The water-quenched(WQ)2195 Al−Li alloy was subjected to stretching at different temperatures,from room temperature(RT)to−196℃(CT),to investigate the effect of cryogenic deformation on the aging precipitation behavior...The water-quenched(WQ)2195 Al−Li alloy was subjected to stretching at different temperatures,from room temperature(RT)to−196℃(CT),to investigate the effect of cryogenic deformation on the aging precipitation behaviors and mechanical properties.The precipitation kinetics of the T1 phase and the microstructures in peak aging state were investigated through the differential scanning calorimetric(DSC)tests and electron microscopy observation.The results show that−196℃deformation produces a high dislocation density,which promotes the precipitation of the T1 phase and refines its sizes significantly.In addition,the grain boundary precipitates(GBPs)of−196℃-stretched samples are suppressed considerably due to the high dislocation density in the grain interiors,which increases the ductility.In comparison,the strength remains nearly constant.Thus,it is indicated that cryogenic forming has the potential to provide the shape and property control for the manufacture of critical components of aluminum alloys.展开更多
Strain rate is a critical factor influencing the mechanical response of hexagonal close-packed titanium under cryogenic conditions.In this study,uniaxial tensile tests were performed on commercially pure titanium at 7...Strain rate is a critical factor influencing the mechanical response of hexagonal close-packed titanium under cryogenic conditions.In this study,uniaxial tensile tests were performed on commercially pure titanium at 77 K over a broad strain rate range from 0.001 to 1 s^(-1).A critical strain rate of approximately 0.5 s^(-1)was identified,above which ductility exhibits a pronounced reduction,whereas below this threshold,ductility remains relatively stable.Through comprehensive analyses of strain evolution,deformed microstructure,and fracture morphology,this behavior is attributed to severe localized adiabatic heating resulting from inhomogeneous deformation,rather than conventional twin or shear mechanisms.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
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
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 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
The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by c...The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.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,we comprehensively characterized and optimized a cryogenic pure CsI(pCsI)detector.We utilized a 2 cm×2 cm×2 cm cube crystal coupled with a HAMAMATSU R11065 photomultiplier tube,achieving a rema...In this study,we comprehensively characterized and optimized a cryogenic pure CsI(pCsI)detector.We utilized a 2 cm×2 cm×2 cm cube crystal coupled with a HAMAMATSU R11065 photomultiplier tube,achieving a remarkable light yield of 35.2 PE/ke V_(ee)and an unprecedented energy resolution of 6.9%at 59.54 ke V.Additionally,we measured the scintillation decay time of pCsI,which was significantly shorter than that of CsI(Na)at room temperature.Furthermore,we investigated the impact of temperature,surface treatment and crystal shape on light yield.Notably,the light yield peaked at approximately 20 K and remained stable within the range of 70–100 K.The light yield of the polished crystals was approximately 1.5 times greater than that of the ground crystals,whereas the crystal shape exhibited minimal influence on the light yield.These results are crucial for the design of the 10 kg pCsI detector for the future CLOVERS(coherent elastic neutrino(V)-nucleus scattering at China Spallation Neutron Source(CSNS))experiment.展开更多
Magnesium(Mg)alloys typically suffer from cold brittleness at cryogenic temperatures(CT),where strength significantly increases and ductility decreases with decreasing temperature.This study investigates the improveme...Magnesium(Mg)alloys typically suffer from cold brittleness at cryogenic temperatures(CT),where strength significantly increases and ductility decreases with decreasing temperature.This study investigates the improvement of the strength-ductility balance at CT in Mg-3.6Y(wt.%)alloys with a bimodal grain structure,consisting of fine dynamically recrystallized(DRXed)grains and elongated unDRXed grains.The results demonstrate that the sample with∼50%DRXed region fraction achieves a remarkable strength-ductility synergy at CT.Dislocation strengthening in the unDRXed regions and grain boundary strengthening in the DRXed regions increase the tensile yield strength(TYS)by 1.6 times at CT compared to room temperature(RT).Concurrently,activation of{10¯12}tensile twinning and non-basal slip systems in DRXed regions,including prismatic a and pyramidal I c+a slips,along with abnormal pyramidal slip within unDRXed grains,reduces fracture elongation by only 1%relative to RT.Furthermore,the bimodal grain structure effectively alleviates strain localization through strain partitioning between DRXed and unDRXed grains,leading to the formation of interface-affected zones(IAZs)that promote the accumulation of geometrically necessary dislocations(GNDs)and enhance hetero-deformation-induced(HDI)hardening.At CT,the IAZs become wider and more pronounced,indicating enhanced GND accumulation that promotes stronger strain partitioning and more effective HDI strengthening.This work demonstrates that the bimodal grain structure is an effective approach to overcoming the low-temperature brittleness of Mg alloys,providing valuable insights for the design of high-performance materials for cryogenic applications.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
The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonmen...The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonment.Although commonly used,conventional stimulation techniques such as hydraulic fracturing and acidizing pose environmental risks,high costs,and sensitivity to fluctuations in crude oil prices.Meanwhile,cryogenic liquid nitrogen(LN2)treatment has emerged as an innovative,eco-friendly alternative due to its thermal shock effects,which enhance rock permeability and porosity.Herein,SML core samples are treated with LN2 for 30,60,and 90 min to obtain samples designated as SML_30,SML_60,and SML_90,respectively.These are examined using X-ray diffraction(XRD),atomic force microscopy(AFM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),nanoindentation,and petrophysical measurements to evaluate the changes in their petrophysical,morphological,and micromechanical properties.The post-treatment analysis reveals that LN2 cooling effectively induces micro-cracks,with fracture widths of up to 40μm,along with a substantial increase in surface roughness from 350 to 942 nm.Additionally,micromechanical analysis indicates notable changes in the indentation modulus due to stress-induced alterations in the rock matrix.At optimal LN2 exposure(90 min),the porosity and permeability of the SML sample is more than doubled.These findings provide valuable insights into LN2-induced reservoir enhancements,thereby contributing to a better understanding of fluid flow behavior and hydrocarbon recovery in tight gas reservoirs.Thus,LN2 treatment presents a promising,cost-effective,and environmentally sustainable alternative to conventional stimulation methods.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
In this paper,the multi cross-rolling and cryogenic treatment were adopted to process the AZ31 Mg alloy to study the influence of passes and cryogenic treatment on cross-rolled AZ31 Mg alloy.The tensile properties and...In this paper,the multi cross-rolling and cryogenic treatment were adopted to process the AZ31 Mg alloy to study the influence of passes and cryogenic treatment on cross-rolled AZ31 Mg alloy.The tensile properties and hardness were tested.The microstructure was characterized using electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM)in order to elucidate the influencing mechanism.The results indicate that the treatment method can significantly improve the mechanical properties of AZ31 Mg alloy.The 3-pass sample processed by cryogenic treatment shows the highest strength(351 MPa)and has the highest hardness(76.1HV)and best hardness uniformity(standard deviation=0.9HV).The 2-pass sample has the highest ductility among all the samples but poor hardness evenness.The strengthening mechanism of 3-pass sample can be attributed to the fine grains,bimodal structure,high dislocation density,and precipitation strengthening.Due to repeated heat preservation of 4-pass and 5-pass,their comprehensive performances decrease.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
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
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
The application of radiofrequency(RF)electron guns operating at cryogenic temperatures can enhance the performance of a photoinjector.The low emittance and increased brightness of the electron beams resulting from the...The application of radiofrequency(RF)electron guns operating at cryogenic temperatures can enhance the performance of a photoinjector.The low emittance and increased brightness of the electron beams resulting from the high gradient in the cryogenic photoinjector make it possible to improve the performance of new light sources.As an upgrading scheme for the Shanghai Soft X-ray Free-Electron Laser,this study explores a novel photocathode RF gun by introducing the TM_(02)mode into the cathode cell of a 2.6-cell electron gun,which improves the RF performance,particularly in terms of the monopole field.Furthermore,the optimized cathode cell with the TM_(02)mode can reduce the errors resulting from installation and decrease the dark current with alternative cathodes.In this study,the beam dynamics in a photoinjector were optimized using a 500-pC,5-ps beam,and its feasibility was examined.This paper presents the entire RF design process,including the adjustment of the RF structure,coupler design,local field,and multipole mode suppression to provide theoretical guidance for subsequent manufacturing and assembly.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
基金financially supported by the National Key Research and Development Program of China (No. 2019YFA0708801)the National Natural Science Foundation of China (No. 51875125)。
文摘The water-quenched(WQ)2195 Al−Li alloy was subjected to stretching at different temperatures,from room temperature(RT)to−196℃(CT),to investigate the effect of cryogenic deformation on the aging precipitation behaviors and mechanical properties.The precipitation kinetics of the T1 phase and the microstructures in peak aging state were investigated through the differential scanning calorimetric(DSC)tests and electron microscopy observation.The results show that−196℃deformation produces a high dislocation density,which promotes the precipitation of the T1 phase and refines its sizes significantly.In addition,the grain boundary precipitates(GBPs)of−196℃-stretched samples are suppressed considerably due to the high dislocation density in the grain interiors,which increases the ductility.In comparison,the strength remains nearly constant.Thus,it is indicated that cryogenic forming has the potential to provide the shape and property control for the manufacture of critical components of aluminum alloys.
基金financially supported by the National Key Research&Development Plan(No.2022YFE0110600)the National Natural Science Foundation of China(Nos.52171117,52371113,92263201 and 52175306)+3 种基金Qing Lan Project(No.54944004)the Basic Research Program of Jiangsu(Nos.BK20232011 and BK20232025)the Postdoctoral Fellowship Program of CPSF(No.GZC20233481)Tuoyuan project of Nanjing Tech University(No.20230113)
文摘Strain rate is a critical factor influencing the mechanical response of hexagonal close-packed titanium under cryogenic conditions.In this study,uniaxial tensile tests were performed on commercially pure titanium at 77 K over a broad strain rate range from 0.001 to 1 s^(-1).A critical strain rate of approximately 0.5 s^(-1)was identified,above which ductility exhibits a pronounced reduction,whereas below this threshold,ductility remains relatively stable.Through comprehensive analyses of strain evolution,deformed microstructure,and fracture morphology,this behavior is attributed to severe localized adiabatic heating resulting from inhomogeneous deformation,rather than conventional twin or shear mechanisms.
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 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 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 by the Science and Technology Planning Joint Program of Liaoning Province(Applied Basic Research Project,No.2023JH2/101700054).
文摘The present work aims to investigate the effects of quenching, lamellarizing, and tempering(QLT)heat treatment on the microstructure and mechanical properties of ZG14Ni3Cr1Mo V high-strength low-alloy(HSLA) steel by comparing with traditional quenching and tempering(QT) heat treatment. Following the various QLT heat treatments, a dual-phase microstructure consisting of “soft” ferrite and “hard” tempered bainite is obtained, exhibiting significantly refined grain sizes(38.87 to 46.51 μm for QLT samples) compared to QT samples(64.93 μm). As the lamellar quenching temperature increases from 750 ℃ to 810 ℃, the yield strength and tensile strength of the QLT samples increase, although they remain lower than those of the QT samples. Conversely, elongation at fracture, reduction of area, and the product of strength and elongation synergy decrease, yet consistently exceed QT levels. Notably, the QLT samples demonstrate superior cryogenic impact toughness within the range of-80 ℃ to-120 ℃, achieving optimal values after 910 ℃ quenching + 780 ℃ lamellar quenching + 670 ℃ tempering: 215.97 J at-80 ℃, 207.80 J at-100℃, and 183.17 J at-120 ℃. This exceptional cryogenic toughness is attributed to two key mechanisms in the dual-phase microstructure:(i) a low dislocation density that suppresses crack initiation, and(ii) crack-tip passivation by soft ferrite, coupled with crack deflection and hindrance at high-angle grain boundaries(HAGBs). The results establish QLT as a viable method for enhancing cryogenic toughness in ZG14Ni3Cr1Mo V HSLA steels.
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 Key R&D Program of China(No.2022YFA1602204)the National Natural Science Foundation of China(Nos.12175241,12221005)+2 种基金the Fundamental Research Funds for the Central Universitiesthe International Partnership Program of the Chinese Academy of Sciences(No.211134KYSB20200057)the Double First-Class University Project Foundation of USTC。
文摘In this study,we comprehensively characterized and optimized a cryogenic pure CsI(pCsI)detector.We utilized a 2 cm×2 cm×2 cm cube crystal coupled with a HAMAMATSU R11065 photomultiplier tube,achieving a remarkable light yield of 35.2 PE/ke V_(ee)and an unprecedented energy resolution of 6.9%at 59.54 ke V.Additionally,we measured the scintillation decay time of pCsI,which was significantly shorter than that of CsI(Na)at room temperature.Furthermore,we investigated the impact of temperature,surface treatment and crystal shape on light yield.Notably,the light yield peaked at approximately 20 K and remained stable within the range of 70–100 K.The light yield of the polished crystals was approximately 1.5 times greater than that of the ground crystals,whereas the crystal shape exhibited minimal influence on the light yield.These results are crucial for the design of the 10 kg pCsI detector for the future CLOVERS(coherent elastic neutrino(V)-nucleus scattering at China Spallation Neutron Source(CSNS))experiment.
基金supported by National Key Research&Development Program of China[grant number 2022YFE0110600]National Natural Science Foundation[grant number 52220105003]the State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology[grant number XNDCQQ2910201124].
文摘Magnesium(Mg)alloys typically suffer from cold brittleness at cryogenic temperatures(CT),where strength significantly increases and ductility decreases with decreasing temperature.This study investigates the improvement of the strength-ductility balance at CT in Mg-3.6Y(wt.%)alloys with a bimodal grain structure,consisting of fine dynamically recrystallized(DRXed)grains and elongated unDRXed grains.The results demonstrate that the sample with∼50%DRXed region fraction achieves a remarkable strength-ductility synergy at CT.Dislocation strengthening in the unDRXed regions and grain boundary strengthening in the DRXed regions increase the tensile yield strength(TYS)by 1.6 times at CT compared to room temperature(RT).Concurrently,activation of{10¯12}tensile twinning and non-basal slip systems in DRXed regions,including prismatic a and pyramidal I c+a slips,along with abnormal pyramidal slip within unDRXed grains,reduces fracture elongation by only 1%relative to RT.Furthermore,the bimodal grain structure effectively alleviates strain localization through strain partitioning between DRXed and unDRXed grains,leading to the formation of interface-affected zones(IAZs)that promote the accumulation of geometrically necessary dislocations(GNDs)and enhance hetero-deformation-induced(HDI)hardening.At CT,the IAZs become wider and more pronounced,indicating enhanced GND accumulation that promotes stronger strain partitioning and more effective HDI strengthening.This work demonstrates that the bimodal grain structure is an effective approach to overcoming the low-temperature brittleness of Mg alloys,providing valuable insights for the design of high-performance materials for cryogenic applications.
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.
文摘The Early Eocene Sui Main Limestone(SML)reservoirs in the Qadirpur area are significant hydrocarbon-producing formations but suffer from low permeability and poor reservoir characteristics that lead to well abandonment.Although commonly used,conventional stimulation techniques such as hydraulic fracturing and acidizing pose environmental risks,high costs,and sensitivity to fluctuations in crude oil prices.Meanwhile,cryogenic liquid nitrogen(LN2)treatment has emerged as an innovative,eco-friendly alternative due to its thermal shock effects,which enhance rock permeability and porosity.Herein,SML core samples are treated with LN2 for 30,60,and 90 min to obtain samples designated as SML_30,SML_60,and SML_90,respectively.These are examined using X-ray diffraction(XRD),atomic force microscopy(AFM),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),nanoindentation,and petrophysical measurements to evaluate the changes in their petrophysical,morphological,and micromechanical properties.The post-treatment analysis reveals that LN2 cooling effectively induces micro-cracks,with fracture widths of up to 40μm,along with a substantial increase in surface roughness from 350 to 942 nm.Additionally,micromechanical analysis indicates notable changes in the indentation modulus due to stress-induced alterations in the rock matrix.At optimal LN2 exposure(90 min),the porosity and permeability of the SML sample is more than doubled.These findings provide valuable insights into LN2-induced reservoir enhancements,thereby contributing to a better understanding of fluid flow behavior and hydrocarbon recovery in tight gas reservoirs.Thus,LN2 treatment presents a promising,cost-effective,and environmentally sustainable alternative to conventional stimulation methods.
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Project(52174362)supported by the National Natural Science Foundation of ChinaProject(2023JJ10020)supported by the Natural Science Foundation of Hunan Province,China+3 种基金Project(2024RC7002)supported by the Science and Technology Innovation Program of Hunan Province,ChinaProject(2024CY2-GJHX-71)supported by the Shaanxi Provincial Key R&D ProgramProject supported by the Yancheng“Talent Plan of Yellow Sea Pearl”for Leading Talent Project,ChinaProject(2019GK1012)supported by the Hunan Innovative Province Construction Special Program,China。
文摘In this paper,the multi cross-rolling and cryogenic treatment were adopted to process the AZ31 Mg alloy to study the influence of passes and cryogenic treatment on cross-rolled AZ31 Mg alloy.The tensile properties and hardness were tested.The microstructure was characterized using electron backscatter diffraction(EBSD),transmission electron microscopy(TEM),and scanning electron microscopy(SEM)in order to elucidate the influencing mechanism.The results indicate that the treatment method can significantly improve the mechanical properties of AZ31 Mg alloy.The 3-pass sample processed by cryogenic treatment shows the highest strength(351 MPa)and has the highest hardness(76.1HV)and best hardness uniformity(standard deviation=0.9HV).The 2-pass sample has the highest ductility among all the samples but poor hardness evenness.The strengthening mechanism of 3-pass sample can be attributed to the fine grains,bimodal structure,high dislocation density,and precipitation strengthening.Due to repeated heat preservation of 4-pass and 5-pass,their comprehensive performances decrease.
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 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supported by the National Natural Science Foundation of China(Nos.12222513 and 12405178)。
文摘The application of radiofrequency(RF)electron guns operating at cryogenic temperatures can enhance the performance of a photoinjector.The low emittance and increased brightness of the electron beams resulting from the high gradient in the cryogenic photoinjector make it possible to improve the performance of new light sources.As an upgrading scheme for the Shanghai Soft X-ray Free-Electron Laser,this study explores a novel photocathode RF gun by introducing the TM_(02)mode into the cathode cell of a 2.6-cell electron gun,which improves the RF performance,particularly in terms of the monopole field.Furthermore,the optimized cathode cell with the TM_(02)mode can reduce the errors resulting from installation and decrease the dark current with alternative cathodes.In this study,the beam dynamics in a photoinjector were optimized using a 500-pC,5-ps beam,and its feasibility was examined.This paper presents the entire RF design process,including the adjustment of the RF structure,coupler design,local field,and multipole mode suppression to provide theoretical guidance for subsequent manufacturing and assembly.
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.
