查看更多>>摘要：A comparative analysis is performed on the structural damage response and associated mechanisms in lanthanum aluminate and yttrium aluminate crystals under various irradiation conditions by a combi-nation of experimental and theoretical approaches.Under low-energy Au+ irradiation,the damage accu-mulation curve shows a higher damage rate for LaAlO3 crystals than YAlO3 crystals.The relatively low irradiation tolerance of LaAlO3 to the action of nuclear collisions is ascribed to the large amorphization cross-section and effective cross-section for defect-stimulated amorphization.Under swift Ar12+,Ni19+and Kr17+ irradiation with different ion energies and velocities,the formed highly-disordered/amorphous latent tracks with different morphologies in pristine and predamaged crystals are discussed,and the corresponding electronic energy loss and lattice temperature thresholds are quantitatively determined.Compared to YAlO3,LaAlO3 exhibits lower sensitivity and higher damage tolerance to the electronic en-ergy loss process,attributing to its relatively high recrystallization efficiency during the rapid quench-ing process.Furthermore,the introduction of lattice defects into LaAlO3 and YAlO3 crystals considerably enhances the sensitivity and intensity of thermal spike response to the electronic energy loss,and the induced effective modification of track morphologies demonstrates the synergistic effect between the electronic energy loss and pre-existing defects created by nuclear collisions.In this case,even under the action of electronic energy loss below the threshold,the lattice temperature in the nuclear-collision damaged crystalline system could still meet the criterion for track production.The irradiation energy deposited to atoms and induced lattice temperature evolution discussed in this work provide a deeper insight into the complex processes involved in irradiation-induced latent track behaviors.
查看更多>>摘要：The flattening test,using one pair paralleled plates to flatten tube structure radially,is generally em-ployed to examine the ductility of tube used in once through steam generator (OTSG).This study fo-cuses on the stress condition and deformation mechanism analysis on the concentrated stress regions of Ti-2Al-2.5Zr alloy tube during the flattening test.Firstly,the finite element analysis was performed using the commercial software ABAQUS to determine the stress condition.Secondly,the Electron Back-Scattered Diffraction (EBSD) was implemented to observe the microstructure evolution of Ti-2Al-2.5Zr alloy.Finally,Schmid law was employed to analyze the activated deformation mechanism under condi-tion of the complex stress.It was found that the condition of the complex stress in stress concentration regions,including tension and compression regions,can be simplified into two directional stresses con-dition.In grains whose c-axis is nearly towards TD and ND,the strain is mainly accommodated by pris-matic slip,whereas in grains whose c-axis deviates about 45° from ND to TD mainly by basal slip.The{10-12} extensive twin and corresponding parent grain orientation mainly relied on the stress condition.Additionally,the intergranular twin pairs connected at common grain boundaries (GBs) with high strain compatibility were found at low angle GBs,which were activated under a combination of macro stress and strain compatibility effect.
查看更多>>摘要：Copper/steel is a typical bimetal functional material,combining the excellent electrical and thermal con-ductivity of copper alloy and the high strength and hardness of stainless steel.There has been recent interest in manufacturing copper/steel bimetal by directed energy deposition (DED) due to its layer-by-layer method.However,cracks tend to form on the copper/steel interface because of the great difference in thermal expansion coefficient and crystal structure between copper and steel.In this work,interfa-cial characteristics and mechanical properties of the copper/steel bimetal were studied from one layer to multilayers.The laser power has a great influence on the Cu element distribution of the molten pool,affecting the crack formation dramatically on the solidification stage.Cracks tend to form along colum-nar grain boundaries because of the Cu-rich liquid films and spherical particles in the cracks.Crack-free and good metallurgical bonding copper/steel interface is formed at a scanning velocity of 800 mm/min and the laser power of 3000 W.The ultimate tensile strength (UTS) and the break elongation (EL) of the vertically combined crack-free copper/steel bimetal are 238.2 ± 4.4 MPa and 20.6 ± 0.7％,respec-tively.The fracture occurs on the copper side instead of the copper/steel interface,indicating that the bonding strength is higher than that of the Cu-Cr alloy.The UTS of the horizontally combined crack-free copper/steel bimetal is 746.7 ± 22.6 MPa,which is 200％ higher than that of the Cu-Cr alloy substrate.The microhardness is 398.6 ± 5.4 HV at the steel side and is 235.3 ± 64.1 HV at the interface,which is 400％ higher than that of the Cu-Cr alloy substrate.This paper advances the understanding of the inter-facial characteristics of heterogeneous materials and provides guidance and reference for the fabrication of multi-material components by DED.
查看更多>>摘要：Implant-related infection is one of the most catastrophic complications after surgery,since it may trigger osteomyelitis and necessitate reoperation,increasing the pain suffered by and the burden placed on the patient.Producing a new alloy with an antibacterial effect for use as a biomedical material is an urgent requirement.In this article,Ti-6Al-4V-5Cu was synthesized under two different heat treatment schemes(solution temperatures of 850 ℃ and 950 ℃).Through comprehensive observation of the microstructure,phase,copper ion release,biocompatibility,corrosion resistance and antibacterial effect in vitro and in vivo,it was determined that cell viability and corrosion resistance of Ti-6Al-4V-5Cu was better than Ti-6Al-4 V.More importantly,the obtained alloy,especially samples treated at 850 ℃,showed prominent antibacterial ability.Meanwhile,we also found that the main antibacterial mechanism of the alloy was contact sterilization via the extensive precipitation of Ti2Cu instead of Cu ion release,and the content,surface area of Ti2Cu could affect the antibacterial effect.These findings provide a very promising scheme by which to balance the biocompatibility and antibacterial effect of Ti-based,Cu-bearing alloys,which could improve their performance in orthopedic and dental applications.
查看更多>>摘要：The construction of built-in electric field is generally considered as an effective strategy to enhance pho-tocatalytic performance due to its significant role in charge separation.Herein,a built-in electric field within g-C3N4 hollow nanospheres co-doped with sulfur and oxygen and modified in-situ Ni2P is pro-posed.Ni2P/SO-HC3N4 exhibits significantly enhanced board spectrum photocatalytic properties for hy-drogen precipitation (5.21 mmol h-1 g-1) and photocatalytic Cr(Ⅵ) reduction without the use of noble metal.It also achieves high photocatalytic sterilization activity and remarkable stability when used to completely inactivate E.coli (107) in 60 min under Vis-NIR light irradiation.The enhanced performance is attributed to the formation of a curved hollow sphere structure,which promotes the electron transfer between the inner and outer layers.In addition,co-doping inhibits the recombination of photogenerated carriers,and the built-in electric field recombined with Ni2P facilitates the electron transfer between the composite interfaces.This design strategy demonstrates an original method of devising multifunctional photocatalysts with enhanced activity and stability.
查看更多>>摘要：Super-high strength NbTaTiZr high-entropy alloys (NbTaTiZr HEAs) have been successfully fabricated by the mechanical alloying (MA) with spark plasma sintering (SPS) technology,which is 2-fold compared with that of NbTaTiZr HEAs prepared by vacuum arc melting (VAM).After the SPS process,the bulk NbTa-TiZr alloy samples are provided with dual-phase body-centered cubic (BCC) structure and nanoscale grain size about 500 nm that is obviously smaller than that of NbTaTiZr HEA fabricated by VAM.When the sin-tering temperature is 800 ℃,the compressive fracture strength is the highest reaching at 2511 ± 78 MPa.When the sintering temperature is 1000 ℃,the fracture strain is the highest reaching at 12.8％,and com-pressive fracture strength and yield strength also reach at 2274 ± 91 MPa and 2172 ± 47 MPa,respec-tively.The excellent mechanical properties of bulk NbTaTiZr alloy samples are attributed to the merits of MA and SPS,and the collaboration effect of ultra-fine grains strengthening,solid solution strengthening and interstitial solid solution strengthening.
查看更多>>摘要：Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic tempera-tures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy (SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A re-cently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the un-derlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in con-trast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.
查看更多>>摘要：Variant selection under specific applied stresses during precipitation of α plates from prior-β matrix in Ti-6Al-4 V was investigated by 3D phase field simulations.The model incorporates the Burgers transfor-mation path from β to α phase,with consideration of interfacial energy anisotropy,externally applied stresses and elastic interactions among α variants and β matrix.The Gibbs free energy and atomic mo-bility data are taken from available thermodynamic and kinetic databases.It was found that external stresses have a profound influence on variant selection,and the selection has a sensitive dependence,as evidenced by both interaction energy calculations and phase field simulations.Compared with normal stresses,shear stresses applied in certain directions were found more effective in accelerating the trans-formation,with a stronger preference to fewer variants.The volume fractions of various α variants and the final microstructure were determined by both the external stress and the elastic interaction among different variants.The α clusters formed by variants with Type2 misorientation ([11-20]/60°) relation were found more favored than those with Type4 ([1055-3]/63.26°) under certain applied tensile stress such as along < 111 >β.The mechanical properties of different microstructures from our phase field simu-lation under different conditions were calculated for different loading conditions,utilizing crystal plastic finite element simulation.The mechanical behavior of the various microstructures from phase field sim-ulation can be evaluated well before the alloys are fabricated,and therefore it is possible to select mi-crostructure for optimizing the mechanical properties of the alloy through thermomechanical processing based on the two types of simulations.
查看更多>>摘要：A novel three-dimensional hierarchical WO3 photoelectrode was prepared by solvothermal method,and ZnO was deposited on its surface by electrochemical method.The WO3/ZnWO4/ZnO multiphase-heterojunction photoelectrode was prepared by further annealing treatment to explore the photoinduced cathodic protection (CP) performance.Compared with WO3 and ZnO,the photoinduced CP and electron storage capacity performance of WO3/ZnWO4/ZnO is significantly improved in 3.5％ NaCl solution without adding any hole scavenger.The electron storage capacity of the WO3/ZnWO4/ZnO heterojunction makes it possible to continuously protect metallic materials in the dark after switching off the light,which can realize long-term and effective photoinduced CP.
查看更多>>摘要：The excellent properties of the multi-principal element alloys (e.g.,the CoCrNi medium-entropy alloy)make them a perfect candidate for structure materials.Their low strength and poor wear-resistance,however,limit considerably their applications.In this study,a lamellar eutectic microstructure was in-troduced by addition of Hf into CoCrNi alloy to produce a series of CoCrNiHfx (x=0.1,0.2,0.3 and 0.4)eutectic medium-entropy alloys.A homogeneous eutectic microstructure with an alternate array of the soft FCC solid-solution phase and the hard Laves phase was identified for the as-cast CoCrNiHf0.3 alloy.After an investigation of the microstructure,mechanical and tribological properties,it was found that the hardness (plasticity) increases (decreases) with the increasing volume fraction of the Laves phase and the CoCrNiHf0.3 eutectic alloy exhibits both good plasticity and high strength.The wear behavior is strongly dependent on the applied normal load.For a low normal load,its tribological behavior follows the At-chard's equation and a higher hardness due to Hf addition can resist plastic deformation and abrasive wear.When the normal load is high enough,the hypoeutectic or hypereutectic alloy,which possessing either high strength or good ductility but not at the same time,exhibit a poor wear resistance.In com-parison,the full eutectic CoCrNiHf0.3 alloy with a superior combination of strength and toughness shows the best wear performance,as it can significantly reduce fracture during wear.
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