查看更多>>摘要：Simultaneously achieving high elasticity,low modulus,and high strength in Ti alloy has been a long-standing challenge.In this study,cold rolling was conducted to modulate the martensitic transformation of the Ti-15Nb-5Zr-4Sn-1Fe alloy to address this challenge.The 10％cold rolling process was primarily ac-commodated by a novel stress-induced sequential β-to-α"-to-α'martensitic transformation accompanied by the disappearance of ω phase,which was sufficient to induce adequate martensite and defects to sup-press the initial rapid stress-induced martensitic transformation,without destroying the equiaxed shape of prior β grains.Consequently,the novel sequential phase transformation led to a substantial decrease in Young's modulus by 50.5％while increasing the strength,resulting in an excellent combination of large near-linear elasticity of 2.34％,low modulus of 45 GPa,and high strength of 1093 MPa.The obtained large near-linear elasticity was mainly contributed by the concurrent low modulus and high strength obeying Hooke's law.These findings provide valuable insights into the attainment of concurrent high elasticity and low modulus in Ti alloys by regulating the stress-induced sequential martensitic transformation.
Vlad Alexandru LukacsRadu StirbuOana Andreea ConduracheLavinia Petronela Curecheriu...
13-24页
查看更多>>摘要：The functional properties of BaTiO3 ceramics,produced by using the same pressing/sintering strategy from nanopowders with two distinct morphologies(cuboidal/equiaxed nanoparticles)and similar parti-cle sizes,are comparatively investigated.The sintered ceramics exhibit similar nanoscale structures,with faceted crystalline grains and crystalline inclusions,clean grain boundaries and well-defined 90° lamellar domains extending in some entire grains or finer nanodomains inside grain regions.The differences in the functional behavior originating from the different nanopowder morphology are described in terms of the nanoparticle assembly during the pressing step.The numerically simulated green body densification indicated a more efficient assembly resulting in higher density for the cubic particles(0.90 vs.0.84 rel-ative density)and a more homogeneous pore distribution in the spherical-derived ones.As a result of the higher density after sintering,the functional properties are enhanced in cuboid-originated ceramics.For comparison,the ceramic produced from cubic nanoparticles sintered at T1/T2=1250/800 ℃ shows higher permittivity(room temperature value of～2100-cubic vs.～1700-rounded),enhanced ferroelec-tric characteristics(cubic:Ps=8.57 μC cm-2,Pr=0.95 μC cm-2,and Ec=2.3 kV cm-1,with respect to Ps=6.06 μC cm-2,Pr=0.4 μC cm-2,and Ec=1.4 kV cm-1,for spherical-derived ones,measured at Emax=29.3 kV cm-1)and a stronger dc-field dependence of their permittivity of～12％(cubic)vs.only～2％(spherical),for a dc-applied field in the range of-15 kV cm-1＜Edc＜15 kV cm-1.In contrast,the spherical particles-derived ceramics contain fewer defects and have a more homogeneous and finer porosity distribution in the ceramic volume and consequently,they are more stable and sustain larger field applications in comparison with the cubic-derived counterparts.
查看更多>>摘要：The low photoelectric conversion efficiency of photoelectrode is an important factor that limits the ap-plication in photoelectrochemical cathodic protection(PECCP)field for marine anti-corrosion of metallic structures.In this work,a photoelectrode of TiO2/CdZnS/ZnS triple-phase heterojunction was fabricated by loading the narrow-band CdZnS associated with the broad-band ZnS via hydrothermal and continuous ion layer adsorption methods,respectively.The composite of CdZnS enhances the photoelectric conver-sion ability of TiO2,while the ZnS composite can prevent the CdZnS from photo-corrosion and suppress the spillover of the photogenerated electrons.The three-phase heterostructure effectively improves the PECCP performance on 316 L stainless steel(SS)under simulated solar irradiation,especially in 3.5 wt％NaCl solution without the sacrificial agent.In addition,the prepared TiO2/CdZnS/ZnS photoelectrode also performs anti-biofouling effect evidenced by the high removal efficiency of Pseudomonas aeruginosa(P.aeruginosa),which can be attributed to the oxidizability of photogenerated holes.The TiO2/CdZnS/ZnS triple-phase heterojunction with desirable performance is a promising semiconductor material for the applications of PECCP and anti-biofouling.
查看更多>>摘要：The heightened piezoelectric performance observed in most explored perovskite systems is typically at-tributed to the electric-field-induced phase transition near the morphotropic phase boundary(MPB)or polymorphic phase boundary(PPB).This study,however,unveils a distinct piezoelectric enhancement mechanism in the xPb(Nb2/3Ni1/3)O3-(1-x)Pb(Zr0.3Ti0.7)O3(PNN-PZT)system,diverging from the MPB/PPB-centered piezoelectric systems.Notably,the composition with x=0.55,positioned close to the tetragonal-pseudocubic(T-PC)phase boundary,achieves an unprecedented piezoelectric coefficient(d33)of 1264 pC/N,while retaining a tetragonal local structure.Importantly,on a local scale,electric fields do not in-cite phase transitions,suggesting that the exceptional piezoelectric performance in PNN-PZT stems from polarization extension near the T-PC boundary.Distinct from other mechanisms,the relative permittivity significantly increases post-poling due to this particular enhancement process.The dielectric behavior in poled specimens does not exhibit a conspicuous change at the ferroelectric-relaxor transition tempera-ture.However,both the relative permittivity and planar electromechanical coupling coefficient experience a sharp rise in the temperature range of-25 ℃ to 25 ℃.This investigation underscores the pivotal role of designing compositionally-driven T-PC phase boundaries,presenting a promising avenue for enhancing piezoelectric properties in ferroelectric ceramics.
查看更多>>摘要：Hypoeutectic Al-Si alloys are becoming increasingly popular in automotive and aerospace engineering fields due to their excellent overall performance,and grain refinement is regarded as an important way to improve casting and mechanical properties.Titanium(Ti)is a basic element for grain refinement;thus,a certain amount of Ti is often included in Al-Si alloys.In the present work,the changes in the grain re-finement,mechanical,and casting properties of Al-Si alloys with different Ti concentration levels under various grain refinement conditions were systematically investigated.The specific roles of Ti in the het-erogeneous nucleation of α-Al grains were summarized,and the formation mechanism of Ti-rich zones in Al-Si alloys was revealed.Excess Ti concentration could not efficiently reduce the grain size of Al-Si alloys and eventually resulted in inferior mechanical and casting qualities;hence,the recommended Ti concentration level for the aluminum alloy grades of A356 and A357 is ≤ 0.1 wt％.Furthermore,an opti-mized technique for the grain refinement of hypoeutectic Al-Si alloys was presented.A small amount of an Al-TCB master alloy was introduced to achieve the best grain refinement and mechanical properties in a trace Ti environment.The addition of 0.5 wt％of the Al-TCB master alloy at the Ti concentration level of 0.06 wt％increased the ultimate tensile strength,elongation,and quality index of the Al-7Si-0.45Mg alloy to 328.8±5.0 MPa,14.4％±0.6％,and 970.7±33.1 MPa,respectively.
查看更多>>摘要：The high-entropy alloy(HEA)superconductor,Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6(Ta-Nb-Hf-Zr-Ti),is systematically studied to examine changes in superconducting critical properties,critical temperature(Tc),critical cur-rent density(Jc),and upper critical field(Hc2),concerning thermal treatment conditions.Annealing condi-tion affects Jc more significantly than Tc and Hc2,with a large improvement of flux pinning force density(Fp).The Jc of bare sample is reduced to 10 A cm-2 at an applied magnetic field of approximately 1.5 T,whereas the sample annealed at 550 ℃ for 12 h exhibits Jc＞100 kA cm-2 up to around 4 T.Furthermore,the Vickers hardness(HVIT)of the Ta-Nb-Hf-Zr-Ti HEA superconductor notably increases from～384 to 528 HVIT following a 24-h annealing at 500 ℃.These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.
查看更多>>摘要：We have realized efficient photopatterning and high-quality ZrO2 films through combustion synthesis and manufactured resistive random access memory(RRAM)devices with excellent switching stability at low temperatures(250 ℃)using these approaches.Combustion synthesis reduces the energy required for ox-ide conversion,thus accelerating the decomposition of organic ligands in the UV-exposed area,and pro-moting the formation of metal-oxygen networks,contributing to patterning.Thermal analysis confirmed a reduction in the conversion temperature of combustion precursors,and the prepared combustion ZrO2 films exhibited a high proportion of metal-oxygen bonding that constitutes the oxide lattice,along with an amorphous phase.Furthermore,the synergistic effect of combustion synthesis and UV/O3-assisted photochemical activation resulted in patterned ZrO2 films forming even more complete metal-oxygen networks.RRAM devices fabricated with patterned ZrO2 films using combustion synthesis exhibited ex-cellent switching characteristics,including a narrow resistance distribution,endurance of 103 cycles,and retention for 105 s at 85 ℃,despite low-temperature annealing.Combustion synthesis not only enables the formation of high-quality metal oxide films with low external energy but also facilitates improved photopatterning.
查看更多>>摘要：The vacancy defect exhibits a remarkable improvement in the dehydriding property of MgH2@Ni-CNTs.However,the corresponding mechanism is still not fully understood.Herein,the impact of vacancy de-fects on the dehydrogenation properties of MgH2@Ni-CNTs was studied by DFT simulation,and the corre-sponding models were constructed based on MS.The dehydrogenation process of MgH2 can be regarded as the dissociation of Mg-H and desorption of H2 from the MgH2 surface.In view of the whole dehydro-genation,the dissociation of H-is the rate-determining step,which is the main reason for restricting the dehydrogenation kinetics.Compared with vacancy vacancy-defective MgH2(001)surface,the appearance of vacancy defects on the(110)surface substantially reduces the energy barrier required for H disso-ciation to 0.070 Ha.The reason is that vacancy defects accelerate the transition of electrons from the H-s orbit to the Mg2+3s orbit,resulting in a decrement of the Mg-H bond strength,which makes H atoms more easily dissociated from the MgH2(110)surface.Therefore,the existence of vacancy defects improves the dehydriding kinetic of MgH2.Most importantly,this research offers crucial directions for developing hydrogen storage materials as well as a potential fix for the slow dehydrogenation kinetics of nano-confined MgH2.
查看更多>>摘要：The combination of S-scheme heterojunction and photothermal effect is a promising strategy to achieve efficient CO2 photoreduction into solar fuel due to the boosted charge carrier separation efficiency and faster surface reaction rate.Herein,unique photothermal-coupled TiO2/Bi2S3 S-scheme heterojunction nanofibers were fabricated and applied to a full-spectrum CO2 photoreduction system.Density functional theory calculation and experimental analyses have confirmed the generation of the internal electric field and the S-scheme electron transfer pathway,leading to a highly efficient charge carrier separation.Thanks to the excellent photothermal conversion capacity of Bi2S3,the photogenerated electron transfer rate,and surface reaction rate were further accelerated in hybrid photocatalysts.Under the synergistic effect of S-scheme heterojunction and photothermal effects,the optimal TiO2/Bi2S3 nanofibers achieved 7.65 μmol h-1 of CH4 production rate,which is 5.24 times higher than that of pristine TiO2.Moreover,the mor-phology reconstruction of Bi2S3 in hybrids facilitates the CH4 selectivity was significantly improved from 64.2％to 88.7％.Meanwhile,the CO2 photoreduction reaction route over TiO2/Bi2S3 nanofibers was in-vestigated based on in-situ Fourier transform infrared spectra.This work provides some useful hints for designing highly efficient photothermal-coupled photocatalysts for CO2 photoreduction.
查看更多>>摘要：High levels of Al and Ti in superalloy compositions normally lead to cracking formation during the laser powder bed fusion process,while these elements are key constituents of strengthening phases.In the cur-rent study,a novel Co-based superalloy with the basic chemical composition of Co-Al-W-Ta-Ti resolved this contradiction,indicating that the part was formed without cracking and simultaneously contained a large amount of strengthening precipitates in the microstructure fabricated via laser powder bed fusion.The printability,microstructures,and mechanical properties of the sample were analysed before and af-ter heat treatment,providing a potential superalloy that can replace Ni-based superalloys fabricated by additive manufacturing in aerospace and other industries with higher temperature and more efficiency.
NETL
NSTL
万方数据