Due to its unique properties,helium is critical in scientific research and industrial innovation,particularly in cryogenics;however,its scarcity necessitates efficient resource utilization.Through a review of the hist...Due to its unique properties,helium is critical in scientific research and industrial innovation,particularly in cryogenics;however,its scarcity necessitates efficient resource utilization.Through a review of the historical development of the helium industry,this study comprehensively evaluates the value,sources,production methods,supply dynamics,and sustainability challenges of helium.The processes and mechanisms of helium enrichment,along with effective exploration methods,are systematically analyzed here.We recommend focusing on the development of technologies for helium preservation,recovery,and extraction,particularly the extraction technology for helium-poor fields.Market analysis indicates that no imminent crisis in the global helium supply is expected before 2060.Thus,enhancing helium resource protection technologies is essential to improve its economic utilization and management while providing a timely reference for the scientific community.展开更多
This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to298 K and strain rates from 10^(-4)/s...This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to298 K and strain rates from 10^(-4)/s to 10^(-2)/s.Scanning electron microscopy is utilized to analyze the fracture morphology,aiming to reveal the fracture behavior at various temperatures.The applicability of the Zener-Hollomon parameter and the Johnson-Cook model in describing the flow stress of Ti-6Al-4V at cryogenic temperatures is analyzed.Moreover,a constitutive relationship modeling method based on the variational recurrent networks is proposed.Mechanical test results show a significant increase in the strength of equiaxed Ti-6Al-4V alloy under cryogenic conditions while the plastic deformation process is shortened.However,the fracture analysis indicates that even at 77 K,the fracture process is still dominated by ductile fracture,and brittle fracture does not occur within the range of 77 K to 298 K.The fitting results validate the performance of the Zener-Hollomon parameter and the Johnson-Cook model in describing the deformation flow stress of Ti-6Al-4V alloy at cryogenic temperatures.The results also indicate that the proposed constitutive relationship modeling method based on the variational recurrent network performs better,making it a potential method for widespread applications.展开更多
Minimum quantity lubrication(MQL),as a new sustainable and eco-friendly alternative cooling/lubrication technology that addresses the limitations of dry and wet machining,utilizes a small amount of lubricant or coolan...Minimum quantity lubrication(MQL),as a new sustainable and eco-friendly alternative cooling/lubrication technology that addresses the limitations of dry and wet machining,utilizes a small amount of lubricant or coolant to reduce friction,tool wear,and heat during cutting processes.MQL technique has witnessed significant developments in recent years,such as combining MQL with other sustainable techniques to achieve optimum results,using biodegradable lubricants,and innovations in nozzle designs and delivery methods.This review presents an in-depth analysis of machining characteristics(e.g.,cutting forces,temperature,tool wear,chip morphology and surface integrity,etc.)and sustainability characteristics(e.g.,energy consumption,carbon emissions,processing time,machining cost,etc.)of conventional MQL and hybrid MQL techniques like cryogenic MQL,Ranque-Hilsch vortex tube MQL,nanofluids MQL,hybrid nanofluid MQL and ultrasonic vibration assisted MQL in machining of aeronautical materials.Subsequently,the latest research and developments are analyzed and summarized in the field of MQL,and provide a detailed comparison between each technique,considering advantages,challenges,and limitations in practical implementation.In addition,this review serves as a valuable source for researchers and engineers to optimize machining processes while minimizing environmental impact and operational costs.Ultimately,the potential future aspects of MQL for research and industrial execution are discussed.展开更多
A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hard...A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.展开更多
Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstra...Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.展开更多
Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the...Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the kinetics of reverse austenite transformation,strain hardening behavior,and toughening mechanism were further investigated.The lamellarized specimens possess low yield strength but high toughness,especially cryogenic toughness.Lamellarization leads to the development of film-like reversed austenite at the martensite block and lath boundaries,refining the martensite structure and lowering the equivalent grain size.Kinetic analysis of austenite reversion based on the JMAK model shows that the isothermal transformation is dominated by the growth of reversed austenite,and the maximum transformation of reversed austenite is reached at the peak temperature(750℃).The strain hardening behavior based on the modified Crussard-Jaoul analysis indicates that the reversed austenite obtained from lamellarization reduces the proportion of martensite,significantly hindering crack propagation via martensitic transformation during the deformation.As a consequence,the QLT specimens exhibit high machinability and low yield strength.Compared with the QT specimen,the ductile-brittle transition temperature of the QLT specimens decreases from-116 to-130℃due to the low equivalent grain size and reversed austenite,which increases the cleavage force required for crack propagation and absorbs the energy of external load,respectively.This work provides an idea to improve the cryogenic toughness of marine 10Ni5CrMoV steel and lays a theoretical foundation for its industrial application and comprehensive performance improvement.展开更多
The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments co...The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments conducted at different temperatures.Dynamic recovery and recrystallization of SAC305 solder alloy at room temperature(RT,293 K)activate a softening process.Conversely,intersecting and none-intersecting deformation twins,embedded in body-centered tetragonal Sn,enhance tensile strength and stabilize strain hardening rate,while suppressing the elongation of the alloy at LNT.The irreconcilable velocity difference between twin thickening(~8μm/s)and dislocation slip(4μm/s)results in premature brittle fracture,during the linear hardening and DBT.Moreover,the secondary phases degrade the mechanical property of SAC305 solder alloy,and micro-cracks appear between Cu_(6)Sn_(5)and Ag_(3)Sn in the eutectic matrix.展开更多
Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformati...Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformation.In this study,high-resolution transmission electron microscopy(HRTEM)and molecular dy-namics(MD)simulations were used to investigate the atomic arrangements and crystalline defects of deformation-induced γ-austenite→ε-martensite→α'-martensite and γ→α'martensitic transforma-tions in 316 L SS at 15 and 173 K.Theγ→εtransformation involves the glide of Shockley partial dislocations on(111)γplanes without a change in atomic spacing.The formation of anα'inclusion in a singleε-band is achieved by a continuous lattice distortion,accompanied by the formation of a tran-sition zone ofα'and the expansion of the average atomic spacings due to dislocation shuffling.Asα'grows further intoγ,the orientation relationship(OR)of theα'changes by lattice bending.This pro-cess follows the Bogers-Burgers-Olson-Cohen model despite it not occurring on intersecting shear bands.Stacking faults and twins can also serve as nucleation sites forα'at 173 K.We also found that direct transformation of γ→α'occurs by the glide of √6aγ[11(2)]/12 dislocations on every(111)γplane with misfit dislocations.Overall,this study provides,for the first time,insights into the atomic-scale mech-anisms of various two-step and one-step martensitic transformations induced by cryogenic deformation and corresponding local strain,enhancing our understanding of the role of martensitic transformation under ultra-cryogenic-temperature deformation in controlling the properties.展开更多
This brief presents a cryogenic voltage reference circuit designed to operate effectively across a wide temperature range from 30 to 300 K.A key feature of the proposed design is utilizing a current subtraction techni...This brief presents a cryogenic voltage reference circuit designed to operate effectively across a wide temperature range from 30 to 300 K.A key feature of the proposed design is utilizing a current subtraction technique for temperature compensation of the reference current,avoiding the deployment of bipolar transistors to reduce area and power consumption.Implemented with a 0.18-μm CMOS process,the circuit achieves a temperature coefficient(TC)of 67.5 ppm/K,which was not achieved in previous works.The design can also attain a power supply rejection(PSR)of 58 d B at 10 k Hz.Meanwhile,the average reference voltage is 1.2 V within a 1.6%3σ-accuracy spread.Additionally,the design is characterized by a minimal power dissipation of 1μW at 30 K and a compact chip area of 0.0035 mm~2.展开更多
The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-...The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-spun(Fe_(0.5)Co_(0.5))_(75)B_(21)Nb_(4) metallic glasses(MGs)is studied.On the premise of maintaining a fully amorphous phase,appropriate CT and relaxation annealing are conducive to achieving the synergistic effect of increasing saturation magnetization(M_(s))and reducing coercivity(H_(c)).Shallow CT at 213 K optim-ally enhances the soft magnetic properties of MGs.Given its low activation energy of nucleation and increased activation energy of growth,appropriate CT is beneficial for achieving uniform annealed nanocrystals in amorphous phases.The correlation between free volumes(FVs)and potential energy suggests that the variation in Hc depends on the expansion and contraction behavior of amorphous phases after different CT processes.The fitting formulas of H_(c)–d_(m) and Ms–Hv correlations demonstrate that soft magnetic parameters have a solid linear relationship with the contents of FVs and degree of dense random packing.Moreover,pitting resistance is improved by ap-propriate CT and relaxation annealing.This improvement is characterized by the promotion of the stability of the Nb-rich passive film formed during electrochemical corrosion in 3.5wt%NaCl solution.展开更多
A cryogenic visible calibration and image evaluation facility(VCCIEF) was constructed to assess the effectiveness of electrical capacitance tomography systems in cryogenic conditions,known as Cryo-ECT.This facility wa...A cryogenic visible calibration and image evaluation facility(VCCIEF) was constructed to assess the effectiveness of electrical capacitance tomography systems in cryogenic conditions,known as Cryo-ECT.This facility was utilized to conduct dynamic,real-time imaging trials with liquid nitrogen(LN2).The actual flow patterns were captured using a camera and contrasted with the imaging outcomes.The capacitance data collected from these experiments were subsequently processed using three distinct methods:linear back projection,Landweber iteration,a fully connected deep neural network,and a convolutional neural network.This allowed for a comparative analysis of the performance of these algorithms in practical scenarios.The findings from the LN2 experiments demonstrated that the Cryo-ECT system,when integrated with the VCCIEF,was capable of successfully executing calibration,generating flow patterns,and performing imaging tasks.The system provided observable,clear,and precise phase distributions of the liquid nitrogen-vaporous nitrogenflow within the pipeline.展开更多
This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress condition...This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress conditions.Erichsen cupping tests were conducted to quantitatively evaluate the deformation capacity at room temperature(298 K)and cryogenic temperatures.The findings reveal a strong temperature dependence on the formability of the HEA.A decrease in the deformation temperature from 298 to 93 K causes a significant increase in both the Erichsen index(IE)(from 9.8 to 12.4 mm)and the expansion rate(δ)of surface area(from 51.6%to 76.3%),as well as a reduction in the average deviation(η)of thickness(from 55.1%to 44.4%),signifying its ultrahigh formability and uniform deformation capability at cryogenic temperature.This enhancement is attributed to the transition in the deformation mechanism from single dislocation slip at 298 K to a cooperative of plastic deformation mechanisms at 93 K,involving dislocation slip,stacking faults(SFs),Lomer-Cottrell(L-C)locks and multi-scale nanotwins.The lower stacking fault energy of the alloy facilitates these deformation mechanisms,particularly the formation of SFs and nanotwins,which enhance ductility and strength by providing additional pathways for plastic deformation.These mechanisms collectively contribute to delaying plastic instability,thereby improving the overall formability.This work provides a comprehensive understanding of the underlying reasons for the enhanced formability of HEAs at cryogenic temperatures,offering valuable insights for their practical use in challenging environments.展开更多
The serrated flow behavior,known as the Portevin-Le Chatelier(PLC)effect,is commonly observed during high-temperature deformation.In this study,we report a serrated flow behavior in FeCoCrNiMo0.2 high-entropy alloy(HE...The serrated flow behavior,known as the Portevin-Le Chatelier(PLC)effect,is commonly observed during high-temperature deformation.In this study,we report a serrated flow behavior in FeCoCrNiMo0.2 high-entropy alloy(HEA),which is mediated by nano-twinning and phase transformation at cryogenic temperatures.During uniaxial tensile deformation at 77 K,the alloy exhibited the formation of high-density deformation nano-twinning,cross-twinning,stacking faults(SFs)and Lomer-Cottrell locks(L-C locks).Additionally,the lower stacking fault energy(SFE)at low temperatures promotes the formation of the 9R phase.The high-density twin boundaries effectively hinder dislocation movement,leading to the instability of plastic deformation and promoting the serrated flow behavior.Furthermore,the rapid and unstable transformation of the 9R phase contributes to the pronounced serrated flow behavior.Nano-twinning,SFs,cross-twinning,L-C locks and 9R phase collectively induce a dynamic Hall-Petch effect,enhancing the strength-ductility synergy and strain-hardening ability of deformed alloy at 77 K.Our work provides valuable insights into the mechanism of tensile deformation at cryogenic temperatures in single-phase FCC HEA.展开更多
Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si allo...Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si alloy has been a problem for many years.In this study,the effect of deep cryogenic treatment(DCT)on the microstructure and mechanical properties of Al-12Si-4Cu-2Ni-Mg alloy with addition of Al-Ti-C-B master alloy was fully investigated.Results show that the average grain size of the alloy is greatly reduced from 0.92 mm to 0.50 mm,and the eutectic Si and Al7Cu4Ni precipitates are spheroidized and refined in Al-12Si-4Cu-2Ni-Mg after DCT for 24 h and aging treatment.Thereby these changes of microstructures result in a significant increment of about 22.5%in elongation and a slight enhancement of about 6.8%in tensile strength.Moreover,the refinement of microstructure also significantly improves the fatigue life of the alloy.展开更多
This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace appl...This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.展开更多
As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In or...As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In order to address this challenge,deep cryogenic treatment(DCT)as a new process applied in the field of EHEAs was proposed in this study.The effects of different DCT times on the microstructure and mechanical properties of AlCoCrFeNi2.1 EHEAs were studied,mainly focusing on the flake structure of FCC+B2 layer.The experimental results suggest that with the extension of the DCT time,the dislocation density in the FCC phase increases significantly.The spherical BCC precipitate phase is generated within the B2 phase,and the average size of this newly generated precipitate phase gradually decreases.Increasing the number of dislocations and precipitate phases is of great significance to improve the mechanical properties.The AlCoCrFeNi2.1 EHEA exhibits excellent comprehensive mechanical properties after DCT for 36 h.Compared with the as-cast state,the tensile strength at room temperature reaches 1,034.51 MPa,increased by 5.74%.The plasticity reaches 21.72%,which is increased by 11.79%.The results show that the tensile strength and ductility of AlCoCrFeNi2.1 EHEAs are balanced and improved after DCT,which are more suitable as advanced structural materials.In addition,the introduction of the DCT process to EHEAs solves the problem of environmental pollution caused by traditional heat treatment process.This study provides useful guidance for using the DCT process to strengthen the mechanical properties of“lamellar+block”type EHEAs.展开更多
In this study,Mg-Gd-Y-(Sm)-Zr(GW-(Sm))alloys were subjected to compression tests at both 293 and 77 K.The effect of Sm addition on the plastic deformation mechanism of Mg-Gd-Y-Zr(GW)alloy was investigated,and a detail...In this study,Mg-Gd-Y-(Sm)-Zr(GW-(Sm))alloys were subjected to compression tests at both 293 and 77 K.The effect of Sm addition on the plastic deformation mechanism of Mg-Gd-Y-Zr(GW)alloy was investigated,and a detailed analysis was conducted on the relationships between mechanical responses and the microstructure of the alloys.The findings suggest that dislocation slip plays a predominant role in the plastic deformation of GW-(Sm)alloys.The addition of Sm reduces the stacking fault energy(SFE)of the alloy,which promotes<c+a>slip and inhibits twinning.Meanwhile,Sm plays a role in solution strengthening,causing an elevation in the flow stress of the alloy.At cryogenic temperature(CT),the critical resolved shear stress(CRSS)of dislocation slip is increased,so the dislocation motion requires greater external force.In addition,the extensive crossed twins exhibited in the microstructure,which shorten the dislocation slip path and enhance the grain boundary strengthening.This research contributes to the advancement of plastic deformation theories for magnesium-rare earth(Mg-RE)alloys.展开更多
In this work,we aim to develop a novel post-treatment process combining cryogenic and pulsed electric field treatment to enhance WC-Co cemented carbides.The results show a 15.62%increase in hardness from 1831.38 to 21...In this work,we aim to develop a novel post-treatment process combining cryogenic and pulsed electric field treatment to enhance WC-Co cemented carbides.The results show a 15.62%increase in hardness from 1831.38 to 2117.38 HV30,a 9.60%rise in fracture toughness from 9.06 to 9.93 MPa·m^(1/2),while the friction coefficient decreases from 0.63 to 0.47.Through the residual stress evolution,WC orientation change and the martensitic transformation of Co,and the internal enhancement mechanism of cryogenic combined with pulsed electric field treatment are revealed.The electron wind generated by the pulsed electric field can efficiently reduce the residual stress induced by cryogenic process.The evolution of residual stress promotes the base slip of WC,increasing the degree of{0001}orientation.In addition,the degree of martensitic transformation of Co intensifies,with the hcp-Co/fcc-Co ratio rising from 0.41%to 17.86%.The enhanced WC{0001}orientation and increased hcp-Co content contribute to significant improvements in hardness and wear resistance.This work provides a novel efficient enhancement strategy for ceramics and alloys,with the potential to be a mainstream strengthening method in the future.展开更多
Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Desi...Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications.In this study,three gadolinium-transition metal-based high entropy oxides(HEOs)of Gd(Fe_(1/4)Ni_(1/4)Al_(1/4)Cr_(1/4))O_(3),Gd(Fe_(1/5)Ni_(1/5)Al_(1/5)Cr_(1/5)Co_(1/5))O_(3),and Gd(Fe_(1/6)Ni_(1/6)Al_(1/6)Cr_(1/6)Co_(1/6)Mn_(1/6))O_(3)were designed and systematically characterized regarding their structural and cryogenic magnetic properties.These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure,reveal a second-order magnetic transition at low temperatures,and exhibit significant cryogenic MCEs.The magnetocaloric performances of the present HEOs,identified by magnetic entropy changes,relative cooling power,and temperature-averaged entropy changes,were com-parable with recently reported candidate materials.The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.展开更多
Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an e...Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an effective way to enhance the resistance to HIC. The present study focused on the relationship between the retained austenite (RA) and HIC behavior in NiCrMoV/Nb multi-alloying ultra-strength steel. Results demonstrated that the maximum volume fraction of RA of 9.31% was obtained for QL30T specimen. After the deep cryogenic pretreatment, the volume fraction of RA reduced to 8.8%. RA could reduce the effective diffusion coefficient, while deep cryogenic pretreatment increased the susceptibility of the steel to HIC by a maxim of 14.8%. This was mainly due to the transformation of retained austenite into martensite, degrading the mechanical properties under hydrogen-charged condition. In addition, the deep cryogenic pretreatment had a significant effect on the crack initiation and propagation, with the intergranular (IG) fracture becoming the dominant fracture mode where an increase in the number of secondary cracks in the section. The interfaces of RA and matrix, as well as the grain boundaries, were the preferred sites for cracks initiation.展开更多
基金the Strategic Pilot Science and Technology Projects of Chinese Academy of Sciences,China(No.XDC10040000).
文摘Due to its unique properties,helium is critical in scientific research and industrial innovation,particularly in cryogenics;however,its scarcity necessitates efficient resource utilization.Through a review of the historical development of the helium industry,this study comprehensively evaluates the value,sources,production methods,supply dynamics,and sustainability challenges of helium.The processes and mechanisms of helium enrichment,along with effective exploration methods,are systematically analyzed here.We recommend focusing on the development of technologies for helium preservation,recovery,and extraction,particularly the extraction technology for helium-poor fields.Market analysis indicates that no imminent crisis in the global helium supply is expected before 2060.Thus,enhancing helium resource protection technologies is essential to improve its economic utilization and management while providing a timely reference for the scientific community.
基金supported by the National Natural Science Foundation of China(No.52275116)。
文摘This paper investigates the uniaxial tensile mechanical properties and flow behavior of Ti-6Al-4V alloys with equiaxed microstructure at cryogenic temperatures ranging from 77 K to298 K and strain rates from 10^(-4)/s to 10^(-2)/s.Scanning electron microscopy is utilized to analyze the fracture morphology,aiming to reveal the fracture behavior at various temperatures.The applicability of the Zener-Hollomon parameter and the Johnson-Cook model in describing the flow stress of Ti-6Al-4V at cryogenic temperatures is analyzed.Moreover,a constitutive relationship modeling method based on the variational recurrent networks is proposed.Mechanical test results show a significant increase in the strength of equiaxed Ti-6Al-4V alloy under cryogenic conditions while the plastic deformation process is shortened.However,the fracture analysis indicates that even at 77 K,the fracture process is still dominated by ductile fracture,and brittle fracture does not occur within the range of 77 K to 298 K.The fitting results validate the performance of the Zener-Hollomon parameter and the Johnson-Cook model in describing the deformation flow stress of Ti-6Al-4V alloy at cryogenic temperatures.The results also indicate that the proposed constitutive relationship modeling method based on the variational recurrent network performs better,making it a potential method for widespread applications.
基金financially supported by the National Natural Science Foundation of China(Nos.92160301,92060203,52175415,and 52205475)the Science Center for Gas Turbine Project(Nos.P2022-AB-IV-002-001 and P2023-B-IV-003-001)+2 种基金the Natural Science Foundation of Jiangsu Province(No.BK20210295)the Superior Postdoctoral Project of Jiangsu Province(No.2022ZB215)the National Key Laboratory of Science and Technology on Helicopter Transmission in NUAA(No.HTL-A-22G12).
文摘Minimum quantity lubrication(MQL),as a new sustainable and eco-friendly alternative cooling/lubrication technology that addresses the limitations of dry and wet machining,utilizes a small amount of lubricant or coolant to reduce friction,tool wear,and heat during cutting processes.MQL technique has witnessed significant developments in recent years,such as combining MQL with other sustainable techniques to achieve optimum results,using biodegradable lubricants,and innovations in nozzle designs and delivery methods.This review presents an in-depth analysis of machining characteristics(e.g.,cutting forces,temperature,tool wear,chip morphology and surface integrity,etc.)and sustainability characteristics(e.g.,energy consumption,carbon emissions,processing time,machining cost,etc.)of conventional MQL and hybrid MQL techniques like cryogenic MQL,Ranque-Hilsch vortex tube MQL,nanofluids MQL,hybrid nanofluid MQL and ultrasonic vibration assisted MQL in machining of aeronautical materials.Subsequently,the latest research and developments are analyzed and summarized in the field of MQL,and provide a detailed comparison between each technique,considering advantages,challenges,and limitations in practical implementation.In addition,this review serves as a valuable source for researchers and engineers to optimize machining processes while minimizing environmental impact and operational costs.Ultimately,the potential future aspects of MQL for research and industrial execution are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.92263201,51927801,and 52001160)the National Key Research and Development Program of China(Grant No.2020YFA0405900).
文摘A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.
基金supported by the Tianjin Science and Technology Plan Project(No.22JCQNJC01280)the Central Funds Guiding the Local Science and Technology Development of Hebei Province(Nos.226Z1001G and 226Z1012G)+1 种基金the National Natural Science Foundation of China(No.52002109,52071124)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.
基金financially supported by the National Key K&D Program of China(No.2023YFE0200300)the National Natural Science Foundation of China(Nos.52174303and 51874084)the Program of Introducing Talents of Discipline to Universities(No.B21001)。
文摘Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the kinetics of reverse austenite transformation,strain hardening behavior,and toughening mechanism were further investigated.The lamellarized specimens possess low yield strength but high toughness,especially cryogenic toughness.Lamellarization leads to the development of film-like reversed austenite at the martensite block and lath boundaries,refining the martensite structure and lowering the equivalent grain size.Kinetic analysis of austenite reversion based on the JMAK model shows that the isothermal transformation is dominated by the growth of reversed austenite,and the maximum transformation of reversed austenite is reached at the peak temperature(750℃).The strain hardening behavior based on the modified Crussard-Jaoul analysis indicates that the reversed austenite obtained from lamellarization reduces the proportion of martensite,significantly hindering crack propagation via martensitic transformation during the deformation.As a consequence,the QLT specimens exhibit high machinability and low yield strength.Compared with the QT specimen,the ductile-brittle transition temperature of the QLT specimens decreases from-116 to-130℃due to the low equivalent grain size and reversed austenite,which increases the cleavage force required for crack propagation and absorbs the energy of external load,respectively.This work provides an idea to improve the cryogenic toughness of marine 10Ni5CrMoV steel and lays a theoretical foundation for its industrial application and comprehensive performance improvement.
基金supported by the National Natural Science Foundation of China(No.51775141)。
文摘The inherent brittle behavior and ductile-to-brittle transition(DBT)mechanism of Sn−3.0Ag−0.5Cu(SAC305)solder alloy at the liquid nitrogen temperature(LNT,77 K)were investigated through uniaxial tensile experiments conducted at different temperatures.Dynamic recovery and recrystallization of SAC305 solder alloy at room temperature(RT,293 K)activate a softening process.Conversely,intersecting and none-intersecting deformation twins,embedded in body-centered tetragonal Sn,enhance tensile strength and stabilize strain hardening rate,while suppressing the elongation of the alloy at LNT.The irreconcilable velocity difference between twin thickening(~8μm/s)and dislocation slip(4μm/s)results in premature brittle fracture,during the linear hardening and DBT.Moreover,the secondary phases degrade the mechanical property of SAC305 solder alloy,and micro-cracks appear between Cu_(6)Sn_(5)and Ag_(3)Sn in the eutectic matrix.
基金supported by the Henry Royce Institute for Advanced Materials,funded through Engineering and Physical Sciences Research Council(EPSRC)grants EP/R00661X/1,EP/S019367/1,EP/P025021/1,and EP/P025498/1.
文摘Liquefied natural gas storage and transportation as well as space propulsion systems have sparked inter-est in the martensitic transformation and behaviours of 316 L stainless steels(SS)under ultra-cryogenic deformation.In this study,high-resolution transmission electron microscopy(HRTEM)and molecular dy-namics(MD)simulations were used to investigate the atomic arrangements and crystalline defects of deformation-induced γ-austenite→ε-martensite→α'-martensite and γ→α'martensitic transforma-tions in 316 L SS at 15 and 173 K.Theγ→εtransformation involves the glide of Shockley partial dislocations on(111)γplanes without a change in atomic spacing.The formation of anα'inclusion in a singleε-band is achieved by a continuous lattice distortion,accompanied by the formation of a tran-sition zone ofα'and the expansion of the average atomic spacings due to dislocation shuffling.Asα'grows further intoγ,the orientation relationship(OR)of theα'changes by lattice bending.This pro-cess follows the Bogers-Burgers-Olson-Cohen model despite it not occurring on intersecting shear bands.Stacking faults and twins can also serve as nucleation sites forα'at 173 K.We also found that direct transformation of γ→α'occurs by the glide of √6aγ[11(2)]/12 dislocations on every(111)γplane with misfit dislocations.Overall,this study provides,for the first time,insights into the atomic-scale mech-anisms of various two-step and one-step martensitic transformations induced by cryogenic deformation and corresponding local strain,enhancing our understanding of the role of martensitic transformation under ultra-cryogenic-temperature deformation in controlling the properties.
基金supported in part by the National Key Research and Development Program of China(2021YFA0715503)。
文摘This brief presents a cryogenic voltage reference circuit designed to operate effectively across a wide temperature range from 30 to 300 K.A key feature of the proposed design is utilizing a current subtraction technique for temperature compensation of the reference current,avoiding the deployment of bipolar transistors to reduce area and power consumption.Implemented with a 0.18-μm CMOS process,the circuit achieves a temperature coefficient(TC)of 67.5 ppm/K,which was not achieved in previous works.The design can also attain a power supply rejection(PSR)of 58 d B at 10 k Hz.Meanwhile,the average reference voltage is 1.2 V within a 1.6%3σ-accuracy spread.Additionally,the design is characterized by a minimal power dissipation of 1μW at 30 K and a compact chip area of 0.0035 mm~2.
基金support from the National Natural Science Foundation of China(No.52271146)New 20 Items of Colleges and Universities in Jinan,China(No.202228111)University of Jinan Disciplinary Cross-Convergence Construction Project 2023,China(No.XKJC-202311).
文摘The effect of cryogenic treatment(CT)and relaxation annealing on the average nearest neighboring distance of atom(dm),ther-modynamic stability,soft magnetic properties,microhardness(Hv),and corrosion resistance of as-spun(Fe_(0.5)Co_(0.5))_(75)B_(21)Nb_(4) metallic glasses(MGs)is studied.On the premise of maintaining a fully amorphous phase,appropriate CT and relaxation annealing are conducive to achieving the synergistic effect of increasing saturation magnetization(M_(s))and reducing coercivity(H_(c)).Shallow CT at 213 K optim-ally enhances the soft magnetic properties of MGs.Given its low activation energy of nucleation and increased activation energy of growth,appropriate CT is beneficial for achieving uniform annealed nanocrystals in amorphous phases.The correlation between free volumes(FVs)and potential energy suggests that the variation in Hc depends on the expansion and contraction behavior of amorphous phases after different CT processes.The fitting formulas of H_(c)–d_(m) and Ms–Hv correlations demonstrate that soft magnetic parameters have a solid linear relationship with the contents of FVs and degree of dense random packing.Moreover,pitting resistance is improved by ap-propriate CT and relaxation annealing.This improvement is characterized by the promotion of the stability of the Nb-rich passive film formed during electrochemical corrosion in 3.5wt%NaCl solution.
基金supported by the National Natural Science Foundation of China(51976177)the National Key Research and Development Program of China(2022YFB4000047)。
文摘A cryogenic visible calibration and image evaluation facility(VCCIEF) was constructed to assess the effectiveness of electrical capacitance tomography systems in cryogenic conditions,known as Cryo-ECT.This facility was utilized to conduct dynamic,real-time imaging trials with liquid nitrogen(LN2).The actual flow patterns were captured using a camera and contrasted with the imaging outcomes.The capacitance data collected from these experiments were subsequently processed using three distinct methods:linear back projection,Landweber iteration,a fully connected deep neural network,and a convolutional neural network.This allowed for a comparative analysis of the performance of these algorithms in practical scenarios.The findings from the LN2 experiments demonstrated that the Cryo-ECT system,when integrated with the VCCIEF,was capable of successfully executing calibration,generating flow patterns,and performing imaging tasks.The system provided observable,clear,and precise phase distributions of the liquid nitrogen-vaporous nitrogenflow within the pipeline.
基金supported by the National Natural Science Foundation of China(Nos.52371025 and 52371106)Guangdong Major Project of Basic and Applied Basic Research(No.2020B0301030001)Shenzhen Fund 2021 Basic Research General Programme(No.JCYJ20210324115400002).
文摘This work investigates how temperature and microstructural evolution affect the formability of face-centered cubic(fcc)structured CoCrFeNiMn_(0.75)Cu_(0.25) high entropy alloy(HEA)sheets under complex stress conditions.Erichsen cupping tests were conducted to quantitatively evaluate the deformation capacity at room temperature(298 K)and cryogenic temperatures.The findings reveal a strong temperature dependence on the formability of the HEA.A decrease in the deformation temperature from 298 to 93 K causes a significant increase in both the Erichsen index(IE)(from 9.8 to 12.4 mm)and the expansion rate(δ)of surface area(from 51.6%to 76.3%),as well as a reduction in the average deviation(η)of thickness(from 55.1%to 44.4%),signifying its ultrahigh formability and uniform deformation capability at cryogenic temperature.This enhancement is attributed to the transition in the deformation mechanism from single dislocation slip at 298 K to a cooperative of plastic deformation mechanisms at 93 K,involving dislocation slip,stacking faults(SFs),Lomer-Cottrell(L-C)locks and multi-scale nanotwins.The lower stacking fault energy of the alloy facilitates these deformation mechanisms,particularly the formation of SFs and nanotwins,which enhance ductility and strength by providing additional pathways for plastic deformation.These mechanisms collectively contribute to delaying plastic instability,thereby improving the overall formability.This work provides a comprehensive understanding of the underlying reasons for the enhanced formability of HEAs at cryogenic temperatures,offering valuable insights for their practical use in challenging environments.
基金supported by the National Natural Science Foundation of China(Nos.52474403,52364050 and 52301137)Guizhou Provincial Program on Commercialization of Scientific and Technological Achievements(No.[2023]001)+2 种基金Guizhou Province Science and Technology Project(No.[2022]050)Guiyang city Science and Technology Project(No.[2023]48-16)the Central Government in Guidance of Local Science and Technology Development Funds(No.[2024]032).
文摘The serrated flow behavior,known as the Portevin-Le Chatelier(PLC)effect,is commonly observed during high-temperature deformation.In this study,we report a serrated flow behavior in FeCoCrNiMo0.2 high-entropy alloy(HEA),which is mediated by nano-twinning and phase transformation at cryogenic temperatures.During uniaxial tensile deformation at 77 K,the alloy exhibited the formation of high-density deformation nano-twinning,cross-twinning,stacking faults(SFs)and Lomer-Cottrell locks(L-C locks).Additionally,the lower stacking fault energy(SFE)at low temperatures promotes the formation of the 9R phase.The high-density twin boundaries effectively hinder dislocation movement,leading to the instability of plastic deformation and promoting the serrated flow behavior.Furthermore,the rapid and unstable transformation of the 9R phase contributes to the pronounced serrated flow behavior.Nano-twinning,SFs,cross-twinning,L-C locks and 9R phase collectively induce a dynamic Hall-Petch effect,enhancing the strength-ductility synergy and strain-hardening ability of deformed alloy at 77 K.Our work provides valuable insights into the mechanism of tensile deformation at cryogenic temperatures in single-phase FCC HEA.
基金financially supported by Shandong Province Aluminum Manufacturing and Application Innovation and Entrepreneurship Community projectShandong Province key Research and Development Plan(2021ZLGX01,2021SFGC1001,2023CXPT024)Shandong Province Youth Taishan project。
文摘Near-eutectic Al-Si alloys are widely used in automotive manufacturing due to their superior wear resistance and high temperature performance.Because of high Si content,the grain refinement of near-eutectic Al-Si alloy has been a problem for many years.In this study,the effect of deep cryogenic treatment(DCT)on the microstructure and mechanical properties of Al-12Si-4Cu-2Ni-Mg alloy with addition of Al-Ti-C-B master alloy was fully investigated.Results show that the average grain size of the alloy is greatly reduced from 0.92 mm to 0.50 mm,and the eutectic Si and Al7Cu4Ni precipitates are spheroidized and refined in Al-12Si-4Cu-2Ni-Mg after DCT for 24 h and aging treatment.Thereby these changes of microstructures result in a significant increment of about 22.5%in elongation and a slight enhancement of about 6.8%in tensile strength.Moreover,the refinement of microstructure also significantly improves the fatigue life of the alloy.
基金Project(2021GK1040) supported by the Major Projects of Scientific and Technology Innovation of Hunan Province,ChinaProjects(52375398,52171018) supported by the National Natural Science Foundation of China+1 种基金Project(Kfkt2023-09) supported by the Open Research Fund of State Key Laboratory of Precision Manufacturing for Extreme Service Performance,Central South University,ChinaProject(E2021203059) supported by the Natural Science Foundation of Hebei Province,China。
文摘This study investigates the differences in microstructural control between cryogenic forging combined with pre-deformation(PCF)and traditional thermal forging(TTF)for 7050 aluminum forgings intended for aerospace applications.The PCF process,utilizing cryogenic deformation,significantly refines the coarse grains at the surface of the forgings,resulting in a finer and more uniform microstructure,thereby effectively addressing the issue of surface coarse grains associated with traditional methods.The findings indicate that the PCF process can accumulate higher stored energy,facilitating static recrystallization(SRX)during subsequent heat treatment and enhancing the microstructural uniformity.Utilizing various analytical techniques,including optical microscopy(OM),electron backscatter diffraction(EBSD),and transmission electron microscopy(TEM).This study reveals the superiority of the PCF process in terms of strain accumulation,dislocation density,and grain refinement.In conclusion,this method offers advantages in enhancing the performance and microstructural uniformity of 7050 aluminum forgings,presenting new opportunities for applications in the aluminum forging industry.
基金financially supported by the National Natural Science Foundation of China(Nos.52301061,52204394)the Joint Fund Project of Science and Technology Plan of Liaoning Province(No.2023-MSLH-250)the Science and the Technology Program of Liaoning Provincial Department of Education(No.JYTQN2023286)。
文摘As a typical eutectic high-entropy alloy(EHEA),AlCoCrFeNi2.1 exhibits excellent casting properties.However,the imbalance between strength and plasticity hinders its application as an advanced structural material.In order to address this challenge,deep cryogenic treatment(DCT)as a new process applied in the field of EHEAs was proposed in this study.The effects of different DCT times on the microstructure and mechanical properties of AlCoCrFeNi2.1 EHEAs were studied,mainly focusing on the flake structure of FCC+B2 layer.The experimental results suggest that with the extension of the DCT time,the dislocation density in the FCC phase increases significantly.The spherical BCC precipitate phase is generated within the B2 phase,and the average size of this newly generated precipitate phase gradually decreases.Increasing the number of dislocations and precipitate phases is of great significance to improve the mechanical properties.The AlCoCrFeNi2.1 EHEA exhibits excellent comprehensive mechanical properties after DCT for 36 h.Compared with the as-cast state,the tensile strength at room temperature reaches 1,034.51 MPa,increased by 5.74%.The plasticity reaches 21.72%,which is increased by 11.79%.The results show that the tensile strength and ductility of AlCoCrFeNi2.1 EHEAs are balanced and improved after DCT,which are more suitable as advanced structural materials.In addition,the introduction of the DCT process to EHEAs solves the problem of environmental pollution caused by traditional heat treatment process.This study provides useful guidance for using the DCT process to strengthen the mechanical properties of“lamellar+block”type EHEAs.
基金supported by the National Natural Science Foundation of China(Nos.52275322 and 51875127).
文摘In this study,Mg-Gd-Y-(Sm)-Zr(GW-(Sm))alloys were subjected to compression tests at both 293 and 77 K.The effect of Sm addition on the plastic deformation mechanism of Mg-Gd-Y-Zr(GW)alloy was investigated,and a detailed analysis was conducted on the relationships between mechanical responses and the microstructure of the alloys.The findings suggest that dislocation slip plays a predominant role in the plastic deformation of GW-(Sm)alloys.The addition of Sm reduces the stacking fault energy(SFE)of the alloy,which promotes<c+a>slip and inhibits twinning.Meanwhile,Sm plays a role in solution strengthening,causing an elevation in the flow stress of the alloy.At cryogenic temperature(CT),the critical resolved shear stress(CRSS)of dislocation slip is increased,so the dislocation motion requires greater external force.In addition,the extensive crossed twins exhibited in the microstructure,which shorten the dislocation slip path and enhance the grain boundary strengthening.This research contributes to the advancement of plastic deformation theories for magnesium-rare earth(Mg-RE)alloys.
基金supported by the National Natural Science Foundation of China(Nos.U21A20399 and 52274407)Liaoning Province Applied Basic Research Program(No.2022JH2/101300212).
文摘In this work,we aim to develop a novel post-treatment process combining cryogenic and pulsed electric field treatment to enhance WC-Co cemented carbides.The results show a 15.62%increase in hardness from 1831.38 to 2117.38 HV30,a 9.60%rise in fracture toughness from 9.06 to 9.93 MPa·m^(1/2),while the friction coefficient decreases from 0.63 to 0.47.Through the residual stress evolution,WC orientation change and the martensitic transformation of Co,and the internal enhancement mechanism of cryogenic combined with pulsed electric field treatment are revealed.The electron wind generated by the pulsed electric field can efficiently reduce the residual stress induced by cryogenic process.The evolution of residual stress promotes the base slip of WC,increasing the degree of{0001}orientation.In addition,the degree of martensitic transformation of Co intensifies,with the hcp-Co/fcc-Co ratio rising from 0.41%to 17.86%.The enhanced WC{0001}orientation and increased hcp-Co content contribute to significant improvements in hardness and wear resistance.This work provides a novel efficient enhancement strategy for ceramics and alloys,with the potential to be a mainstream strengthening method in the future.
基金supported by the National Natural Science Foundation of China(No.52171174).The authors acknowledge Dr.Chao Zhang from the Instrumentation Service Center for Physical Sciences at Westlake University for magnetization measurements.
文摘Cryogenic magnetic cooling based on the principle of the magnetocaloric effects(MCEs)of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits.Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications.In this study,three gadolinium-transition metal-based high entropy oxides(HEOs)of Gd(Fe_(1/4)Ni_(1/4)Al_(1/4)Cr_(1/4))O_(3),Gd(Fe_(1/5)Ni_(1/5)Al_(1/5)Cr_(1/5)Co_(1/5))O_(3),and Gd(Fe_(1/6)Ni_(1/6)Al_(1/6)Cr_(1/6)Co_(1/6)Mn_(1/6))O_(3)were designed and systematically characterized regarding their structural and cryogenic magnetic properties.These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure,reveal a second-order magnetic transition at low temperatures,and exhibit significant cryogenic MCEs.The magnetocaloric performances of the present HEOs,identified by magnetic entropy changes,relative cooling power,and temperature-averaged entropy changes,were com-parable with recently reported candidate materials.The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances.
文摘Hydrogen-induced cracking (HIC) is one of the most complex material problems that hydrogen can diffuse into and interact with microstructure, degrading their mechanical properties. Microstructural modification is an effective way to enhance the resistance to HIC. The present study focused on the relationship between the retained austenite (RA) and HIC behavior in NiCrMoV/Nb multi-alloying ultra-strength steel. Results demonstrated that the maximum volume fraction of RA of 9.31% was obtained for QL30T specimen. After the deep cryogenic pretreatment, the volume fraction of RA reduced to 8.8%. RA could reduce the effective diffusion coefficient, while deep cryogenic pretreatment increased the susceptibility of the steel to HIC by a maxim of 14.8%. This was mainly due to the transformation of retained austenite into martensite, degrading the mechanical properties under hydrogen-charged condition. In addition, the deep cryogenic pretreatment had a significant effect on the crack initiation and propagation, with the intergranular (IG) fracture becoming the dominant fracture mode where an increase in the number of secondary cracks in the section. The interfaces of RA and matrix, as well as the grain boundaries, were the preferred sites for cracks initiation.
