Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures,as well as the interactions betw...Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures,as well as the interactions between the dislocations and nano-precipitates within the nanotwins.The simulation results demonstrate that both the yield stress and flow stress in the nanotwinned NiCo-based alloys with nano-precipitates decrease as the temperature rises,because the higher temperatures lead to the generation of more defects during yielding and lower dislocation density during plastic deformation.Moreover,the coherent L12 phase exhibits excellent thermal stability,which enables the hinderance of dislocation motion at elevated temperatures via the wrapping and cutting mechanisms of dislocations.The synergistic effect of nanotwins and nano-precipitates results in more significant strengthening behavior in the nanotwinned NiCo-based alloys under high temperatures.In addition,the high-temperature mechanical behavior of nanotwinned NiCo-based alloys with nano-precipitates is sensitive to the size and volume fraction of the microstructures.These findings could be helpful for the design of nanotwins and nano-precipitates to improve the high-temperature mechanical properties of NiCo-based alloys.展开更多
Silver selenide(Ag_(2)Se)stands out as a promising thermoelectric(TE)material,particularly for applications near room temper-atures.This research presents a novel approach for the fabrication of bulk Ag_(2)Se samples ...Silver selenide(Ag_(2)Se)stands out as a promising thermoelectric(TE)material,particularly for applications near room temper-atures.This research presents a novel approach for the fabrication of bulk Ag_(2)Se samples at a relatively low temperature(170℃)using the cold sintering process(CSP)with AgNO_(3)solution as a transient liquid agent.The effect of AgNO_(3)addition during CSP on the micro-structure and TE properties was investigated.The results from phase,composition and microstructure analyses showed that the introduc-tion of AgNO_(3)solution induced the formation of Ag nano-precipitates within the Ag_(2)Se matrix.Although the nano-precipitates do not af-fect the phase and crystal structure of orthorhombicβ-Ag_(2)Se,they suppressed crystal growth,leading to reduced crystallite sizes.The samples containing Ag nano-precipitates also exhibited high porosity and low bulk density.Consequently,these effects contributed to sig-nificantly enhanced electrical conductivity and a slight decrease in the Seebeck coefficient when small Ag concentrations were incorpor-ated.This resulted in an improved average power factor from~1540μW·m^(−1)·K^(−2)for pure Ag_(2)Se to~1670μW·m^(−1)·K^(−2)for Ag_(2)Se with additional Ag precipitates.However,excessive Ag addition had a detrimental effect on the power factor.Furthermore,thermal conductiv-ity was effectively suppressed in Ag_(2)Se fabricated using AgNO_(3)-assisted CSP,attributed to enhanced phonon scattering at crystal inter-faces,pores,and Ag nano-precipitates.The highest figure-of-merit(zT)of 0.92 at 300 K was achieved for the Ag_(2)Se with 0.5wt%Ag dur-ing CSP fabrication,equivalent to>20%improvement compared to the controlled Ag_(2)Se without extra Ag solution.Thus,the process outlined in this study presents an effective strategy to tailor the microstructure of bulk Ag_(2)Se and enhance its TE performance at room temperature.展开更多
To resolve the strength-ductility trade-off problem for high-strength Mg alloys,we prepared a high performance Mg-8Gd-3Y-0.5 Zr(wt%)alloy with yield strength of 371 MPa,ultimate tensile strength of 419MPa and elongati...To resolve the strength-ductility trade-off problem for high-strength Mg alloys,we prepared a high performance Mg-8Gd-3Y-0.5 Zr(wt%)alloy with yield strength of 371 MPa,ultimate tensile strength of 419MPa and elongation of 15.8%.The processing route involves extrusion,pre-deformation and aging,which leads to a bimodal structure and nano-precipitates.Back-stress originated from the deformationincompatibility in the bimodal-structure alloy can improve ductility.In addition,dislocation density in coarse grains increased during the pre-deformation strain of 2%,and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment.The chain-like nanoprecipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.展开更多
High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipit...High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipitates of the spray-formed fine-grained Al-Cu-Mg alloy during rapid cold stamping deformation.Results show that the extruded Al-Cu-Mg alloy undergoes obvious re-dissolution and re-precipitation during the rapid cold-stamping deformation process.The plasticθ′phase has a slower re-dissolution rate than the brittle S′phase.The long strip-shaped S′phases and the acicularθ′phases in Al-Cu-Mg alloy after three passes of cold stamping basically re-dissolved to form a supersaturated solid solution.A large number of fine granular balanceθphases precipitate after four passes of rapid cold-stamping deformation.Rapid cold stamping deformation causes the S′phase andθ′phase to break and promote the nano-precipitate phases to re-dissolve.The high distortion free energy of the matrix promotes the precipitation of the equilibriumθphase,and the hardness of the alloy obviously increases from HB 55 to HB 125 after the rapid cold stamping process.展开更多
Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles ...Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.展开更多
Fe-12Cr-2.5W-x Si-0.4Ti-0.3Y_(2)O_(3)alloys were fabricated by mechanical alloying and vacuum sintering.The effect of sintering temperature and Si content on the microstructure and properties of the alloy was investig...Fe-12Cr-2.5W-x Si-0.4Ti-0.3Y_(2)O_(3)alloys were fabricated by mechanical alloying and vacuum sintering.The effect of sintering temperature and Si content on the microstructure and properties of the alloy was investigated systematically.The experimental results show that the relative density and tensile strength of the alloy were increased with the elevating of sintering temperature and Si content within a certain range.The alloy with 1wt%Si sintered at 1350℃exhibited superior properties,and the relative density and tensile strength were 96.8%and 692.7 MPa,respectively.HAADF and EDAX analysis of nano-precipitation in the matrix indicated that Si could combine with Y,Ti,and O in the sintering process,which was uniformly distributed with the size of 10 nm.Portion of Y_(2)O_(3)had not completely dissolved in the milling process,which was retained in the matrix of the alloy.展开更多
The effect of adding a small amount of Ag on the microstructure evolution and superplastic properties of Mg-Y-Er-Zn(WEZ612) alloys was systematically studied.The basal texture of the refined WEZ612 alloy produced by e...The effect of adding a small amount of Ag on the microstructure evolution and superplastic properties of Mg-Y-Er-Zn(WEZ612) alloys was systematically studied.The basal texture of the refined WEZ612 alloy produced by equal channel angular pressing was altered to a non-basal structure upon the addition of Ag.Ag addition also refined the grain size and promoted the formation of a large number of nano-14H-long period stacking ordered phases.Using high-resolution transmission electron microscopy,many nano-precipitated phases were detected on the basal plane of the Mg-Y-Er-Zn-1Ag(WEZ612-1Ag) alloy,The nano-precipitated phases on the basal plane improved the thermal stability of the alloy,lowered the deformation activation energy(Q),and improved the stress sensitivity index(m).At 523 K with a strain rate of 10^(-2) s^(-1),the Q value of WEZ612 was higher than that of WEZ612-1Ag(299.14 and 128.5 kJ mol^(-1),respectively).In contrast,the m value of the WEZ612 alloy(0.16) was lower than that of the WEZ612-1Ag alloy(0.46).At 623 K with a tensile rate of 10^(-2) s^(-1),the WEZ612 and WEZ612-1Ag alloys were elongated by 182% and 495%,respectively,with the latter exhibiting high-strain-rate and low-temperature superplasticity.The improved superplasticity of the WEZ612-1Ag alloy is attributed to the nano-precipitated phases,which effectively limit the cavity extension during superplastic deformation.展开更多
Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The mic...Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The microstructures of the milled powder and bulk alloy were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Mechanical properties of the extruded alloy were examined by mechanical testing machine. The results show that after BM, the particle size and microstructures of the mixed alloy powder change obviously. After 48 h BM, the average size of mixed powder is about 30 nm, and then after hot extrusion, the average size of grains reaches about 70 rim. The compressive strength of the extruded alloy reaches 710 MPa under certain conditions of milling time and composition. As a result of the identification of the nano-/micro-strueture-property relationship of the samples, such high strength is attributed mainly to the nanocrystalline grains of a（Al） and nanoscaled FeNiCrCoAl3 particles, and the fine secondary phase of Al2Cu and Fe-rich phases.展开更多
A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-...A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.展开更多
A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid so...A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid solution and aging”process,the superfine(Fe,Ni)_(2)TiSi-L2_(1)particles densely precipitate within the ferritic grain and subsequently transform into the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase.In the meanwhile,the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase are also observed.These nanoscale microstructural evolutions result in a remarkable increase in hardness(100-300 HV)and severe embrittlement.When the“cold rolling and aging”process is used,the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening ef-fect.Superhigh yield strength of 1700 MPa with 4%elongation at break is achieved.This key improvement in mechanical properties is mainly attributed to the pre-cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary.These findings could shed light on the further exploration of the precipitation site via optimal processing strategies.展开更多
Low-carbon advanced nanostructured steels have been developed for various structural engineering applications, including bridges, automobiles, and other strength-critical applications such as the reactor pressure vess...Low-carbon advanced nanostructured steels have been developed for various structural engineering applications, including bridges, automobiles, and other strength-critical applications such as the reactor pressure vessels in nuclear power stations. The mechanical performances and applications of these steels are strongly dependent on their microstructural features. By controlling the size,number density, distribution, and types of precipitates, it is possible to produce nanostructured steels with a tensile strength reaching as high as 2 GPa while keeping a decent tensile elongation above 10% and a reduction of area as high as 40%. Besides, through a careful control of strength contributions from multiple strengthening mechanisms, the nanostructured steels with superior strengths and low-temperature impact toughness can be obtained by avoiding the temper embrittlement regime. With appropriate Mn additions, these nanostructured steels can achieve a triple enhancement in ductility(total tensile elongation, TE of ~30%) at no expense of strengths(yield strength, YS of ~1100 to 1300 MPa, ultimate tensile strength, UTS of ~1300 to 1400 MPa). More importantly, these steels demonstrate good fabricability and weldability. In this paper, the microstructure-property relationships of these advanced nanostructured steels are comprehensively reviewed. In addition, the current limitations and future development of these nanostructured steels are carefully discussed and outlined.展开更多
Microbiologically influenced corrosion(MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry.Copper...Microbiologically influenced corrosion(MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry.Copper(Cu) in steels can not only provide aging precipitation strengthening, but also kill bacterium,offering a special biofunction to steels. Based on the chemical composition of traditional X80 pipeline steel, two Cu-bearing pipeline steels(1% Cu and 2% Cu) were fabricated in this study. The microstructure,mechanical properties and antibacterial property against sulphate-reducing bacteria(SRB) and Pseudomonas aeruginosa(P. aeruginosa) were studied. It was found that the novel pipeline steel alloyed by 1%Cu exhibited acicular ferrite microstructure with nano-sized Cu-rich precipitates distribution in the matrix, resulting in better mechanical properties than the traditional X80 steel, and showed good MIC resistance as well. The pitting corrosion resistance of 1% Cu steel in as-aged condition was significantly better than that of X80 steel. A possible antibacterial mechanism of the Cu-bearing pipeline steel was proposed.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.12072317)the Natural Science Foundation of Zhejiang Province(Grant No.LZ21A020002)+2 种基金Ligang Sun gratefully acknowledges the support received from the Guangdong Basic and Applied Basic Research Foundation(Grant No.22022A1515011402)the Science,Technology and Innovation Commission of Shenzhen Municipality(Grant No.GXWD20231130102735001)Development and Reform Commission of Shenzhen(Grant No.XMHT20220103004).
文摘Molecular dynamics simulations are performed to investigate the mechanical behavior of nanotwinned NiCo-based alloys containing coherent L12 nano-precipitates at different temperatures,as well as the interactions between the dislocations and nano-precipitates within the nanotwins.The simulation results demonstrate that both the yield stress and flow stress in the nanotwinned NiCo-based alloys with nano-precipitates decrease as the temperature rises,because the higher temperatures lead to the generation of more defects during yielding and lower dislocation density during plastic deformation.Moreover,the coherent L12 phase exhibits excellent thermal stability,which enables the hinderance of dislocation motion at elevated temperatures via the wrapping and cutting mechanisms of dislocations.The synergistic effect of nanotwins and nano-precipitates results in more significant strengthening behavior in the nanotwinned NiCo-based alloys under high temperatures.In addition,the high-temperature mechanical behavior of nanotwinned NiCo-based alloys with nano-precipitates is sensitive to the size and volume fraction of the microstructures.These findings could be helpful for the design of nanotwins and nano-precipitates to improve the high-temperature mechanical properties of NiCo-based alloys.
基金supported by the National Research Council of Thailand(NRCT)(Nos.N42A650237 and N41A661163)the National Science,Research and Innovation Fund(NSRF)via the Fundamental Fund of Khon Kaen Universitythe NSRF via the Program Management Unit for Human Resources&Institutional Development,Research and Innovation(No.B37G660011).
文摘Silver selenide(Ag_(2)Se)stands out as a promising thermoelectric(TE)material,particularly for applications near room temper-atures.This research presents a novel approach for the fabrication of bulk Ag_(2)Se samples at a relatively low temperature(170℃)using the cold sintering process(CSP)with AgNO_(3)solution as a transient liquid agent.The effect of AgNO_(3)addition during CSP on the micro-structure and TE properties was investigated.The results from phase,composition and microstructure analyses showed that the introduc-tion of AgNO_(3)solution induced the formation of Ag nano-precipitates within the Ag_(2)Se matrix.Although the nano-precipitates do not af-fect the phase and crystal structure of orthorhombicβ-Ag_(2)Se,they suppressed crystal growth,leading to reduced crystallite sizes.The samples containing Ag nano-precipitates also exhibited high porosity and low bulk density.Consequently,these effects contributed to sig-nificantly enhanced electrical conductivity and a slight decrease in the Seebeck coefficient when small Ag concentrations were incorpor-ated.This resulted in an improved average power factor from~1540μW·m^(−1)·K^(−2)for pure Ag_(2)Se to~1670μW·m^(−1)·K^(−2)for Ag_(2)Se with additional Ag precipitates.However,excessive Ag addition had a detrimental effect on the power factor.Furthermore,thermal conductiv-ity was effectively suppressed in Ag_(2)Se fabricated using AgNO_(3)-assisted CSP,attributed to enhanced phonon scattering at crystal inter-faces,pores,and Ag nano-precipitates.The highest figure-of-merit(zT)of 0.92 at 300 K was achieved for the Ag_(2)Se with 0.5wt%Ag dur-ing CSP fabrication,equivalent to>20%improvement compared to the controlled Ag_(2)Se without extra Ag solution.Thus,the process outlined in this study presents an effective strategy to tailor the microstructure of bulk Ag_(2)Se and enhance its TE performance at room temperature.
基金This work was supported financially by the National Key Research and Development Plan(No.2016YFB0301103)the National Natural Science Foundation of China(Nos.51771109 and 51631006)the Shanghai Rising-Star Program(No.16QB1402800).
文摘To resolve the strength-ductility trade-off problem for high-strength Mg alloys,we prepared a high performance Mg-8Gd-3Y-0.5 Zr(wt%)alloy with yield strength of 371 MPa,ultimate tensile strength of 419MPa and elongation of 15.8%.The processing route involves extrusion,pre-deformation and aging,which leads to a bimodal structure and nano-precipitates.Back-stress originated from the deformationincompatibility in the bimodal-structure alloy can improve ductility.In addition,dislocation density in coarse grains increased during the pre-deformation strain of 2%,and the dislocations in coarse grains can promote the formation of chain-like nano-precipitates during aging treatment.The chain-like nanoprecipitates can act as barriers for dislocations slip and the existing mobile dislocations enable good ductility.
基金Project(2019JJ60050) supported by the Natural Science Foundation of Hunan Province,China
文摘High-resolution transmission electron microscopy(TEM),X-ray diffractometry(XRD),energy dispersive spectroscopy(EDS)and hardness test were used to study the re-dissolution and re-precipitation behavior of nano-precipitates of the spray-formed fine-grained Al-Cu-Mg alloy during rapid cold stamping deformation.Results show that the extruded Al-Cu-Mg alloy undergoes obvious re-dissolution and re-precipitation during the rapid cold-stamping deformation process.The plasticθ′phase has a slower re-dissolution rate than the brittle S′phase.The long strip-shaped S′phases and the acicularθ′phases in Al-Cu-Mg alloy after three passes of cold stamping basically re-dissolved to form a supersaturated solid solution.A large number of fine granular balanceθphases precipitate after four passes of rapid cold-stamping deformation.Rapid cold stamping deformation causes the S′phase andθ′phase to break and promote the nano-precipitate phases to re-dissolve.The high distortion free energy of the matrix promotes the precipitation of the equilibriumθphase,and the hardness of the alloy obviously increases from HB 55 to HB 125 after the rapid cold stamping process.
文摘Nanoparticles of biodegradable methoxy poly(ethylene glycol)-b-polyester amphiphilic diblock copolymers have widely investigated for use as controlled release drug delivery carriers. In this work, blend nanoparticles of methoxy poly(ethylene glycol)-b-poly(D,L-lactide) (MPEG-b-PDLL) and methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (MPEG- b-PCL) were prepared by nano-precipitation method without any surfactants. 1H-NMR spectra showed significant difference in integral peak areas, suggesting the nanoparticles with different MPEG-b-PDLL/MPEG-b-PCL blend ratios can be prepared. Transmission electron microscope revealed the blend nanoparticles had nearly spherical in shape with smooth surface. Average size of the blend nanoparticles obtained from light-scattering analysis slightly decreased with increase in blend ratio of MPEG-b-PCL. The MPEG-b-PDLL and MPEG-b-PCL were amorphous and semi-crystalline, respectively. Thermal transition properties of the blend nanoparticles were studied with differential scanning calorimetry (DSC). The DSC results showed that glass transition temperatures of the blend nanoparticles decreased and heats of melting steadily increased, while the melting temperature did not change as the MPEG-b-PCL blend ratio increased. This indicates the miscibility of MPEG-b-PDLL and MPEG-b-PCL in the amorphous phase of the blend nanoparticles. Thermogravimetric analysis showed that the blend nanoparticles clearly exhibited two thermal decomposition steps due to MPEG-b-PDLL decomposition followed with MPEG-b-PCL. The blend nanoparticles had two temperatures of maximum decomposition rate (Td, max) accorded to each blend component. The Td, max of MPEG-b- PDLL phase significantly decreased, while Td, max of MPEG-b-PCL phase did not change as the MPEG-b-PCL blend ratio increased. These results suggested that the desired thermal properties of blend nanoparticles can be tailored by varying the blend ratio.
基金Funded by the Natural Science Foundation of China(No.51801140)the Fundamental Research Funds for the Central Universities(No.WUT3120619103)。
文摘Fe-12Cr-2.5W-x Si-0.4Ti-0.3Y_(2)O_(3)alloys were fabricated by mechanical alloying and vacuum sintering.The effect of sintering temperature and Si content on the microstructure and properties of the alloy was investigated systematically.The experimental results show that the relative density and tensile strength of the alloy were increased with the elevating of sintering temperature and Si content within a certain range.The alloy with 1wt%Si sintered at 1350℃exhibited superior properties,and the relative density and tensile strength were 96.8%and 692.7 MPa,respectively.HAADF and EDAX analysis of nano-precipitation in the matrix indicated that Si could combine with Y,Ti,and O in the sintering process,which was uniformly distributed with the size of 10 nm.Portion of Y_(2)O_(3)had not completely dissolved in the milling process,which was retained in the matrix of the alloy.
基金supported by the Postgraduate Research and Practice Innovation Program of Jiangsu Province (SJKY19_0460)the National Natural Science Foundation of China (Grant No.51979099 & 51774109)+2 种基金Natural Science Foundation of Jiangsu Province of China (Grant No.BK20191303)The Key Research and Development Project of Jiangsu Province of China (Grant No.BE2017148)Postgraduate Education Reform Project of Jiangsu Province (JGLX19_027)。
文摘The effect of adding a small amount of Ag on the microstructure evolution and superplastic properties of Mg-Y-Er-Zn(WEZ612) alloys was systematically studied.The basal texture of the refined WEZ612 alloy produced by equal channel angular pressing was altered to a non-basal structure upon the addition of Ag.Ag addition also refined the grain size and promoted the formation of a large number of nano-14H-long period stacking ordered phases.Using high-resolution transmission electron microscopy,many nano-precipitated phases were detected on the basal plane of the Mg-Y-Er-Zn-1Ag(WEZ612-1Ag) alloy,The nano-precipitated phases on the basal plane improved the thermal stability of the alloy,lowered the deformation activation energy(Q),and improved the stress sensitivity index(m).At 523 K with a strain rate of 10^(-2) s^(-1),the Q value of WEZ612 was higher than that of WEZ612-1Ag(299.14 and 128.5 kJ mol^(-1),respectively).In contrast,the m value of the WEZ612 alloy(0.16) was lower than that of the WEZ612-1Ag alloy(0.46).At 623 K with a tensile rate of 10^(-2) s^(-1),the WEZ612 and WEZ612-1Ag alloys were elongated by 182% and 495%,respectively,with the latter exhibiting high-strain-rate and low-temperature superplasticity.The improved superplasticity of the WEZ612-1Ag alloy is attributed to the nano-precipitated phases,which effectively limit the cavity extension during superplastic deformation.
基金Project(2012CB619503)supported by the Nation Basic Research Program of ChinaProject(2013AA031001)supported by the National High Technology Research and Development Program of ChinaProject(2012DFA50630)supported by the International Science&Technology Cooperation Program of China
文摘Different proportions of commercial 2024 aluminum alloy powder and FeNiCrCoA13 high entropy alloy （HEA） powder were ball-milled （BM） for different time. The powder was consolidated by hot extrusion method. The microstructures of the milled powder and bulk alloy were examined by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. Mechanical properties of the extruded alloy were examined by mechanical testing machine. The results show that after BM, the particle size and microstructures of the mixed alloy powder change obviously. After 48 h BM, the average size of mixed powder is about 30 nm, and then after hot extrusion, the average size of grains reaches about 70 rim. The compressive strength of the extruded alloy reaches 710 MPa under certain conditions of milling time and composition. As a result of the identification of the nano-/micro-strueture-property relationship of the samples, such high strength is attributed mainly to the nanocrystalline grains of a（Al） and nanoscaled FeNiCrCoAl3 particles, and the fine secondary phase of Al2Cu and Fe-rich phases.
基金supported by National Key Research and Development Program of China (No. 2021 YFB3701000)the National Natural Science Foundation of China (Nos. U2167213 and 51971053)+1 种基金the Young Elite Scientists Sponsorship Program by China Association for Science and Technology (Nos. 2019-2021QNRC001, 20192021QNRC002, and 2019-2021QNRC003)and the Fundamental Research Funds for the Central Universities (No. N2202020)
文摘A novel low-cost Mg-Al-Ca-Zn-Mn-based alloy was developed to simultaneously improve its strength and ductility.The high yield strength of 411 MPa and the high elongation to failure of~8.9%have been achieved in the as-extruded Mg-1.3Al-1.2Ca-0.5Zn-0.6Mn(wt%)sample.Microstructure characterizations showed that the high strength is mainly associated with the ultra-fined dynamically recrystallized(DRXed)grains.Moreover,high-density dislocations in the un-DRXed region and nano-precipitates are distributed among theα-Mg matrix.The high ductility property can be ascribed to the high volume fraction of DRXed grains with a much randomized texture,as well as the formations of high-density subgrains in the un-DRXed grain regions.
基金This work was financially funded by the National Natural Science Foundation of China(Nos.51971082 and 52001098)the National Post-doctoral Program for Innovative Talents(No.BX20200103)the China Post-doctoral Science Foundation(No.2020M681092).The authors would like to thank Dr.Ivan Povstugar at ZEA-。
文摘A typical G-phase strengthened ferritic model alloy(1Ti:Fe-20Cr-3Ni-1Ti-3Si,wt.%)has been carefully studied using both advanced experimental(EBSD,TEM and APT)and theoretical(DFT)techniques.During the classic“solid solution and aging”process,the superfine(Fe,Ni)_(2)TiSi-L2_(1)particles densely precipitate within the ferritic grain and subsequently transform into the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase.In the meanwhile,the elemental segregation at grain boundaries and the resulting precipitation of a large amount of the(Ni,Fe)_(16)Ti_(6)Si_(7)-G phase are also observed.These nanoscale microstructural evolutions result in a remarkable increase in hardness(100-300 HV)and severe embrittlement.When the“cold rolling and aging”process is used,the brittle fracture is effectively suppressed without loss of nano-precipitation strengthening ef-fect.Superhigh yield strength of 1700 MPa with 4%elongation at break is achieved.This key improvement in mechanical properties is mainly attributed to the pre-cold rolling process which effectively avoids the dense precipitation of the G-phase at the grain boundary.These findings could shed light on the further exploration of the precipitation site via optimal processing strategies.
基金supported by the National Natural Science Foundation of China (51801169)Hong Kong Research Grant Council (CityU Grant 9360161, 9042635, 9042879)the internal funding from the City University of Hong Kong (CityU 9380060)。
文摘Low-carbon advanced nanostructured steels have been developed for various structural engineering applications, including bridges, automobiles, and other strength-critical applications such as the reactor pressure vessels in nuclear power stations. The mechanical performances and applications of these steels are strongly dependent on their microstructural features. By controlling the size,number density, distribution, and types of precipitates, it is possible to produce nanostructured steels with a tensile strength reaching as high as 2 GPa while keeping a decent tensile elongation above 10% and a reduction of area as high as 40%. Besides, through a careful control of strength contributions from multiple strengthening mechanisms, the nanostructured steels with superior strengths and low-temperature impact toughness can be obtained by avoiding the temper embrittlement regime. With appropriate Mn additions, these nanostructured steels can achieve a triple enhancement in ductility(total tensile elongation, TE of ~30%) at no expense of strengths(yield strength, YS of ~1100 to 1300 MPa, ultimate tensile strength, UTS of ~1300 to 1400 MPa). More importantly, these steels demonstrate good fabricability and weldability. In this paper, the microstructure-property relationships of these advanced nanostructured steels are comprehensively reviewed. In addition, the current limitations and future development of these nanostructured steels are carefully discussed and outlined.
基金supported financially by the Shenyang Science and Technology Research Funding(No.18-013-0-53)the Shenzhen Science and Technology Research Funding(No.JCYJ20160608153641020)
文摘Microbiologically influenced corrosion(MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry.Copper(Cu) in steels can not only provide aging precipitation strengthening, but also kill bacterium,offering a special biofunction to steels. Based on the chemical composition of traditional X80 pipeline steel, two Cu-bearing pipeline steels(1% Cu and 2% Cu) were fabricated in this study. The microstructure,mechanical properties and antibacterial property against sulphate-reducing bacteria(SRB) and Pseudomonas aeruginosa(P. aeruginosa) were studied. It was found that the novel pipeline steel alloyed by 1%Cu exhibited acicular ferrite microstructure with nano-sized Cu-rich precipitates distribution in the matrix, resulting in better mechanical properties than the traditional X80 steel, and showed good MIC resistance as well. The pitting corrosion resistance of 1% Cu steel in as-aged condition was significantly better than that of X80 steel. A possible antibacterial mechanism of the Cu-bearing pipeline steel was proposed.
