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.

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.

Fracture pattern evolution of SnAgCu−SnPb mixed solder joints at cryogenic temperature

The effect of cryogenic temperatures on the mechanical properties and fracture mechanism of SnAgCu−SnPb mixed solder joints was investigated.The results showed that the tensile strength of mixed solder joints first increased with the increase of Pb content and reached its maximum at 22.46 wt.%Pb;subsequently,it decreased as Pb content increased.However,cryogenic temperatures improved the tensile strength of the solder joints.Both Pb content and cryogenic temperature caused the fracture mode of the mixed solder joints to change;however,temperature remained the main influencing factor.As the temperature fell from 298 to 123 K,the failure pattern in the solder joints transformed from ductile fracture to quasi-ductile fracture to quasi-brittle fracture and finally,to brittle fracture.

Flow behavior and fracture of Al−Mg−Si alloy at cryogenic temperatures

The tensile and fracture behaviors of AA6061 alloy were investigated in order to provide quantitative data about this alloy at cryogenic temperatures.Specimens of AA6061 alloy were solution heat treated before tensile tests at 298,173 and 77 K and tested at strain rates in the range from 0.1 to 0.0001 s^(−1).The results indicate the suppression of the Portevin−Le Chatelier(PLC)effect and dynamic strain aging(DSA)at 77 K.In contrast,at 298 K,a remarkable serrated flow,characteristic of the PLC effect,is observed.Furthermore,the tensile behavior at 77 K,compared with that observed at 173 and 298 K,shows a simultaneous increase in strength,uniform elongation,modulus of toughness,strain-hardening exponent and strain rate sensitivity,which is related to a decrease in the dynamic recovery rate at low temperature.These responses are reflected on the fracture morphology,since the dimple size decreases at 77 K,while the area covered by dimples increases.Comparisons of the Johnson−Cook model show that a good agreement can be obtained for tests at 173 and 77 K,in which DSA is suppressed.

Mechanical properties and microstructural evolution of ultrafine grained zircaloy-4 processed through multiaxial forging at cryogenic temperature

The mechanical properties and microstructural evolution of zircaloy-4 subjected to cumulative strains of 1.48,2.96,4.44 and 5.91 through multiaxial forging（MAF） at cryogenic temperature（77 K） were investigated.The mechanical properties of the MAF treated alloy were measured through universal tensile testing and Vickers hardness testing equipment.The zircaloy-4 deformed up to a cumulative strain of 5.91 showed improvement in both ultimate tensile strength and hardness from 474 MPa to 717 MPa and from HV 190 to HV 238,respectively,as compared with the as-received alloy.However,there was a noticeable decrement in ductility（from 18%to 3.5%） due to the low strain hardening ability of deformed zircaloy-4.The improvement in strength and hardness of the deformed alloy is attributed to the grain size effect and higher dislocation density generated during multiaxial forging.The microstructural evolutions of deformed samples were characterized by optical microscopy and transmission electron microscopy（TEM）.The evolved microstructure at a cumulative strain of 5.91 obtained after MAF up to 12 cycles depicted the formation of ultrafine grains with an average size of 150-250 nm.

A Warming Structure for Piezoelectric Stack Working in Cryogenic Temperature

It is widely acknowledged that the performance of a piezoelectric stack would decline with the temperature decreasing,which will exert negative influence on its application in low-temperature environment.Therefore,a convenient and efficient warming structure for the piezoelectric stack is proposed in this paper to solve this problem.Based on the theoretical analysis of heat transfer,two heating modes,namely,overall heating and local heating are analyzed and compared.Moreover,experimental tests are conducted to evaluate the effectiveness of the structure.Based on the results,it can be concluded that the theoretical results are confirmed with experimental results.Besides,the temperature and performance of the piezoelectric stack are kept stable as temperature varies from 10℃to-70℃,which manifests the feasibility of the structure.Therefore,this paper could be an available reference for those engaged in cryogenic investigation of smart materials and structures.

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. [

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.

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.

Tribological properties of PTFE-based fabric composites at cryogenic temperature

Fabric composites are widely employed in self-lubricating bearing liners as solid lubrication materials.Although the tribological behaviors of fabric composites have been extensively studied,the cryogenic tribological properties and mechanisms have been scarcely reported and are largely unclear to instruct material design for aerospace and other high-tech applications.Herein,the tribological properties of polytetrafluoroethylene(PTFE)-based hybrid-fabric composites were investigated at cryogenic and ambient temperatures in the form of pin-on-disk friction under heavy loads.The results suggest that the friction coefficients of the hybrid-fabric composites obviously increase with a decrease in wear when the temperature drops from 25 to−150°C.Moreover,thermoplastic polyetherimide(PEI),as an adhesive for fabric composites,has better cryogenic lubrication performance than thermosetting phenol formaldehyde(PF)resin,which can be attributed to the flexible chemical structure of PEI.The excellent lubrication performance of hybrid-fabric composites is attributed to the transfer film formed by PTFE fibers on the surface of fabrics.

Molecular levers enable anomalously enhanced strength and toughness of cellulose nanocrystal at cryogenic temperature

The quest for widespread applications especially in extreme environments accentuates the necessity to design materials with robust mechanical and thermodynamic stabilities.Almost all existing materials yield temperature-variant mechanical properties,essentially determined by their different atomic bonding regimes.In general,weak non-covalent interactions are considered to diminish the structural anti-destabilization of covalent crystals despite the toughening effect.Whereas,starting from multiscale theoretical modeling,we herein reveal an anomalous stabilizing effect in cellulose nanocrystals(CNCs)by the cooperation between the non-covalent hydrogen bonds and covalent glucosidic skeleton,namely molecular levers(MLs).It is surprising to find that the hydrogen bonds in MLs behave like covalent bindings under cryogenic conditions,which provide anomalously enhanced strength and toughness for CNCs.Thermodynamic analyses demonstrate that the unique dynamical mechanical behaviors from ambient to deep cryogenic temperatures are synergetic results of the intrinsic temperature dependence veiled in MLs and the overall thermo-induced CNC destabilization/amorphization.As the consequence,the variation trend of mechanical strength exhibits a bilinear temperature dependence with~77 K as the turning point.Our underlying investigations not only establish the bottom–up interrelations from the hydrogen bonding thermodynamics to the crystal-scale mechanical properties,but also facilitate the potential application of cellulose-based materials at extremely low temperatures such as those in outer space.

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.

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.

Single-fundamental-mode cryogenic(3.6 K)850-nm oxideconfined VCSEL

Cryogenic oxide-confined vertical-cavity surface-emitting laser(VCSEL)has promising application in cryogenic optical interconnect for cryogenic computing.In this paper,we demonstrate a cryogenic 850-nm oxide-confined VCSEL at around 4 K.The cryogenic VCSEL with an optical oxide aperture of 6.5μm in diameter can operate in single fundamental mode with a side-mode suppression-ratio of 36 dB at 3.6 K,and the fiber-coupled output power reaches 1 mW at 5 mA.The small signal modulation measurements at 298 and 292 K show the fabricated VCSEL has the potential to achieve a high modulation bandwidth at cryogenic temperature.

Novel Co-free high performance TRIP and TWIP medium-entropy alloys at cryogenic temperatures

Recently,high-and medium-entropy alloys(HEAs and MEAs) have been found to exhibit excellent cryogenic mechanical properties,but most of them contain high-priced Co element.Therefore,developing HEAs or MEAs with high strength and ductility and relatively low cost is urgent.In this work,novel Cofree Fex Mn(75-x) Ni(10)Cr(15)(x=50 and 55 at.%) MEAs were developed,which exhibit a good combination of low cost,high strength and ductility at cryogenic temperature.It was found that the Fe(50)Mn(25)Ni(10)Cr(15)MEA exhibits a combination of cryogenic tensile strength of^0.98 GPa and ductility of^83 %.The excellent cryogenic mechanical properties were attributed to joint of twinning-induced plasticity(TWIP) and transformation-induced plasticity(TRIP) effects.The present study sheds light on developing low cost MEAs with high perfo rmance for cryogenic-tempe rature applications.

Twinning Behavior of a Basal Textured Commercially Pure Titanium Alloy TA2 at Ambient and Cryogenic Temperatures

Twinning greatly affects the microstructure and mechanical performance of titanium alloys.The twinning behavior of a basal textured commercially pure titanium TA2 plates rolled to 4% reduction at the ambient and cryogenic temperatures has been investigated.Microstructures of the rolled samples were investigated by optical microscope（OM）and the twinning analysis was carried out based on orientation data collected by electron back-scatter diffraction（EBSD）.{1122}contraction twins,{1124}contraction twins and {1012}extension twins have been observed.Twinning mode activity varied with rolling temperature.Twinning is considered as the dominant deformation mechanism during rolling at both temperatures for the strain condition.Larger proportion of grains activates twinning during cryorolling,and greater number and more diverse types of twins are observed;manifestly related to the suppression of dislocation slips at the cryogenic temperature.{1122}contraction twins are the dominate twin type within samples rolled at both temperatures.Several{1124}contraction twins are observed in the cryorolled sample while there are only a few in the sample rolled at room temperature.A few tiny{1012}twins have been identified in both samples.{1124}contraction twins are preferentially activated at cryogenic deformation temperature and the{1012}extension twins may result in local strain accommodation.

Effects of cryogenic temperature on tensile and impact properties in a medium-entropy VCoNi alloy

Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy(SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A recently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the underlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in contrast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.

Suppression of grain boundary migration at cryogenic temperature in an extremely fine nanograined Ni-Mo alloy

Microindentation creep tests on an electrodeposited extremely fine(4.9 nm) nanograined(ng) Ni-14.2 at.% Mo(Ni-14.2 Mo) at both room temperature(RT) and liquid nitrogen temperature(LNT) demonstrated that lowering temperature retarded softening in the ng Ni-Mo alloy. The obtained strain rate sensitivity at LNT was one order of magnitude lower than that at RT. Microstructural characterization revealed that mechanically-driven grain boundary(GB) migration was greatly suppressed by lowering temperature,which might be ascribed to the presence of solute Mo atoms that significantly retarded coupled GB motion at LNT. Deformation was instead carried by shear bands.