Reliable ferroelectricity down to cryogenic temperature in wakeup free Hf_(0.5)Zr_(0.5)O_(2)thin films by thermal atomic layer deposition

The performance and reliability of ferroelectric thin films at temperatures around a few Kelvin are critical for their application in cryo-electronics.In this work,TiN/Hf_(0.5)Zr_(0.5)O_(2)/TiN capacitors that are free from the wake-up effect are investigated systematically from room temperature(300 K)to cryogenic temperature(30 K).We observe a consistent decrease in permittivity(εr)and a progressive increase in coercive electric field(Ec)as temperatures decrease.Our investigation reveals exceptional stability in the double remnant polarization(2P_(r))of our ferroelectric thin films across a wide temperature range.Specifically,at 30 K,a 2P_(r)of 36μC/cm^(2)under an applied electric field of 3.0 MV/cm is achieved.Moreover,we observed a reduced fatigue effect at 30 K in comparison to 300 K.The stable ferroelectric properties and endurance characteristics demonstrate the feasibility of utilizing HfO_(2)based ferroelectric thin films for cryo-electronics applications.

Research and Prediction on the Properties of Concrete at Cryogenic Temperature Based on Gray Theory

To solve the cryogenic temperature problems faced by all-concrete liquefied natural gas(ACLNG)storage tanks during servicing,a low temperature resistant and high strength concrete(LHC)was designed from the perspectives of reducing water-binder ratio,removing coarse aggregates,optimizing composite mineral admixture and utilizing steel fibers.The variation laws of compressive and tensile strength,elastic modulus and Poisson’s ratio for C60 concrete and LHC were compared and analyzed under the temperatures from 10 to-165℃through uniaxial compression and tensile tests.The rapid freezing method was adopted to analyze the evolution process of mass and relative dynamic elastic modulus loss rates for C60 and LHC in 0-300 freeze-thaw cycles.The gas permeability test was carried out,and the laws of gas permeability coefficient varied with temperature and cryogenic freeze-thaw cycles were obtained.Then,the grey dynamic model GM(1,1)was used to predict the variation laws of physical and mechanical parameters on the basis of the test data.The test results demonstrate that the compressive strength,elastic modulus and Poisson’s ratio for both C60 and LHC increase significantly from 10 to-165℃,but the specific variation laws are difierent,and there is a phenomenon that some parameters decrease after reaching a critical temperature range for C60.The uniaxial tensile strength increases first and then decreases as temperature decreases,and finally increases slightly at-165℃for both C60 and LHC.The mass and relative dynamic elastic modulus loss rates of LHC are much lower than that of C60 under different freeze-thaw cycles.The gas permeability coefficient of C60 declines gradually with the drop of temperature,and increases gradually with the number of freeze-thaw cycles while the gas permeability coefficient of LHC basically remains stable and is much lower than that of C60.Therefore,such a conclusion can be drawn that LHC has better properties at cryogenic temperature.On the premise of providing consistent functional mode,GM(1,1)can predict the test data with high accuracy,which well reflects the variation laws of relevant parameters.

Microstructural characteristics of AZ31 alloys rolled at room and cryogenic temperatures and their variation during annealing

This study investigates the microstructural characteristics of AZ31 Mg alloys rolled at room temperature(RT)and cryogenic temperature(CT)and the variation in their microstructure and hardness during subsequent annealing.Cryorolling induces the formation of more side cracks than does RT rolling,because of the reduction in the ability of the material to accommodate deformation at CT.Numerous{10-11}contraction and{10-11}-{10-12}double twins are formed in both the material rolled at RT and that rolled at CT,because the grains of the initial material are favorably oriented for{10-11}twinning under rolling.The RT-rolled material has a higher dislocation density than the cryorolled material,and more twins are uniformly distributed throughout the former material.As a result,static recrystallization during subsequent annealing is more pronounced in the RT-rolled material,which results in the formation of a highly recrystallized homogeneous microstructure after annealing.In contrast,the formed twins are predominantly present along the shear bands in the cryorolled material,as a result of which this material has an inhomogeneous bi modal structure containing a large amount of coarse unrecrystallized grains after annealing.The hardness of the annealed RT-rolled material is higher than that of the annealed cryorolled material owing to the finer grain structure of the former.

THERMAL CONDUCTIVITY OF Al-Li ALLOY AT CRYOGENIC TEMPERATURES

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Experimental Study on Bonding Properties Between Steel Strand and Concrete at Cryogenic Temperatures

To study the bonding properties between steel strand and concrete at room and cryogenic temperatures, a series of center pullout experiments were conducted on 96 bonding anchorage specimens at the lowest temperature of-165 ℃. The impacts on the bonding property of such parameters as the temperature, concrete strength, the relative concrete cover thickness, and the relative anchorage length were analyzed. The test results indicate that the changes in temperature have a clear effect on the bonding property between steel strand and concrete. As the temperature decreases, the bond stress, which corresponds to a 1 mm slip of steel strand in relation to concrete, and the ultimate bond strength initially increase and subsequently decrease at the inflection point of-80 ℃. The impact of the concrete strength on the bonding property, as shown by the tensile strength and the moisture content interaction, indicates that the bond stress vs concrete strength curve initially increases and later decreases with a decrease in temperature; the bond stress vs concrete cover thickness curve linearly increases, but the bond stress vs anchorage length curve linearly decreases at first and finally levels off.

Numerical simulation of deep cryogenic treatment electrode tip temperature for spot welding aluminum alloy

Deep cryogenic treatment technology of electrodes is put forward to improve electrode life of resistance spot welding of aluminum alloy LF2. Deep cryogenic treatment makes electrode life for spot welding aluminum alloy improve. The specific resistivity of the deep cryogenic treatment electrodes is tested and experimental results show that specific resistivity is decreased sharply. The temperature field and the influence of deep cryogenic treatment on the electrode tip temperature during spot welding aluminium alloy is studied by numerical simulation method with the software ANSYS. The axisymmetric finite element model of mechanical, thermal and electrical coupled analysis of spot welding process is developed. The numerical simulation results show that the influence of deep cryogenic treatment on electrode tip temperature is very large.

Phenomenological modelling of flow behaviour of 20MnMoNi55 reactor pressure vessel steel at cryogenic temperature with different strain rates

In the present study a phenomenological constitutive model is developed to describe the flow behaviour of 20MnMoNi55 low carbon reactor pressure vessel (RPV) steel at sub-zero temperature under different strain rates. A set of uniaxial tensile tests is done with the variation of strain rates and temperature ranging from 10^-4s^-1 to 10^-1s^-1 and -80℃ to 140℃ respectively. From the experimental data, family of flow curves at different temperatures and strain rates are generated and fitted exponentially. The strain rate and temperature dependence of the coefficients of the exponential flow curves are extracted from these curves and characterised through a general phenomenological constitutive coupled equation. The coefficients of this coupled equation are optimised using genetic algorithm. Finite element simulation of tensile tests at different strain rates and temperatures are done using this coupled equation in material model of Abaqus FEA software and validated with experimental results. The novelties of proposed model are:(a) it can predict precisely the flow behaviour of tensile tests (b) it is a simple form of equation where fitting parameters are both function of strain rate ratio and temperature ratio,(c) it has ability to characterize flow behaviour with decreasing subzero temperatures and increasing strain rates.

Role of remote Coulomb scattering on the hole mobility at cryogenic temperatures in SOI p-MOSFETs

The impacts of remote Coulomb scattering(RCS)on hole mobility in ultra-thin body silicon-on-insulator(UTB SOI)p-MOSFETs at cryogenic temperatures are investigated.The physical models including phonon scattering,surface roughness scattering,and remote Coulomb scatterings are considered,and the results are verified by the experimental results at different temperatures for both bulk(from 300 K to 30 K)and UTB SOI(300 K and 25 K)p-MOSFETs.The impacts of the interfacial trap charges at both front and bottom interfaces on the hole mobility are mainly evaluated for the UTB SOI p-MOSFETs at liquid helium temperature(4.2 K).The results reveal that as the temperature decreases,the RCS due to the interfacial trap charges plays an important role in the hole mobility.

Effect of cryogenic temperature characteristics on 0.18-μm silicon-on-insulator devices

The experimental results of the cryogenic temperature characteristics on 0.18-μm silicon-on-insulator（SOI） metaloxide-silicon（MOS） field-effect-transistors（FETs） were presented in detail. The current and capacitance characteristics for different operating conditions ranging from 300 K to 10 K were discussed. SOI MOSFETs at cryogenic temperature exhibit improved performance, as expected. Nevertheless, operation at cryogenic temperature also demonstrates abnormal behaviors, such as the impurity freeze-out and series resistance effects. In this paper, the critical parameters of the devices were extracted with a specific method from 300 K to 10 K. Accordingly, some temperature-dependent-parameter models were created to improve fitting precision at cryogenic temperature.

CT Image-based Analysis on the Defect of Polypropylene Fiber Reinforced High-Strength Concrete at High Temperatures

With the application of X-ray computed tomography（CT） technology of C80 high-strength concrete with polypropylene fiber at elevated temperatures, the microscopic damage evolution process observation and image building could be obtained, based on the statistics theory and numerical analysis of the combination of concrete internal defects extension and evolution regularity of microscopic structure. The expermental results show that the defect rate has changed at different temperatures and can determine the concrete degradation threshold temperatures. Also, data analysis can help to establish the evolution equation between the defect rate and the effect of temperature damage, and identify that the addition of polypropylene fibers in the high strength concrete at high temperature can improve cracking resistance.

Investigation on the temperature distribution and strength of flat steel ribbon wound cryogenic high-pressure vessel

By analyzing heat transfer on the wall of flat steel ribbon wound vessel (FSRWV), a numerical model of temperature distribution on the entire wall (including inner core wall, flat steel ribbons, outside cylinder of jacket and insulating layer) was established by the authors. With the model, the temperature distribution and the length change in the vessel walls and flat steel ribbons in low temperature are calculated and analyzed. The results show that the flat steel ribbon wound cryogenic high-pressure vessel is simpler in structure, safer and easier to manufacture than those of conventional ones.

Mechanical properties and deformation behavior of Ti-5Al-2.5ZrELI alloy used at cryogenic temperature

The mechanical properties and deformation behavior of Ti 5Al 2.5 ZrELI alloy compared with Ti 5Al 2.5 SnELI at 4.2?K, 20?K and 293?K were investigated. The results show that the new titanium alloy Ti 5Al 2.5ZrELI has more consistent properties because of its uniform microstructure and less segregation. It has good elongation and ductility. The fracture surfaces are covered with elongated dimples at cryogenic temperatures. The deformation mode at 293?K, 20?K and 4.2?K are twinning and slipping. [

Electrical characteristics of AlInN/GaN HEMTs under cryogenic operation

Electrical properties of an AIlnN/GaN high-electron mobility transistor （HEMT） on a sapphire substrate are investigated in a cryogenic temperature range from 295 K down to 50 K. It is shown that drain saturation current and conductance increase as transistor operation temperature decreases. A self-heating effect is observed over the entire range of temperature under high power consumption. The dependence of channel electron mobility on electron density is investigated in detail. It is found that aside from Coulomb scattering, electrons that have been pushed away from the AIInN/GaN interface into the bulk GaN substrate at a large reverse gate voltage are also responsible for the electron mobility drop with the decrease of electron density.

CT引导下腰交感神经射频热凝术治疗糖尿病周围神经病变的效果及安全性

目的 探讨CT引导下腰交感神经射频热凝术治疗糖尿病周围神经病变(DPN)的效果,并分析其安全性。方法 将100例DPN患者随机分为对照组和研究组,每组50例,对照组给予CT引导下化学毁损术,研究组给予CT引导下腰交感神经射频热凝术治疗。比较两组患者临床治疗效果,包括治疗前、治疗后7 d、治疗后30 d、治疗后90 d疼痛情况,治疗前、治疗后30 min、治疗后1 d、治疗后3 d皮肤温度,治疗前、治疗后90 d症状评分、神经传导速度及并发症发生情况。结果 研究组患者临床治疗效果优于对照组,且治疗总有效率为88.00%,明显高于对照组的70.00%(P<0.05)。治疗后7、30、90 d两组患者视觉模拟评分法(VAS)评分较治疗前均降低(P<0.05),且研究组患者VAS评分明显低于对照组(P<0.05);治疗后30 min、1 d、3 d研究组患者皮肤温度较治疗前均升高(P<0.05),治疗后3 d对照组患者皮肤温度较治疗前升高(P<0.05),治疗后30 min、1 d、3 d研究组患者皮肤温度明显高于对照组(P<0.05);治疗后90 d两组患者密歇根糖尿病性周围神经病评分(MDNS)、神经系统症状评分(NSS)较治疗前均降低(P<0.05),且研究组患者MDNS、NSS评分明显低于对照组(P<0.05);治疗后90 d两组患者正中神经、腓总神经的感觉神经传导速度(SNCV)、运动神经传导速度(MNCV)较治疗前均升高(P<0.05),且研究组患者正中神经、腓总神经的SNCV、MNCV明显高于对照组(P<0.05);研究组患者并发症发生率为0,明显低于对照组的16.00%(P<0.05)。结论 CT引导下腰交感神经射频热凝术治疗DPN可有效减轻疼痛,改善皮肤温度和症状,提高神经传导速度,且安全性高。

Influence of interstitial content on mechanical properties of new type of near α titanium alloy at cryogenic temperature

The influence of interstitial content on mechanical properties of a new type of near α titanium alloy(Ti-Zr-Mo-Nb-Sn) at cryogenic temperature was studied. The results show that interstitial content affects the mechanical properties of the alloy at cryogenic temperature. Interstitial element atoms solving into lattice causes the increasing of degree of distortion,which limits the sliding and twinning of dislocations. Reducing interstitial content is beneficial to generation of dislocation sliding and deformation twins. With interstitial element content reducing,the impact toughness and the elongation of the alloy decrease rapidly while the strength decreases weakly. To obtain good over-all properties at cryogenic temperature,the interstitial element content in this alloy must be controlled to extra low grade.

Effects of Grain Size and Cryogenic Temperature on the Strain Hardening Behavior of VCoNi Medium‑Entropy Alloys

The mechanical behavior of VCoNi medium-entropy alloys with five different grain sizes at three different temperatures was investigated.The VCoNi alloys with different grain sizes exhibit a traditional strength–ductility trade-off at 77 K,194 K and 293 K.Both the yield strength and the uniform elongation of the VCoNi alloys with similar grain size increase with decreasing the deformation temperature from 293 to 77 K.Obvious strain hardening rate recovery characterized by an evident up-turn behavior at stage II is observed in VCoNi alloys with the grain size above 11.1μm.It is found that the extent of the strain hardening rate recovery increases with increasing grain size or decreasing deformation temperature.This may mainly result from the faster increase in the dislocation multiplication rate caused by the decrease in the dislocation mean free path,the decrease in the absorption of dislocations by grain boundaries and the dynamic recovery from the cross-slip with increasing grain size,as well as the suppressed dynamic recovery at cryogenic temperatures.The critical grain sizes for the occurrence of the recovery of strain hardening rate are determined to be around 9.5μm,8.3μm and 3μm for alloys deformed at 293 K,194 K and 77 K,respectively.The basic mechanism for the strain hardening behavior of the VCoNi alloys associated with grain size and deformation temperature is analyzed.

TEMPERATURE FIELD CONTROL PRINCIPLE AND CONTROL MODELS FOR CRYOGENIC MACHINING SYSTEM

Cryogenic machining is a new technology which makes use of the special mechanicalprcperties of niaterials in a cryogenic or a 'super cold' state for machining. The control of acryogenic machining system(CMS)is one of the key problems which need to be solved for practi-cal cryogenic machining A temperature field control principle is presented which calculates theheat source temperature in the light of the tool temperature field information, and a control mod-el of three-dimensional dynamic temperature field for CMS is established, and the boundary con-ditions and the heat source of temperature field in orthogonal cutting are discussed. Based on theinvestigation of the control feature and technique. a prototype system for controlling CMS is crea-ted.

Excellent strength-ductility combination of Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy at cryogenic temperatures

In the present study,a face-centered cubic non-equiatomic Cr_(26)Mn_(20)Fe_(20)Co20Ni_(14) high-entropy alloy(HEA)with a low stacking fault energy of 17.6 mJ m^(−2) was prepared by vacuum induction melting,forging and annealing processes.The recrystallized sample is revealed to exhibit an excellent combination of strength and ductility over a wide temperature range of 4.2–293 K.With decreasing temperature from 293 to 77 K,the ductility and ultimate tensile strength(UTS)gradually increase by 30% to 95% and 137% to 1020 MPa,respectively.At the lowest temperature of 4.2 K,the ductility keeps 65% and the UTS increases by 200% to 1300 MPa,which exceed those published in the literature,including conventional 300 series stainless steels.Detailed microstructural analyses of this alloy reveal a change of deformation mechanisms from dislocation slip and nano-twinning at 293 K to nano-phase transformation at 4.2 K.The cooperation and competition of multiple nano-twinning and nano-phase transformation are responsible for the superior tensile properties at cryogenic temperatures.Our study provides experimental evidence for potential cryogenic applications of HEAs.

CT三维重建引导低温等离子射频消融联合臭氧及胶原酶治疗腰椎间盘突出症的疗效分析

目的探讨CT三维重建引导低温等离子射频消融联合臭氧和胶原酶治疗腰椎间盘突出症的疗效。方法回顾性选取2019年7月至2020年7月在秦皇岛市第一医院住院治疗的腰椎间盘突出症患者64例,根据治疗方案不同分为观察组和对照组,每组各32例。对照组采用CT三维重建引导低温等离子射频消融联合臭氧注射,观察组在对照组基础上行经骶裂孔入路胶原酶髓核溶解术,术后随访6个月。采用视觉模拟评分法(VAS)评估治疗前和治疗后3 d、1个月、3个月、6个月时疼痛程度。分别测定治疗前和治疗后3 d红细胞沉降率(ESR)、C反应蛋白(CRP)和白细胞计数(WBC)水平。采用改良Macnab标准评定临床疗效,计算治疗后1、3、6个月优良率。观察并记录两组患者随访期间并发症发生情况。结果治疗后,两组患者VAS评分较治疗前均大幅度降低,且观察组治疗后3、6个月时VAS评分为(1.91±1.15)、(1.47±0.76)分,均低于对照组[(3.75±1.50)、(2.38±1.04)分],差异均有统计学意义(P<0.05)。治疗后,两组患者ESR、CRP、WBC均增加,差异均有统计学意义(P<0.05),但两组治疗后上述指标比较,差异均无统计学意义(P>0.05)。观察组治疗后6个月的优良率为87.50%,高于对照组(65.63%),差异有统计学意义(P<0.05)。随访期间,所有患者均无软组织及椎管内血肿、神经受损、腰椎间盘感染等相关并发症发生。结论CT三维重建引导低温等离子射频消融联合臭氧和胶原酶治疗腰椎间盘突出症疗效确切,且安全性较高,具有临床应用价值。

Wear-resistant CoCrNi multi-principal element alloy at cryogenic temperature

Traditional high strength engineering alloys suffer from serious surface brittleness and inferior wear performance when servicing under sliding contact at cryogenic temperature.Here,we report that the recently emerging CoCrNi multi-principal element alloy defies this trend and presents dramatically enhanced wear resistance when temperature decreases from 273 to 153 K,surpassing those of cryogenic austenitic steels.The temperature-dependent structure characteristics and deformation mechanisms influencing the cryogenic wear resistance of CoCrNi are clarified through microscopic observation and atomistic simulation.It is found that sliding-induced subsurface structures show distinct scenarios at different deformation temperatures.At cryogenic condition,significant grain refinement and a deep plastic zone give rise to an extended microstructural gradient below the surface,which can accommodate massive sliding deformation,in direct contrast to the strain localization and delamination at 273 K.Meanwhile,the temperature-dependent cryogenic deformation mechanisms(stacking fault networks and phase transformation)also provide additional strengthening and toughening of the subsurface material.These features make the CoCrNi alloy particularly wear resistant at cryogenic conditions and an excellent candidate for safety–critical applications.