查看更多>>摘要：Al-V-B master alloy is promising for refining Al-Si alloys,yet its optimal composition with superior effi-cacy remains to be explored.In this work,the evolution of refining phases in the Al-10Si/Al-V-B system with different V∶B ratios was evaluated by thermodynamic calculations,based on which the Al-V-B refin-ers with V∶B =1∶1 and 5∶1 were designed.Refining trails demonstrated that they could significantly re-duce the grain size of Al-10Si (wt.％) alloy from 1736 to 184-245μm with industrial addition amount.De-tailed examinations results clarify that when V∶B ratio is 1∶1 the nucleation particle is (V,Al)B2,which has a VB2-AlB2 core-shell structure and therefore presents the nucleation capability as AlB2 particle.When V.∶B ratio is as high as 5∶1,the nucleation particle is pure VB2.Density functional theory (DFT) calculation indicates that (0001) VB2/(111) α-Al interface has the lowest interfacial energy such that highest nucleation potency among other types of diboride/α-Al interfaces under consideration.The outcomes of this work provide fundamental guidance to develop superior V-B based refiners for Al-Si alloys.
查看更多>>摘要：Thermally insulating and fire-resistant carbon composite foams are prepared by consolidating natural cot-ton fibre dispersed in aqueous sucrose solution by filter-pressing followed by drying and carbonization.The compressive strength (5 kPa to 1.4 MPa) and thermal conductivity (0.069 to 0.185 W m-1 K-1)depend on the foam density (0.06 to 0.31 gcm-3) which is modulated by varying the sucrose solutions concentration (100 to 700 g L-1).Partially flexible to the rigid transition of the carbon composite foams occurs at sucrose concentration above 200 g L-1.The tubular carbon fibre formed from cotton is welded at their contact points by the amorphous carbon produced from sucrose leading to partial flexibility at low sucrose concentration and advancement of fibre-to-fibre bonding area at higher sucrose concentra-tion results in rigid foam.The porosity in the inter-fibre space and lumen of the carbonized cotton fibre contributes to the low thermal conductivity.The carbon composite foams prepared at a sucrose solution concentration of 500 g L-1 and above are amenable to machining using conventional machines and tools.The rigid carbon foams show EMI shielding effectiveness and specific shielding effectiveness in the ranges of 21.5 to 38.9 dB and 108-138 dB cm3 g-1,respectively.
查看更多>>摘要：Metal antimony (Sb) is a promising anode material of potassium-ion batteries (PIBs) for its high theoreti-cal capacity but limited by its inferior cycle stability due to the serious volume expansion during cycling.Herein,we design and construct a kind of low-crystalline Sb nanoparticles coated with amorphous Sb2O3 and dispersed into three-dimensional porous carbon via a strategy involving NaCl template-assisted in-situ pyrolysis and subsequent low-temperature heat-treated in air.Significantly,the crystallinity and ratio of Sb/Sb2O3 have been precisely tuned and controlled,and the optimized sample of HTSb@Sb2O3@C-4 displays a high reversible specific capacity of 543.9 mAh g-1 at 03 A g-1,superior rate capability and excellent cycle stability (～273 mAh g-1 at 2 A g-1 after 2000 cycles) as an anode of PIBs.The outstanding potassium-ion storage performance can be ascribed to the appropriate crystallinity and the multiple-buffer-matrix structure comprising an interconnected porous conductive carbon to relieve the volume changes and suppress the aggregation of Sb,a Sb nanoparticle core to shorten the ion transport path-ways and decrease the mechanical stress,and a low-crystalline Sb2O3 as the shell to consolidate the interface between Sb and carbon as well as facilitate the rapid electron transport.The dynamic analysis shows that the composite is mainly controlled by pseudocapacitance mechanism.This work provides a novel thought to design high-performance composite electrode in energy storage devices.
查看更多>>摘要：Surface passivation is a common method to improve the resistance of thermal degradation of nitride phosphors.However,such a surface passivation generally needs extra processes and decreases the photo-luminescence property of the phosphors.In this work,both the thermal stability and photoluminescence property of a red phosphor Sr2Si5N8∶Eu are improved through the addition of BN.The influence of B on the crystal structure and the valence state of active ions was analyzed by experimental characterization.First-principles calculations were applied to analyze the formation energy of N vacancies,which influ-ence the resistance of thermal degradation.Finally,combining with experimental characterization and calculations,the enhancing mechanism of thermal stability and photoluminescence by B was studied.
查看更多>>摘要：To construct a structure with a structure-inducing function favors the personalized design and processing of the implant.Pulse lasers provide convenient conditions for the preparation of functional structures.The laser with a wavelength of 355 nm and pulse width of 50 ns was employed to prepare the structure with cauliflower-like (C_f),sputtered droplets (S_d),and lattice (L_t) characteristics.We analyzed the influence of laser process parameters on the formation of morphology,roughness,surface chemical composition(X-ray photoelectron spectroscopy,XPS),phase,and wettability of titanium alloys.We ascertained the proliferation and osteogenic differentiation of mesenchymal stem cells (MSCs) on C_f,S_d,and L_t struc-tures.The results showed that multiple depositions,aggregation,and oxidation of droplets with a thick oxide layer played an essential role in forming the C_f.With the reduction of scanning speed (v) and pitch(Dy),pollutants containing O-C=O were removed,and the chemical composition of the surface gradually transformed from Ti,Ti2O3,and TiO2 to complete TiO2.The rough C_f structure had super-hydrophilic and underwater oleophobic properties,and the near-surface was mostly rutile.Nevertheless,the high in-terfacial tension and fractal dimension inhibited cell adhesion and proliferation.Interestingly,the stem cells had outstanding osteogenic differentiation on the surface of the S_d structure with higher hardness(450 HV) and appropriate roughness (Sa=1μm).The L_t had a gradient of roughness and hardness at low laser spot overlap.Stem cells adhered and migrated to the ablation ring under locally amplified traction,and there was excellent osteogenic differentiation through mechanotransduction.
查看更多>>摘要：A combination of both conventional and advanced high-resolution characterization techniques was ap-plied to study the modified layers on the surface of three composite Al-Cr arc cathodes with identical nominal composition of Al-50 at.％ Cr but varying powder grain sizes.The results revealed that the mod-ified layers consist mainly of metastable phases such as Cr solid solution,high temperature cubic Al8Cr5,supersaturated Al solid solution,and icosahedral quasicrystal.The metastable phase formation indicates that high cooling rates were involved during the solidification of molten material produced in the arc craters during cathode spot events.The average cooling rate was estimated to be 106 K/s based on sec-ondary dendrite arm spacing measurements and supporting phase-field based simulations.The formation mechanisms of the modified layers are discussed based on the obtained results and the current literature.
查看更多>>摘要：Multiple ballistic impacts are carried out on a 2024-T4 aluminum alloy by spherical steel projectiles (5-mm diameter) at ～400 m s-1,to investigate its dynamic deformation and damage.The ballistic impact process is captured with high-speed photography.Postmortem samples are characterized with optical imaging,three-dimensional laser scanning,microhardness testing and electron backscatter diffraction.With increasing number of impacts,crater diameter increases slightly,but crater depth and crater volume increase significantly,and strain accumulation leads to microhardness increase overall.Crater parameters all follow power-law relations with the number of impacts.Twin-like deformation bands and macroscopic deformation twins are produced by impact as a result of spontaneous dislocation self-pinning under high strain rate,large shear deformation.Under multiple impacts,shear strain accumulation in the arc-shaped region of the crater induces deformation twinning when it exceeds a critical value (～ 1.1-1.6).It is highly possible that the deformation twins are related to deformation bands,since they both share one set of the {111} pole with the initial matrix grain.A finite element method model is optimized to repro-duce experimental observations and interpret deformation mechanisms.
Seong-Tae KimJong Min ParkKwi-Il ParkSang-Eun Chun...
175-182页
查看更多>>摘要：Composites were prepared,through hot pressing,using carbon materials with different pore size distribu-tions as additives for commercial Bi0.5Sb1.5Tes thermoelectric material (BST,p-type).Thermoelectric prop-erties of the composites were measured in a temperature range of 298-473 K.Thermal conductivity of the composites,especially lattice thermal conductivity,was effectively decreased due to the mesoporous properties of the incorporated carbon additives.The electrical conductivity of the composites slightly de-creased due to the electron scattering at the interface between the carbon material and the commercial BST matrix.The composite with 0.2 vol.％ mesoporous carbon powder (36％ mesoporosity) exhibited a figure of merit value approximately 10.7％ higher than that of commercial BST without additives.This be-havior resulted in 116％ improved output power in the composite block-based single element compared with a bare BST thermoelectric block.The enhanced figure of merit was attributed to the effective re-duction of lattice thermal conductivity by acoustic phonons scattering at the interface between the BST matrix and the mesoporous carbon as well as at the pore surfaces within the mesoporous carbon.By utilizing mesoporous carbon materials used in this study,the shortcomings and economic difficulties of the composite process with low dimensional carbon additives (carbon nanotubes,graphene,and nanodi-amond) can be overcome for extensive practical applications.Mesoporous carbon powder with a tailored porosity distribution revealed the validity of bulk-type carbon additives to enhance the figure of merit of commercial thermoelectric materials.
查看更多>>摘要：In the present study,a fully lamellar Ti6Al4V alloy was severely deformed by high pressure torsion (HPT)process under a pressure of 7.5 GPa up to 10 revolutions.Experimental results revealed that the micro-hardness of Ti6Al4V was increased remarkably by about ～41％ and saturated at about 432 Hv after the HPT process.A relatively uniform bulk nanostructured Ti6Al4V alloy with an average grain size of about 52.7 nm was obtained eventually,and no obvious formation of metastable ω phase was detected by XRD analysis.For the first time,the tribological properties of the HPT processed Ti6Al4V alloy were investi-gated by a ball-on-disc test at room temperature under a dry condition.It was found that HPT process had a great influence on the friction and wear behaviors of Ti6Al4V alloy.With increasing the number of HPT revolutions,both friction coefficient and spedfic wear rate were obviously decreased due to the reduction of abrasion and adhesion wears.After being deformed by 10 HPT revolutions,the friction co-efficient was reduced from about 0.49 to 0.37,and the specific wear rate was reduced by about 48g.The observations in this study indicated that HPT processed Ti6Al4V alloys had good potential in structural applications owing to their greatly improved mechanical and tribological properties.
查看更多>>摘要：Surgical prostheses and implants used in hard-tissue engineering should satisfy all the clinical,mechani-cal,manufacturing,and economic requirements in order to be used for load-bearing applications.Metals,and to a lesser extent,polymers are promising materials that have long been used as load-bearing bioma-terials.With the rapid development of additive manufacturing (AM) technology,metallic and polymeric implants with complex structures that were once impractical to manufacture using traditional process-ing methods can now easily be made by AM.This technology has emerged over the past four decades as a rapid and cost-effective fabrication method for geometrically complex implants with high levels of accuracy and precision.The ability to design and fabricate patient-specific,customized structural bioma-terials has made AM a subject of great interest in both research and clinical settings.Among different AM methods,laser powder bed fusion (L-PBF) is emerging as the most popular and reliable AM method for producing load-bearing biomaterials.This layer-by-layer process uses a high-energy laser beam to sinter or melt powders into a part patterned by a computer-aided design (CAD) model.The most impor-tant load-bearing applications of L-PBF-manufactured biomaterials include orthopedic,traumatological,craniofacial,maxillofacial,and dental applications.The unequalled design freedom of AM technology,and L-PBF in particular,also allows fabrication of complex and customized metallic and polymeric scaffolds by altering the topology and controlling the macro-porosity of the implant.This article gives an overview of the L-PBF method for the fabrication of load-bearing metallic and polymeric biomaterials.
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