查看更多>>摘要：We report laser cladding of pure titanium on a CoCrMo alloy using directed energy deposition.Using electron microscopy,the microstructural evolution upon varying the process parameters,especially laser power and powder feed rate,was investigated in relation to crack formation.Cladding layers showing dilution rates of more than 5％contained cracks due to the formation of the brittle Co2Ti intermetallic phase.The observed cracks could be ascribed to a mismatch in thermal expansion and a resulting stress of more than 440 MPa acting on the Co2Ti phase,as determined by density functional theory and nanoin-dentation.Furthermore,an excess laser energy caused chemical inhomogeneity and unmelted Ti powder particles,while a deficient laser energy resulted in a lack of fusion.Neither cracks nor partially melted powders were observed for a powder feed rate of 3 g/min and a laser power of 225-300 W,for which the dilution rate was minimized to less than 5％.For such samples,the cladding layers comprised pureα-Ti and a uniform CoTi interface with Co2Ti islands.
Bohong ZhangJie ChenPengfei Wang Bingtao SunYu Cao...
111-119页
查看更多>>摘要：The inverse gradient-grained CoCrFeMnNi high-entropy alloy with a desirable mechanical property that evades the strength-ductility trade-off is fabricated by the process of cold rolling and subsequent laser surface heat-treatment.Due to the gradually decayed thermal effect along with the thickness,the grain size increases from the hard core to the soft surface in terms of the inverse gradient-grained sample,which is in good consistent with the microhardness profiles.The hetero-deformation induced strengthen-ing and strain hardening caused by the inverse gradient-grained structure improve the strength-ductility combination,as well as the high-order hierarchal nanotwins due to the enhanced interaction with dis-locations.For the laser surface heat-treatment technique,the strength and ductility are significantly in-creased by enlarging the microhardness difference and decreasing the thermal stress.Considering the high volume fraction of gradient-grained layer and a great deal of high-order hierarchal nanotwins in the central region,the laser surface heat-treatment technique is a promising way to produce the gradient-structured materials without thickness limitation.
查看更多>>摘要：Polymeric biomaterials such as polylactic acid(PLA)play a prominent role in the advancement of biomedical additive manufacturing(AM).PLA offers indeed a very advantageous combination of thermo-mechanical properties and functional attributes,as it is biobased,biodegradable,biocompatible and easy to print.However,PLA can be damaged by common sterilization methods and is sensitive to most chemi-cal disinfectants,and this may impair its widespread usage.One of the most promising ways to overcome this shortcoming is to provide PLA with embedded antibacterial activity by the addition of appropriate fillers such as zinc oxide(ZnO)nanoparticles.After a detailed introduction to the basic properties of PLA and ZnO nanoparticles,the present review analyzes the main variables that govern the antibacte-rial activity of PLA-ZnO nanocomposites.Current applications and related manufacturing processes are also presented to showcase the importance of having embedded antibacterial functions in demanding applications such as food packaging and wound dressing.Emphasis is then placed on the emerging lit-erature of the AM of PLA-ZnO nanocomposites,with a focus on fused filament fabrication(also known as fused deposition modeling).Existing gaps and hurdles related to the development and 3D printing of such composites is critically discussed.It is envisioned that a deeper understanding of the processability,thermo-mechanical behavior,biocompatibility and antibacterial efficacy of additively manufactured PLA-ZnO nanocomposites will foster their adoption in the biomedical field and,ultimately,in all circumstances where it is crucial to limit infection transmission.
查看更多>>摘要：A very coarse-grained(335 μm)Fe41Mn25Ni24CO8Cr2 high-entropy alloy with a single FCC phase was cold rolling to a 80％reduction in thickness using the differential speed rolling technique with various speed ratios(SRs)ranging between 1 and 4.As the SR was increased,the volume fraction of the region of high-density micro-shear bands increased to accommodate the higher shear strain.At SR=4,the en-tire thickness of the sheet was covered with micro-shear bands,and ultrafine(sub)grains with a size of 1.4 μm were uniformly formed along the shear bands.A continuous dynamic recrystallization(CDRX)mechanism occurred during rolling,and a higher SR accelerated the CDRX process.During conventional rolling(at SR=1),a brass{110}<112)orientation texture with minor components of S{123}<634)and Cu{112}<111>orientations developed.At higher SRs,shear texture developed as the main type,while the development of rolling texture was suppressed.The microstructure at SR=4 obtained after annealing at 973 K showed a fully recrystallized microstructure composed of a five times smaller grain size(4 μm)with a higher intensity of y fiber texture compared with that prepared by conventional rolling.The sam-ples processed with high SRs exhibited better tensile properties compared with the conventionally rolled sample in terms of strength and ductility after annealing.The current results demonstrate that by using differential speed rolling with a high SR,one can achieve a significantly finer and more homogeneous mi-crostructure,stronger shear texture,and superior tensile mechanical properties for an FCC high-entropy alloy compared to that obtained by conventional rolling.The strength of the as-rolled and annealed sam-ples was quantitatively explained by considering the contribution of grain size and dislocation density to strengthening.
查看更多>>摘要：Implant-associate infection(IAI)is a major cause of failure of bone implant materials,and one of the significant challenges in clinical managements.A synergistic coating strategy combining montmorillonite(MMT)sustained release,adsorption of bacteria and gentamicin(GS)bactericidal is proposed herein to tackle infection issues.Surface morphology,microstructure and chemical composition of the samples were investigated using SEM,XRD,FT-IR and XPS.Electrochemical experiments and immersion experi-ments reveal that corrosion resistance of Mg samples with GS/MMT coatings was higher than that of bare Mg alloy substrate in DMEM solution.In vitro studies demonstrated that the GS/MMT coating had a significant inhibitory effect on Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus).The viability of MC3T3-E1 cells was 92.7％after a co-culturing for 72 h.After a subcutaneous transplantation of 90 days,the survival rate was 100％for GS/MMT-coated Mg alloy specimens with no infection at the im-plantation sites and no toxic damage to liver,kidney and local muscles pathological sections.This study provides a novel method for the preparation of sustained-release antimicrobial coatings on biodegradable Mg alloys as promising candidates for orthopedic implant materials.
查看更多>>摘要：Sustainable energy conversion and storage provide feasible approaches towards green energy solutions and carbon neutralization.The high cost and complex fabrication process of advanced energy nanoma-terials,however,has impeded the practical application of emerging sustainable technologies.The direct use of earth-abundant natural minerals which contain active elements for effective catalysis and energy storage should be a promising approach to achieve affordable sustainable energy supply and green fuel generations.Herein,as typical examples of activating natural minerals for electrocatalysis,two common minerals,pyrite and chalcopyrite,are activated via a one-step phase transformation strategy.Through a facile thermal reduction process,the minerals are completely transformed into active pyrrhotite(FeS)and haycockite(Cu4Fe5S8)phases.The thermal reduction resulting phase transformation can lead to sig-nificant surface disordering and can contribute to the catalytic activity by offering favourable electronic structure for intermediates adsorption,abundant surficial active centres,and substantial surface redox pairs.The activated minerals are examined for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)catalysis.The obtained haycockite phase delivers the best performance towards acidic HER and alkaline OER.Further phase optimization is performed via loading a low percentage of iridium nan-oclusters on the haycockite phase deposited onto a carbon cloth substrate,through which an overpoten-tial as low as 310 mV for achieving 10 mA cm-2 and a small Tafel slope of 55.6 mV dec-1 are recorded for alkaline OER.This work demonstrates the feasibility of the direct use of cost-effective natural resources for addressing the current energy-related issues and paves a way to reach affordable practical emerging sustainable technologies.
查看更多>>摘要：Safe,compact,lightweight and cost-effective hydrogen storage is one of the main challenges that need to be addressed to effectively deploy the hydrogen economy.LiAlH4,as a solid-state hydrogen storage mate-rial,presents several advantages such as high hydrogen storage capacity,low price and abundant sources.Unfortunately,neither thermodynamic nor kinetic properties of dehydrogenation for LiAlH4 can fulfill the requirements of practical application.Thus,a series of spinel ferrite nanoparticles such as XFe2O4(X=Ni,Co,Mn,Cu,Zn,Fe)were prepared by using the modified thermal decomposition method,and then doped into LiAlH4 by using ball milling.Our results show that LiAlH4 doped with 7 wt％NiFe2O4 starts to release hydrogen at 69.1℃,and the total amount of hydrogen released is 7.29 wt％before 300℃.The activation energies of the two-step hydrogen release reactions of LiAlH4 doped with 7 wt％NiFe2O4 are 42.32 kJ mol-1 and 71.42 kJ mol-1,which are 59.0％and 63.6％lower than those of as-received LiAlH4,respec-tively.Combining the density functional theory(DFT)calculations,we reveal that both the presence of NiFe2O4 and in-situ formed Al4Ni3 in ball-milling decrease the desorption energy barrier of Al-H bonding in LiAlH4 and accelerate the breakdown of Al-H bonding through the interfacial charge transfer and the dehybridization of the Al-H cluster.Thus,the experimental and theoretical results open a new avenue toward designing high effective catalysts applied to LiAlH4 as a candidate for hydrogen storage.
查看更多>>摘要：Carbon nitride(g-C3N4)is an attractive photocatalyst but commonly suffers from high photogenerated electron-hole recombination rate,low specific surface area,and narrow visible-light response range.Herein,3D ordered macroporous(3DOM)g-C3N4/CdS was constructed by a feasible and inexpensive syn-thesis strategy of using template and light-assisted methods to solve the above problems.The formed heterostructure with suitable morphology,band structure,and extended light absorption range is bene-ficial to promoting photocatalytic H2 generation.3DOM g-C3N4/CdS exhibits a high H2 produce rate of 718.6 umol h-1 g-1,which is 73.3 times higher than that of g-C3N4 and 25.4 times higher than that of 3DOM g-C3N4.The 3DOM structure can effectively increase the path length of light of g-C3N4,improve the light energy conversion efficiency,and shorten the carrier transport distance.CdS enhances visible-light response and produces many surface sites.Constructing a stable and tight interface between 3DOM g-C3N4 and CdS can promote the migration of photogenerated electrons and holes and consequently the visible-light catalytic activity.This study offers an effective designing strategy for heterostructure photo-catalysts to achieve high activity and stable solar H2 production.
查看更多>>摘要：Obviously planar anisotropy due to'TD split'orthotropic texture(TD indicates Transverse direction)al-ways exist in the Rare-earth(RE)or Ca containing Mg alloy sheets,which is likely caused by the low-reduction rolling(and annealing)as revealed in our previous research.In this work,the as-cast billets of a ZWK100 alloy were subjected to final-pass heavy reduction rolling(FHRR)at 500℃with different reductions(30％-70％)after rough rolling,aiming to investigate the reduction effect on the microstruc-ture and texture formation.The results show that FHRR with higher reductions above 50％is in favor of shear banding formation but has little effect on the as-deformed texture components,and the excel-lent formability with single-pass reduction up to 70％is mainly ascribed to the activation of prismatic<a>slip.FHRR with reduction above 50％and annealing can generate uniform grain structures of～10 μm and symmetrical'oblique-line split'texture in(0001)pole figures,with basal poles tilting by about 50° from ND(Normal direction)towards some oblique-line of TD and RD(Rolling direction)as well as uniform distribution of counter lines as an annular shape,resulting in excellent elongation to failure of～50％and ultra-low planar anisotropy △r2 of～0.1 and high stretch formability(Erichsen value:8.1).The formation'oblique-line split'texture in(0001)pole figures is mainly correlated with the preferred growth tendency of grains with[2111]-[1212]//RD,which was suggested to relate to the high mobility of some special boundaries such as 40°-45°[1010](∑14).The influences of starting textures on the mechanical properties,planar anisotropy and related deformation modes,as well as their correlations with the stretch formabil-ity were comparatively investigated with the'TD split'orthotropic texture as a counterpoint.
查看更多>>摘要：In this work,the microstructure of titania coating fabricated on the surface of hydrostatically extruded titanium grade 4 with the use of the micro-arc oxidation method was studied.The surface topography and microstructure investigations performed with atomic force microscopy and scanning and transmis-sion electron microscopy revealed that,by using an Na2HPO4 electrolyte,a well-adherent porous coating is produced on the top surface and side walls of the extruded rod.The distribution of chemical elements was analyzed by using energy dispersive X-ray spectroscopy.The chemical elements dissolved in the elec-trolyte(Na,P and O)incorporated into the coating.Sodium locates preferentially in the outer part of the coating,while phosphorus and oxygen are distributed throughout the whole coating.The most relevant finding shows that a grain refinement caused by a hydrostatic extrusion provoked an increase in density of high-angle grain boundaries(HAGB),which in turn secured the formation of a continuous amorphous layer close to the substrate.The presence of this layer compensates for the effect of anisotropic substrate,producing a comparable and homogenous microstructure with a large number of micropores.
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