High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here...High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.展开更多
The tradeoff between strength and corrosion resistance restricts the development of low-alloyed magnesium(Mg)alloys.In this work,a low-alloyed Mg-1Sm-0.8Mn-0.5Ca-0.4Zn alloy was prepared through a simple process of co...The tradeoff between strength and corrosion resistance restricts the development of low-alloyed magnesium(Mg)alloys.In this work,a low-alloyed Mg-1Sm-0.8Mn-0.5Ca-0.4Zn alloy was prepared through a simple process of conventional casting followed by proper hotextrusion.The as-extruded alloy exhibits a very high yield strength of 402 MPa,an acceptable elongation of 5%,and a low corrosion rate of 0.56 mm y^(-1) which is close to that of high-purity Mg,and such comprehensive properties are superior to most reported Mg alloys,whether high alloying or low alloying.The special fine microstructure is responsible for high strength,including fine dynamic recrystallized(DRXed)grains,strong textured un-DRXed grains,dislocations and uniformly dispersed nano-spaced α-Mn nano-precipitates.An important finding of this study is that the corrosion film microstructure has amorphous characteristics,and this inevitably contributes to the high film protectiveness,and finally improves the corrosion resistance of the as-extruded alloy with relatively strong micro-galvanic corrosion tendency.In addition,the influence of micro/submicron-sized Mg_(2)Ca with anodic nature and nano-sized cathode α-Mn precipitates with strong strengthening effect on the corrosion film is also discussed.This study suggests that the strength-corrosion tradeoff can be evaded by regulating the microstructure of alloy substrate and corrosion film in the low-alloyed Mg alloy.展开更多
The low strength of Mg-Li alloys sets a limit to lightweight applications.Introducing crystal defects(twins,dislocations,and SFs)is a distinctive strategy for maintaining good mechanical properties of metallic materia...The low strength of Mg-Li alloys sets a limit to lightweight applications.Introducing crystal defects(twins,dislocations,and SFs)is a distinctive strategy for maintaining good mechanical properties of metallic materials.A lamellar-structured Mg-4Li-3Al-0.4Ca alloy with high performance was prepared by hot extrusion and rotary swaging.The as-swaged alloy exhibits excellent mechanical properties with tensile strength,yield strength,elongation to failure,and specific strength of 391 MPa,312 MPa,14.2%,and 238.4 kN m kg^(-1),respectively.The average grain size of the as-swaged alloy is 160±23 nm,and the microstructure is mainly composed of lamellar structures,twins,ultrafine grains,and nano-grains.The abundant lamellar structures and twins promote the storage of dislocations and SFs,leading to the formation of twin-twin interactions and enhancing strain hardening.The formation of UFG and NG by dynamic recrystallization further improves the yield strength.Shearable second phases play a critical role in enhancing the yield strength and ductility.More importantly,extensive planar dislocation glide and(c+a)dislocations efficiently relax the local stress concentrations,and thus improve the ductility.展开更多
The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing t...The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing this dilemma via the balance between grain refinement and weakening of dynamic precipitation is proposed and applied on a Mg-10.95Gd-2.06Ag(wt%)alloy treated by sequential processing of equalchannel angular pressing(ECAP),hot rolling and aging.The hot rolling leads to a noticeable dissolution of the dynamic precipitates intensively formed during prior ECAP,together with a tolerable grain growth.Meanwhile,numerous multi-twinning-induced lamellar bands(LBs)demarcated by coaxial grain boundaries(CGBs)subdivide the grains.For the first time,a quadruple twinning pattern for the formation of CGB with a misorientation of~135°is raised.During post-rolling aging,besides the commonβ’andγ”precipitates and theβnano-particles whose Gd/Ag ratio is much lower than that of dynamically precipitatedβparticles,theβ”/βT precipitates,CGB segregation,and stacking fault(SF)-associated segregation/γ’precipitates within LBs,are also involved with the precipitation structure.Benefiting from this complex precipitation structure,a good age-hardening ability manifested by the aging-induced tensile yield strength(TYS)increment reaching 115 MPa is attained.Combining with the strengthening from grain boundaries,dislocations,solutes,and basal texture,a high TYS of 447 MPa is achieved.展开更多
As a biomass material with biodegradability and biocompatibility, sodium alginate (SA) is a good candidate for constructing hydrogels for tissue-mimicking and biomedical scaffold fabricating through extrusion-based 3D...As a biomass material with biodegradability and biocompatibility, sodium alginate (SA) is a good candidate for constructing hydrogels for tissue-mimicking and biomedical scaffold fabricating through extrusion-based 3D printing technology. However, the mechanical strength and stiffness of alginate hydrogels are still not comparable with biological tissues such as tendons and the printability of SA solutions is often poor. Here, a novel strategy for 3D printing of alginate hydrogels with high mechanical performance is developed by using glycerol as a co-solvent for SA solutions. The addition of glycerol (GL) enables the formation of a homogenous SA/GL solution with a high solid content of 12–20 wt.% and endows crosslinked SA hydrogels with high stretchability. By applying uniaxial stretches, hydrogel filaments prepared with concentrated SA/GL solutions reveal a high tensile strength of 36.6–161.3 MPa, Young's modulus of 59.2–1964.2 MPa, and elongation at break of 8.5 %–106.2 % due to the high orientated and closely packed SA chains. SA/GL solutions become more solid-like with increasing SA concentration, and the solution with a solid content of 16 wt.% exhibits optimal 3D printability because of the appropriate rheological properties and thixotropic behavior. By designing the deforming-and-fixing process, 3D printed high-strength alginate hydrogels with complex structures are prepared, broadening the application of alginate hydrogels in load-bearing and biomedical fields.展开更多
Different stress states have a significant influence on the magnitude of the microscopic plastic strain and result in the development of the microstructure evolution.As a result,a comprehensive understanding of the di...Different stress states have a significant influence on the magnitude of the microscopic plastic strain and result in the development of the microstructure evolution.As a result,a comprehensive understanding of the different scale variation on microstructure evolution during bending deformation is essential.The advanced high strength dual-phase(DP1180)steel was investigated using multiscale microstructure-based 3D representative volume element(RVE)modelling technology with emphasis on understanding the relationship between the microstructure,localised stress-strain evolution as well as the deformation characteristics in the bending process.It is demonstrated that the localised development in bending can be more accurately described by microscopic deformation when taking into account microstructural properties.Microstructure-based 3D RVEs from each chosen bending condition generally have comparable localisation properties,whilst the magnitudes and intensities differ.In addition,the most severe localised bands are predicted to occur close to the ferrite and martensite phase boundaries where the martensite grains are close together or have a somewhat sharp edge.The numerically predicted results for the microstructure evolution,shear bands development and stress and strain distribution after 3-point bending exhibit a good agreement with the relevant experimental observations.展开更多
This article reports a systematic investigation on the relationship between the microstructure evolution and mechanical properties of as-cast Mg-9.5Gd-2.3Y-1Zn-0.5Zr(VW92,wt.%)alloy during aging treatment.The results ...This article reports a systematic investigation on the relationship between the microstructure evolution and mechanical properties of as-cast Mg-9.5Gd-2.3Y-1Zn-0.5Zr(VW92,wt.%)alloy during aging treatment.The results indicate that the alloy exhibits obvious double peak-aging characteristics at 180℃,200℃,and 220℃;the first peak-aging appeared at 96 h,48 h,and 48 h,respectively,while the second peak-aging occurred at 204 h,180 h,and 180 h,respectively.Moreover,the strengths of the first peak-aging were higher than those of the second peak-aging.Consequently,the first peak-aging at 200℃ achieved the best mechanical properties,with ultimate tensile strength(UTS),yield strength(YS),and elongation(EL)of 380(±2.0)MPa,255(±1.8)MPa,and 12.8(±1.7)%,respectively.While the strength decreased in the second peak-aging,the elongation increased to 17.2(±0.5)%.The first peak-aging strengthening is ascribed to the participation of the nano-β' phases in the matrix and the long period stacking ordered(LPSO)phases at grain boundaries(GBs).Additionally,the second peak-aging strengthening is associated with the emergence of a relatively new 3D structure comprising longchain-like structural phases β'+β'_(F) tβ_(1),γ' phases,and LPSO phases within the grain,combined with the fine and uniform LPSO phases at the GBs.展开更多
Fine-grained Mg-6Zn-4Y alloy was prepared by an ingot metallurgy process with hot extrusion at 300 ℃.The microstructure was studied by XRD,OM,SEM and TEM,and the tensile properties were tested at room temperature.The...Fine-grained Mg-6Zn-4Y alloy was prepared by an ingot metallurgy process with hot extrusion at 300 ℃.The microstructure was studied by XRD,OM,SEM and TEM,and the tensile properties were tested at room temperature.The results show that the alloy is composed of α-Mg and W-phase.The microstructure of the as-extruded alloy has a bimodal grain size distribution.The fine grains with the mean size of 1.2 μm are formed by dynamic recrystallization.The coarse grains（about 23% in area fraction） are unrecrystallized regions which are elongated along extrusion direction.The engineering stress—strain curve shows a pronounced yield point.The ultimate tensile strength,yield strength,and elongation are（371±10） MPa,（350±5） MPa and（7±2）%,respectively.The high strengths are attributed to the fine-grained matrix structure enhanced by W-phase particles,nano-scaled precipitates,and strong basal plane texture.展开更多
Eight high strength concrete (HSC) prisms strengthened with continuous carbon fiber sheet(CFS)were tested.As a result of the confinement provided by CFS,the concrete would fail at a greater strain than the unconfined ...Eight high strength concrete (HSC) prisms strengthened with continuous carbon fiber sheet(CFS)were tested.As a result of the confinement provided by CFS,the concrete would fail at a greater strain than the unconfined and then a significant increase in ductility can be achieved.The lateral pressure exerted by CFS would increase the compressive strength of the concrete,resulting in higher load bearing capacity.This paper proposes the stress strain curve of this kind of hybrid specimen,which agrees well with the test results.Based on the stress strain relationship and the assumptions proposed in this paper,a computer program was developed to analyze HSC columns,confined by CFS,which were subjected to axial compression and biaxial bending.The results shown in this paper indicate that the ductility of HSC column is significantly improved and the strength is also increased by some degree.展开更多
Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression ...Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression and biaxial bending is studied. The main factors affecting the flexural behavior of T shaped high strength concrete members are loading angle, axial compression ratio and reinforcement ratio.展开更多
China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed...China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed the non-argent Lanthanum-tellurium-copper alloy as a substitute for industry argent-copper. In our research, we were able to successfully apply rare earth lanthanum to copper alloy. The defects as porosity, inclusion, etc. originating from nonvacuum melting processing were controlled. Fine grain was obtained. Meanwhile, the comprehensive properties of the copper alloy, such as strength, conductivity and thermal conductivity were improved. The research results in increasing conductivity and thermal conductivity by 5% and 15%, respectively, while the tensile strength is increased by 6% higher than Ag-Cu alloy. The anti-electric corrosion property is good, and there is no argent-cadmium steam population originating from the electric arc effect. The addition of lanthanum further reduces the content of oxygen and hydrogen. The optimum quantity of the addition of RE lanthanum in the copper alloy is 0.010% - 0.020% .展开更多
As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys....As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.展开更多
Two types of steel, C-Mn-CrMo B microalloyed steel and C-Mn-Mo-Nb-Cu-B microalloyed steel, are designed to develop 1000 MPa ultra high strength steel. Two kinds of processes, thermomeehanical controlled process （TMCP...Two types of steel, C-Mn-CrMo B microalloyed steel and C-Mn-Mo-Nb-Cu-B microalloyed steel, are designed to develop 1000 MPa ultra high strength steel. Two kinds of processes, thermomeehanical controlled process （TMCP） combined with traditional off-line quenching and tempering （QT） process versus controlled rolling process （CR） combined with direct quenching and tempering （DQ＋T） process, are applied. The effect of heat treatment processing mode on the microstructure and mechanical properties is studied. The relationship between microstructure and mechanical properties is investigated by SEM and TEM. After tempering at 450 to 550 ℃ for 1 h, the steel produced by TMCP＋QT process shows combination of excellent strength and low temperature toughness. The yield strength is above 1 000 MPa, elongation above 15% and impact energy at -40 ℃ more than 30 J. After tempering at 450 ℃, a large number of ε-Cu particles precipitated in C-Mn-Mo-Nb-Cu-B steel produced by CR＋DQ＋T process lead to a significant increase in yield strength. And after tempering at 500 to 600 ℃, the yield strength of the steel is further improved to 1 030 MPa because of precipitates, such as nitride or carbide of niobium, carbide of molybedenum and vanadium. When the tempering temperature is increased above 620 ℃, the yield strength is still higher than 1 000 MPa and elongation is above 20% and impact energy at --40 ℃ is more than 35 J. After tempering at above 500 ℃, the toughness of the steel treated by TMCP＋QT process is superior to that of steel by CR＋DQ＋T process.展开更多
In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. Among advanced high strength steels, dual phase （DP） steels have gained a great attention owing to a co...In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. Among advanced high strength steels, dual phase （DP） steels have gained a great attention owing to a combination of high strength and good formability. However, high strength usually increases the spring-back behavior of the material, which creates problems for the parts during the assembly. Thus, the uniaxial tensile deformation and spring-back behaviors of DP600 advanced high strength steel were investigated in rolling （0°）, diagonal （45°） , and transverse （90°） directions in the temperature range from room temperature （RT） to 300 ℃. All tests were performed at a deformation speed of 25 mm/min. A V-shaped die （60°） was used for the spring-back measurements. The results indicated that the formability and spring-back of the material were decreased with increasing the temperatures. The material showed complex behaviors in different directions and at different temperatures.展开更多
Lightweight structure is an important method to increase vehicle fuel efficiency.High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight.However,...Lightweight structure is an important method to increase vehicle fuel efficiency.High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight.However,the lightweight structures must show the improved capability for structural rigidity and crash energy absorption.Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles.Currently,many research works focus on component level axial crash testing and simulation of high strength steels.However,the effects of high strength steel parts to the impact of auto body are not considered.The goal of this research is to study the application of hot forming high strength steel(HFHSS)in order to evaluate the potential using in vehicle design for lightweight and passive safety.The performance of HFHSS is investigated by using both experimental and analytical techniques.In particular,the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body.Automotive components made of HFHSS and general high strength steel(GHSS)are considered in this study.The material characterization of HFHSS is carried out through material experiments.The finite element method,in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP)crash test.The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated.The results from the simulation analyses of HFHSS are compared with those of GHSS.The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact.Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts.Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts.The experiments and simulation are conducted to the HFHSS parts on auto body.The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.展开更多
To develop the Q960 high-strength quenched and tempered steel plates for construction machinery,the effects of quenching and tempering treating regime on the microstructures and mechanical properties were investigated...To develop the Q960 high-strength quenched and tempered steel plates for construction machinery,the effects of quenching and tempering treating regime on the microstructures and mechanical properties were investigated.The results show that the perfect austenization and fine grain size can be achieved by the optimum quenching process that is quenching temperature 900℃ and holding time 20min.Considering performance and production efficiency,the optimum tempering process parameters are found that tempering temperature 600℃ and holding time 40min.The excellent overall properties of specimens with tempered sorbite microstructure can be ultimately obtained.The yield strength is 1030MPa,tensile strength 1080MPa,percentage elongation 16.8% and the Charpy impact energy 144J at-40℃.All these indexes come up to the National Standard GB/T 16270-2009.展开更多
A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that ado...A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.展开更多
Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The eff...Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.展开更多
The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steel...The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.展开更多
As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In ...As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51904278,51974288 and 52071300)the Special Funding Projects for Local Science and Technology Development guided by the Central Committee(YDZJSX2021C007,YDZJSX2021B020 and YDZX20191400004587)+4 种基金the Key Research and Development Project of Shanxi Province(202102050201004,202102150401002,202202050201015)the Scientific and Technological Innovation Talent Team Project of Shanxi Province(202204051002020)the Basic Research Program of Shanxi Province(20210302123218,202203021212126,202203021221096)the Foundation of the State Key Laboratory of Advanced Metallurgy,USTB(K22-11)the Special Project for Transformation of Scientific Achievements(202204021301025).
文摘High strength steels exhibit superior mechanical properties due to the unique microstructure,which successfully solves the drawback of the inevitable strength-toughness trade-off that occurs in traditional alloys.Here we investigated the effect of matrix and precipitates on mechanical properties of Cr-Ni-Mo-V/Nb steel after water quenching and tempering(150-500℃).The results showed that the microstructure of the present steel is noticeably tuned by changing the tempering temperature.An excellent combination of strength(a yield strength of 1308 MPa with a total elongation of 8.2%)and toughness(Charpy V-notch impact toughness of 40.5 J/cm^(2))is obtained upon tempering at 200℃.This is attributed to the lath martensite containing high dislocation density,the martensite-twin substructure,and the strengthening effects of the precipitated needle-likeε-carbides and spherical VC particles.The acicularε-carbides are replaced by the rod-shaped Fe_(3)C at the tempering temperature of 350℃,resulting in the remarkable deterioration in strength,hardness,and elongation.Spheroidized carbides formed at a tempering temperature of 500℃ are beneficial to the enhancement of the elongation and toughness,but the strength decreases due to the matrix softening caused by the recovery of dislocation.
基金the support of the National Natural Science Foundation of China(52471126,52071093)the Natural Science Foundation of Heilongjiang Province of China(LH2023E059)the Scientific and Technological Developing Scheme of Jilin Province(SKL202302038).
文摘The tradeoff between strength and corrosion resistance restricts the development of low-alloyed magnesium(Mg)alloys.In this work,a low-alloyed Mg-1Sm-0.8Mn-0.5Ca-0.4Zn alloy was prepared through a simple process of conventional casting followed by proper hotextrusion.The as-extruded alloy exhibits a very high yield strength of 402 MPa,an acceptable elongation of 5%,and a low corrosion rate of 0.56 mm y^(-1) which is close to that of high-purity Mg,and such comprehensive properties are superior to most reported Mg alloys,whether high alloying or low alloying.The special fine microstructure is responsible for high strength,including fine dynamic recrystallized(DRXed)grains,strong textured un-DRXed grains,dislocations and uniformly dispersed nano-spaced α-Mn nano-precipitates.An important finding of this study is that the corrosion film microstructure has amorphous characteristics,and this inevitably contributes to the high film protectiveness,and finally improves the corrosion resistance of the as-extruded alloy with relatively strong micro-galvanic corrosion tendency.In addition,the influence of micro/submicron-sized Mg_(2)Ca with anodic nature and nano-sized cathode α-Mn precipitates with strong strengthening effect on the corrosion film is also discussed.This study suggests that the strength-corrosion tradeoff can be evaded by regulating the microstructure of alloy substrate and corrosion film in the low-alloyed Mg alloy.
基金supported by the National Natural Science Foundation of China(Nos.52371093 and 52171104)the National Key Research and Development Program of China(No.2021YFB3701100)the Chongqing Research Program of Basic Research and Frontier Technology,China(Nos.CSTB2023NSCQ-BSX0036 and cstc2021ycjh-bgzxm0086).
文摘The low strength of Mg-Li alloys sets a limit to lightweight applications.Introducing crystal defects(twins,dislocations,and SFs)is a distinctive strategy for maintaining good mechanical properties of metallic materials.A lamellar-structured Mg-4Li-3Al-0.4Ca alloy with high performance was prepared by hot extrusion and rotary swaging.The as-swaged alloy exhibits excellent mechanical properties with tensile strength,yield strength,elongation to failure,and specific strength of 391 MPa,312 MPa,14.2%,and 238.4 kN m kg^(-1),respectively.The average grain size of the as-swaged alloy is 160±23 nm,and the microstructure is mainly composed of lamellar structures,twins,ultrafine grains,and nano-grains.The abundant lamellar structures and twins promote the storage of dislocations and SFs,leading to the formation of twin-twin interactions and enhancing strain hardening.The formation of UFG and NG by dynamic recrystallization further improves the yield strength.Shearable second phases play a critical role in enhancing the yield strength and ductility.More importantly,extensive planar dislocation glide and(c+a)dislocations efficiently relax the local stress concentrations,and thus improve the ductility.
基金supported by the National Natural Science Foundation of China(Grant Nos.51979099&51774109)Natural Science Foundation of Jiangsu Province of China(Grant No.BK 20191303)+2 种基金Key Research and Development Project of Jiangsu Province of China(Grant No.BE2017148)Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX22_0632)Suqian Sci&Tech Program(Grant No.K202113).
文摘The dilemma of choosing between superb grain boundary strengthening and excellent precipitation strengthening is commonly faced in the pursuit of high-strength age-hardenable Mg alloys.Here,a strategy for addressing this dilemma via the balance between grain refinement and weakening of dynamic precipitation is proposed and applied on a Mg-10.95Gd-2.06Ag(wt%)alloy treated by sequential processing of equalchannel angular pressing(ECAP),hot rolling and aging.The hot rolling leads to a noticeable dissolution of the dynamic precipitates intensively formed during prior ECAP,together with a tolerable grain growth.Meanwhile,numerous multi-twinning-induced lamellar bands(LBs)demarcated by coaxial grain boundaries(CGBs)subdivide the grains.For the first time,a quadruple twinning pattern for the formation of CGB with a misorientation of~135°is raised.During post-rolling aging,besides the commonβ’andγ”precipitates and theβnano-particles whose Gd/Ag ratio is much lower than that of dynamically precipitatedβparticles,theβ”/βT precipitates,CGB segregation,and stacking fault(SF)-associated segregation/γ’precipitates within LBs,are also involved with the precipitation structure.Benefiting from this complex precipitation structure,a good age-hardening ability manifested by the aging-induced tensile yield strength(TYS)increment reaching 115 MPa is attained.Combining with the strengthening from grain boundaries,dislocations,solutes,and basal texture,a high TYS of 447 MPa is achieved.
基金supported by the National Natural Science Foundation of China(Nos.52203025,52072193,52361165657,and U22A20131)the Shandong Provincial Natural Science Foundation(Nos.ZR2021JQ16,ZR2023YQ040,and ZR2022QE266)the Shandong Provincial College Students'Innovation and Entrepreneurship Training Program(No.S202311065122)。
文摘As a biomass material with biodegradability and biocompatibility, sodium alginate (SA) is a good candidate for constructing hydrogels for tissue-mimicking and biomedical scaffold fabricating through extrusion-based 3D printing technology. However, the mechanical strength and stiffness of alginate hydrogels are still not comparable with biological tissues such as tendons and the printability of SA solutions is often poor. Here, a novel strategy for 3D printing of alginate hydrogels with high mechanical performance is developed by using glycerol as a co-solvent for SA solutions. The addition of glycerol (GL) enables the formation of a homogenous SA/GL solution with a high solid content of 12–20 wt.% and endows crosslinked SA hydrogels with high stretchability. By applying uniaxial stretches, hydrogel filaments prepared with concentrated SA/GL solutions reveal a high tensile strength of 36.6–161.3 MPa, Young's modulus of 59.2–1964.2 MPa, and elongation at break of 8.5 %–106.2 % due to the high orientated and closely packed SA chains. SA/GL solutions become more solid-like with increasing SA concentration, and the solution with a solid content of 16 wt.% exhibits optimal 3D printability because of the appropriate rheological properties and thixotropic behavior. By designing the deforming-and-fixing process, 3D printed high-strength alginate hydrogels with complex structures are prepared, broadening the application of alginate hydrogels in load-bearing and biomedical fields.
基金supported by HBIS Group under the Grant No.IRIS 200506003.
文摘Different stress states have a significant influence on the magnitude of the microscopic plastic strain and result in the development of the microstructure evolution.As a result,a comprehensive understanding of the different scale variation on microstructure evolution during bending deformation is essential.The advanced high strength dual-phase(DP1180)steel was investigated using multiscale microstructure-based 3D representative volume element(RVE)modelling technology with emphasis on understanding the relationship between the microstructure,localised stress-strain evolution as well as the deformation characteristics in the bending process.It is demonstrated that the localised development in bending can be more accurately described by microscopic deformation when taking into account microstructural properties.Microstructure-based 3D RVEs from each chosen bending condition generally have comparable localisation properties,whilst the magnitudes and intensities differ.In addition,the most severe localised bands are predicted to occur close to the ferrite and martensite phase boundaries where the martensite grains are close together or have a somewhat sharp edge.The numerically predicted results for the microstructure evolution,shear bands development and stress and strain distribution after 3-point bending exhibit a good agreement with the relevant experimental observations.
基金supported by National Natural Science Foundation of China(No.U21A2048)the Science and Technology Research Program of the Chongqing Municipal Education Commission(No.KJZDK202201108)+2 种基金Academician in Chongqing Leaded Guidance Project of Science,Technology Innovation(No.CSTB2023YSZX-JCX0006)the Science and Technology Research Project of Chongqing Municipal Education Commission(No.KJQN202101126)Chongqing Natural Science Foundation(No.CSTB2024NSCQ-MSX0574).
文摘This article reports a systematic investigation on the relationship between the microstructure evolution and mechanical properties of as-cast Mg-9.5Gd-2.3Y-1Zn-0.5Zr(VW92,wt.%)alloy during aging treatment.The results indicate that the alloy exhibits obvious double peak-aging characteristics at 180℃,200℃,and 220℃;the first peak-aging appeared at 96 h,48 h,and 48 h,respectively,while the second peak-aging occurred at 204 h,180 h,and 180 h,respectively.Moreover,the strengths of the first peak-aging were higher than those of the second peak-aging.Consequently,the first peak-aging at 200℃ achieved the best mechanical properties,with ultimate tensile strength(UTS),yield strength(YS),and elongation(EL)of 380(±2.0)MPa,255(±1.8)MPa,and 12.8(±1.7)%,respectively.While the strength decreased in the second peak-aging,the elongation increased to 17.2(±0.5)%.The first peak-aging strengthening is ascribed to the participation of the nano-β' phases in the matrix and the long period stacking ordered(LPSO)phases at grain boundaries(GBs).Additionally,the second peak-aging strengthening is associated with the emergence of a relatively new 3D structure comprising longchain-like structural phases β'+β'_(F) tβ_(1),γ' phases,and LPSO phases within the grain,combined with the fine and uniform LPSO phases at the GBs.
基金Project (50271054) supported by the National Natural Science Foundation of ChinaProject (20070700003) supported by the Doctorate Programs Foundation of Ministry of Education of China+1 种基金Project (102102210031) supported by the Science and Technologies Foundation of Henan Province, ChinaProject (2010A430008) supported by the Natural Science Foundation of Henan Educational Committee of China
文摘Fine-grained Mg-6Zn-4Y alloy was prepared by an ingot metallurgy process with hot extrusion at 300 ℃.The microstructure was studied by XRD,OM,SEM and TEM,and the tensile properties were tested at room temperature.The results show that the alloy is composed of α-Mg and W-phase.The microstructure of the as-extruded alloy has a bimodal grain size distribution.The fine grains with the mean size of 1.2 μm are formed by dynamic recrystallization.The coarse grains（about 23% in area fraction） are unrecrystallized regions which are elongated along extrusion direction.The engineering stress—strain curve shows a pronounced yield point.The ultimate tensile strength,yield strength,and elongation are（371±10） MPa,（350±5） MPa and（7±2）%,respectively.The high strengths are attributed to the fine-grained matrix structure enhanced by W-phase particles,nano-scaled precipitates,and strong basal plane texture.
文摘Eight high strength concrete (HSC) prisms strengthened with continuous carbon fiber sheet(CFS)were tested.As a result of the confinement provided by CFS,the concrete would fail at a greater strain than the unconfined and then a significant increase in ductility can be achieved.The lateral pressure exerted by CFS would increase the compressive strength of the concrete,resulting in higher load bearing capacity.This paper proposes the stress strain curve of this kind of hybrid specimen,which agrees well with the test results.Based on the stress strain relationship and the assumptions proposed in this paper,a computer program was developed to analyze HSC columns,confined by CFS,which were subjected to axial compression and biaxial bending.The results shown in this paper indicate that the ductility of HSC column is significantly improved and the strength is also increased by some degree.
文摘Based on experiments, a computer program is developed. The calculated results agree well with the experimental results. The flexural behavior of T shaped high strength concrete members subjected to axial compression and biaxial bending is studied. The main factors affecting the flexural behavior of T shaped high strength concrete members are loading angle, axial compression ratio and reinforcement ratio.
基金Project supported by the National Scientific and Technological Achievements Spread Project (2004EC00299)Science and Technology Type Middle and Small Business Technique Invention Fund (04C26225121390)
文摘China is quite poor in argent resource. Roughly 80% of this industrial argent is imported every year. In order to improve the situation, we took advantage of rare earth (RE) mineral resource and successfully developed the non-argent Lanthanum-tellurium-copper alloy as a substitute for industry argent-copper. In our research, we were able to successfully apply rare earth lanthanum to copper alloy. The defects as porosity, inclusion, etc. originating from nonvacuum melting processing were controlled. Fine grain was obtained. Meanwhile, the comprehensive properties of the copper alloy, such as strength, conductivity and thermal conductivity were improved. The research results in increasing conductivity and thermal conductivity by 5% and 15%, respectively, while the tensile strength is increased by 6% higher than Ag-Cu alloy. The anti-electric corrosion property is good, and there is no argent-cadmium steam population originating from the electric arc effect. The addition of lanthanum further reduces the content of oxygen and hydrogen. The optimum quantity of the addition of RE lanthanum in the copper alloy is 0.010% - 0.020% .
基金supported by the National Natural Science Foundation of China(51201103&51304135)the Specialized Research Fund for the Doctoral Program of Higher Education(20110073120008)+2 种基金the New Century Excellent Talents in University of Ministry of Education of China(NCET-11-0329)the Program of Shanghai Subject Chief of Engineering(14XD1425000)the Assembly Pre-research Project(51312030706)
文摘As most Mg alloy products are now produced by a casting process,the development of high strength cast Mg alloys can promote their further applications and has already become one of the hot research areas of Mg alloys.The present paper reviews the strengthening mechanisms,tensile properties and modification results of commercial high strength cast Mg alloys;as well as the development of Mg-Gd,Mg-Nd and Mg-Sn based alloys.It concludes that precipitation strengthening is the most important strengthening mechanism in high strength cast Mg alloys,which contributes more than 60%of yield strength in solution&peak-aged(T6)cast Mg alloys.For the yield strength,the alloys follow the sequence of Mg-Gd(Y)-Ag>Mg-Gd(Y)-Zn>Mg-Gd-Y/Sm/Nd>Mg-Y-Nd(WE series)>ZK61>Mg-Nd>AZ91>Mg-Sn.Mg-Gd(Y)-Ag based alloys are the strongest cast Mg alloys at present,followed by Mg-Gd(Y)-Zn based alloys.The high yield strengths of Mg-Gd(Y)-Ag and Mg-Gd(Y)-Zn cast alloys are due to the co-precipitation of basal and prismatic meta-stable phases.
文摘Two types of steel, C-Mn-CrMo B microalloyed steel and C-Mn-Mo-Nb-Cu-B microalloyed steel, are designed to develop 1000 MPa ultra high strength steel. Two kinds of processes, thermomeehanical controlled process （TMCP） combined with traditional off-line quenching and tempering （QT） process versus controlled rolling process （CR） combined with direct quenching and tempering （DQ＋T） process, are applied. The effect of heat treatment processing mode on the microstructure and mechanical properties is studied. The relationship between microstructure and mechanical properties is investigated by SEM and TEM. After tempering at 450 to 550 ℃ for 1 h, the steel produced by TMCP＋QT process shows combination of excellent strength and low temperature toughness. The yield strength is above 1 000 MPa, elongation above 15% and impact energy at -40 ℃ more than 30 J. After tempering at 450 ℃, a large number of ε-Cu particles precipitated in C-Mn-Mo-Nb-Cu-B steel produced by CR＋DQ＋T process lead to a significant increase in yield strength. And after tempering at 500 to 600 ℃, the yield strength of the steel is further improved to 1 030 MPa because of precipitates, such as nitride or carbide of niobium, carbide of molybedenum and vanadium. When the tempering temperature is increased above 620 ℃, the yield strength is still higher than 1 000 MPa and elongation is above 20% and impact energy at --40 ℃ is more than 35 J. After tempering at above 500 ℃, the toughness of the steel treated by TMCP＋QT process is superior to that of steel by CR＋DQ＋T process.
基金Item Sponsored by Scientific and Technological Research Council of Turkey(107 M596)
文摘In recent years, the use of advanced high strength steels in automotive industry has been increased remarkably. Among advanced high strength steels, dual phase （DP） steels have gained a great attention owing to a combination of high strength and good formability. However, high strength usually increases the spring-back behavior of the material, which creates problems for the parts during the assembly. Thus, the uniaxial tensile deformation and spring-back behaviors of DP600 advanced high strength steel were investigated in rolling （0°）, diagonal （45°） , and transverse （90°） directions in the temperature range from room temperature （RT） to 300 ℃. All tests were performed at a deformation speed of 25 mm/min. A V-shaped die （60°） was used for the spring-back measurements. The results indicated that the formability and spring-back of the material were decreased with increasing the temperatures. The material showed complex behaviors in different directions and at different temperatures.
基金supported by National Natural Science Foundation of China(Grant No.19832020)National Science Fund of Outstanding Youths of China(Grant No.10125208)+1 种基金Chongqing Municipal Programs for Science and Technology Development of China(Grant No.CSTC,2007AA4008)National Key Technology R&D Program of China(Grant No.2006BA104B04-2)
文摘Lightweight structure is an important method to increase vehicle fuel efficiency.High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight.However,the lightweight structures must show the improved capability for structural rigidity and crash energy absorption.Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles.Currently,many research works focus on component level axial crash testing and simulation of high strength steels.However,the effects of high strength steel parts to the impact of auto body are not considered.The goal of this research is to study the application of hot forming high strength steel(HFHSS)in order to evaluate the potential using in vehicle design for lightweight and passive safety.The performance of HFHSS is investigated by using both experimental and analytical techniques.In particular,the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body.Automotive components made of HFHSS and general high strength steel(GHSS)are considered in this study.The material characterization of HFHSS is carried out through material experiments.The finite element method,in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme(C-NCAP)crash test.The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated.The results from the simulation analyses of HFHSS are compared with those of GHSS.The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact.Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts.Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts.The experiments and simulation are conducted to the HFHSS parts on auto body.The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.
文摘To develop the Q960 high-strength quenched and tempered steel plates for construction machinery,the effects of quenching and tempering treating regime on the microstructures and mechanical properties were investigated.The results show that the perfect austenization and fine grain size can be achieved by the optimum quenching process that is quenching temperature 900℃ and holding time 20min.Considering performance and production efficiency,the optimum tempering process parameters are found that tempering temperature 600℃ and holding time 40min.The excellent overall properties of specimens with tempered sorbite microstructure can be ultimately obtained.The yield strength is 1030MPa,tensile strength 1080MPa,percentage elongation 16.8% and the Charpy impact energy 144J at-40℃.All these indexes come up to the National Standard GB/T 16270-2009.
基金Item Sponsored by High Technology Development Program of China(2001AA332020)
文摘A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.
文摘Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.
基金supported by the National Science and Technology Infrastructure Platforms Construction Projects of China (Grant No2005DKA10400)the National Science Foundation of China (No50871021)
文摘The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.
文摘As a structural material with low density and high strength, super-highstrength aluminum alloys have a future for wide application. However, its poor stress corrosionresistance (SCC) restricts further development. In present, retrogression and re-ageing (RRA)treatment, which can improve both strength and SCCR of 7XXX series alloy, is a best method to solvethis problem. The effect of RRA treatment on the microstructure evolution of a new type lowfrequency electric-magnetic casting Al-9.OZn-2.45Mg-2.2Cu-0.15Zr alloy was investigated using DSCand TEM technologies. The results show that the typical microstructure of the alloy at T6 conditionis characterized by both fine eta' and GP zone homogeneously distributed in the matrix andcontinuous r) particles occurred on the grain-boundary. After RRA treatment, the matrixprecipitations are mainly fine and dispersed eta' and eta phases, being coarser and more stable thanthat from T6 temper. While, the grain-boundary microstructure is very close to that resulting fromT73 temper. High retrogression temperature and long retrogression time leads to a more stablemicrostructure after re-ageing.
