Ultrastrong and ductile BCC high-entropy alloys with low-density via dislocation regulation and nanoprecipitates

The high strength is a typical advantage of body-centered-cubic high-entropy alloys(BCC–HEAs).However,brittleness and weak strain-hardening ability are still their Achilles'heel.Here,extraordinary strength together with good tensile ductility are achieved in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(100-x)Al_(x) alloys(at.%,x=10 and 20)at room temperature.Relatively low densities of less than 6 g/cm^(3)are exhibited in these alloys.Designing nanoprecipitates and diversifying dislocation motions are the keys to achieving such salient breakthrough.It is worth noting that the tensile strength of 1.8 GPa in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(80)Al_(20)alloy is a record-high value known in reported BCC–HEAs,as well as a tensile strain over 8%.Furthermore,the maximum strain of~25%in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(90)Al_(10)alloy can challenge existing limit value,and is accompanied with a tensile strength of 1.2 GPa.The current work does not only provide novel ultra-strong and tough structural materials with low density,but also sheds new light on designing BCC–HEAs with attractive performances and strain-hardening ability.

High-temperature strength-coercivity balance in a FeCo-based soft magnetic alloy via magnetic nanoprecipitates

Precipitation strengthening is an effective approach to enhance the strength of soft magnetic alloys for applications at high temperatures,while inevitably results in deterioration in coercivity due to the pinning effect on the domain wall movement.Here,we realize a good combination of high-temperature strength and ductility(ultimate tensile strength of 564 MPa and elongation of~20%,respectively)as well as low coercivity(6.97 Oe)of FeCo-2V-0.3Cr-0.2Mo soft magnetic alloy through introducing high-density magnetic nanoprecipitates.The magnetic nanoprecipitates are characterized by FeCo-based phase with disordered body-centered cubic structure,which enables the alloy to have a low coercivity.In addition,these nanoprecipitates can impede the dislocation motion and suppress the brittle fracture,which lead to a high tensile strength and ductility.This work provides a guideline to enhance strength and ductility while maintaining low coercivity in soft magnetic alloys via magnetic nanoprecipitates.

Effect of rapid cold stamping on fracture behavior of long strip S′phase in Al−Cu−Mg alloy

High-angle annular dark-field scanning transmission electron microscopy and selected area electron diffraction techniques were used to study the mechanism that underlies the influence of rapid cold-stamping deformation on the fracture behavior of the elongated nanoprecipitated phase in extruded Al−Cu−Mg alloy.Results show that the interface between the long strip-shaped S′phase and the aluminum matrix in the extruded Al−Cu−Mg alloy is flat and breaks during rapid cold-stamping deformation.The breaking mechanisms are distortion and brittle failure,redissolution,and necking.The breakage of the long strip S′phase increases the contact surface between the S′phase and the aluminum matrix and improves the interfacial distortion energy.This effect accounts for the higher free energy of the S′phase than that of the matrix and creates conditions for the redissolution of solute atoms back into the aluminum matrix.The brittle S′phase produces a resolved step during rapid cold-stamping deformation.This step further accelerates the diffusion of solute atoms and promotes the redissolution of the S′phase.Thus,the S′phase necks and separates,and the long strip-shaped S′phase in the extruded Al−Cu−Mg alloy is broken into a short and thin S′phase.

Enhanced transdermal delivery of meloxicam by nanocrystals: Preparation, in vitro and in vivo evaluation

Meloxicam(MLX) is efficient in relieving pain and inflammatory symptoms, which, however, is limited by the poor solubility and gastrointestinal side effects. The objective of this study is to develop a nanocrystal formulation to enhance transdermal delivery of MLX. MLX nanocrystals were successfully prepared by the nanoprecipitation technique based on acidbase neutralization. With poloxamer 407 and Tween 80(80/20, w/w) as mixed stabilizers,MLX nanocrystals with particle size of 175 nm were obtained. The crystalline structure of MLX nanocrystals was confirmed by both differential scanning calorimetry and X-ray powder diffractometry. However, the nanoprecipitation process reduced the crystallinity of MLX.Nanocrystals increased both in vitro and in vivo transdermal permeation of MLX compared with the solution and suspension counterparts. Due to the enhanced apparent solubility and dissolution as well as the facilitated hair follicular penetration, nanocrystals present a high and prolonged plasma MLX concentration. And 2.58-and 4.4-fold increase in AUC0 →2 4 h was achieved by nanocrystals comparing with solution and suspension, respectively. In conclusion, nanocrystal is advantageous for transdermal delivery of MLX.

Polymeric assembled nanoparticles through kinetic stabilization by confined impingement jets dilution mixer for fluorescence switching imaging

Traditional fluorescence switching molecules achieving the state change between on and off states commonly based on UV irradiation. However, it is worth noting that UV irradiation is harmful to both the cancer cells and the normal cells. To achieve fluorescence switching under visible wavelength and avoid complicate molecular design, a fluorophore of 2,4,5,6-tetrakis(carbazol-9-yl)-1,3-dicyanobenzene(4Cz IPN) and a quencher of diarylethene(DAE) were physically incorporated within the biocompatible block copolymer poly(lactic-co-glycolic acid)-b-poly(ethylene glycol)(PLGA-b-PEG) to form 4Cz IPNDAE nanoparticles(NPs) through flash nanoprecipitation(FNP). By using the FNP method, the NPs were prepared within milliseconds in a confined impingement jets dilution(CIJ-D) mixer. Quenching and recovery of fluorescence could achieve in the presence of DAE under 475 nm and 560 nm irradiation.Appropriate structure and fluorescent properties of the nanoparticles can be tuned by external conditions for their efficient fluorescence resonance energy transfer(FRET) in a kinetic stabilization process. This NPs formation process was further optimized by varying the dilution ratio, Reynolds number(Re) and polymer concentration to modulate the mixing and particle nucleation and growth process. The size and fluorescence switching properties of the NPs were systematically investigated in solution and in cellular uptake experiments. This work is anticipated to provide a simple and highly effective engineering strategy for the modulation of fluorescence switching nanoparticles and beneficial to its engineering application.

Study on Confined Impinging Jet Mixer and Mechanism of Flash Nanoprecipitation

Nanoparticles have been given considerable attention and applied in many fields because of their properties that are superior to and more distinct than those of conventional materials. In practice, a stable and reproducible manufacturing process is highly desirable. This review presents the flash nanoprecipitation, a new technique that can rapidly produce nanoparticles. Moreover, the mixing process, the mechanism of particle formation, and the mixer design are discussed.Furthermore, the factors controlling the size stability of the produced nanoparticles are summarised in this review.

Enhancing pharmaceutical potential and oral bioavailability of Allium cepa nanosuspension in male albino rats using response surface methodology

Objective:To enhance the pharmaceutical potential and oral bioavailability of quercetin contents of Allium cepa peel extract by novel nanosuspension technology.Methods:Nanoprecipitation approach was successfully used for the formulation of nanosuspension.To obtain pharmaceutical-grade nanosuspension with minimum particle size and polydispersity index,sodium lauryl sulphate was selected as a stabilizer.Important formulation parameters were statistically optimized by the response surface methodology approach.The optimized nanosuspension was subjected to stability and in vitro dissolution testing and characterized by scanning electron microscopy,atomic force microscopy,Fourier transform infrared spectroscopy,and zeta sizer.To evaluate the preeminence of nanosuspension over coarse suspension,comparative bioavailability studies were carried out in male albino rats.The pharmaceutical potential of developed nanosuspension was evaluated by antioxidant,antimicrobial,and toxicity studies.Results:The optimized nanosuspension showed an average particle size of 275.5 nm with a polydispersity index and zeta potential value of 0.415 and−48.8 mV,respectively.Atomic force microscopy revealed that the average particle size of nanosuspension was below 100 nm.The formulated nanosuspension showed better stability under refrigerated conditions.Nanosuspension showed an improved dissolution rate and a 2.14-fold greater plasma concentration of quercetin than coarse suspension.Moreover,the formulated nanosuspension exhibited enhanced antioxidant and antimicrobial potential and was non-toxic.Conclusions:Optimization of nanosuspension effectively improves the pharmaceutical potential and oral bioavailability of Allium cepa extract.

Development and evaluation of a hot-rolled 780 MPa steel sheet with an ultra-high expansion ratio

This paper explores the development of a 780 MPa hot-rolled high-strength steel with an ultra-high hole expansion ratio(HER) by using a nanoprecipitation-controlled technology.Systematic analysis and evaluation of an industrially produced steel sheet have been performed to investigate the microstructure, nanoprecipitates, tensile properties, HER,bendability, and forming limit diagram.The newly developed 780 MPa hot-rolled high-strength steel sheet is composed of a fully ferritic microstructure of approximately 5 μm with precipitates of approximately 4-5 nm in ferrite grain interiors.The yield strength and tensile strength can reach above 700 and 780 MPa, respectively.Moreover, the fractured elongation is higher than 19% in the transversal direction, and the average HER exceeds 70%.Furthermore, the newly developed 780 MPa high-strength steel has good bendability reaching R/t=0.2 at 90°.Compared with the conventional 780 MPa high-strength steel, the newly developed 780 MPa high-strength steel exhibits superior forming ability, which is suitable for the production of complex components.High-cycle fatigue indicates that the fatigue limit of the newly developed high-strength steel is 430 MPa under a stress ratio of r=-1,indicating good fatigue properties.The excellent combined mechanical properties of the newly developed 780 MPa high-strength steel are attributed to the grain-refined ferritic microstructure with nanoprecipitates in ferrite grain interiors.

Dye Regeneration Kinetics of C343-Sensitized Nickel Oxide Investigated by Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) feedback mode has been used to investigate kinetics of dye regeneration in DSSC. Organic dye C343 and CW1 are used as sensitizers for nickel oxide (NiO) photoelectrochemical cells. The influence of film thickness on dye regeneration kinetics in the films for NiO/C343 for six different films was investigated. SECM was used to analyze effective rate constant, keff and reduction rate kred, absorption cross section, Φhv for the dye regeneration process. The data reveal a significant variation of keff and kred with a variation of light intensity, sample thickness and dye difference. This research found remarkable dependence of the dye regeneration kinetic parameters on illumination flux, dye types and film thickness of electrode.

Antioxidant and Cytotoxic Activities of Clove Oil Nanoparticles and Evaluation of Its Size and Retention Efficiency

A derivation of the nanoprecipitation technique without the presence of surfactants to reduce the nanoparticle size is herein proposed. The absence of surfactant in the nanoprecipitation technique allows capturing particles with a smaller diameter than nanoparticles containing surfactants, facilitating the migration of antioxidant nanoparticles in film packaging. Biodegradable PLA nanoparticles with clove oil were produced and characterized by dynamic light scattering, zeta potential, Fourier transform infrared spectroscopy, retention efficiency, cytotoxicity, and antioxidant activity. The particle sizes obtained were smaller than those commonly produced by nanoprecipitation, monodispersed and stable for 6 months. The antioxidant activity showed that the encapsulated form of clove oil had greater antioxidant activity than unencapsulated clove oil. The addition of PLA nanoparticles decreased the cytotoxic action of eugenol, the main antioxidant component of clove oil.

High strength Al_(0.7)CoCrFeNi_(2.4)hypereutectic high entropy alloy fabricated by laser powder bed fusion via triple-nanoprecipitation

Eutectic high-entropy alloys,composed of FCC/B2 phases with a narrow solidification interval and excel-lent fluidity,have become a new hotspot in additive manufacturing.Nevertheless,their microstructures exhibit significant sensitivity to processing parameters,feedstocks,and composition,ultimately limiting the alloys’engineering applications.Here,a hypereutectic Al_(0.7)CoCrFeNi_(2.4)alloy with a low cracking sus-ceptibility index was designed by Thermo-Calc calculation and fabricated by laser powder bed fusion.Results show that the as-printed Al_(0.7)CoCrFeNi_(2.4)alloy manifests a stable cellular structure,coupled with appreciable ultimate tensile strength(≥1200 MPa)and ductility(≥20%)over a wide range of process-ing parameters.After aging at 800℃for 30 min,outstanding strength(1500 MPa)and elongation(15%)were obtained.Considerable mechanical properties after aging stem from a triple strengthening mecha-nism,i.e.,L1_(2) nanoprecipitates and rod-shaped B2 particles within the FCC matrix,along with Cr-enriched spherical nanoparticles in the B2 phase.Meanwhile,hierarchical structure,i.e.,FCC dominated matrix,a discontinuous B2 phase,a precipitation-free zone in the B2 phase,and a K-S orientation relationship be-tween FCC and B2,facilitate to maintain excellent plasticity.These results guide designing HEAs by AM with controllable microstructures and outstanding mechanical properties for industrial applications.

Preparation of microparticles and nanoparticles using membrane-assisted dispersion,micromixing,and evaporation processes

Synthetic microporous membranes are increasingly used for energy-efficient and controlled production of micro-and nanoparticles and micro-and nanoemulsions with tuneable morphology and physico-chemical properties through various micromixing,emulsification,and evaporation processes.In emul-sification processes,the membrane pores are used for dispersed phase injection and size-controlled generation of droplets and droplet-templated particles.In micromixing processes,membrane is utilised as a micromixer for mixing two miscible liquids,usually solvent and antisolvent-rich solutions,which leads to the creation of supersaturation and subsequent nanoprecipitation or crystallisation.In mem-brane evaporation processes,membrane is used to prevent phase dispersion while allowing efficient molecular diffusion of solvent and/or antisolvent vapour through gas-filled pores.Membrane dispersion processes can be operated continuously by decoupling shear stress on the membrane surface from cross flow using tube insets,flow pulsations,swirling flow,membrane oscillations or membrane rotations.Droplet generation and solidification can be performed continuously in a single pass by connecting membrane module with a downstream reactor.Membrane dispersion processes can be used for pro-duction of nanoparticles such as nanovesicles(liposomes,micelles,ethosomes,and niosomes),nanogels,polymeric,lipid and metallic nanoparticles,and nanocrystals.The main advantages of membrane-assisted particle generation are in low energy consumption,controlled geometry and hydrodynamic conditions at the microscale level,flexible throughput due to modular and scalable design of membrane devices,and a wide choice of available microporous membranes with various wall porosities,wetta-bilities,pore sizes,and pore morphologies to suit different applications.

Template-free nanostructured particle growth via a one-pot continuous gradient nanoprecipitation

Engineered nanoparticles have emerged as new types of materials for a wide range of applications from therapeutics to energy.Still,fabricating nanomaterials presenting complex inner morphologies and shapes in a simple manner remains a great challenge.Herein,we report the template-free one-pot continuous gradient nanoprecipitation of different types of non-compatible polymers to spontaneously form nanostructured particles.The continuous addition of antisolvent induces precipitation and(re)organization of polymer chains at the forming particle interface,ultimately and naturally developing complex inner morphologies and shapes while particle grows.This low-energy-cost bottom-up assembly approach applies to various functional polymers,possibly embedded with metal nanoparticles,for continuous growth into well-organized nanoparticles.UV crosslinking of the particles and core removal allows both confirming the building process and leading to hollow or multivoid nanomaterials.

Cu-assisted austenite reversion and enhanced TRIP effect in maraging stainless steels

Control of the formation and stability of reverted austenite is critical in achieving a favorable combination of strength,ductility,and toughness in high-strength steels.In this work,the effects of Cu precipitation on the austenite reversion and mechanical properties of maraging stainless steels were investigated by atom probe tomography,transmission electron microscopy,and mechanical tests.Our results indicate that Cu accelerates the austenite reversion kinetics in two manners:first,Cu,as an austenite stabilizer,increases the equilibrium austenite fraction and hence enhances the chemical driving force for the austenite formation,and second,Cu-rich nanoprecipitates promote the austenite reversion by serving as heterogeneous nucleation sites and providing Ni-enriched chemical conditions through interfacial segregation.In addition,the Cu precipitation hardening compensates the strength drop induced by the formation of soft reverted austenite.During tensile deformation,the metastable reverted austenite transforms to martensite,which substantially improves the ductility and toughness through a transformation-induced plasticity(TRIP)effect.The Cu-added maraging stainless steel exhibits a superior combination of a yield strength of~1.3 GPa,an elongation of~15%,and an impact toughness of~58 J.

Control of dislocation density maximizing precipitation strengthening effect

The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing the ductility.Stable nanoprecipitates have been successfully acquired by nanostructural design,but the number density of nanoprecipitates cannot be further increased.Researchers attempted to enhance number density by introducing highly potent nucleation sites(e.g.,dislocations).However,there remains controversy over the influence of dislocations on the nucleation and growth of coherent nanoprecipitates with minimized nucleation barrier.Here,Cu-rich nanoprecipitates in an HSLA steel,as a typical type of coherent nanoprecipitates,are investigated.By combining analytical calculation and experiments,we show that dislocations are harmful for the formation of large numbered Cu-rich nanoprecipitates in a certain density range.Insufficient dislocations deprive solute atoms which decrease homogenous precipitation that cannot be compensated by the increase in heterogeneous precipitation.Under such circumstance,Cu-rich nanoprecipitates have smaller number density but larger size and higher fraction of incoherent structures due to rapid Ostwald ripening.As a result,by controlling dislocation density,the yield strength is increased by 24%without obvious loss in ductility as compared with traditional solution-quench-age process.Our work would help to optimize composition and processing routes that fully exploit the nanoprecipitation strengthening effect.

Atomic-scale characterization of multiple precipitating species in a precipitation-hardened martensitic stainless steel

Multiple precipitating species in a 2.2 GPa grade precipitation-hardened martensitic stainless steel with balanced ductility were characterized at atomic scale by atom probe tomography.The results indicated that the clustering of solute atoms was promoted with progressive aging treatments.(Cr,Mo)-rich carbide(M_(2)C)precipitated at the linear dislocations in the as-aged steels.Obvious segregation of Cr,Mo,and C at phase boundaries favored the precipitation of carbide and caused the formation of Cr-lean domains.Spinodal decomposition of martensitic matrix during aging led to the substantial precipitation of fine Cr-rich(α′Cr)phase.Compared with the first aging treated samples,a synergistic enhancement of both strength and ductility of the secondary aging treated(SAT)samples was primarily ascribed to the enhanced precipitation of Cr-rich phase.Additionally,Ni-rich filmy reversed austenite precipitated at the lath boundary,which was beneficial to the ductility of SAT samples.

Ultrastrong and ductile(CoCrNi)_(94)Ti_(3)Al_(3)medium-entropy alloys via introducing multi-scale heterogeneous structures

The coarsening-grained single-phase face-centered cubic(fcc)medium-entropy alloys(MEAs)normally exhibit insufficient strength for some engineering applications.Here,superior mechanical properties with ultimate tensile strength of 1.6 GPa and fracture strain of 13.1%at ambient temperature have been achieved in a(CoCrNi)_(94)Ti_(3)Al_(3)MEA by carefully architecting the multi-scale heterogeneous structures.Electron microscopy characterization indicates that the superior mechanical properties mainly originated from the favorable heterogeneous fcc matrix(1-40μm)and the coherent sphericalγ’precipitates(10-100 nm),together with a high number density of crystalline defects(2-10 nm),including dislocations,small stacking faults,Lomer-Cottrell locks,and ultrafine deformation twins.

Heterogeneous lamella design to tune the mechanical behaviour of a new cost-effective compositionally complicated alloy

A heterogeneous lamella(HL)design strategy was applied to manipulate mechanical properties of a new cost-effective Fe_(35)Ni_(35)Cr_(25)Mo_(5)compositionally complicated alloy(CCA).The HL structure was produced by single-step heat treatment(800℃for 1 h)after cold rolling.This HL structure consists of alternative lamellae regions of coarse-grained FCC matrix(5-20μm),and regions containing ultra-fine grains or subgrains(200-500 nm)together with nanoprecipitates(20-500 nm)and annealing twins.As compared with other cost-effective CCAs,the 800℃annealed sample with HL structure demonstrated a comparable tensile property,with yield strength over 1.0 GPa and total elongation of~13%.Formation of the annealing twins and nanoprecipitates decorated HL structure was a result of the concurrent partial recrystallization and precipitation ofσphase at the shear bands with a high density of lattice defects(e.g.high-density dislocation walls and deformation twins).The latter restricted the growth of recrystallized grains,leading to the formation of ultrafine subgrains within the HL structure.The high yield strength resulted from the multistage hetero-deformation induced(HDI)strengthening and precipitation strengthening associated with heterogeneous lamella structures containing nanoprecipitates.The ductility was originated from the coexistence of multiple deformation mechanisms,which started with dislocation slip and formation of stacking faults at the initial stage,followed by nano-twinning at the higher strain level.This HL design strategy,comprising composition and thermomechanical process designs,and the resultant microstructure tuning,open a broader window for the development of cost-effective CCAs with enhanced performance.

Ultrastrong steel strengthened by multiple shearable nanostructures

Precipitation of multiple strong nanoprecipitates is crucial for the development of ultrahigh-strength structural materials with a strength of 2.5 GPa or above.Nevertheless,the ductility usually loses rapidly with strength due to limited dislocation mobility and high cracking tendency if coarse non-deformable precipitates are employed.Herein,we report a 2.5 GPa maraging steel strengthened by an ultrahigh den-sity of intermeshed shearable nanostructures consisting of Ni(Al,Fe)nanoprecipitates and Mo-rich(∼30 at.%)disordered clusters,both of which assume coherent interfaces.The fully coherent B2-Ni(Al,Fe)par-ticles precipitate in an extremely fast fashion,effectively accelerating local aggregation of low-diffusivity Mo atoms and promoting the formation of Mo-rich clusters surrounding them.This elemental partition was found to be further enhanced by Co addition via depleting both residual Al and Mo within the ma-trix,leading to the formation of copious yet fine intermeshed nanostructures.During plastic deformation,the interlocked nanostructures not only enhance local cutting stress by combining long-range elastic and short-range chemically ordering effects but also improve dislocation activity and resist shear-induced plastic instability.The multiple shearable nanostructures endow decent ductility(>6%)of the 2.5 GPa steel,suggesting a new paradigm for designing ultrastrong steels.

Application of flash nanoprecipitation to fabricate poorly water-soluble drug nanoparticles

Nanoparticles are considered to be a powerful approach for the delivery of poorly watersoluble drugs. One of the main challenges is developing an appropriate method for preparation of drug nanoparticles. As a simple, rapid and scalable method, the flash nanoprecipitation(FNP) has been widely used to fabricate these drug nanoparticles, including pure drug nanocrystals, polymeric micelles,polymeric nanoparticles, solid lipid nanoparticles, and polyelectrolyte complexes. This review introduces the application of FNP to produce poorly water-soluble drug nanoparticles by controllable mixing devices, such as confined impinging jets mixer(CIJM), multi-inlet vortex mixer(MIVM) and many other microfluidic mixer systems. The formation mechanisms and processes of drug nanoparticles by FNP are described in detail. Then, the controlling of supersaturation level and mixing rate during the FNP process to tailor the ultrafine drug nanoparticles as well as the influence of drugs, solvent, anti-solvent, stabilizers and temperature on the fabrication are discussed. The ultrafine and uniform nanoparticles of poorly watersoluble drug nanoparticles prepared by CIJM, MIVM and microfluidic mixer systems are reviewed briefly. We believe that the application of microfluidic mixing devices in laboratory with continuous process control and good reproducibility will be benefit for industrial formulation scale-up.