Laser-welded Ti-6Al-4 V is prone to severe residual stresses,microstructural variation,and structural de-fects which are known detrimental to the mechanical properties of weld joints.Residual stress removal is typical...Laser-welded Ti-6Al-4 V is prone to severe residual stresses,microstructural variation,and structural de-fects which are known detrimental to the mechanical properties of weld joints.Residual stress removal is typically applied to weld joints for engineering purposes via heat treatment,in order to avoid prema-ture failure and performance degradation.In the present work,we found that proper welding residual stresses in laser-welded Ti-6Al-4 V sheets can maintain better ductility during uniaxial tension,as op-posed to the stress-relieved counterparts.A detailed experimental investigation has been performed on the deformation behaviours of Ti-6Al-4 V butt welds,including residual stress distribution characteriza-tions by focused ion beam ring-coring coupled with digital image correlation(FIB-DIC),X-ray comput-erized tomography(CT)for internal voids,and in-situ DIC analysis of the subregional strain evolutions.It was found that the pores preferentially distributed near the fusion zone(FZ)boundary,where the compressive residual stress was up to-330 MPa.The removal of residual stress resulted in a changed failure initiation site from the base material to the FZ boundary,the former with ductile and the latter with brittle fracture characteristics under tensile deformation.The combined effects of residual stresses,microstructures,and internal pores on the mechanical responses are discussed in detail.This work high-lights the importance of inevitable residual stress and pores in laser weld pieces,leading to key insights for post-welding treatment and service performance evaluations.展开更多
Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified ...Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified heat treatment(MHT)process that only involves a single-step aging at 650℃ for 4 h to achieve high strength,high ductility,and low residual stress simultaneously in a laser powder bed fusion(LPBF)-processed Inconel 718(IN718)alloy.The MHT treated alloy exhibits comparable tensile strength(1368 MPa)to the conventional solution plus two-step aging(SA)treated alloy(1398 MPa),while the tensile elongation(∼21.7%for MHT treated alloy and 13.4%for SA treated alloy)is 60%higher and the residual stress(∼195 MPa)is 20%lower than the SA treated alloy.The balanced high performance of the MHT IN718 alloy was mainly attributed to the precipitation of abundantγ’’phase with a size of∼5 nm,while the original nano-sized Laves precipitates and dislocation cells were mostly retained.The finer size and higher fraction ofγ”of the MHT sample mainly result from the dislocation structure and compositional variations in the as-built IN718,which promotes precipitation during aging.The retention of Laves phase,and cellular dislocation network in the MHT alloy also contributes to work hardening during tension and suspends the occurrence of necking.This study unveils a unique strengthening and toughening mechanism in the Ni-based superalloy produced by LAM with the presence of abundant Laves precipitates and provides a simple,low energy-consumption and cost-effective heat treatment route for achieving desirable mechanical properties.展开更多
A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hard...A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.展开更多
Quantifying the residual stress at micron-scale is crucial for comprehending the trans-and inter-granular deformation mechanisms and the influence of heat treatment,but remains technically challenging.This study utili...Quantifying the residual stress at micron-scale is crucial for comprehending the trans-and inter-granular deformation mechanisms and the influence of heat treatment,but remains technically challenging.This study utilized focused ion beam and digital image correlation(FIB-DIC)techniques to assess residual stress within the dendrite stem and arm of nickel-based single-crystal superalloys.The influence of hot isostatic pressing(HIP)on the microstructure and residual stress was also elucidated.Our results revealed that the residual stresses in the dendrite stem and arm regions manifest as tensile stress along the x-axis and compressive stress along the y-axis,with a range of−720 MPa to 680 MPa.HIP treatment effectively improved microstructure and regulated residual stress in nickel-based single-crystal superalloys,leading to a rapid reduction in residual stress levels.The present study lays a solid theoretical groundwork for optimizing processing strategies to regulate residual stress and enhance mechanical properties in next-generation single-crystal superalloys.展开更多
An in-situ plasma spark sintering(SPS)apparatus,coupled with laboratory X-ray microscopy,was uti-lized to three-dimensionally investigate the dynamic evolution process of 7055 aluminum alloy during SPS process.The inf...An in-situ plasma spark sintering(SPS)apparatus,coupled with laboratory X-ray microscopy,was uti-lized to three-dimensionally investigate the dynamic evolution process of 7055 aluminum alloy during SPS process.The influences of sintering temperatures and particle morphology on the sintering kinetics were discussed in detail.It was observed that elevating the sintering temperatures enhanced both the rate of densification and the final compactness of the alloy.Furthermore,three-dimensional quantitative analysis of pore evolution indicated that greater discrepancies in powder size between neighboring par-ticles facilitated pore elimination during sintering by increasing available interstitial spaces.Mechanistic analysis rationalized these observations by attributing the enhanced sintering kinetics to the greater par-ticle size disparity,which resulted in higher necking curvature and accelerated densification.The present study therefore provides a comprehensive three-dimensional in-situ quantitative analysis on the dynamic SPS process,and is expected to advance the current comprehension of sintering mechanisms at the mi-cron scale.展开更多
In this study,we developed an in-situ hot-pressing sintering(HPS)device that can be coupled to a lab-oratory X-ray microscope,offering laboratory-available observation of the morphology evolution.With the help of this...In this study,we developed an in-situ hot-pressing sintering(HPS)device that can be coupled to a lab-oratory X-ray microscope,offering laboratory-available observation of the morphology evolution.With the help of this device,in-situ three-dimensional(3D)visualizations of the microstructural evolution of 7055 aluminum alloys during the HPS process were conducted.The 3D results revealed that the twodimensional(2D)methods usually underestimated sintering neck width and exhibited significant standard deviation in statistical analysis.Benefiting from the precise microstructure characterization of the insitu 3D methods,the diffusion activation energy for the sintering of 7055 alloys was calculated,and the quantitative relationship between the sintering temperature and the sintering process was constructed.Moreover,it was experimentally found an accelerative effect of satellite particles on the sintering process,and its mechanisms were discussed.The satellite particles enhanced the curvature near the sintering neck and thus increased the sintering driving stress,promoting the densification process.These findings provide new insights for optimizing sintering processes.展开更多
Characterizing the microstructure and deformation mechanism associated with the performances and properties of metallic materials is of great importance in understanding the microstructure-property relationship.The pa...Characterizing the microstructure and deformation mechanism associated with the performances and properties of metallic materials is of great importance in understanding the microstructure-property relationship.The past few decades have witnessed the rapid development of characterization techniques from optical microscopy to electron microscopy,although these conventional methods are generally limited to the sample surface because of the intrinsic opaque nature of metallic materials.Advanced synchrotron radiation(SR)facilities can produce X-rays with strong penetrability and high spatiotemporal resolution,and thereby enabling the non-destructive visualization of full-field structural information in three dimensions.Tremendous endeavors were devoted to the 3 rd generation SR over the past three decades,in which X-ray beams have been focused down to 100 nm.In this paper,recent progresses on SR-related characterization technologies were reviewed,with particular emphases on the fundamentals of synchrotron X-ray imaging and synchrotron X-ray diffraction,as well as their applications in the in situ observations of material preparation(e.g.,in situ dendrite growth during solidification)and service under extreme environment(e.g.,in situ mechanics).Future innovations toward next-generation SR and newly emerging SRbased technologies such as dark-field X-ray microscopy and Bragg coherent X-ray diffraction imaging were also advocated.展开更多
Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein,...Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein, mono-phase ceramics of indium tin oxides(ITO) were sintered for epsilon-negative materials in MHz-k Hz frequency regions. Electrical conductivity and complex permittivity were analyzed with DrudeLorentz oscillator model. Carriers’ characters were measured based on Hall effect and the magnitude and frequency dispersion of negative permittivity were mainly determined by carrier concentration.Temperature-dependent dielectric properties further proved the epsilon-negative behaviors were closely associated with free carriers’ collective responses. It’s found that negative permittivity of ITO ceramics was mainly caused by plasma oscillations of free carriers, while the dielectric loss was mainly attributed to conduction loss. Negative permittivity realized here was related to materials intrinsic nature and this work preliminarily determined the mechanism of negative permittivity in doped ceramics from the perspective of carriers.展开更多
The layered structural parameters have been reported to be critical for tuning the tensile properties of laminated metals.Here,we investigated the effects of the thickness ratio(rc/f)of coarse-grained layers(CLs)to fi...The layered structural parameters have been reported to be critical for tuning the tensile properties of laminated metals.Here,we investigated the effects of the thickness ratio(rc/f)of coarse-grained layers(CLs)to fine-grained layers(FLs)on the enhanced ductility of the laminated Al.The local strain evolution demonstrates that the strain delocalization ability of laminated Al is improved with the decrease of rc/f.The interfacial strain gradients,which can produce extra work hardening,gradually approach and cover the CLs with the rc/fdecreasing,explaining the trend of uniform elongation in laminated Al with various rc/f.The integrated fracture morphology characterization reveals that the increase of the rc/fleads to an improvement in the tolerance of the interfacial microcracks,which is corresponding to the variation of fracture elongation in the laminated Al.Moreover,there is an evident transition of transverse propagation path of interfacial microcracks from the CLs to FLs with increasing the rc/f.Based on a geometrical criterion of microcracks connectivity,the preferential transverse propagation path of interfacial microcracks in these laminated Al was rationalized.The calculation based on this criterion also predicted the critical rc/fcorresponding to the optimal combination of strength and fracture elongation.This work deepens the understanding of the role of structural parameters of laminated metals in achieving the strength and ductility synergy.展开更多
The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is benefici...The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.展开更多
Recently great effort s have been focused on designing high-performance microwave absorbers using sustainable biomass resources,but there remains a lack of green and efficient fabrication methods.Herein,inspired by na...Recently great effort s have been focused on designing high-performance microwave absorbers using sustainable biomass resources,but there remains a lack of green and efficient fabrication methods.Herein,inspired by natural porous character of biomass waste,we demonstrated a green one-step route to convert waste coffee grounds into porous C/Fe hybrids,and further explored their potential applications for broadband and high-efficiency microwave absorption.In this design,the WCG-20-750(incorporated 20 wt%Fe(C_(5)H_(7)O_(2))_(3)catalyst and carbonized at 750℃)exhibited porous microstructure with the highest char yield of 55.45 wt%.Furthermore,the as-prepared C/Fe hybrids from WCG-20-750 displayed excellent microwave absorption performances.Typically,the minimum reflection loss(RL_(min))reached to-52.86 dB and the widest effective absorption bandwidth(EAB)was 6.40 GHz at the thickness of 3.0 mm.This work provides an economically viable and environmentally friendly strategy to convert biomass wastes into value-added microwave absorbers,ultimately making contributions to the upcycling of renewable biomass resources and the fostering of sustainable environment.展开更多
As one of the heterostructures,the layered structure has attracted extensive research interests as it could regulate the deformation mechanisms[1-3].A remarkable combination of strength and ductility has been achieved...As one of the heterostructures,the layered structure has attracted extensive research interests as it could regulate the deformation mechanisms[1-3].A remarkable combination of strength and ductility has been achieved in layered metals,including CuCu[4-6],Cu-Ni[7],Cu-Al[8,9],Cu-Ti[10],Ti-Ti[11,12],and Ti-Al[13-15].During deformation,mechanical mismatch(discrepancies of yield strength,work hardening,etc.)between component layers leads to mutual constraints,which generates local stress and local strain that deviate from the applied counterparts[16-18].As a result,the activation of additional deformation mechanisms is promoted in layered metals,such as slip systems with low Schmid factor or high critical resolved shear stress[19,20].展开更多
In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K co...In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K compared to its counterparts at 298 K.The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study.The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K,whereas at 77 K,vague grain surfaces dominate,indicating the simultaneous operation of multiple slip systems.Transmission electron microscopy(TEM)analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic temperature,confirming the activation of multiple slip systems.The accumulation of dislocations facilitated by these multiple slip systems,combined with the high dislocation density,contributes to strain hardening and remarkable uniform elongation at 77 K.A modified dislocation density-based crystal plasticity model,incorporating the effect of grain boundary hardening(GBH)and temperature,was developed to gain a better understanding of the underlying mechanisms governing alloy’s strength and plasticity.The GBH effect significantly enhances statistically stored dislocation(SSD)density and screw dislocation proportion,which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature.These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic applications.展开更多
In this study,the real 3D model of the feather shaft that is composed of medulla and cortex is characterized by X-ray computer tomography,and the structural features are quantitatively analyzed.Compression and tensile...In this study,the real 3D model of the feather shaft that is composed of medulla and cortex is characterized by X-ray computer tomography,and the structural features are quantitatively analyzed.Compression and tensile tests are conducted to evaluate the mechanical performance of the feather shaft and cortex at different regions.The analysis of the 3D model shows that the medulla accounts for∼70%of the shaft volume and exhibits a closed-cell foam-like structure,with a porosity of 59%.The cells in the medulla show dodecahedron and decahedron morphology and have an equivalent diameter of∼30μm.In axial compression,the presence of medulla enhances the shaft stability.Especially,the combined effect of the medulla and cortex increases the buckling strength of the middle and distal shaft by 77%and 141%,respectively,compared to the calculated value of the shaft using linear mixed rule.The tensile properties of the cortex along the shaft axis are anisotropic because of the different fiber structures.As the fiber orientation gradually becomes uniform in the axial direction,the Young’s modulus and tensile strength of the cortex on the dorsal gradually increase from calamus to the distal shaft,and the fracture mode changes from tortuous fracture to V-shaped fracture.The cortex on the lateral shows the opposite trend,that is the distal shaft becomes weaker due to fiber tangles.展开更多
Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys u...Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.展开更多
As one of the heterostructures,the layered structure has attracted extensive research interest as it achieves superior properties to individual components.The layer interface is considered a critical fac-tor in determ...As one of the heterostructures,the layered structure has attracted extensive research interest as it achieves superior properties to individual components.The layer interface is considered a critical fac-tor in determining the mechanical properties of layered metals,where heterogeneity across the interface results in the strengthening of the soft layer and forming an interfacial stress gradient in the hard layer.However,there is still limited research associated with the formation of interfacial stress gradients in the hard layer,as stress measurement at high spatial resolution remains technically challenging.In the present study,we experimentally quantified the formation of interfacial stress gradients in the Ti layer of Ti/Al layered metal upon tension using in-situ high-energy X-ray diffraction(XRD).The analysis cou-pling in-situ high-energy XRD and in-situ electron back-scattered diffraction(EBSD)suggested that the interfacial stress gradient in the Ti layer rapidly rose as the Al layer was insufficient to accommodate the deformation of Ti.During the later deformation stage,collective effects of dislocation motion and geometrically necessary dislocation(GND)accumulation in the Al layer determined the evolution of in-terfacial stress gradients.The maximum interfacial stress gradient is below 0.4 MPa/μm in Ti layers,with a constant range width of 35μm independent of the macroscopic strain.The present study therefore opens a new window to local stress modification using incompatible component deformation,which is instructive for the design and fabrication of high-performance layered metals.展开更多
Tumor-targeted radiopharmaceuticals have become an attractive modality for tumor diagnosis and treatment in clinics.However;their wide clinical applications are seriously impeded by poor tumor targeting;rapid systemic...Tumor-targeted radiopharmaceuticals have become an attractive modality for tumor diagnosis and treatment in clinics.However;their wide clinical applications are seriously impeded by poor tumor targeting;rapid systemic clearance;and short tumor retention.Therefore;developing advanced radiopharmaceuticals with great tumor specificity and prolonged retention time is highly desirable for efficient tumor treatment.Herein;we report a tumor-targeted covalently anchoring strategy that selectively crosslinks the radiopharmaceuticals to intratumoral macromolecules for prolonged tumor theranostics.A covalent multi-targeted radiopharmaceutical(CMTR)d-IR-2(^(125)IRGD)that includes a sulfenic acid-reactive 1,3-cyclohexanedione group was developed.We demonstrated this probe could specifically accumulate at the tumor site and bind to the sulfenated proteins that are overexpressed within tumors;which greatly prevents the efflux of probes in tumor tissues while having faster clearance in healthy tissues resulting in 12 h longer tumor retention than conventional probes for sensitive NIR and SPECT/CT detection of tumors in vivo.More notably;the ^(131)I-labeled probe could significantly suppress the growth of lung tumor A549.We thus envision that this work may offer a promising approach to developing effective radiopharmaceuticals for precise diagnosis and treatment of various tumors.展开更多
RNA interfering therapy has emerged as a promising therapeutic modality to treat cancer.The specific and efficient delivery of RNA into a tumor is crucial for achieving effective cancer gene therapy but remains a huge...RNA interfering therapy has emerged as a promising therapeutic modality to treat cancer.The specific and efficient delivery of RNA into a tumor is crucial for achieving effective cancer gene therapy but remains a huge challenge.Herein,we report a novel furin-responsive small interfering RNA(siRNA)delivery vehicle with multiple functions for colorectal tumor treatment.A peptide-based siRNA delivery vehicle RVRR-P18-Gd,consisting of furin enzyme-specific peptide substrate Arg-Val-Arg-Arg(RVRR)with positive charge for siRNA binding,a Gd(III)chelated 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid(DOTA)(DOTA-Gd)for magnetic resonance imaging,and purpurin 18 as photosensitizer for photodynamic therapy(PDT),was rationally designed and synthesized.Taking advantage of the cationic amphiphilic feature,RVRR-P18-Gd molecules spontaneously self-assembled with negatively charged Hif-1αsiRNA into stable nanoparticles via attractive electrostatic interaction,which effectively prevented siRNA degradation by nucleases,prolonged the circulation half-life,and enhanced tumor accumulation.Moreover,the specific release of Hif-1αsiRNA mediated by endogenous furin significantly downregulated Hif-1αexpression in colorectal cancer cells,resulting in enhanced therapeutic susceptibility,and with the PDT effect,effectively suppressed HCT116 tumor growth in living mice.This work highlights a powerful and universal approach to precisely deliver siRNA to targeted tumors for efficient synergistic therapy.展开更多
基金supported by the National Key Re-search&Development Plan of China(No.2020YFA0405900)the Major Research Plan of the National Natural Science Foundation of China(No.92263201)Y.P.Xia would like to thank the support by the Jiangsu Funding Program for Excellent Postdoctoral Talent.All authors thank the Advanced Material Research Institute of Jiangsu Industrial Technology Research Institute(JITRI,Suzhou,China)for the experimental support.
文摘Laser-welded Ti-6Al-4 V is prone to severe residual stresses,microstructural variation,and structural de-fects which are known detrimental to the mechanical properties of weld joints.Residual stress removal is typically applied to weld joints for engineering purposes via heat treatment,in order to avoid prema-ture failure and performance degradation.In the present work,we found that proper welding residual stresses in laser-welded Ti-6Al-4 V sheets can maintain better ductility during uniaxial tension,as op-posed to the stress-relieved counterparts.A detailed experimental investigation has been performed on the deformation behaviours of Ti-6Al-4 V butt welds,including residual stress distribution characteriza-tions by focused ion beam ring-coring coupled with digital image correlation(FIB-DIC),X-ray comput-erized tomography(CT)for internal voids,and in-situ DIC analysis of the subregional strain evolutions.It was found that the pores preferentially distributed near the fusion zone(FZ)boundary,where the compressive residual stress was up to-330 MPa.The removal of residual stress resulted in a changed failure initiation site from the base material to the FZ boundary,the former with ductile and the latter with brittle fracture characteristics under tensile deformation.The combined effects of residual stresses,microstructures,and internal pores on the mechanical responses are discussed in detail.This work high-lights the importance of inevitable residual stress and pores in laser weld pieces,leading to key insights for post-welding treatment and service performance evaluations.
基金financially supported by the Ministry of Science and Technology of China via the National Key Research&Development Plan(Nos.2022YFB3707105 and 2020YFA0405900)Jiangsu Department of Science and Technology via Provincial Key Research&Development(Industrial Foresight and Key Core Technology,No.BE2021037)+1 种基金Department of the National Science Foundation of China(No.52204390)the Natural Science Foundation of Jiangsu Province(No.BK20202010).
文摘Laser additively manufactured(LAM)Ni-based superalloys commonly exhibit low strength and high residual stress in the as-built state,requiring post-heat treatment to improve mechanical properties.We propose a modified heat treatment(MHT)process that only involves a single-step aging at 650℃ for 4 h to achieve high strength,high ductility,and low residual stress simultaneously in a laser powder bed fusion(LPBF)-processed Inconel 718(IN718)alloy.The MHT treated alloy exhibits comparable tensile strength(1368 MPa)to the conventional solution plus two-step aging(SA)treated alloy(1398 MPa),while the tensile elongation(∼21.7%for MHT treated alloy and 13.4%for SA treated alloy)is 60%higher and the residual stress(∼195 MPa)is 20%lower than the SA treated alloy.The balanced high performance of the MHT IN718 alloy was mainly attributed to the precipitation of abundantγ’’phase with a size of∼5 nm,while the original nano-sized Laves precipitates and dislocation cells were mostly retained.The finer size and higher fraction ofγ”of the MHT sample mainly result from the dislocation structure and compositional variations in the as-built IN718,which promotes precipitation during aging.The retention of Laves phase,and cellular dislocation network in the MHT alloy also contributes to work hardening during tension and suspends the occurrence of necking.This study unveils a unique strengthening and toughening mechanism in the Ni-based superalloy produced by LAM with the presence of abundant Laves precipitates and provides a simple,low energy-consumption and cost-effective heat treatment route for achieving desirable mechanical properties.
基金supported by the National Natural Science Foundation of China(Grant Nos.92263201,51927801,and 52001160)the National Key Research and Development Program of China(Grant No.2020YFA0405900).
文摘A solid solution 6063 aluminium alloy features an exceptional combination of strength and ductility at 77 K.Here,the deformation mechanisms responsible for superior strength-ductility synergy and excellent strain hardening capacity at a cryogenic temperature of the alloy were comparatively investigated by insitu electron backscatter diffraction(EBSD)observations coupled with transmission electron microscopy(TEM)characterization and fracture morphologies at both 298 and 77 K.It is found that kernel average misorientation(KAM)mappings and quantified KAM in degree suggest a higher proportion of geometrically necessary dislocations(GNDs)at 77 K.The existence of orientation scatter partitions at 77 K implies the activation of multiple slip systems,which is consistent with the results of potential slip systems calculated by Taylor axes.Furthermore,dislocation tangles characterized by brief and curved dislocation cells and abundant small dimples have been observed at 77 K.This temperature-mediated activation of dislocations facilitates the increased dislocations,thus enhancing the strain hardening capacity and ductility of the alloy.This research enriches cryogenic deformation theory and provides valuable insights into the design of high-performance aluminium alloys that are suitable for cryogenic applications.
基金financially supported by the National Key Research&Development Plan(No.2020YFA0405900)the National Natural Science Foundation of China(Nos.52171117,52371113,and 92263201)+1 种基金the Tuoyuan Project of Nanjing Tech University(No.20230113)the Technological Projects from CRCC Qishuyan Institute Co.,LTD(No.BS24125).
文摘Quantifying the residual stress at micron-scale is crucial for comprehending the trans-and inter-granular deformation mechanisms and the influence of heat treatment,but remains technically challenging.This study utilized focused ion beam and digital image correlation(FIB-DIC)techniques to assess residual stress within the dendrite stem and arm of nickel-based single-crystal superalloys.The influence of hot isostatic pressing(HIP)on the microstructure and residual stress was also elucidated.Our results revealed that the residual stresses in the dendrite stem and arm regions manifest as tensile stress along the x-axis and compressive stress along the y-axis,with a range of−720 MPa to 680 MPa.HIP treatment effectively improved microstructure and regulated residual stress in nickel-based single-crystal superalloys,leading to a rapid reduction in residual stress levels.The present study lays a solid theoretical groundwork for optimizing processing strategies to regulate residual stress and enhance mechanical properties in next-generation single-crystal superalloys.
基金the National Key Research&Development Plan(Grant No.2021YFA1600702)the Qing Lan Project,Tuoyuan project of Nanjing Tech University(Grant No.20230113)the project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions(PAPD).
文摘An in-situ plasma spark sintering(SPS)apparatus,coupled with laboratory X-ray microscopy,was uti-lized to three-dimensionally investigate the dynamic evolution process of 7055 aluminum alloy during SPS process.The influences of sintering temperatures and particle morphology on the sintering kinetics were discussed in detail.It was observed that elevating the sintering temperatures enhanced both the rate of densification and the final compactness of the alloy.Furthermore,three-dimensional quantitative analysis of pore evolution indicated that greater discrepancies in powder size between neighboring par-ticles facilitated pore elimination during sintering by increasing available interstitial spaces.Mechanistic analysis rationalized these observations by attributing the enhanced sintering kinetics to the greater par-ticle size disparity,which resulted in higher necking curvature and accelerated densification.The present study therefore provides a comprehensive three-dimensional in-situ quantitative analysis on the dynamic SPS process,and is expected to advance the current comprehension of sintering mechanisms at the mi-cron scale.
基金supported by the National Key Research&Development Plan(No.2021YFA1600702)the National Natural Science Foundation of China(Nos.92263201,52301155,and 52001161).
文摘In this study,we developed an in-situ hot-pressing sintering(HPS)device that can be coupled to a lab-oratory X-ray microscope,offering laboratory-available observation of the morphology evolution.With the help of this device,in-situ three-dimensional(3D)visualizations of the microstructural evolution of 7055 aluminum alloys during the HPS process were conducted.The 3D results revealed that the twodimensional(2D)methods usually underestimated sintering neck width and exhibited significant standard deviation in statistical analysis.Benefiting from the precise microstructure characterization of the insitu 3D methods,the diffusion activation energy for the sintering of 7055 alloys was calculated,and the quantitative relationship between the sintering temperature and the sintering process was constructed.Moreover,it was experimentally found an accelerative effect of satellite particles on the sintering process,and its mechanisms were discussed.The satellite particles enhanced the curvature near the sintering neck and thus increased the sintering driving stress,promoting the densification process.These findings provide new insights for optimizing sintering processes.
基金financially supported by the National Key Research and Development Plan(Grant Nos.2020YFA0405900,2017YFA0403803)the National Natural Science Foundation of China(Grant No.51927801)the Natural Science Foundation of Jiangsu Province(Grant No.BK20202010)。
文摘Characterizing the microstructure and deformation mechanism associated with the performances and properties of metallic materials is of great importance in understanding the microstructure-property relationship.The past few decades have witnessed the rapid development of characterization techniques from optical microscopy to electron microscopy,although these conventional methods are generally limited to the sample surface because of the intrinsic opaque nature of metallic materials.Advanced synchrotron radiation(SR)facilities can produce X-rays with strong penetrability and high spatiotemporal resolution,and thereby enabling the non-destructive visualization of full-field structural information in three dimensions.Tremendous endeavors were devoted to the 3 rd generation SR over the past three decades,in which X-ray beams have been focused down to 100 nm.In this paper,recent progresses on SR-related characterization technologies were reviewed,with particular emphases on the fundamentals of synchrotron X-ray imaging and synchrotron X-ray diffraction,as well as their applications in the in situ observations of material preparation(e.g.,in situ dendrite growth during solidification)and service under extreme environment(e.g.,in situ mechanics).Future innovations toward next-generation SR and newly emerging SRbased technologies such as dark-field X-ray microscopy and Bragg coherent X-ray diffraction imaging were also advocated.
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Future Plan for Young Talent of Shandong University(No.2016WLJH40)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘Negative permittivity has been widely studied in various metamaterials and percolating composites, of which the anomalous dielectric behavior was attributed to critical structural properties of building blocks.Herein, mono-phase ceramics of indium tin oxides(ITO) were sintered for epsilon-negative materials in MHz-k Hz frequency regions. Electrical conductivity and complex permittivity were analyzed with DrudeLorentz oscillator model. Carriers’ characters were measured based on Hall effect and the magnitude and frequency dispersion of negative permittivity were mainly determined by carrier concentration.Temperature-dependent dielectric properties further proved the epsilon-negative behaviors were closely associated with free carriers’ collective responses. It’s found that negative permittivity of ITO ceramics was mainly caused by plasma oscillations of free carriers, while the dielectric loss was mainly attributed to conduction loss. Negative permittivity realized here was related to materials intrinsic nature and this work preliminarily determined the mechanism of negative permittivity in doped ceramics from the perspective of carriers.
基金financially supported by the National Key Research&Development Program of China(Nos.2020YFA0405900 and 2017YFA0403803)the National Natural Science Foundation of China(Nos.51927801 and 51971075)the Natural Science Foundation of Jiangsu Province(No.BK20202010)。
文摘The layered structural parameters have been reported to be critical for tuning the tensile properties of laminated metals.Here,we investigated the effects of the thickness ratio(rc/f)of coarse-grained layers(CLs)to fine-grained layers(FLs)on the enhanced ductility of the laminated Al.The local strain evolution demonstrates that the strain delocalization ability of laminated Al is improved with the decrease of rc/f.The interfacial strain gradients,which can produce extra work hardening,gradually approach and cover the CLs with the rc/fdecreasing,explaining the trend of uniform elongation in laminated Al with various rc/f.The integrated fracture morphology characterization reveals that the increase of the rc/fleads to an improvement in the tolerance of the interfacial microcracks,which is corresponding to the variation of fracture elongation in the laminated Al.Moreover,there is an evident transition of transverse propagation path of interfacial microcracks from the CLs to FLs with increasing the rc/f.Based on a geometrical criterion of microcracks connectivity,the preferential transverse propagation path of interfacial microcracks in these laminated Al was rationalized.The calculation based on this criterion also predicted the critical rc/fcorresponding to the optimal combination of strength and fracture elongation.This work deepens the understanding of the role of structural parameters of laminated metals in achieving the strength and ductility synergy.
基金supported by the National Natural Science Foundation of China(Nos.51771104,51871146,51971119)the Natural Science Foundation of Shandong Province(No.ZR2020YQ32)the Innovation Program of Shanghai Municipal Education Commission(No.2019-01-07-00-10-E00053)。
文摘The development of negative permittivity materials in multifunctional applications requests expansion of their operating frequency and improvement of stability of negative permittivity.Low electron density is beneficial to reduce plasma frequency so that negative permittivity is achieved in kHz region.Negative permittivity achieved by percolating composites is restricted in practicality due to its instability nature at high temperatures.To achieve temperature-stable negative permittivity in kHz region,monophase La_(1-x)Ba_(x)CoO_(3)ceramics were prepared,and the transition from dielectric to metal was elaborated in the perspective of electrical conductivity and negative permittivity.The plasma-like negative permittivity is attained in kHz region,which is interpreted by the collective oscillation of low electron density.The temperature-stable negative permittivity is based on the fact that the plasmonic state will not be undermined at high temperatures.In addition,zero-crossing behavior of real permittivity is observed in La_(0.9)Ba_(0.1)CoO_(3)sample,which provides a promising alternative to designing epsilon-near-zero materials.This work makes the La_(1-x)Ba_(x)CoO_(3)system a source material for achieving effective negative permittivity.
基金supported by Taishan Scholar Constructive Engineering Foundation(No.tsqn202103079)the Talent Start-up Foundation of Qingdao University of Science and Technology(No.202203870).
文摘Recently great effort s have been focused on designing high-performance microwave absorbers using sustainable biomass resources,but there remains a lack of green and efficient fabrication methods.Herein,inspired by natural porous character of biomass waste,we demonstrated a green one-step route to convert waste coffee grounds into porous C/Fe hybrids,and further explored their potential applications for broadband and high-efficiency microwave absorption.In this design,the WCG-20-750(incorporated 20 wt%Fe(C_(5)H_(7)O_(2))_(3)catalyst and carbonized at 750℃)exhibited porous microstructure with the highest char yield of 55.45 wt%.Furthermore,the as-prepared C/Fe hybrids from WCG-20-750 displayed excellent microwave absorption performances.Typically,the minimum reflection loss(RL_(min))reached to-52.86 dB and the widest effective absorption bandwidth(EAB)was 6.40 GHz at the thickness of 3.0 mm.This work provides an economically viable and environmentally friendly strategy to convert biomass wastes into value-added microwave absorbers,ultimately making contributions to the upcycling of renewable biomass resources and the fostering of sustainable environment.
基金financially supported by the National Key Research&Development Plan(Nos.2020YFA0405900,2017YFA0403803,2017YFB0703103)the National Natural Science Foundation of China(Nos.51927801 and 52171117)the Natural Science Foundation of Jiangsu Province(No.BK20202010)。
文摘As one of the heterostructures,the layered structure has attracted extensive research interests as it could regulate the deformation mechanisms[1-3].A remarkable combination of strength and ductility has been achieved in layered metals,including CuCu[4-6],Cu-Ni[7],Cu-Al[8,9],Cu-Ti[10],Ti-Ti[11,12],and Ti-Al[13-15].During deformation,mechanical mismatch(discrepancies of yield strength,work hardening,etc.)between component layers leads to mutual constraints,which generates local stress and local strain that deviate from the applied counterparts[16-18].As a result,the activation of additional deformation mechanisms is promoted in layered metals,such as slip systems with low Schmid factor or high critical resolved shear stress[19,20].
基金supported by the National Natural Science Foundation of China(Nos.92263201,51927801,52001160,and 52205378)the National Key Research&Development Plan(Nos.2020YFA0405900 and 2019YFA0708801)Natural Science Foundation of Jiangsu Province(No.BK20202010).
文摘In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening capacity at 77 K compared to its counterparts at 298 K.The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study.The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K,whereas at 77 K,vague grain surfaces dominate,indicating the simultaneous operation of multiple slip systems.Transmission electron microscopy(TEM)analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic temperature,confirming the activation of multiple slip systems.The accumulation of dislocations facilitated by these multiple slip systems,combined with the high dislocation density,contributes to strain hardening and remarkable uniform elongation at 77 K.A modified dislocation density-based crystal plasticity model,incorporating the effect of grain boundary hardening(GBH)and temperature,was developed to gain a better understanding of the underlying mechanisms governing alloy’s strength and plasticity.The GBH effect significantly enhances statistically stored dislocation(SSD)density and screw dislocation proportion,which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature.These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic applications.
基金We acknowledge the financial support by the National Key Research and Development Program of China(No.2017YFA0403803)Liaoning Revitalization Talents Program(No.XLYC1808005)the fundamental research funds for the central universities.
文摘In this study,the real 3D model of the feather shaft that is composed of medulla and cortex is characterized by X-ray computer tomography,and the structural features are quantitatively analyzed.Compression and tensile tests are conducted to evaluate the mechanical performance of the feather shaft and cortex at different regions.The analysis of the 3D model shows that the medulla accounts for∼70%of the shaft volume and exhibits a closed-cell foam-like structure,with a porosity of 59%.The cells in the medulla show dodecahedron and decahedron morphology and have an equivalent diameter of∼30μm.In axial compression,the presence of medulla enhances the shaft stability.Especially,the combined effect of the medulla and cortex increases the buckling strength of the middle and distal shaft by 77%and 141%,respectively,compared to the calculated value of the shaft using linear mixed rule.The tensile properties of the cortex along the shaft axis are anisotropic because of the different fiber structures.As the fiber orientation gradually becomes uniform in the axial direction,the Young’s modulus and tensile strength of the cortex on the dorsal gradually increase from calamus to the distal shaft,and the fracture mode changes from tortuous fracture to V-shaped fracture.The cortex on the lateral shows the opposite trend,that is the distal shaft becomes weaker due to fiber tangles.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.52175306,52205347)the Natural Science Foundation of Shandong Province(Grant No.ZR2021QE181)the China Postdoctoral Science Foundation(Grant No.2022M712432)。
文摘Nickel-based single crystal superalloys have become the main structural materials of the aero-engines due to excellent high-temperature strength.The micro defects evolution of nickel-based single crystal superalloys under shear deformation was investigated by molecular dynamics(MD)simulations in the present study.It is found that the interfacial dislocations decompose into Shockley dislocations under low shear stress,resulting in the plastic deformation of the Ni phase.The initial plastic deformation of the Ni3Al phase is caused by Shockley dislocations cutting into the Ni3Al phase.The following deformation from low temperature to medium temperature is controlled by dislocation slip,but the deformation at high temperature is changed.It is also found that the microvoid evolution can be divided into void growth and coalescence during shear deformation.The microvoid could prevent dislocation entanglement,accelerate dislocation decomposition,and promote earlier plastic deformation under relatively low temperatures.
基金supported by the National Key Re-search&Development Plan(No.2022YFE0110600)the National Natural Science Foundation of China(Nos.52201122,92263201,52171117,and 52371113)+1 种基金the Jiangsu Funding Program for Excel-lent Postdoctoral Talent(No.2022ZB366)the China Postdoc-toral Science Foundation Funded Project(No.2023M731636).
文摘As one of the heterostructures,the layered structure has attracted extensive research interest as it achieves superior properties to individual components.The layer interface is considered a critical fac-tor in determining the mechanical properties of layered metals,where heterogeneity across the interface results in the strengthening of the soft layer and forming an interfacial stress gradient in the hard layer.However,there is still limited research associated with the formation of interfacial stress gradients in the hard layer,as stress measurement at high spatial resolution remains technically challenging.In the present study,we experimentally quantified the formation of interfacial stress gradients in the Ti layer of Ti/Al layered metal upon tension using in-situ high-energy X-ray diffraction(XRD).The analysis cou-pling in-situ high-energy XRD and in-situ electron back-scattered diffraction(EBSD)suggested that the interfacial stress gradient in the Ti layer rapidly rose as the Al layer was insufficient to accommodate the deformation of Ti.During the later deformation stage,collective effects of dislocation motion and geometrically necessary dislocation(GND)accumulation in the Al layer determined the evolution of in-terfacial stress gradients.The maximum interfacial stress gradient is below 0.4 MPa/μm in Ti layers,with a constant range width of 35μm independent of the macroscopic strain.The present study therefore opens a new window to local stress modification using incompatible component deformation,which is instructive for the design and fabrication of high-performance layered metals.
基金supported by the National Natural Science Foundation of China(T2325019,22077092)the Basic Research Program of Jiangsu(BK20243030)+3 种基金the Special Project of“Technological Innovation”Project of CNNC Medical Industry Co.Ltd.(ZHYLYB2021001)the Four“Batches”Innovation Project of Invigorating Medical through Science and Technology of Shanxi Province(2022XM19)the Open Project Program of the State Key Laboratory of Radiation Medicine and Protection(GZK12024016,GZK12023050,GZK12024013)a Project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘Tumor-targeted radiopharmaceuticals have become an attractive modality for tumor diagnosis and treatment in clinics.However;their wide clinical applications are seriously impeded by poor tumor targeting;rapid systemic clearance;and short tumor retention.Therefore;developing advanced radiopharmaceuticals with great tumor specificity and prolonged retention time is highly desirable for efficient tumor treatment.Herein;we report a tumor-targeted covalently anchoring strategy that selectively crosslinks the radiopharmaceuticals to intratumoral macromolecules for prolonged tumor theranostics.A covalent multi-targeted radiopharmaceutical(CMTR)d-IR-2(^(125)IRGD)that includes a sulfenic acid-reactive 1,3-cyclohexanedione group was developed.We demonstrated this probe could specifically accumulate at the tumor site and bind to the sulfenated proteins that are overexpressed within tumors;which greatly prevents the efflux of probes in tumor tissues while having faster clearance in healthy tissues resulting in 12 h longer tumor retention than conventional probes for sensitive NIR and SPECT/CT detection of tumors in vivo.More notably;the ^(131)I-labeled probe could significantly suppress the growth of lung tumor A549.We thus envision that this work may offer a promising approach to developing effective radiopharmaceuticals for precise diagnosis and treatment of various tumors.
基金the National Science Foundation of China(grant no.22077092)the Open Project Program of the State Key Laboratory of Radiation Medicine and Protection(grant no.GZK1202140)+2 种基金Science and Technology Development Plan of Suzhou(grant no.SLJ2022018)Scientific Research Project of Suzhou Commission of Health(grant no.GSWS2020028)a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
文摘RNA interfering therapy has emerged as a promising therapeutic modality to treat cancer.The specific and efficient delivery of RNA into a tumor is crucial for achieving effective cancer gene therapy but remains a huge challenge.Herein,we report a novel furin-responsive small interfering RNA(siRNA)delivery vehicle with multiple functions for colorectal tumor treatment.A peptide-based siRNA delivery vehicle RVRR-P18-Gd,consisting of furin enzyme-specific peptide substrate Arg-Val-Arg-Arg(RVRR)with positive charge for siRNA binding,a Gd(III)chelated 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid(DOTA)(DOTA-Gd)for magnetic resonance imaging,and purpurin 18 as photosensitizer for photodynamic therapy(PDT),was rationally designed and synthesized.Taking advantage of the cationic amphiphilic feature,RVRR-P18-Gd molecules spontaneously self-assembled with negatively charged Hif-1αsiRNA into stable nanoparticles via attractive electrostatic interaction,which effectively prevented siRNA degradation by nucleases,prolonged the circulation half-life,and enhanced tumor accumulation.Moreover,the specific release of Hif-1αsiRNA mediated by endogenous furin significantly downregulated Hif-1αexpression in colorectal cancer cells,resulting in enhanced therapeutic susceptibility,and with the PDT effect,effectively suppressed HCT116 tumor growth in living mice.This work highlights a powerful and universal approach to precisely deliver siRNA to targeted tumors for efficient synergistic therapy.
