenite and impurity segregation between laths or blocks.However,when the tempering temperature is higher than 500℃,the hardness（HV）is lower than 330 and the fracture mechanism changes to ductile fracture due to the spheroidization and coarsening of cementite.Additions of Mo and Ni have no significant effects on the carbides morphologies at low tempering temperatures,but improve the resistance to softening and embrittling for steels when tempered at above 350℃.
基金supported by National Natural Science Foundation of China(Nos.50171054 and 50671085)National High Technical Research and Development Programme of China(No.2007AA03Z521).
文摘A series of experiments were carried out to study the influence of low temperature plasma nitriding on the mechanical properties of AISI 420 martensitic stainless steel. Plasma nitriding experiments were carried out for 15 h at 350℃ by means of DC- pulsed plasma in 25%N2＋ 75%H2 atmosphere. The microstructure, phase composition, and residual stresses profiles of the nitrided layers were determined by optical microscopy and X-ray diffraction. The microhardness profiles of the nitridied surfaces were also studied. The fatigue life, sliding wear, and erosion wear loss of the untreated specimens and plasma nitriding specimens were determined on the basis of a rotating bending fatigue tester, a ball-on-disc wear tester, and a solid particle erosion tester. The results show that the 350℃ nitrided surface is dominated by c-Fe3N and ON, which is supersaturated nitrogen solid solution. They have high hardness and chemical stabilities. So the low temperature plasma nitriding not only increases the surface hardness values but also improves the wear and erosion resistance. In addition, the fatigue limit of AISI 420 steel can also be improved by plasma nitriding at 350℃ because plasma nitriding produces residual compressive stress inside the modified layer.
文摘This paper deals with finite element study of the scanning induction heating of the magnetic steel sheets in transversal flux devices,taking into account the magnetic nonlinearity and the dependence on temperature of steel properties.The decrease of the non-uniformity of the transversal profile of sheet heating as effect of the magnetic or electromagnetic screening of the sheet lateral sides was proved.
文摘The current study investigates the influence of temperature on a one-dimensional piezoelectric phononic crystal using tunable resonant frequencies. Analytical and numerical examples are introduced to emphasize the influence of temperature on the piezoelectric phononic crystals. It was observed that the transmission spectrum of a one-dimensional phononic crystal containing a piezoelectric material（0.7 PMN-0.3 PT） can be changed drastically by an increase in temperature.The resonant peak can be shifted toward high or low frequencies by an increase or decrease in temperature, respectively.Therefore, we deduced that temperature can exhibit a large tuning in the phononic band gaps and in the local resonant frequencies depending on the presence of a piezoelectric material. Such result can enhance the harvesting energy from piezoelectric materials, especially those that are confined in a phononic crystal.
基金the National Natural Science Foundation of China(Grant No.U21B2080,52305351,52275324)the China Postdoctoral Science Foundation(Grant No.2023M730838)+1 种基金the Heilongjiang Provincial Postdoctoral Science Foundation(Grant No.LBH-Z22128)the Natural Science Foundation of Heilongjiang Province(Grant No.LH2023E039).
文摘With a high energy efficiency,low geometric limitation,and low cracking susceptivity to cracks,wire arc additive manufacturing(WAAM)has become an ideal substitute for casting in the manufacturing of load-bearing high strength aluminum components in aerospace industry.Recently,in scientific researches,the room temperature mechanical performance of additive manufactured high strength aluminum alloys has been continuously broken through,and proves these alloys can achieve comparable or even higher properties than the forged counterpart.Since the aluminum components for aerospace usage experience high-low temperature cycling due to the absence of atmosphere protection,the high temperature performances of additive manufactured high strength aluminum alloys are also important.However,few research focuses on that.A special 2319Ag Sc with 0.4 wt.%Ag and 0.2 wt.%Sc addition designed for high temperature application is deposited successfully via cold metal transfer(CMT)based on WAAM.The microstructures and high temperature tensile properties are investigated.The results show that the as-deposited 2319Ag Sc alloy presents an alternate distribution of columnar grains and equiaxed grains with no significant textures.Main second phases are Al_(2)Cu and Al3Sc,while co-growth of Al_(2)Cu and bulk Al_(3)Sc is found on the grain boundary.During manufacturing,nanoscale Al_(2)Cu can precipitate out from the matrix.Ag and Mg form nano-scaleΩphase on the Al_(2)Cu precipitates.At 260℃,average yield strengths in the horizontal direction and vertical direction are 87 MPa±2 MPa,87 MPa±4 MPa,while average ultimate tensile strengths are 140 MPa±7 MPa,141 MPa±11 MPa,and average elongations are 11.0%±2.5%,13.5%±3.0%.Anisotropy in different directions is weak.
基金supported by the Fundamental Research Funds for the Central Universities (No. 2011QNB05)the National Basic Research Program of China (No. 2007CB209400)+2 种基金the National Natural Science Foundation of China (Nos. 51074166 and 51104128)the Research Project for Ministry of Housing and Urban-Rural Development of China (No. 2011-K3-5)the Innovation Project of Graduate Students in Jiangsu Province (No. CX09B_108Z)
文摘The experimental tests for limestone specimens at 700 °C in uniaxial compression were carried out to inves- tigate the mechanical effects of loading rates on limestone by using a MTS810 rock mechanics servo- controlled testing system considering the loading rate as a variable. The mechanical properties of limestone such as the stress-strain curve, variable characteristics of peak strength and the modulus of elasticity of limestone were studied under the strain rates ranging from 1.1 10à5 to 1.1 10à1 sà1. (1) Sharp decreases were shown for the peak strength and elastic modulus of limestone from 1.1 10à5 to 1.1 10à4 sà1 at 700 °C as well as a downward trend was shown from 1.1 10à4 to 1.1 10à1 sà1 with the rise of the strain rate. (2) The peak strain increased from 1.1 10à5 to 1.1 10à4 sà1, however, there was no obvious changes shown for the peak strain of limestone from 1.1 10à4 to 1.1 10à1 sà1. These results can provide valuable references for the rock blasting effect and design of mine.
文摘Effects of lanthanum on microstructure and mechanical properties of ZL702 alloy at room and high temperature conditions are studied. The experiment shows that high temperature intermetallics reticularly distributing at grain boundary are formed with La and Al, Si, Fe etc. elements of alloy, which enhances the thermal stability of the alloy. With appropriate content of La (0.10%～ 0.15%), the mechanical properties of the alloy, such as strength, at room temperature and high temperature can be improved.
基金Project supported by the Young Scientists Fund of the National Natural Science Foundation of China (Grant No. 10904030)the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20091301120002)
文摘High-temperature thermoelectric transport property measurements have been performed on the highly c-axis oriented Bi2Sr2Co20v thin films prepared by pulsed laser deposition on LaA1Oa （001）. Both the electric resistivity p and the seebeck coefficient S of the film exhibit an increasing trend with the temperature from 300 K-1000 K and reach up to 4.8 m. cm and 202 V/K at 980 K, resulting in a power factor of 0.85 mW/mK which are comparable to those of the single crystalline samples. A small polaron hopping conduction can be responsible for the conduction mechanism of the film at high temperature. The results demonstrate that the Bi2Sr2Co2Oy thin film has potential application has high temperature thin film thermoelectric devices,
基金the financial support from the National Science and Technology Key Projects(2008ZX05056-002-03-04 and 2008ZX05030-005-07-03)
文摘With the rapid development of deepwater drilling operations,more and more complex technical challenges have to be faced due to the rigorous conditions encountered.One of these challenges is that the drilling fluid used must had good rheological properties at low temperatures and high ability to inhibit hydrate formation.Synthetic drilling fluid has been widely applied to deepwater drilling operations due to its high penetration rate,excellent rheological properties,good ability to prevent hydrate formation,and high biodegradability.A synthetic drilling fluid formulation was developed in our laboratory.The rheological properties of this drilling fluid at low temperatures （0-20 °C） were tested with a 6-speed viscometer and its ability to inhibit hydrate formation was evaluated at 20 MPa CH 4 gas and 0 °C by differential scanning calorimetry （DSC）.Several factors influencing the low temperature rheological properties of this synthetic drilling fluid were studied in this paper.These included the viscosity of the base fluid,the amount of CEMU and organic clay,and the water volume fraction.
