Highly Efficient Broadband Achromatic Microlens Design Based on Low-Dispersion Materials

Metalenses with achromatic performance offer a new opportunity for high-quality imaging with an ultracompact configuration;however,they suffer from complex fabrication processes and low focusing efficiency.In this study,we propose an efficient design method for achromatic microlenses on a wavelength scale using materials with low dispersion,an adequately designed convex surface,and a thickness profile distribution.By taking into account the absolute chromatic aberration,relative focal length shift(FLS),and numerical aperture(NA),microlens with a certain focal length can be realized through our realized map of geometric features.Accordingly,the designed achromatic microlenses with low-dispersion fused silica were fabricated using a focused ion beam,and precise surface profiles were obtained.The fabricated microlenses exhibited a high average focusing efficiency of 65%at visible wavelengths of 410-680 nm and excellent achromatic capability via white light imaging.Moreover,the design exhibited the advantages of being polarization-insensitive and near-diffraction-limited.These results demonstrate the effectiveness of our proposed achromatic microlens design approach,which expands the prospects of miniaturized optics such as virtual and augmented reality,ultracompact microscopes,and biological endoscopy.

Effect of Lamellar Orientation on Crack Paths in PST Crystals of γ-TiAl BasedAlloys

The effect of lamellar orientation on crack paths in PST crystals of y-TiAl based alloys was investigated by in-situ SEM technique. The results indicate that the crack paths in PST crystals of y-TiAl based alloys are strongly dependent on lamellar orientation ofPST crystals, and the differently oriented PST crystals show different nucleation and propagation mechanisms of crack, resulting in different levels of fracture toughness.

Effect of Refiner Plate Bar Angle and Pulp Properties on the Low Consistency Refining Efficiency in Terms of Power Consumption

Power consumption is the energy source of the impact on fibers or pulp during low-consistency(LC)pulp refining,and the strength of refining affects refining quality and efficiency.The pulp properties,operating parameters,and bar parameters of the refiner plates are important parameters affecting refining efficiency,which can be defined as the ratio of net to total refining power.In this study,LC refining trials for pulps with different consistencies and fiber lengths were conducted using five isometric straightbar plates with different bar angles to explore the influences of the plate bar angle and pulp properties on the no-load power,impact capacity on fibers and refining efficiency.It was found that the no-load power of the LC refining process decreased with an increase in the plate bar angle while increased when pulp with higher consistency was refined under the same refining conditions.However,the effect of pulp consistency on the no-load power can be neglected when refining is conducted using plates with larger bar angles.Meanwhile,a critical bar angle for straight-bar plates in LC refining may exist,which has the strongest impact on the pulp and highest refining efficiency under the same refining conditions.In addition,the impact capacity of the plate on the pulp and refining efficiency in LC refining can be enhanced by appropriately increasing the pulp consistency and average fiber length when the bar angle of the refiner plate with a sector angle of 40°is less than 30°.Therefore,the efficiency and power consumption of the LC refining process can be adjusted by optimizing the pulp consistency and bar parameters of the refining plates.

Interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308L stainless steel weld metal

In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reactor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The interactive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiatedδ-ferrite.For the effect of irradiation on the microstructure and hardening of thermally agedδ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spinodal decomposition,leading to a limited effect on hardening of thermally agedδ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interaction can causeδ-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.

Tailoring the austenite characteristics via dual nanoparticles to synergistically optimize the strength-ductility in cold rolled medium Mn steel

In this work,we proposed a novel Cu/θdual nanoparticles strategy to tailor the austenite characteris-tics of a medium Mn steel via a tempering-annealing process to optimize the mechanical properties.We explored the effects of Cu-rich particles and cementite precipitated in the tempering process on the austenite reversion during the subsequent annealing process.Both experiments and numerical simula-tions verified that the austenite inherited from cementite had a finer size and a higher Mn enrichment compared with the austenite originating from the tempered martensite matrix.In addition,quantitative evaluations revealed that the pinning effect exerted by the Cu-rich particles could significantly hinder theα/γinterface migration and the recrystallized grain growth,thereby further refining the final mi-crostructure.With contributions from the effects of dual nanoprecipitates on the austenite reversion,the heterogeneous austenite grains inherited from varying nucleation sites ensured the sustained and gradual deformation-induced martensite and twinning formation.Therefore,the Cu-added steels subjected to a tempering-annealing process achieved synergetic enhancement of the tensile strength from 1055 MPa to 1250 MPa and elongation from 33%to 45%.This strategy may provide new guidance for the development and alloy design of high-performance medium Mn steels.

Microstructure evolution of in-situ nanoparticles and its comprehensive effect on high strength steel

A novel steel strengthened by nanoparticles was investigated in this study. A Fe-based high-strength steel was developed by the trace-element regional supply method during deoxidization to generate in situ nanoparticles with a high number density in the matrix. The results show that the endogenous nanoparticles are aluminum oxide (AI2O3) and titanium oxide (Ti3O5) formed in the liquid melt. Al2O3 functioned as a heterogeneous nucleation site for MnS during solidification;the size of the resultant complex inclusions was approximately 1-2 jjim. Furthermore, 13 nm Nb(C,N) precipitates grew with the Ti30 5 during the tempering process. These in situ nanopartides strongly affected refining of the grain and inclusions. The investigated steel was strengthened more than 200 MPa by precipitation strengthening and more than 265 MPa by grain refinement strengthening according to the Ashby-Orowan mechanism and the Hall-Petch relationship, respectively.

Investigation of stress corre-sion cracking under anodic dissolution control

This review is about stress corrosion cracking (SCC) under anodic dissolution control. The section 1 is the methods distinguishing SCC controlled by anodic dissolution from those by hydrogen. The section 2 presents hydrogen-enhanced corrosion and SCC under anodic dissolution control. The section 3 demonstrates corrosion-enhanced localized plasticity and corrosion-induced deformation localization, which are the fundaments of new mechanism of SCC. The section 4 is an overview of the proposed mechanisms of SCC under anodic dissolution control. The last section proposes a new mechanism of SCC.

Lifecycle of cobalt-based alloy for artificial joints:From bulk material to nanoparticles and ions due to bio-tribocorrosion

The release of debris and ions from metallic artificial joints during bio-tribocorrosion posed a severe threat to patient health.In this work,the lifecycle of a Co Cr Mo alloy was presented by investigating the subsurface microstructure transformation in-vitro.The results showed that the originally coarse grains changed to nano-grains(NGs)on the top region of the alloy,and nanoparticles(NPs)were torn off the surface,which were then blocked by the tribo-film.The agglomerated alloy NPs contained in the tribofilm transformed into debris after being removed from the alloy surface.The majority of the torn-off NPs were corroded and released ions into solution due to their high chemical activities.

Remarkably enhanced piezo-photocatalytic performance in BaTiO_(3)/CuO heterostructures for organic pollutant degradation

Introducing polarization field of piezoelectric materials is an effective strategy to improve photocatalytic performance.In this study,a new type of BaTiO_(3)/CuO heterostructure catalyst was designed and synthesized to achieve high piezo-photocatalytic activity through the synergy of heterojunction and piezoelectric effect.The BaTiO_(3)/CuO heterostructure shows a significantly enhanced piezo-photocatalytic degradation efficiency of organic pollutants compared with the individual BaTiO_(3) nanowires(NWs)and CuO nanoparticles(NPs).Under the co-excitation of ultrasonic vibration and ultraviolet radiation,the optimal degradation reaction rate constant k of polarized BaTiO_(3)/CuO heterostructure on methyl orange(MO)dye can reach 0.05 min^(−1),which is 6.1 times of photocatalytic rate and 7 times of piezocatalytic rate.The BaTiO_(3)/CuO heterostructure with remarkable piezo-photocatalytic behavior provides a promising strategy for the development of high-efficiency catalysts for wastewater purification,and it also helps understand the coupling mechanism between piezoelectric effect and photocatalysis.

Corrosion form transition of mooring chain in simulated deep-sea environments:Remarkable roles of dissolved oxygen and hydrostatic pressure

The corrosion form and mechanical properties deterioration of mooring chain steel in simulated deep-sea environments were investigated.With the increase of ocean depth,not only the pressure increases,but also the dissolved oxygen content decreases.These two factors affect corrosion evolution of mooring chain steel in simulated deep-sea environments,which was studied for the first time.Compared with uniform corrosion of mooring chain steel in shallow sea with sufficient oxygen,low dissolved oxygen leads to the corrosion dominated by pitting with pit covers.Meanwhile,hydrostatic pressure distinctly accelerates pitting initiation and propagation.The higher the hydrostatic pressure is,the more serious the pitting is.For failure mechanism of unstressed mooring chain steel serving in simulated deep-sea environments,both absorbed hydrogen and corrosion morphology can degrade the ductility of mooring chain steel,in which the leading factor depends on the service time.The severe pitting is the main factor and causes remarkable ductility loss of the steel after long-term immersion.But hydrogen plays an important role on elongation loss in early stage.

Significant influence of trace Li on the mechanical properties, corrosion behavior, and antibacterial properties of biodegradable Zn–4Cu alloys

In this work,trace Li was introduced to strengthen Zn–4Cu alloys.The results indicated that trace amounts of Li contributed to a significant increase in strength,resulting in an acceptable loss of elongation at fracture.Additionally,Li in the form of LiZn_(4) led to more intensive galvanic corrosion,which accelerated the early corrosion rate.The release of a large amount of Zn^(2+),caused by the addition of Li,affected the phase composition of the main Zn-containing corrosion products.Moreover,the inhibition effect of the alloy on Staphylococcus aureus(S.aureus)was enhanced by the addition of 0.02 wt.%Li.

High-performance bifunctional polarization switch chiral metamaterials by inverse design method

Multifunctional polarization controlling plays an important role in modern photonics,but their designs toward broad bandwidths and high efficiencies are still rather challenging.Here,by applying the inverse design method of model-based theoretical paradigm,we design cascaded chiral metamaterials for different polarization controls in oppositely propagating directions and demonstrate their broadband and high-efficiency performance theoretically and experimentally.Started with the derivation of scattering matrix towards specified polarization control,a chiral metamaterial is designed as a meta-quarter-wave plate for the forward propagating linearly polarized wave,which converts the x-or y-polarized wave into a nearly perfect left-or right-handed circularly polarized wave;intriguingly,it also serves as a 45°polarization rotator for the backward propagating linearly polarized waves.This bifunctional metamaterial shows a high transmission as well as a broad bandwidth due to the Fabry–Perot-like interference effect.Using the similar approach,an abnormal broadband meta-quarter-wave plate is achieved to convert the forward x-and y-polarized or the backward y-and x-polarized waves into left-and right-handed circularly polarized waves with high transmission efficiencies.The integration of multiple functions in a single structure endows the cascaded chiral metamaterials with great interests for the high-efficiency polarization-controlled applications.

Stress corrosion cracking and its anisotropy of a PZT ferroelectric ceramics

Stress corrosion cracking (SCC) of a PZT ferroelectric ceramics in various media, such as moist at-mosphere, silicon oil, methanol, water and formamide, and its anisotropy have been investigated at constant load test using a single-edge notched tensile specimen. The results showed that SCC could occur in all media, and the threshold stress intensity factor of SCC in water and formamide, KISCC, revealed anisotropy. The KISCC for poling direction parallel to the crack plane, aISCC,Kwas greater than that perpendicular to the crack plane, bISCC,K similar to the anisotropy of fracture toughness KIC; however, the anisotropy factor of KISCC, which was abISCCISCC/KK=1.8 (in formamide) and 2.1 (in water), was larger than that of KIC, which is abICIC/KK=1.4. The stress-induced 90?domain switching causes the anisotropy of KIC and KISCC, besides, the resistance of SCC also has anisotropy.

Novel bake hardening mechanism for bainite-strengthened complex phase steel

In the automobile industry,stamping and paint baking processes are used to strengthen components,and this not only saves costs,but also further reduces the bodyweight of automobiles.In this work,the bake hardening mechanism of the complex phase(CP)steel CP980 was explored by comparing it with that of DP1180,which has a clear bake hardening mechanism and a carbon content similar to that of CP980.By analyzing the bake hardening response and the microstructural changes of the two steels,we found that the bake hardening process of CP980 was divided into three stages.In the first two stages,the carbon atoms diffused into dislocations to form Cottrell atmosphere pinning dislocations,and excess car-bon atoms formed carbon clusters or low-temperature carbide pinning dislocations that were similar to DP1180.In the third stage,the dislocation acted as rapid channels for carbon diffusion,and fine cementite gradually formed when the carbon clusters gathered at the dislocations as precursors,resulting in pre-cipitation hardening.This novel bake-hardening(BH)mechanism is crucial for obtaining a comprehensive understanding of the strain-baking behavior of advanced high-strength steals(AHSS).

Machine learning assisted prediction of dielectric temperature spectrum of ferroelectrics

In material science and engineering,obtaining a spectrum from a measurement is often time-consuming and its accurate prediction using data mining can also be difficult.In this work,we propose a machine learning strategy based on a deep neural network model to accurately predict the dielectric temperature spectrum for a typical multi-component ferroelectric system,i.e.,(Ba_(1−x−y)Ca_(x)Sr_(y))(Ti_(1−u−v−w)Zr_(u)Sn_(v)Hf_(w))O_(3).The deep neural network model uses physical features as inputs and directly outputs the full spectrum,in addition to yielding the octahedral factor,Matyonov–Batsanov electronegativity,ratio of valence electron to nuclear charge,and core electron distance(Schubert)as four key descriptors.Owing to the physically meaningful features,our model exhibits better performance and generalization ability in the broader composition space of BaTiO3-based solid solutions.And the prediction accuracy is superior to traditional machine learning models that predict dielectric permittivity values at each temperature.Furthermore,the transition temperature and the degree of dispersion of the ferroelectric phase transition are easily extracted from the predicted spectra to provide richer physical information.The prediction is also experimentally validated by typical samples of(Ba_(0.85)Ca_(0.15))(Ti_(0.98–x)Zr_(x)Hf_(0.02))O_(3).This work provides insights for accelerating spectra predictions and extracting ferroelectric phase transition information.

Correlation between multi-factor phase diagrams and complex electrocaloric behaviors in PNZST antiferroelectric ceramic system

Ferroelectric(FE)phase transition with a large polarization change benefits to generate large electrocaloric(EC)effect for solid-sate and zero-carbon cooling application.However,most EC studies only focus on the single-physical factor associated phase transition.Herein,we initiated a comprehensive discussion on phase transition in Pb_(0.99)Nb_(0.02)[(Zr_(0.6)Sn_(0.4))1−xTix]_(0.98)O_(3)(PNZST100x)antiferroelectric(AFE)ceramic system under the joint action of multi-physical factors,including composition,temperature,and electric field.Due to low energy barrier and enhanced zero-field entropy,the multi-phase coexistence point(x=0.12)in the composition–temperature phase diagram yields a large positive EC peak of maximum temperature change(ΔT_(max))=2.44 K(at 40 kV/cm).Moreover,the electric field–temperature phase diagrams for four representative ceramics provide a more explicit guidance for EC evolution behavior.Besides the positive EC peaks near various phase transition temperatures,giant positive EC effects are also brought out by the electric field-induced phase transition from tetragonal AFE(AFET)to low-temperature rhombohedral FE(FER),which is reflected by a positive-slope boundary in the electric field–temperature phase diagram,while significant negative EC responses are generated by the phase transition from AFET to high-temperature multi-cell cubic paraelectric(PEMCC)with a negative-slope phase boundary.This work emphasizes the importance of phase diagram covering multi-physical factors for high-performance EC material design.

Large electrocaloric effect over a wide temperature span in lead-free bismuth sodium titanate-based relaxor ferroelectrics

For efficient solid-state refrigeration technologies based on electrocaloric effect(ECE),it is a great challenge of simultaneously obtaining a large adiabatic temperature change(DT)within a wide temperature span(Tspan)in lead-free ferroelectric ceramics.Here,we studied the electrocaloric effect(ECE)in(1-x)(Na_(0.5)Bi_(0.5))TiO_(3)-xCaTiO_(3)((1-x)NBT-xCT)and explored the combining effect of morphotropic phase boundary(MPB)and relaxor feature.The addition of CT not only constructs a MPB region with the coexistence of rhombohedral and orthorhombic phases,but also enhances the relaxor feature.The ECE peak appears around the freezing temperature(Tf),and shifts toward to lower temperature with the increasing CT amount.The directly measured ECE result shows that the ceramic of x=0.10,which is in the MPB region,has an optimal ECE property of DTmax=1.28 K@60℃under 60 kV/cm with a wide Tspan of 65C.The enhanced ECE originates from the electric-field-induced transition between more types of polar nanoregions and long-range ferroelectric macrodomains.For the composition with more relaxor feature in the MPB region,such as x?0.12,the ECE is relatively weak under low electric fields but it exhibits a sharp increment under a sufficiently high electric field.This work provides a guideline to develop the solidestate cooling devices for electronic components.

Low-fired Y-type hexagonal ferrite for hyper frequency applications

Y-type hexagonal ferrite with planar magnetocrystalline anisotropy has ultrahigh cut-off frequency up to GHz and excellent magnetic properties in hyper frequency range,so that is regarded as the most suitable material in correpongding inductive devices and components.The technology of low temperature cofired ceramics for surface-mounted multilayer chip components needs ferrite to be sintered well under 900℃to avoid the melting and diffusion of Ag inner electrode during the cofiring process.To lower the sintering temperature of Y-type hexagonal ferrite,there are several methods,(1)using nano-sized starting powders,(2)substitution by low-melting elements,(3)adding sintering additives,and(4)introducing lattice defect.In this paper,the effects of different methods on the sintering behavior and the magnetic properties were discussed in detail.

Ultrasensitive Frequency Shifting of Dielectric Mie Resonance near Metallic Substrate

Dielectric resonators on metallic surface can enhance far-field scattering and boost near-field response having promising applications in nonlinear optics and reflection-type devices.However,the dependence of gap size between dielectric resonator and metallic surface on Mie resonant frequency is complex and desires a comprehensive physical interpretation.Here,we systematically study the effect of metallic substrate on the magnetic dipole(MD)resonant frequency at X-band by placing a high permittivity CaTiO_(3) ceramic block on metallic substrate and regulating their gap size.The simulated and experimental results show that there are two physical mechanisms to codetermine the metallic substrate-induced MD frequency.The greatly enhanced electric field pair in the gap and the coupling of MD resonance with its mirror image are decisive for small and large gaps,respectively,making the MD resonant frequency present an exponential blue shift first and then a slight red shift with increasing gap size.Further,we use the two mechanisms to explain different frequency shifting properties of ceramic sphere near metallic substrate.Finally,taking advantage of the sharp frequency shifting to small gaps,the ceramic block is demonstrated to accurately estimate the thickness or permittivity of thin film on metallic substrate through a governing equation derived from the method of symbolic regression.We believe that our study will help to understand the resonant frequency shifting for dielectric particle near metallic substrate and give some prototypes of ultrasensitive detectors.

Statistical in situ scanning electron microscopy investigation on the failure of oxide scales

Oxide scales play a pivotal role in obstructing surface chemical and electrochemical reactions,hence hindering chemo-mechanical effects such as liquid metal embrittlement of steels.Therefore,the critical conditions and failure mechanism of the oxide film are of major interest in the safe service of steels.Though in situ microscopic methods may directly visualize the failure mechanism,they are often challenged by the lack of statistically reliable evaluation of the critical conditions.Here,by combining in situ scanning electron microscopy with a tapered specimen tensile test in a single experiment,we uniquely achieve a mechanistic study with statistically reliable quantification of the critical strains for each step of the dynamic process of film rupture.This is demonstrated with the oxide films formed on a ferrite-martensite steel in liquid lead-bismuth eutectic alloy at elevated temperatures,with in situ results falling right into the predictions of the statistical analysis.Explicitly,the integrated experimental methodology may facilitate the materials genome engineering of steels with superior service performance.