Evolution of lamellar structure in Ti-47Al-2Nb-2Cr-0.2W alloy sheet

The Ti-47Al-2Nb-2Cr-0.2W alloy sheets were obtained by hot pack rolling. The as-rolled sheet has an inhomogeneous duplex microstructure composed of elongated gamma grains and lamellar colonies. Heat treatments were conducted on the as-rolled sheets. The results show that the microstructures with different sizes and grain boundary morphologies were developed after different heat treatments. A coarse fully lamellar structure can be refined if the heating time, together with the cooling rate, is appropriately controlled. The grain growth exponent is found to be approximately 0.2, and the activation energy of grain boundary migration of the alloy is around 225 kJ/mol.

Subtransus deformation mechanisms of TC11 titanium alloy with lamellar structure

Isothermal compression tests are applied to study the deformation mechanisms of TCll titanium alloy with lamellar structure under the deformation temperature range of 890-995 ℃ and strain rate range of 0.01-10 s^-1. According to the flow stress data obtained by compression tests, the deformation activations are calculated based on kinetics analysis of high temperature deformation, which are then used for deformation mechanism analysis combined with microstructure investigation. The results show that deformation mechanisms vary with deformation conditions： at low strain rate range, the deformation mechanism is mainly dislocation slip; at low temperature and high strain rate range, twinning is the main mechanism; at high temperature and high strain rate range, the deformation is mainly controlled by diffusion offl phase.

LAMELLAR STRUCTURE OF THERMOTROPIC LIQUID CRYSTALLINE POLYMERS

The lamellar structure of a thermotropic aromatic polyester with flexible spacer has beenstudied by using transmission electron microscopy. It was found that the lamellar structure couldbe observed in the crystalline samples of this semirigid polymer crystallized from different states.The thickness of lamellae is around 10 nm, which is similar to that of the conventional polymersof flexible chain molecules. The molecular chains in the lamellae are oriented in the thicknessdirection as determined by electron diffraction. The possibility of molecular chains folding in the lamellae has been discussed.

Photo-cured phase change energy storage material with photo-thermal conversion, self-cleaning and electromagnetic shielding performances via the lamellar structure strengthened by segment rearrangement of dynamic disulfide bond

At present,phase change materials(PCMs)with single function hardly meet the needs of advanced intelligent materials in practical applications,and the multifunction integration is the current trend.However,photo-cured multifunctional PCMs are hampered by insufficient transparency due to adding functional fillers,such as carbon and metal materials.The novel strategy is necessary to overcome this limitation.Here,a photo-cured multifunctional PCM is prepared by using the design of a lamellar structure composing the photo-cured phase change polymer layer and the functional fillers layer.The curing of the phase change polymer is realized by the photo-induced"thiol-ene"click reaction,and reversible dynamic disulfide bonds are introduced into the PCM,which not only gives the phase change crosslinked network reprocessability,but also strengthens the interface layer by the chain rearrangement to form a stable composite structure.The carboxylated multiwalled carbon nanotubes(CCNTs)and silver nanowires(AgNWs),as functional fillers,give the PCM photo-thermal conversion,self-cleaning and electromagnetic shielding(EMI SE)performances.Its phase change latent heat and photo-thermal conversion can reach 105.2 J/g and 78.5%,and the water contact angle is 142°with self-cleaning performance.In addition,due to the dense and well-developed conductive path formed by AgNWs layer on the PCM surface,the EMI SE effect can reach 39 dB with only 6.3%(in mass)filler content and 7.2%phase change latent heat loss.As far as we know,this is the first report about photo-cured PCMs with self-cleaning,photo-thermal conversion and EMI SE performances.

Effects of processing parameters on fabrication defects,microstructure and mechanical properties of additive manufactured Mg–Nd–Zn–Zr alloy by selective laser melting process

Mg–3Nd–0.2Zn–0.4Zr(NZ30K,wt.%)alloy is a new kind of high-performance metallic biomaterial.The combination of the NZ30K Magnesium(Mg)alloy and selective laser melting(SLM)process seems to be an ideal solution to produce porous Mg degradable implants.However,the microstructure evolution and mechanical properties of the SLMed NZ30K Mg alloy were not yet studied systematically.Therefore,the fabrication defects,microstructure,and mechanical properties of the SLMed NZ30K alloy under different processing parameters were investigated.The results show that there are two types of fabrication defects in the SLMed NZ30K alloy,gas pores and unfused defects.With the increase of the laser energy density,the porosity sharply decreases to the minimum first and then slightly increases.The minimum porosity is 0.49±0.18%.While the microstructure varies from the large grains with lamellar structure inside under low laser energy density,to the large grains with lamellar structure inside&the equiaxed grains&the columnar grains under middle laser energy density,and further to the fine equiaxed grains&the columnar grains under high laser energy density.The lamellar structure in the large grain is a newly observed microstructure for the NZ30K Mg alloy.Higher laser energy density leads to finer grains,which enhance all the yield strength(YS),ultimate tensile strength(UTS)and elongation,and the best comprehensive mechanical properties obtained are YS of 266±2.1 MPa,UTS of 296±5.2 MPa,with an elongation of 4.9±0.68%.The SLMed NZ30K Mg alloy with a bimodal-grained structure consisting of fine equiaxed grains and coarser columnar grains has better elongation and a yield drop phenomenon.

CREEP OF A POLYCRYSTALLINE NEAR γ-TiAl Alloy WITH A LAMELLAR MICROSTRUCTURE

Creep of a polycrystalline near γ-TiAl alloy in two fully lamellar conditions is presented. A lamellar structure with fine interface spacing and planar grain boundaries provides improved creep resistance. The lamellar structure with wide interface spacing and interlocked grain boundaries has <1/2 the creep life, five times the minimum strain rate and greater tertiary strain.Creep strain is accommodated by dislocation motion in soft grains, but the strain rate is controlled by hard grains. The resistance to fracture is controlled by the grain boundary morphology, with planar boundaries causing intergranular fracture.To maximize the creep resistance of near γ-TiAl with a lamellar microstructure requires narrow lamellar interface spacing and interlocked lamellae along grain boundaries.

LAMELLAR MICROSTRUCTURE IN DUPLEX Ti-Al-V INTERMETALLIC COMPOUND

The morphology and crystallographic orientation of(α_2+γ)lamellar structure in duplex Ti-47.5Al-2.5V intermetallic compound have been studied by means of TEM, microdiffraction as well as 180° and non-180° rotation twinning analysis.A possible atomic model of the interface was suggested.Thus,approach was made to a mechanism on complex nucleation of α_2+γ two phases along α-Ti interface,and growth of α_2/γ/γ_1/α_2 or α_2/γ/α_2/γ as fundamental structural unit.

Formation of Stable Lamellar Gel Structure Containing Pseudoceramide and Its Evaluation of Barrier Recovery Function

We formulated new skin care cosmetics with lamella structure in which high amount of pseudo-ceramides were incorporated. Consistency of this lamellar gel creams were checked for 1 month on various temperatures and for 1 year on RT. Generally, multi-lamellar emulsion shows typical Maltese cross on polarized microscope, but Maltese cross was not found in case of these creams; Multi-lamellar structure of the creams could be identifed by small-angle X-ray scattering （SAXS）. To evaluate skin barrier recovery function, we applied one of this creams and a vehicle cream to forearm skin which is tape-stripped to remove barrier layer to see if they infuence mass of molecules related to barrier function. 96 h after application, we found that this lamellar gel cream promoted synthesis of ceramides, amino acids and NMFs, thereby enhanced barrier recovery function.

Microstructure stability of Ti_2Al N/Ti-48Al-2Cr-2Nb composite at 900 °C

Microstructure stability of in situ synthesized Ti2AlN/Ti-48Al-2Cr-2Nb composite during aging at 900 ℃ was investigated by XRD, OM and TEM, and the unreinforced Ti-48Al-2Cr-2Nb alloy was also examined for comparison. The result showed that in the TiAl alloy,α2 lamellae thinned and were broken down, and became discontinuous with increasing aging time. The decomposition ofα2 lamella toγ which was characterized by parallel decomposition and breakdown ofα2 lamellae led to the degradation of the lamellar structure. While in the composite, lamellar structure remained relatively stable even after aging at 900 ℃ for 100 h. No breakdown ofα2 lamellae except parallel decomposition and precipitation of fine nitride particles was observed. The better microstructural stability of the composite was mainly attributed to the precipitation of Ti2AlN particles at theα2/γ interface which played an important role in retarding the coarsening of lamellar microstructure in the matrix of composite.

Dual-Defect Engineering Strategy Enables High-Durability Rechargeable Magnesium-Metal Batteries

Rechargeable magnesium-metal batteries(RMMBs)are promising next-generation secondary batteries;however,their development is inhibited by the low capacity and short cycle lifespan of cathodes.Although various strategies have been devised to enhance the Mg^(2+)migration kinetics and structural stability of cathodes,they fail to improve electronic conductivity,rendering the cathodes incompatible with magnesium-metal anodes.Herein,we propose a dual-defect engineering strategy,namely,the incorporation of Mg^(2+)pre-intercalation defect(P-Mgd)and oxygen defect(Od),to simultaneously improve the Mg^(2+)migration kinetics,structural stability,and electronic conductivity of the cathodes of RMMBs.Using lamellar V_(2)O_(5)·nH_(2)O as a demo cathode material,we prepare a cathode comprising Mg_(0.07)V_(2)O_(5)·1.4H_(2)O nanobelts composited with reduced graphene oxide(MVOH/rGO)with P-Mgd and Od.The Od enlarges interlayer spacing,accelerates Mg^(2+)migration kinetics,and prevents structural collapse,while the P-Mgd stabilizes the lamellar structure and increases electronic conductivity.Consequently,the MVOH/rGO cathode exhibits a high capacity of 197 mAh g^(−1),and the developed Mg foil//MVOH/rGO full cell demonstrates an incredible lifespan of 850 cycles at 0.1 A g^(−1),capable of powering a light-emitting diode.The proposed dual-defect engineering strategy provides new insights into developing high-durability,high-capacity cathodes,advancing the practical application of RMMBs,and other new secondary batteries.

Achieving High Strength-plasticity of Nanoscale Lamellar Grain Extracted from Gradient Lamellar Nickel

Traditional metallic materials usually face a dilemma between high strength and poor strain hardening capacity.However,heterogeneous structured metallic materials have been found to obviously overcome the trade-of.Herein,gradient lamellar structure was fabricated through ultrasound-aided deep rolling technique in pure Ni with high stacking fault energy after heat treatment.The gradient lamellar Ni was successively divided into the four regions.In-situ micropillar compression tests were conducted in diferent regions to reveal the corresponding microscopic mechanical properties.Microscopic characterization techniques were performed to explore underlying deformation mechanisms and the efects of microstructural parameters on deformation behaviors.This work demonstrates that the micropillar with near nanoscale lamellar thickness possesses excellent strength and plasticity.On one hand,the reason for high strength of near nanoscale micropillar is that the strength of micropillar increases with the decrease of lamellar thickness according to the Hall-Petch efect.On the other hand,numerous lamellar grain boundaries perpendicular to the loading direction is found to hinder the motion of slip bands,resulting in great strain hardening capacity in the near nanoscale lamellar micropillar.

Effect of annealing on the microstructures and Vickers hardness at room temperature of intermetallics in Mo-Si system

The microstructures and Vickers hardness at room temperature of arc-meltingprocessed intermetallics of Mo_5Si_3-MoSi_2 hypoeutectic alloy and hypereutectic alloy annealed at1200℃ for different time were investigated. Lamellar structure consisted of Mo_5Si_3 (D8m) phaseand MoSi_2 (C11_b) phase was observed in all the alloys. For Mo_5Si_3-MoSi_2 hypoeutectic alloy, thelamellar structure was found only after annealing and developed well with fine spacing on the orderof hundred nanometers after annealing at 1200℃ for 48 h. But when the annealing time was up to 96h, the well-developed lamellar structure was destroyed. For Mo_5Si_3-MoSi_2 hypereutectic alloy, thelamellar structure was found both before and after annealing. However the volume fraction andspacing of the lamellar structure did not change significantly before and after annealing. Theeffects of the formation, development and destruction of lamellar structure on Vickers hardness ofalloys were also investigated. When Mo_5Si_3-MoSi_2 hypoeutectic alloy annealed at 1200℃ for 48 h,the Vickers hardness was improved about 19% compared with that without annealing and formation oflamellar structure. The highest Vickers hardness of Mo5Si3-MoSi_2 hypereutectic was increasing about18% when annealing at 1200℃ for 48 h.

Lamellar quasi-solid electrolyte with nanoconfined deep eutectic solvent for high-performance lithium battery

Electrolytes with high-efficiency lithium-ion transfer and reliable safety are of great importance for lithium battery.Although having superior ionic conductivity(10^(−3)–10^(−2) S·cm^(−1)),traditional liquid-state electrolytes always suffer from low lithium-ion transference number(tLi+<0.4)and thus undesirable battery performances.Herein,the deep eutectic solvent(DES)is vacuum-filtered into the~1 nm interlayer channel of vermiculite(Vr)lamellar framework to fabricate a quasi-solid electrolyte(Vr-DES QSE).We demonstrate that the nanoconfinement effect of interlayer channel could facilitate the opening of solvation shell around lithiumion.Meanwhile,the interaction from channel wall could inhibit the movement of anion.These enable high-efficiency lithium-ion transfer:2.61×10^(−4)S·cm^(−1)at 25℃.Importantly,the tLi+value reaches 0.63,which is 4.5 times of that of bulk DES,and much higher than most present liquid/quasi-solid electrolytes.In addition,Vr-DES QSE shows significantly improved interfacial stability with Li anode as compared with DES.The assembled Li symmetric cell can operate stably for 1000 h at 0.1 mA·cm^(−2).The lithium iron phosphate(LFP)|Vr-DES QSE|Li cell exhibits high capacity of 142.1 mAh·g^(−1)after 200 cycles at 25℃ and 0.5 C,with a capacity retention of 94.5%.The strategy of open solvation shell through nanoconfinement effect of lamellar framework may shed light on the development of advanced electrolytes.

Slurry flow characteristics control of 3D printed ceramic core layered structure:Experiment and simulation

Vat photopolymerization 3D printing ceramic technology provides a feasible process for the preparation of complex internal cooling channels for aeroengine single crystal superalloy hollow blades.However,the typical layered structure characteristics of 3D printing ceramic technology led to the anisotropy of ceramic core strength and sintering shrinkage,which greatly affects the performance and accuracy of the complex structure core and requires further research and improvement.Herein,the influence of the thickness of the slurry layer on the flow characteristics of the slurry in the process of the vat photopolymerization 3D printing slurry spreading was systematically studied by the method of simulation and experiment.The simulation results show that the positions of the turbulent zone and maximum velocity zone in the scraper front affect the redistribution of powder particles with different sizes.The layered structure was caused by the redistribution of ceramic particles of different sizes in the slurry layer.By controlling the turbulent flow zone and the maximum velocity zone of the scraper leading edge,the phenomenon of laminar flow can be weakened and the particle redistribution can be improved.With the increase of the thickness of the printing layer,the layered structure appears gradually,and the pores at the interface of the layered structure gradually concentrated into the interfacial pore lines from the uniform distribution,and the crack propagation changes from intergranular micro-crack to interlayer macro-crack.The combination of finite element simulation and experiment,through the slurry flow characteristics to control the layered structure of reductive vat photopolymerization ceramic core 3D printing,the control of crack propagation mode,element distribution and pore evolution of the core was accomplished,which lays a foundation for the performance control of ceramic 3D printing technology.

CHOLESTERIC LIQUID CRYSTALLINE CHARACTER ON THE SURFACE OF CHITOSAN/POLYACRYLIC ACID COMPOSITES

The cholesteric liquid crystalline structure in chitosan/polyacrylic acid composite films was studied by surface techniques. A periodical lamellar-like structure was observed in the permanganic acid etched film surface by both scanning electron microscopy (SEM) and atomic force microscopy (AFM), instead of the thumb-print texture which can be detected with polarized optical microscopy. It is suggested that the periodical lamellar-like structure is induced by the etching selectivity between cholesteric layers due to different molecular arrangement on the film surface. Four kinds of perpendicular disclinations, i.e. chi --> tau (-) + lambda (+), chi --> lambda (-) + tau (+), chi --> tau (-) + tau (+) and chi --> lambda (-) + lambda (+) were found in the composite films from SEM observations. The smallest periodicity of lamellar-like structure (equals to half pitch) is 20 similar to 40 nm measured with AFM.

MECHANISMS OF α_2→α_2/γ PHASE TRANSFORMATION IN A TiAL ALLOY

A Ti-45at.%Al alloy which was solution-treated at 1350℃ for 30 minutes and quenched in water is employed to explore mechanisms of α_2→γphase transformation. The ageing process of the quenched alloy has been in situ studied it has been found that the γ lamellae can precipitate in the α_2 matrix by two mechanisms. When The alloy is aged at 700℃, the stacking faults pre-existing in the α_2 matrix start to grow and more are generated.With the increase of ageing time and ageing temperature the density of stacking faults is increased and the γ lamellae then precipitate. This isα diffusion-controlled process. Alternatively, the γ lamellae may be formed from the α_2 matrix by 1/3(1100) shearing on the (0001) plane. The latter mechanism implies that the strain-induced transformation may occur, which is confirmed by deformation of the quenched alloy.

TEM Studies of δ-TiN_(0．5)→δ′-TiN_(0．5) Ordering Transformation

The nucleation and growth processes of the stoichiometric δ'-TiN_0.5 long-range ordered precipitates duringδ-TiN0.5 →δ'-TiN_0.5 ordering transformation were investigated by transmission electron inicroscopy (TEM).The nucleation of the new δ'-TiN_0.5 phase is homogeneous in the matrix. In general, the nucleation andgrowth of the new δ'-TiN_0.5 phase proceed preferentially on the { 110)M lattice planes of parent δ-TiN_0. s. Theδ'-TiN_0.5 precipitates are always of lamellar features formed by combination of the three equivalent orientationdomains with their habit planes parallel to {11 0 }M planes.

Molecular dynamics study of hydrogen-induced cracking behavior of ferrite–pearlite gas transmission pipeline steel

Hydrogen embrittlement of pipelines depends on the hydrogen-induced cracking behavior of the pipeline steel microstructure.Based on molecular dynamics analysis,the ferrite–cementite(α-Fe/Fe3C)lamellar atomic structure with the Bagaryatskii orientation relationship was established,and stepwise relaxation of the conjugate gradient energy minimization and constant-temperature and constant-pressure relaxation were performed under NPT(the isothermal–isobaric)conditions.The mechanical property curves of theα-Fe/Fe3C models were obtained under different cementite terminal plane structures,and the evolution of the atomic structure was analyzed in detail.In addition,the influence of different hydrogen concentrations,different temperatures,different strain rates,changes in voids,and different micro-degrees of freedom on the deformation and failure mechanism of the model was investigated,aiming to provide a reliable way to explore the micro-mechanism of macro-cracking behavior of pipeline steel.

Ultralight and ordered lamellar polyimide-based graphene foams with efficient broadband electromagnetic absorption

The development of high-performance microwave absorption materials with strong absorption capacity and broad bandwidth is highly desirable in the field of electromagnetic pollution protection.Herein,ultralight polyimide-based graphene foam with ordered lamellar structure is precisely designed and controllably constructed by bidirectional freezing process.More lamellar interfaces formed inside the foam per unit volume effectively facilitate the layer-by-layer dissipation for the vertical incident electromagnetic waves,thereby endowing the foam with efficient broadband electromagnetic absorption performance.More importantly,electromagnetic absorption performance can be controllably adjusted by optimizing impedance distribution and microstructure of skeletons.As a result,the optimized foam with an ultralow density of 9.10 mg/cm^(3)presents a minimum reflection loss value of-61.29 dB at 9.25 GHz and an effective absorption bandwidth of 5.51 GHz(7.06-12.57 GHz,covering the whole X band) when the thickness is 4.75 mm.