Effect of long-period stacking ordered structure on very high cycle fatigue properties of Mg-Gd-Y-Zn-Zr alloys

Magnesium alloys with a long-period stacking ordered(LPSO)structure usually possess excellent static strength,but their fatigue behaviors are poorly understood.This work presents the effect of the LPSO structure on the crack behaviors of Mg alloys in a very high cycle fatigue(VHCF)regime.The LPSO lamellas lead to a facet-like cracking process along the basal planes at the crack initiation site and strongly prohibit the early crack propagation by deflecting the growth direction.The stress intensity factor at the periphery of the faceted area is much higher than the conventional LPSO-free Mg alloys,contributing higher fatigue crack propagation threshold of LPSO-containing Mg alloys.Microstructure observation at the facets reveals a layer of ultrafine grains at the fracture surface due to the cyclic contact of the crack surface,which supports the numerous cyclic pressing model describing the VHCF crack initiation behavior.

Microstructure and mechanical properties of Mg_(94)Zn_2Y_4 extruded alloy with long-period stacking ordered structure

The microstructure and mechanical properties of Mg94Zn2Y4 extruded alloy containing long-period stacking ordered structures were systematically investigated by SEM and TEM analyses. The results show that the 18R-LPSO structure and α-Mg phase are observed in cast Mg94Zn2Y4 alloy. After extrusion, the LPSO structures are delaminated and Mg-slices with width of 50-200 nm are generated. By ageing at 498 K for 36 h, the ageing peak is attained andβ′phase is precipitated. Due to this novel precipitation, the microhardness ofα-Mg matrix increases apparently from HV108.9 to HV129.7. While the microhardness for LPSO structure is stabilized at about HV145. TEM observations and SAED patterns indicate that the β′ phase has unique orientation relationships betweenα-Mg and LPSO structures, the direction in the close-packed planes ofβ′precipitates perpendicular to that ofα-Mg and LPSO structures. The ultimate tensile strength for the peak-aged alloy achieves 410.7 MPa and the significant strength originates from the coexistence ofβ′precipitates and 18R-LPSO structures.

Long-period stacking ordered structures in Mg-3Cu-1Mn-2Zn-1Y damping alloy

14H, 18R and 24R long-period stacking ordered （LPSO） structures were observed in the as-cast Mg-3Cu-1Mn-2Zn-1Y damping alloy using transmission electron microscopy （TEM）. These LPSO structures contained Mg, Y, Cu and Zn and thus they were quaternary phases. Sharp diffraction pattern of the 24R structure was obtained and the angle between and g10024R was measured to be 5.03°. During high resolution TEM observations, lattice fringes with two characteristic spacings were observed within the 24R structure. Based on the experimental results, 6H, 7H and three 8H are suggested as the building blocks of 18R, 14H and 24R structures, respectively. The 24R unit cell can be interpreted as the stacking of 8H building blocks in the same shear direction with a shear angle of about 5.03°. The imperfect 24R structures are in order or disorder arrangements of principal 8H and minor 6H blocks. This double-block structure model is also applicable to other reported defects in LPSO structures.

Influence of the ordered structure of short-chain polymer molecule all-trans-β-carotene on Raman scattering cross section in liquid

We measured the resonant Raman spectra of all-trans-β-carotene in solvents with different densities and concentrations at different temperatures. The results demonstrated that the Raman scattering cross section （RSCS） of short-chain polymer all-trans-β-carotene is extremely high in liquid. Resonance and strong coherent weakly damped CC bond vibrating properties play important roles under these conditions. Coherent weakly damped CC bond vibration strength is associated with molecular ordered structure. All-trans-β-carotene has highly ordered structure and strong coherent weakly damped CC bond vibrating properties, which lead to large RSCS in the solvent with large density and low concentration at low temperature.

Stable immobilization of lithium polysulfides using three-dimensional ordered mesoporous Mn_(2)O_(3) as the host material in lithium-sulfur batteries

Lithium-sulfur batteries(LSBs)have drawn significant attention owing to their high theoretical discharge capacity and energy density.However,the dissolution of long-chain polysulfides into the electrolyte during the charge and discharge process(“shuttle effect”)results in fast capacity fading and inferior electrochemical performance.In this study,Mn_(2)O_(3)with an ordered mesoporous structure(OM-Mn_(2)O_(3))was designed as a cathode host for LSBs via KIT-6 hard templating,to effectively inhibit the polysulfide shuttle effect.OM-Mn_(2)O_(3)offers numerous pores to confine sulfur and tightly anchor the dissolved polysulfides through the combined effects of strong polar-polar interactions,polysulfides,and sulfur chain catenation.The OM-Mn_(2)O_(3)/S composite electrode delivered a discharge capacity of 561 mAh g^(-1) after 250 cycles at 0.5 C owing to the excellent performance of OM-Mn_(2)O_(3).Furthermore,it retained a discharge capacity of 628mA h g^(-1) even at a rate of 2 C,which was significantly higher than that of a pristine sulfur electrode(206mA h g^(-1)).These findings provide a prospective strategy for designing cathode materials for high-performance LSBs.

The chemical environment and structural ordering in liquid Mg-Y-Zn system:An ab-initio molecular dynamics investigation of melt for the formation mechanism of LPSO structure

In an effort to clarify the formation mechanism of LPSO structure in Mg-Y-Zn alloy,the chemical environment and structural ordering in liquid Mg-rich Mg-Y-Zn system are investigated with the aid of ab-initio molecular dynamics simulation.In liquid Mg-rich Mg-Y alloys,the strong Mg-Y interaction is determined,which promotes the formation of fivefold symmetric local structure.For Mg-Zn alloys,the weak Mg-Zn interaction results in the fivefold symmetry weakening in the liquid structure.Due to the coexistence of Y and Zn,the strong attractive interaction is introduced in liquid Mg-Y-Zn ternary alloy,and contributes to the clustering of Mg,Y,Zn launched from Zn.What is more,the distribution of local structures becomes closer to that in pure Mg compared with that in binary Mg-Y and Mg-Zn alloys.These results should relate to the origins of the Y/Zn segregation zone and close-packed stacking mode in LPSO structure,which provides a new insight into the formation mechanism of LPSO structure at atomic level.

The Disintegration of a Floating Ferrofluid Layer into an Ordered Drop System in a Vertical Magnetic Field

Magnetic fluids,also known as ferrofluids,are versatile functional materials with a wide range of applications.These applications span from industrial uses such as vacuum seals,actuators,and acoustic devices to medical uses,including serving as contrast agents for magnetic resonance imaging(MRI),delivering medications to specific locations within the body,and magnetic hyperthermia for cancer treatment.The use of a non-wettable immiscible liquid substrate to support a layer of magnetic fluid opens up new possibilities for studying various fluid flows and related instabilities in multi-phase systems with both a free surface and an interface.The presence of two deformable boundaries within a ferrofluid layer significantly reduces the critical magnetic field strength required to transform the layer into an organized system of drops or polygonal figures evolving according to the intensity,frequency and direction of the considered magnetic field.This paper experimentally investigates this problem by assuming a uniform magnetic field perpendicular to the surface.This specific subject has not been previously explored experimentally.The critical magnetic field intensity required to destabilize the ferrofluid layer is determined based on the layer’s thickness and the fluid’s initial magnetic susceptibility.It is demonstrated that the critical magnetic field strength needed to disrupt the initially continuous ferrofluid layer increases with the layer’s thickness.Conversely,an increase in the ferrofluid’s magnetic susceptibility results in a decrease in the critical magnetic field strength.The emerging droplet structures are analyzed in terms of the number of drops,their size,and the periodicity of their arrangement.The number of droplets formed depends on the initial thickness of the layer,the presence or absence of a stable rupture in the upper layer,and the rate at which the magnetic field strength is increased to the critical value.A characteristic viscous time is proposed to evaluate the decomposition of the ferrofluid layer,which depends on the duration of the magnetic field’s application.The experimental data on the instability of a ferrofluid layer on a liquid substrate are compared with the theoretical results from the study of“magnetic fluid sandwich structures”conducted by Rannacher and Engel.This comparison highlights the similarities and differences between experimental observations and theoretical predictions,providing a deeper understanding of the behavior of ferrofluid layers under the influence of magnetic fields.

Bioinspired flexible,high-strength,and versatile hydrogel with the fiberboard-and-mortar hierarchically ordered structure

The synthetic hydrogels with high water contents are promising for various applications,however,they usually exhibit low mechanical properties.In this work,inspired by the natural biological soft tissues,whose hierarchically ordered fibrous structures result in high strength and good flexibility,a flexible,high-strength,and versatile hydrogel with the fiberboard-and-mortar hierarchically ordered structure(HFMOS)is developed based on ultralong hydroxyapatite(HAP)nanowires and polyacrylic acid(PAA).The as-prepared HFMOS hydrogel has a high water content(~70 wt.%),dense structure,and excellent mechanical properties,and these properties are similar to those of the human cartilage and are superior to many hydrogels reported in the literature.The excellent mechanical properties of the HFMOS hydrogel originate from the combination of the fiberboard-and-mortar hierarchically ordered structure,reinforcement of ultralong HAP nanowires,strong interfacial strength,and multiple energy dissipation pathways.Moreover,thanks to the controllable components and injection procedure,the HFMOS hydrogel with a Janus structure is prepared for particular applications.The HFMOS hydrogel possesses abundant ordered water channels,and can be used for loading,release,and directed delivery of various functional substances.Thus,the as-prepared flexible,high-strength,and versatile HFMOS hydrogel possesses a great potential for various applications such as water purification,pollution treatment,biomedicine,nanofluidic devices,and high-performance structural materials.

Guinier-Preston Zone,Quasicrystal and Long-period Stacking Ordered Structure in Mg-based Alloys,A Review

Both the solid solution and precipitation are mainly strengthening mechanism for the magnesium-based alloys. A great number of alloying elements can be dissolved into the Mg matrix to form the solutes and precipitates.Moreover, the type of precipitates varies with different alloying elements and heat treatments, which makes it quite difficult to understand the formation mechanism of the precipitates in Mg-based alloys in depth. Thus, it is very hard to give a systematical regularity in precipitation process for the Mg-based alloys. This review is mainly focused on the formation and microstructural evolution of the precipitates, as a hot topic for the past few years, including Guinier-Preston Zones, quasicrystals and long-period stacking ordered phases formed in a number of Mg-TM-RE alloy systems, where TM = Al, Zn, Zr and RE = Y,Gd, Hd, Ce and La.

Ordered structure of interlayer constructed with metal-organic frameworks improves the performance of lithium-sulfur batteries

Lithium-sulfur(Li-S)battery has attracted intensive attention in the realm of energy storage owing to its high theoretical capacity and energy density.However,the shuttle effect of soluble lithium polysulfides(LiPSs)between electrodes results in rapid capacity degradation.Herein,a strategy which combines the design of both chemical interaction and microstructure of interlayer was proposed to suppress the shuttle effect.The chemical interaction between different functionalized MOFs and LiPSs was systematically studied to find the best candidate.Furthermore,an interlayer with ordered structure was constructed via the layer-by-layer assembly of metal-organic frameworks(MOFs)on graphene(UiO-66-NH_(2)@graphene)to create sinuous channels which can better impede the diffusion process of LiPSs by the strong adsorption of MOF toward LiPSs.Consequently,in comparison to the battery with a bare separator,the ordered interlayer increased the initial discharge capacity of battery by 28.98%at 1.0 C and lowered the capacity decay rate remarkably from 0.10%to 0.067%per cycle,indicating that the design of chemical interaction and microstructure paves the way for high-performance Li-S batteries.

Spatiotemporally dynamic therapy with shape-adaptive drug-gel for the improvement of tissue regeneration with ordered structure

A spatiotemporally dynamic therapy(SDT)is proposed as a powerful therapeutic modality that provides spatially dynamic responses of drug-carriers for adapting to the wound microenvironment.Herein,dynamic chitosan-poly(ethylene glycol)(CP)Schiff-base linkages are employed to perform SDT by directly converting a liquid drug Kangfuxin(KFX)into a gel formation.The obtained KFX-CP drug-gel with shape-adaptive property is used to treat a representative oral mucositis(OM)model in a spatiotemporally dynamic manner.The KFX-CP drug-gel creates an instructive microenvironment to regulate signaling biomolecules and endogenous cells behavior,thereby promoting OM healing by the rule of dynamically adjusting shape to fit the irregular OM regions first,and then provides space for tissue regeneration,over KFX potion control and the general hydrogel group of CP hydrogel and KFX-F127.Most interestingly,the regenerated tissue has ordered structure like healthy tissue.Therefore,the SDT provides a new approach for the design of next generation of wound dressing and tissue engineering materials.

Corrosion Behavior of Mg-Zn-Y Alloy with Long-period Stacking Ordered Structures

Mg-Zn-Y alloys with long-period stacking ordered structures were prepared by an ingot casting method. The corrosion performance of Mg-Zn-Y alloys was studied by combining gas-collecting test, immersion test and electrochemical measurements in order to determine the corrosion rate and mechanism of the alloys. The results showed that the volume fraction of Mg（12）YZn phase increased and the shape of the Mg（12）YZn phase changed from discontinuous to continuous net-like with increasing Zn and Y content. The corrosion rate of the alloys greatly depended on the distribution and volume fraction of the Mg（12）YZn phase. Corrosion products appeared at the junction of Mg phase and Mg（12）YZn phase, indicating that the Mg（12）YZn phase accelerated galvanic corrosion of Mg matrix. Mg（97）Zn1Y2 alloy shows the lowest corrosion rate due to the continuous distribution of Mg（12）YZn phase.

Role of Ordering Energy in Formation of Grain Structure and Special Boundaries Spectrum in Ordered Alloys with L12 Superstructure

It was revealed that an average energy of special boundaries is proportional to APB energy in the alloys with the L12 superstructure. This fact proves the appearance of the GAPBs in the planes of location of special boundaries in coincidence sites of ordered alloys. It was determined that the more energy of special boundaries in ordered alloys, the more energy of complex stacking fault. There is a correlation between the distribution of special boundaries as a function its relative energy and ordering energy: the more ordering energy, the more degree of washed away of distribution. The correlation between average relative energy of special boundaries and ordering energy was detected: the more ordering energy, the more average energy of special boundaries. The reverse dependence between ordering energy and average number of special boundaries in grains limited by boundaries of general type was discovered.

Ultrasmall NiS_(2)Nanocrystals Embedded in Ordered Macroporous Graphenic Carbon Matrix for Efficiently Pseudocapacitive Sodium Storage

Sodium-ion hybrid capacitor(SIHC)is one of the most promising alternatives for large-scale energy storage due to its high energy and power densities,natural abundance,and low cost.However,overcoming the imbalance between slow Na^(+)reaction kinetics of battery-type anodes and rapid ion adsorption/desorption of capacitive cathodes is a significant challenge.Here,we propose the high-rate-performance NiS_(2)@OMGC anode material composed of monodispersed NiS_(2) nanocrystals(8.8±1.7 nm in size)and N,S-co-doped graphenic carbon(GC).The NiS_(2)@OMGC material has a three-dimensionally ordered macroporous(3DOM)morphology,and numerous NiS_(2) nanocrystals are uniformly embedded in GC,forming a core-shell structure in the local area.Ultrafine NiS_(2) nanocrystals and their nano-microstructure demonstrate high pseudocapacitive Na-storage capability and thus excellent rate performance(355.7 mAh/g at 20.0 A/g).A SIHC device fabricated using NiS_(2)@OMGC and commercial activated carbon(AC)cathode exhibits ultrahigh energy densities(197.4 Wh/kg at 398.8 W/kg)and power densities(43.9 kW/kg at 41.3 Wh/kg),together with a long life span.This outcome exemplifies the rational architecture and composition design of this type of anode material.This strategy can be extended to the design and synthesis of a wide range of high-performance electrode materials for energy storage applications.

Microstructure and tribological behavior of Mg-Gd-Zn-Zr alloy with LPSO structure

A Mg-14.28Gd-2.44Zn-0.54Zr （mass fraction, %） alloy was prepared by conventional ingot metallurgy （I/M）. The microstructure differences in as-cast and solution-treated alloys were investigated. Sliding tribological behaviors of the as-cast and solution-treated alloys were investigated under oil lubricant condition by pin-on-disc configuration. The wear loss and friction coefficients were measured at a load of 40 N and sliding speeds of 30-300 mm/s with a sliding distance of 5000 m at room temperature. The results show that the as-cast alloy is mainly composed ofα-Mg solid solution, the lamellar 14H-type long period stacking ordered （LPSO） structure within matrix, andβ-[（Mg,Zn）3Gd] phase. However, most of theβ-phase transforms to X-phase with 14H-type LPSO structure after solution heat treatment at 773 K for 35 h （T4）. The solution-treated alloy presents low wear-resistance, because the hard β-phase is converted into thermally-stable, ductile and soft X-Mg12GdZn phase with LPSO structure in the alloy.

Three‑Dimensional Ordered Mesoporous Carbon Spheres Modified with Ultrafine Zinc Oxide Nanoparticles for Enhanced Microwave Absorption Properties

Currently,electromagnetic radiation and interference have a significant effect on the operation of electronic devices and human health systems.Thus,developing excellent microwave absorbers have a huge significance in the material research field.Herein,a kind of ultrafine zinc oxide(ZnO)nanoparticles(NPs)supported on three-dimensional(3D)ordered mesoporous carbon spheres(ZnO/OMCS)is prepared from silica inverse opal by using phenolic resol precursor as carbon source.The prepared lightweight ZnO/OMCS nanocomposites exhibit 3D ordered carbon sphere array and highly dispersed ultrafine ZnO NPs on the mesoporous cell walls of carbon spheres.ZnO/OMCS-30 shows microwave absorbing ability with a strong absorption(−39.3 dB at 10.4 GHz with a small thickness of 2 mm)and a broad effective absorption bandwidth(9.1 GHz).The outstanding microwave absorbing ability benefits to the well-dispersed ultrafine ZnO NPs and the 3D ordered mesoporous carbon spheres structure.This work opened up a unique way for developing lightweight and high-efficient carbon-based microwave absorbing materials.

Optimizing the power conversion processes in diluted donor/acceptor heterojunctions towards 19.4%efficiency all-polymer solar cells

All polymer solar cells(all-PSCs)promise mechanically-flexible and morphologically-stable organic photovoltaics and have aroused increased interests very recently.However,due to their disorderly conformation structures within the photoactive film,inefficient charge generation and carrier transport are observed which lead to inferior photovoltaic performance compared to smaller molecular acceptor-based photovoltaics.Here,by diluting PM6 with a cutting-edge polymeric acceptor PY-IT and diluting PY-IT with PM6 or D18,donor-dominating or acceptor-dominating heterojunctions were prepared.Synchrotron X-ray and multiple spectrometer techniques reveal that the diluted heterojunctions receive increased structural order,translating to enhanced carrier mobility,improved exciton diffusion length,and suppressed non-radiative recombination loss during the power conversion.As the results,the corresponding PM6+1%PY-IT/PY-IT+1%D18 and PM6+1%PY-IT/PY-IT+1%PM6 devices fabricated by layer-by-layer deposition received superior power conversion efficiency(PCE)of 19.4%and 18.8%respectively,along with enhanced operational lifetimes in air,outperforming the PCE of 17.5%in the PM6/PY-IT reference device.

Hybrid improper ferroelectricity and phase transition behavior of Li_(2)Nd_(2)Ti_(3)O_(10)ceramics with A-site ordered triple-layer Ruddlesden-Popper structure

Hybrid improper ferroelectricity has been extensively reported through theoretical prediction and experimental investigation in the oxides with Ruddlesden-Popper(R-P)structures.However,the experimentally reported ferroelectric materials based on triple-layer R-P structures are rare,and the weak ferroelectricity impedes its practical application.In the present work,the single-phase Li_(2)Nd_(2)Ti_(3)O_(10)ceramics with A-site cation ordered triple-layer R-P structure was obtained by spark plasma sintering technique,and the crystal structure of P2_(1)ab symmetry was revealed by neutron powder diffraction and transmission electron microscope analysis.Furthermore,the switchable ferroelectricity in Li_(2)Nd_(2)Ti_(3)O_(10)ceramics has been observed at room temperature,and the saturated polarization-electric field hysteresis loop was obtained with P_(r)=0.4μC/cm^(2)under the electric field of 250 kV/cm.The phase transition behavior of Li_(2)Nd_(2)Ti_(3)O_(10)oxides was revealed by the temperature-dependence Raman and dielectric spectra combined with the piezoelectric property.

Microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr alloys

The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.

Microstructure of Si Cones Prepared by Ar^+-Sputtering Si/Mo Target

By Ar+ sputtering onto Si wafers which were surrounded by Mo plates, uniform cones over a large area on the Si surface were formed. Scanning electron microscopic study showed that the cones were formed on the entire surface of the Si wafer. The dimensions of the uniform cones were one micrometer in diameter and 5-6 micrometers high. They were further characterized by means of cross-sectional transmission electron microscopy, with the technique of micro-diffractions. It was found that the cone contained a pure Si regime and a Mo-rich regime. In the binary Mo-Si zone, we identified three distinct areas vertically: (1) domains of Mo-induced Si ordered structures, (2) a small volume of a new Mo3Si2 structural variant, intergrown with the Si ordered structure, and (3) a small amount of pure Mo nanoparticles covering the surface of the cones. The formation of the large and uniform cones may provide a new surface configuration for potential applications in surface science and technology.