查看更多>>摘要：This paper reports the improvement of electrical,ferroelectric and endurance of Hf0.5Zr0.5O2(HZO)thin-film capacitors by implementing W electrode.The W/HZO/W capacitor shows excellent pristine 2Pr values of 45.1 μC/cm2 at±6 V,which are much higher than those of TiN/HZO/W(34.4 μC/cm2)and W/HZO/TiN(26.9 μC/cm2)capacitors.Notably,the maximum initial 2Pr value of W/HZO/W capacitor can reach as high as 57.9 μC/cm2 at±7.5 V.These strong ferroelectric polarization effects are ascribed to the W electrode with a fairly low thermal expansion coefficient which provides a larger in-plane tensile strain compared with TiN electrode,allowing for enhancement of o-phase formation.Moreover,the W/HZO/W capacitor also exhibits higher endurance,smaller wake-up effect(10.1％)and superior fatigue properties up to 1.5×1010cycles compared to the TiN/HZO/W and W/HZO/TiN capacitors.Such improvements of W/HZO/W capacitor are mainly due to the decreased leakage current by more than an order of magni-tude compared to the W/HZO/TiN capacitor.These results demonstrate that capping electrode material plays an important role in the enhancement of o-phase formation,reduces oxygen vacancies,mitigates wake-up effect and improves reliability.
查看更多>>摘要：Ultra-coarse grained cemented carbides are often used under conditions of concurrently applied stress and high temperature.Improvement of high-temperature mechanical performance of ultra-coarse grained cemented carbides is highly desirable but still a big challenge.In this study,it is proposed that the high-temperature compression strength of ultra-coarse cemented carbides can be enhanced by modulating hard matrix grains by activated TaC nanoparticles,through solid solution strengthening of Ta atoms.Based on the designed experiments and microstructural characterizations combined with finite element simu-lations,the grain morphology,stress distribution and dislocation configuration were studied in detail for ultra-coarse grained cemented carbides.The mechanisms of Ta dissolving in WC crystal and strengthen-ing ultra-coarse grains through interaction with dislocations were disclosed from the atomic scale.This study opens a new perspective to modulate hard phases of cemented carbides for improving their high-temperature performance,which will be applicable to a variety of cermet and ceramic-based composite materials.
查看更多>>摘要：High porosity and high strength are usually mutually exclusive in the preparation of ceramic materials.However,high porosity and flexural strength are required for the preparation of complex ceramic cores for hollow turbine blades.In this study,Al2O3 cores with high porosity and high flexural strength were successfully prepared using digital light processing(DLP)3D printing technology.The influence of sin-tering temperature on the microstructure,pore evolution,and flexural strength of the cores were investi-gated.With an increase in the sintering temperature,the porosity of the ceramic cores first increased and then decreased,reaching a maximum value of 35％at 1400℃.The flexural strength increased with the increase in sintering temperature,but at 1400℃the incremental enhancement of flexural strength was greatest.Combined with the core service requirements and core performance,this study selected 1400℃(open porosity of 35.1％and flexural strength of 20.3 MPa)as the optimal sintering temperature for the DLP-3D printed Al2O3 core.
查看更多>>摘要：Surface structure of C/C composites has been regulated through electrochemical corrosion at room tem-perature to modify the residual stress and improve the joining strength when brazed to Nb.The unique crevice corrosion in C/C composites is investigated to reveal the change of corrosion depth and fiber size.The interlacing zone of carbon fiber reinforced brazing alloy replaces the reaction layer in the original joint.Joining area is increased dramatically and the continuous crack will be hindered.The interlacing zone eliminates the stress concentration and relieves the residual stress through reducing the property mismatch.All advantages contribute to the joining quality of C/C-Nb.Shear strength of C/C-Nb joint with 80 μm depth reached 37.7 MPa,which was 1.2 times higher than that of original joint.Surface structure design of C/C composites not only expands the application in structure component,but also exhibits the promising application in energy field.
查看更多>>摘要：Al-2.85 wt％Fe alloy has been subjected to non-equilibrium container-less solidification using a 6.5 m drop tube.Spherical samples were collected and sieved into 7 sizes fractions ranging from 850 μm to 53 μm,with the estimated cooling rates being 150 to 11000 K s-1 respectively.XRD analysis was employed on all droplet size fractions for identification and evolution of the phases,showing that Al,Al6Fe and Al13Fe4 were formed for all sizes while Al5Fe2 was observed only in droplets≤150 μm in diameter.Microstructural evaluation was conducted by using SEM and optical microscopy,showing that droplet larger than 300 μm in diameter exhibited distinct morphologies;microcellular,dendritic α-Al with inter-dendritic Al13Fe4 eutectic and an Al-Al6Fe eutectic region.With increasing cooling rate,the Al-Al6Fe region disappears.EDX analysis reveals that increasing the cooling rate increased the dissolved Fe content in α-Al from 0.37 wt％Fe to 1.105 wt％Fe,and correspondingly the eutectic fraction decreased from 49.7 vol.％to 26.7 vol.％.Measurement of the lamellar spacing allowed the eutectic growth velocity and interfacial undercooling to be calculated,wherein the Al-rich boundary of the eutectic coupled zone could be reconstructed.This shows a coupled zone skewed significantly towards the intermetallic side of the eutectic.In order to understand the effect of non-equilibrium the solidification on the mechanical properties micro hardness of the droplets was measured.The micro-hardness has risen from 55.3 HV0.01 to 66.5 HV0.01 for≥850 μm and≤75 μm droplets,respectively.
查看更多>>摘要：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 forma-tion,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 addi-tion,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 marten-site,which substantially improves the ductility and toughness through a transformation-induced plastic-ity(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.
查看更多>>摘要：MnMX(M=Co or Ni,X=Si or Ge)alloys,experiencing structural transformation between Ni2ln-type hexagonal and TiNiSi-type orthorhombic phases,attract considerable attention due to their potential ap-plications as room-temperature solid refrigerants.Although lots of studies have been carried out on how to tune this transformation and obtain large entropy change in a wide temperature region,the crys-tallography of this martensitic transformation is still unknown.The biggest obstacle for crystallography investigation is to obtain a bulk sample,in which hexagonal and orthorhombic phases coexist,because the MnMX alloys will fragment into powders after experiencing the transformation.For this reason,we carefully tune the transformation temperature to be slightly below 300 K.In that case,a bulk sample with small amounts of orthorhombic phases distributed in hexagonal matrix is obtained.Most impor-tantly,there are no cracks between the two phases.It facilities us to investigate the microstructure using electron microscope.The obtained results indicate that the orientation relationship between hexagonal and orthorhombic structures is[4223]h//[120]0&(0110)h//(001)0 and the habit plane is{2113.26}h.WLR theory is also adopted to calculate the habit plane.The calculated result agrees well with the mea-sured one.Our work reveals the crystallography of hexagonal-orthorhombic transformation for the first time and is helpful for understanding the transformation-associated physical effects in MnMX alloys.
查看更多>>摘要：In this work,we studied the effect of Cr element on the corrosion resistance evolution of weathering steel based on corrosion big data technology.It suggested that corrosion big data technology is suitable for evaluation of the effect of microalloying Cr element on the corrosion evolution behavior of weather-ing steel.New understandings prove that the effect of Cr on the corrosion process is dynamic rather than static,the processes is affected by both of the environmental factors and the electrochemical or chem-ical reactions in the rust layer.Besides,Cr element has both beneficial effect and detrimental effect on the corrosion resistance of weathering steel.The beneficial effect is that the general corrosion resistance of Cr-additional steel is better than that of Cr-free steel,while the detrimental effect is that localized corrosion is intensified as the increase of Cr content in the Cr-additional steel.
查看更多>>摘要：To overcome the dimension limits of immiscible alloys produced by traditional techniques and enhance their mechanical properties,bulk Cu-Fe-based immiscible alloy with abundant nanotwins and stacking faults was successfully produced by selective laser melting(SLM).The SLM-produced bulk immiscible alloy displays a heterogeneous microstructure characterized by micro-scaled y-Fe particles dispersed in fine ε-Cu matrix with a high fraction(～92％)of high-angle grain boundaries.Interestingly,abundant nan-otwins and stacking faults are generated in the interior of nano-scaled y-Fe particles embedded withinε-Cu matrix.The heterogeneous interface of soft domains(ε-Cu)and hard domains(y-Fe)not only in-duces the geometrically necessary dislocations(GNDs)but also affects the dislocation propagation during plastic deformation.Therefore,the bimodal heterogeneous interface,and the resistance of nanotwins and stacking faults to the propagation of partial dislocation make the bulk immiscible alloy exhibit an en-hanced strength of～590 MPa and a good ductility of～8.9％.
查看更多>>摘要：To inhibit the agglomeration of tin-based nanomaterials and simplify the complicated synthesis process,a facile and eco-friendly self-formed template method is reported to synthesize tin submicron spheres dispersed in nitrogen-doped porous carbon(Sn/NPC)by pyrolysis of a mixture of disodium stannous cit-rate and urea.The vital point of this strategy is the formation of Na2CO3 templates during pyrolysis.This self-formed Na2CO3 acts as porous templates to support the formation of NPC.The obtained NPC provides good electronic conductivity,ample defects,and more active sites.Serving as anode for Li-ion batteries,the Sn/NPC electrode obtains a stable discharge capacity of 674.1 mAh/g after 150 cycles at 0.1 A/g.Especially,a high discharge capacity of 331.2 mAh/g can be achieved after 1100 cycles at 3 A/g.Ad-ditionally,a full cell coupled with LiCoO2 as cathode yields a discharge capacity of 524.8 mAh/g after 150 cycles at 0.1 A/g.In-situ XRD is implemented to investigate the alloying/dealloying reaction mechanisms.Density functional theory calculation ulteriorly explicates that NPC heightens intrinsic electronic conduc-tivity,and NPC especially pyrrolic-N and pyridinic-N doping facilitates the Li-adsorption ability.Climbing image nudged elastic band method reveals low Li+diffusion energy barrier in presence of N atoms,which accounts for the terrific electrochemical properties of Sn/NPC electrode.
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