The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality,which has promising application potential in a large number of indust...The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality,which has promising application potential in a large number of industrial areas.In this study,two components composed of ERCuAl-A2 aluminum bronze(CuAl9)and Inconel 718 nickel-based superalloy were fabricated with different deposition orders by wire-arc directed energy deposition.Subject to changes in heat input and thermophysical properties of the substrate,the transition region of the deposited Cu-Ni component with the bottom half of CuAl9 and the top half of Inconel 718 is narrow and serrated.This region features a laminated intermetallic compound layer due to the convection and rapid cooling in the molten pool.In contrast,the Ni-Cu component deposited in the opposite order exhibits a 2 mm gradient transition zone.Within this region,a large number of diverse precipitates were found as well as regional variations in grain size due to the multi-layer partial remelting.Both two components show strong bonds and their tensile specimens tested along the vertical direction always fracture at the softer CuAl9 side.Excellent tensile properties along the horizontal direction were obtained for Cu-Ni(Ultimate tensile strength:573 MPa,yield stress:302 MPa,elongation:22%),while those of Ni-Cu are much lower due to the existence of the solidification cracks in the transition zone.The results from this study provide a reference for the additive manufacturing of Cu/Ni dissimilar alloy components,as well as their microstructure and mechanical properties control.展开更多
Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in thi...Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.展开更多
The development of the Internet of Things(IoT)has brought convenience to people’s lives,but it also introduces significant security risks.Due to the limitations of IoT devices themselves and the challenges of re-host...The development of the Internet of Things(IoT)has brought convenience to people’s lives,but it also introduces significant security risks.Due to the limitations of IoT devices themselves and the challenges of re-hosting technology,existing fuzzing for IoT devices is mainly conducted through black-box methods,which lack effective execution feedback and are blind.Meanwhile,the existing static methods mainly rely on taint analysis,which has high overhead and high false alarm rates.We propose a new directed fuzz testing method for detecting bugs in web service programs of IoT devices,which can test IoT devices more quickly and efficiently.Specifically,we identify external input entry points using multiple features.Then we quickly find sensitive targets and paths affected by external input sources based on sensitive data flow analysis of decompiled code,treating them as testing objects.Finally,we performa directed fuzzing test.We use debugging interfaces to collect execution feedback and guide the programto reach sensitive targets based on programpruning techniques.We have implemented a prototype system,AntDFuzz,and evaluated it on firmware fromten devices across five well-known manufacturers.We discovered twelve potential vulnerabilities,seven of which were confirmed and assigned bug id by China National Vulnerability Database(CNVD).The results show that our approach has the ability to find unknown bugs in real devices and is more efficient compared to existing tools.展开更多
In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition...In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.展开更多
For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as claddin...For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work.Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically.The distribution of intermetallic compounds(IMCs)such asβ-Ti,Ti_(2)Ni,TiNiFe_(0.2),Ti_(2)Ni_(3)Si and TiB_(2)in joints was revealed.The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely.Notably,additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus,leading to fewer IMCs in joints.As a result,both bonding strength and toughness of joints were remarkably improved.The findings em-phasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.展开更多
Memory leak is a common software vulnerability that can decrease the reliability of an application and,in severe cases,even cause program crashes.If there are intentionally triggerable memory leak vulnerabilities in a...Memory leak is a common software vulnerability that can decrease the reliability of an application and,in severe cases,even cause program crashes.If there are intentionally triggerable memory leak vulnerabilities in a program,attackers can exploit these bugs to launch denial-of-service attacks or induce the program to exhibit unexpected behaviors due to low memory conditions.Existing fuzzing techniques primarily focus on improving code coverage,and specialized fuzzing techniques for individual memory-related defects like uncontrolled memory allocation do not address memory leak vulnerabilities.MemLock is the first fuzzing technique to address memory consumption vulnerabilities including memory leakage.However,the coverage-centric guidance mechanism of MemLock introduces a degree of aimlessness in the testing process,that results in low seed quality and slow bug exposure speed.To address this issue,we propose a risk areas guidance-based fuzzing technique called RBZZER.First,RBZZER retains MemLock’s memory consumption-guided mechanism and introduces a novel distance-guided approach to expedite the arrival of fuzzing at the potential memory areas.Second,we introduce a new seed scheduling strategy called risk areas-based seed scheduling,which classifies seeds based on potential memory leak areas in the program and further schedules them,thereby effectively improving the efficiency of discovering memory leak vulnerabilities.Experiments demonstrate that RBZZER outperforms the state-of-the-art fuzzing techniques by finding 52%more program unique crashes than the second-best counterpart.In particular,RBZZER can discover the amount of memory leakage at least 112%more than the other baseline fuzzers.Besides,RBZZER detects memory leaks at an average speed that is 9.10x faster than MemLock.展开更多
To fulfill the demands of applications under severe operational conditions,alloys should possess outstanding wear resistance at elevated temperatures.A Ti-Hf-Nb-V based refractory high entropy alloy(RHEA)was successfu...To fulfill the demands of applications under severe operational conditions,alloys should possess outstanding wear resistance at elevated temperatures.A Ti-Hf-Nb-V based refractory high entropy alloy(RHEA)was successfully produced using the directed energy deposition(DED)technique,which avoided the formation of fatal defects and showcased well-performed mechanical properties across a broad temperature spectrum.Strategic design of the oxidation sequence enabled the early formation of oxide nanolayers,which can form a polycrystalline oxide nanocoating under a complex stress condition to drastically reduce the wear rate from 2.69×10^(-4) mm^(3)·(N·m)^(−1) at room temperature to 6.90×10^(-7) mm^(3)·(N·m)^(−1) at 600℃.These results indicate that the application of additive manufacturing to fabricate RHEAs with superior wear resistance at high temperatures paves the way for the development of functional coatings designed to withstand extreme conditions.展开更多
Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposite...Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposited alloys.This study introduced in-situ ultrasonic rolling(UR)as an innovative method to enhance the corrosion resistance of LDED specimens,and the microstructural characteristics and their correlation with corrosion resistance were deeply investigated.The findings reveal that the LDED-UR specimen exhibits a reduction in both the fraction and size of pores.Under the influence of severe plastic deformation generated by LDED-UR process,fully equiaxed grains appear with a reduced average size of 28.61μm(compared to63.98μm for the LDED specimen with columnar grains).The electrochemical corrosion resistance of the LDED-UR specimen is significantly enhanced compared to the LDED specimen.This enhanced corrosion resistance can be attributed to the low fraction of small-sized pores,the fine and uniformly distributed Cr-enriched ferrite phase,and the formation of a compact and thick passive film due to dense grain boundaries.The insight of the correlation between microstructure and corrosion behavior opens up a new pathway to enhance the corrosion resistance of LDED specimens.展开更多
Dear Editor,This letter is concerned with the problem of time-varying formation tracking for heterogeneous multi-agent systems(MASs) under directed switching networks. For this purpose, our first step is to present so...Dear Editor,This letter is concerned with the problem of time-varying formation tracking for heterogeneous multi-agent systems(MASs) under directed switching networks. For this purpose, our first step is to present some sufficient conditions for the exponential stability of a particular category of switched systems.展开更多
Grain size and texture can be controlled to improve the strength and ductility of magnesium rare-earth(Mg-RE)alloys by alloying.Directed energy deposition-arc(DED-arc)is a typical sub-rapid solidification process that...Grain size and texture can be controlled to improve the strength and ductility of magnesium rare-earth(Mg-RE)alloys by alloying.Directed energy deposition-arc(DED-arc)is a typical sub-rapid solidification process that contributes to the modification of the microstructure.In this paper,a series of novel Mg-3.0Nd-0.2Zn-0.3Zr-xCe(NZ30K-xCe)alloys with different Ce contents(0,0.1,0.3,0.5 wt.%)were prepared by DED-arc.The results show that the experimental alloys have lower porosity(≤0.11%).After adding 0.1 wt.%Ce,the average grain size decreases from 98.9±5.7μm to 49.8±1.0μm,and the texture is significantly weakened.Further additions of Ce(0.3 and 0.5 wt.%)do not lead to significant alterations in the average grain size and texture intensity when compared with the NZ30K-0.1Ce alloy.Grain refinement is related to the constitutional supercooling,and the texture weakening is connected to the solid solubility of Ce in the Mg matrix.The ultimate tensile strength and elongation of NZ30K-0.1Ce alloy are 37.2% and 61.3% higher than those of NZ30K alloy.Grain refinement and texture weakening are the reasons for the better strength-ductility of NZ30K-0.1Ce alloy.展开更多
Recent advances in statistical physics highlight the significant potential of machine learning for phase transition recognition.This study introduces a deep learning framework based on graph neural network to investig...Recent advances in statistical physics highlight the significant potential of machine learning for phase transition recognition.This study introduces a deep learning framework based on graph neural network to investigate non-equilibrium phase transitions,specifically focusing on the directed percolation process.By converting lattices with varying dimensions and connectivity schemes into graph structures and embedding the temporal evolution of the percolation process into node features,our approach enables unified analysis across diverse systems.The framework utilizes a multi-layer graph attention mechanism combined with global pooling to autonomously extract critical features from local dynamics to global phase transition signatures.The model successfully predicts percolation thresholds without relying on lattice geometry,demonstrating its robustness and versatility.Our approach not only offers new insights into phase transition studies but also provides a powerful tool for analyzing complex dynamical systems across various domains.展开更多
Metal-organic frameworks(MOFs)have garnered widespread attention due to their designability and diversity[1].Customization has always been a pursuit of chemists and materials scientists[2].Topology provides a means of...Metal-organic frameworks(MOFs)have garnered widespread attention due to their designability and diversity[1].Customization has always been a pursuit of chemists and materials scientists[2].Topology provides a means of abstracting the complex structures of MOFs by identifying and classifying the fundamental building units and connection patterns,simplifying the understanding of MOF structures[3].展开更多
BACKGROUND Significant gaps in guideline-directed medical therapy(GDMT)for heart failure(HF)stem from shortages of cardiologists and advanced HF providers,as well as a lack of optimal HF management knowledge among hos...BACKGROUND Significant gaps in guideline-directed medical therapy(GDMT)for heart failure(HF)stem from shortages of cardiologists and advanced HF providers,as well as a lack of optimal HF management knowledge among hospitalists.This study compared the impact of optimal medical therapy in HF(OMT-HF)certification on GDMT implementation and patient outcomes between an intervention group(IG)of hospitalists and a standard-of-care comparison group(SOC-CG).METHODS This study was implemented from November 2022 to May 2023.Hospitalized car-diology patients with HF and left ventricular ejection fraction≤40%were rando-mized to IG or SOC-CG.Exclusion criteria included patients in cardiogenic shock,unable to consent,or at high risk.Follow-up was at 30 days post-discharge.Diffe-rences between groups were analyzed using Fisher’s exact test for categorical va-riables and Wilcoxon rank-sum or unpaired t-test for continuous variables.Chan-ges in Minnesota Living with Heart Failure Questionnaire(MLWHFQ)scores were evaluated using a paired t-test.RESULTS IG patients had lower readmission rates[9(42.85%)vs 11(17.46%),P=0.03]and a decreased trend in mortality 30-day post discharge.IG patients also showed greater mean improvements in total(-27.03±24.59 vs-5.85±23.52,P<0.001),physical(-13.8±12.3 vs-2.71±11.16,P<0.001)and emotional(-4.76±8.10 vs-1.42±5.98)dimensions on the MLWHFQ compared to SOC-CG,however,change in emotional dimension did not reach statistical significance.CONCLUSION Hospitalist OMT-HF certification may lead to better 30-day outcomes in hospitalized HF patients including quality of life,mortality and readmission rates.Larger prospective studies are warranted to validate these findings.展开更多
Wire-fed laser-arc directed energy deposition(Wire-fed LA-DED)Technol.improves production speed while maintaining high quality and is particularly suited for manufacturing large,complex aluminum or titanium alloy comp...Wire-fed laser-arc directed energy deposition(Wire-fed LA-DED)Technol.improves production speed while maintaining high quality and is particularly suited for manufacturing large,complex aluminum or titanium alloy components.The geometry of the weld bead(height and width)is influenced by multiple intricate parameters and variables during the manufacturing process.Accurately predicting the weld bead shape enables precise control over the surface flatness of the part,helping to prevent defects such as lack of fusion.This significantly reduces dimensional redundancy,enhances printing efficiency,and optimizes material usage.In this study,a quadratic regression prediction model for weld bead geometry was developed using the response surface methodology(RSM),with predictions generated through several machine learning models.These models included the back-propagation neural network(BPNN),support vector regression(SVR),multi-output support vector regression(MOSVR),extreme learning machine(ELM),and a differential evolution-optimized MOSVR(DE-MOSVR)model.Grid search and cross-validation techniques were utilized to identify the optimal parameters for each model to achieve the best predictive performance.A comparison of these models was conducted,followed by an evaluation of their generalization capabilities using an additional 20 sets of test data.The most accurate predictive model was selected based on a comprehensive assessment.The results showed that the DE-MOSVR model outperformed the others,achieving mean squared error,root mean squared error,mean absolute error,and R^(2) values for width(height)predictions of 0.0411(0.0041),0.2028(0.0639),0.1671(0.0550),and 0.9434(0.9433),respectively.It demonstrated the smallest deviation in the validation set,with mean deviations of 1.97% and 1.68%,respectively.The model we developed was validated through the production of prototype parts,providing valuable reference and guidance for predicting and modeling weld bead morphology in the Wire-fed LA-DED process.展开更多
Here we fabricate LA103Z Mg-Li alloy via wire-arc directed energy deposition(WA-DED),and subsequent aging treatment is employed to improve its mechanical property.Results show that a typical dual-phase microstructure ...Here we fabricate LA103Z Mg-Li alloy via wire-arc directed energy deposition(WA-DED),and subsequent aging treatment is employed to improve its mechanical property.Results show that a typical dual-phase microstructure is formed upon WA-DED,consisting of α-Mg,β-Li,AlLi and Li_(2)MgAl,with negligible porosity,and the core-shell Li_(2)MgAl/AlLi composite particles are also generated.After aging treatment,the microstructure is slightly coarsened,together with the precipitation of nano-sized D0_(3)-Mg_(3)Al particles,as well as the dissolution and the mergence of α-Mg phases.Negligible strength and ductility anisotropies are found for the as-deposited alloy.Significant strength increment is achieved via aging treatment,and the ultimate strength increases by~20%(~34 MPa),reaching 200±1 MPa.Both as-deposited and aged alloys show acceptable uniform elongation,with a transgranular fracture mode.Precipitation strengthening enabled by nano-sized D0_(3)-Mg_(3)Al precipitates is primarily responsible for the strength increment mediated by aging treatment.Grain refinement strengthening and solid solution strengthening provide additional contributions to the improved strength.Our work thus offers an applicable additive manufacturing pathway for the efficient and safety-guaranteed fabrication of Mg-Li alloy components with decent mechanical property.展开更多
Ti and its alloys have been broadly adopted across various industries owing to their outstanding proper-ties,such as high strength-to-weight ratio,excellent fatigue performance,exceptional corrosion resistance and so ...Ti and its alloys have been broadly adopted across various industries owing to their outstanding proper-ties,such as high strength-to-weight ratio,excellent fatigue performance,exceptional corrosion resistance and so on.Additive manufacturing(AM)is a complement to,rather than a replacement for,traditional manufacturing processes.It enhances flexibility in fabricating complex components and resolves machin-ing challenges,resulting in reduced lead times for custom designs.However,owing to distinctions among various AM technologies,Ti alloys fabricated by different AM methods usually present differences in mi-crostructure and defects,which can significantly influence the mechanical performance of built parts.Therefore,having an in-depth knowledge of the scientific aspects of fabrication and material properties is crucial to achieving high-performance Ti alloys through different AM methods.This article reviews the mechanical properties of Ti alloys fabricated by two mainstream powder-type AM techniques:powder bed fusion(PBF)and directed energy deposition(DED).The review examines several key aspects,en-compassing phase formation,grain size and morphology,and defects,and provides an in-depth analysis of their influence on the mechanical behaviors of Ti alloys.This review can aid researchers and engi-neers in selecting appropriate PBF or DED methods and optimizing their process parameters to fabricate high-performance Ti alloys for a wide range of industrial applications.展开更多
Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstrea...Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.展开更多
Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality...Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.展开更多
Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior per...Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior performance due to internal defects and inherent columnar grains.Herein,external ultrasound fields with different powers were successfully introduced into the wire-arc DED of AZ31 Mg alloy.The microstructure,defects,and mechanical properties of the fabricated components were carefully charac-terized and compared.The results show that the external ultrasound fields lead to decreased porosity,complete columnar to equiaxed transition(CET),and enhanced performance.Consequently,the UA90 samples exhibited a remarkable increase of~30%,~45%,and~189%in yield strength,ultimate tensile strength,and elongation,respectively.The dominant mechanisms of enhanced strength-ductility synergy were analyzed in detail.This study thus sheds new light on wire-arc DED of Mg alloy components with excellent performance via external ultrasound fields.展开更多
Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position d...Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position dependence of macroscopic mechanical properties and anisotropy.Therefore,it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity,mechanical properties and superelasticity.In this investigation,the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure,phase composition,phase transformation,microhardness,tensile and superelasticity.The temperature range of solution treatment is 800-1050℃,and the treatment time range is 1-5.5 h.The results show that after solution treatment at 800℃/1 h,the content of precipitated phase decreases,the grain is refined,the microhardness increases,and the mechanical properties in the 0°direction are improved.The strain recovery rate after 10 tensile cycles has increased from 37.13%(as-built)to 49.25%(solid solution treatment).This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.展开更多
基金supported by the Key Research and Development Program of Shaanxi Province(2023-YBGY361)the National Natural Science Foundation of China(52275374 and 52205414)+1 种基金the Postdoctoral Fellowship Program of CPSF(GZC20232098)as well as the Xiaomi Foundation through Xiaomi Young Scholar Program。
文摘The layer-by-layer deposition strategy of additive manufacturing makes it ideal to fabricate dissimilar alloy components with varying functionality,which has promising application potential in a large number of industrial areas.In this study,two components composed of ERCuAl-A2 aluminum bronze(CuAl9)and Inconel 718 nickel-based superalloy were fabricated with different deposition orders by wire-arc directed energy deposition.Subject to changes in heat input and thermophysical properties of the substrate,the transition region of the deposited Cu-Ni component with the bottom half of CuAl9 and the top half of Inconel 718 is narrow and serrated.This region features a laminated intermetallic compound layer due to the convection and rapid cooling in the molten pool.In contrast,the Ni-Cu component deposited in the opposite order exhibits a 2 mm gradient transition zone.Within this region,a large number of diverse precipitates were found as well as regional variations in grain size due to the multi-layer partial remelting.Both two components show strong bonds and their tensile specimens tested along the vertical direction always fracture at the softer CuAl9 side.Excellent tensile properties along the horizontal direction were obtained for Cu-Ni(Ultimate tensile strength:573 MPa,yield stress:302 MPa,elongation:22%),while those of Ni-Cu are much lower due to the existence of the solidification cracks in the transition zone.The results from this study provide a reference for the additive manufacturing of Cu/Ni dissimilar alloy components,as well as their microstructure and mechanical properties control.
基金supported by the National Natural Science Foundation of China(52005264).
文摘Solution and aging treatment were conducted on the laser directed energy deposition(LDED)-prepared carbon nanotubes(CNTs)-reinforced WE43(CNTs/WE43)layers to optimize their microstructure and surface properties in this study.The microstructure of the WE43 and CNTs/WE43 layers was systematically compared.The dissolution of divorced eutectics at the grain boundaries was retarded by CNTs during solution treatment.The spot segregation composed of Mg_(24)Y_(5),CNTs,and Zr cores in the solution treated CNTs/WE43 layer presented a slight decreasing in Y content.The grain growth of both types of layers underwent three stages:slow,rapid,and steady-state.The significant inhibitory effect of CNTs on the grain growth of the LDED WE43 matrix was more pronounced than the promoting effect of temperature,resulting in a 47%increase at 510℃ and a 35%increase at 540℃ in the grain growth exponent compared to the WE43 layers at 510℃.During the subsequent aging treatment at 225℃,the precipitation sequences from plate-shaped β″to plate-shaped and globular β′ were observed in both types of layers.CNTs can facilitate an increase in the nucleation rate of precipitates,but without accelerating precipitation hardening rate.The long and short diameters of the precipitates in peak-aged state were decreased by 48.5%and 43.1%by addition of CNTs,respectively.The wear resistance of both the WE43 and CNTs/WE43 layers can be significantly enhanced through solution and aging treatment.The enhancement in wear resistance for the CNTs/WE43 layers is considerably greater than that of the WE43 layers.
文摘The development of the Internet of Things(IoT)has brought convenience to people’s lives,but it also introduces significant security risks.Due to the limitations of IoT devices themselves and the challenges of re-hosting technology,existing fuzzing for IoT devices is mainly conducted through black-box methods,which lack effective execution feedback and are blind.Meanwhile,the existing static methods mainly rely on taint analysis,which has high overhead and high false alarm rates.We propose a new directed fuzz testing method for detecting bugs in web service programs of IoT devices,which can test IoT devices more quickly and efficiently.Specifically,we identify external input entry points using multiple features.Then we quickly find sensitive targets and paths affected by external input sources based on sensitive data flow analysis of decompiled code,treating them as testing objects.Finally,we performa directed fuzzing test.We use debugging interfaces to collect execution feedback and guide the programto reach sensitive targets based on programpruning techniques.We have implemented a prototype system,AntDFuzz,and evaluated it on firmware fromten devices across five well-known manufacturers.We discovered twelve potential vulnerabilities,seven of which were confirmed and assigned bug id by China National Vulnerability Database(CNVD).The results show that our approach has the ability to find unknown bugs in real devices and is more efficient compared to existing tools.
基金Project(2021YFC2801904) supported by the National Key R&D Program of ChinaProject(KY10100230067) supported by the Basic Product Innovation Research Project,China+3 种基金Projects(52271130,52305344) supported by the National Natural Science Foundation of ChinaProject(ZR2022QE073) supported by the Natural Science Foundation of Shandong Province,ChinaProject(AMGM2021F01) supported by the Science Fund of Shandong Laboratory of Advanced Materials and Green Manufacturing at Yantai,ChinaProject(KY90200210015) supported by Leading Scientific Research Project of CNNC,China。
文摘In this work,ultrasonic energy field assistance combined with tempering treatment is proposed to improve the microstructure and mechanical properties of A517Q alloy steel fabricated by laser directed energy deposition(LDED).The effects of ultrasonic vibration(UV)and tempering treatment on microstructure evolution,microhardness distribution and mechanical properties of deposition layer were studied in detail.The microstructure of UV assisted LDED sample after tempering is mainly composed of tempered sorbite(TS).Due to the improvement of microstructure inhomogeneity and grains refinement,UV assisted LDED sample with tempering treatment obtains excellent mechanical properties.The ultimate tensile strength(UTS),yield strength(YS)and elongation after breaking(EL)reach 765 MPa,657 MPa and 19.5%,the increase ratios of UTS and YS are 14.5%and 33.8%while maintaining plasticity compared to original LDED sample,respectively.It is obvious that ultrasonic vibration combined with tempering is a potential and effective method to obtain uniform microstructure and excellent mechanical properties in metal laser directed energy deposition field.
基金supported by the National Natural Science Foundation of China(No.5230010216)2022 Annual Nanjing New R&D Institutions Joint Technical Tackling Project(No.202208019)+1 种基金Jiangsu Provincial Excellent Postdoctoral Talent Program(No.2022ZB385)the technical support of Nanjing Shangi Institute for Advanced Materials Co.,Ltd.
文摘For searching alternative strategies to improve reliability of titanium and steel dissimilar bimetallic joints manufactured by directed energy deposition with laser beam(DED-LB),pure titanium was considered as cladding deposited on carbon steel substrate with Ni-based alloy interlayers in this work.Effect of different interlayer modification methods on the microstructure evolution and mechanical properties of joints was analyzed systematically.The distribution of intermetallic compounds(IMCs)such asβ-Ti,Ti_(2)Ni,TiNiFe_(0.2),Ti_(2)Ni_(3)Si and TiB_(2)in joints was revealed.The results showed that original deposition cracks caused by residual stress during processing could be alleviated by substrate preheating treatment while suppressed by the modified interlayer with Cr completely.Notably,additional Cr could reduce reaction activity between Ti and Ni atoms by raising laser molten pool liquidus,leading to fewer IMCs in joints.As a result,both bonding strength and toughness of joints were remarkably improved.The findings em-phasize more significance of optimizing Ni-based interlayer composition with Cr than preheating method to improve the mechanical performance of DED-LB joints.
基金supported by the National Key R&D Program of China(No.2021YFB3101803).
文摘Memory leak is a common software vulnerability that can decrease the reliability of an application and,in severe cases,even cause program crashes.If there are intentionally triggerable memory leak vulnerabilities in a program,attackers can exploit these bugs to launch denial-of-service attacks or induce the program to exhibit unexpected behaviors due to low memory conditions.Existing fuzzing techniques primarily focus on improving code coverage,and specialized fuzzing techniques for individual memory-related defects like uncontrolled memory allocation do not address memory leak vulnerabilities.MemLock is the first fuzzing technique to address memory consumption vulnerabilities including memory leakage.However,the coverage-centric guidance mechanism of MemLock introduces a degree of aimlessness in the testing process,that results in low seed quality and slow bug exposure speed.To address this issue,we propose a risk areas guidance-based fuzzing technique called RBZZER.First,RBZZER retains MemLock’s memory consumption-guided mechanism and introduces a novel distance-guided approach to expedite the arrival of fuzzing at the potential memory areas.Second,we introduce a new seed scheduling strategy called risk areas-based seed scheduling,which classifies seeds based on potential memory leak areas in the program and further schedules them,thereby effectively improving the efficiency of discovering memory leak vulnerabilities.Experiments demonstrate that RBZZER outperforms the state-of-the-art fuzzing techniques by finding 52%more program unique crashes than the second-best counterpart.In particular,RBZZER can discover the amount of memory leakage at least 112%more than the other baseline fuzzers.Besides,RBZZER detects memory leaks at an average speed that is 9.10x faster than MemLock.
基金supported by Guangdong Major Project of Basic and Applied Basic Research,China(No.2019B030302010)the Joint Research Scheme sponsored by the Research Grants Council of the Hong Kong Special Administrative Region,China and National Natural Science Foundation of China(Nos.N_PolyU523/20 and 52061160483)+4 种基金the National Natural Science Foundation of China(Nos.52104362,52071222,52471179,52471180 and 52001221)the National Key R&D Program of China(No.2022YFA1603800)the National Key Research and Development Program of China(No.2021YFA0716302)Guangdong Provincial Quantum Science Strategic Initiative(No.GDZX2301001)Guangdong Basic and Applied Basic Research,China(No.2020B1515130007).
文摘To fulfill the demands of applications under severe operational conditions,alloys should possess outstanding wear resistance at elevated temperatures.A Ti-Hf-Nb-V based refractory high entropy alloy(RHEA)was successfully produced using the directed energy deposition(DED)technique,which avoided the formation of fatal defects and showcased well-performed mechanical properties across a broad temperature spectrum.Strategic design of the oxidation sequence enabled the early formation of oxide nanolayers,which can form a polycrystalline oxide nanocoating under a complex stress condition to drastically reduce the wear rate from 2.69×10^(-4) mm^(3)·(N·m)^(−1) at room temperature to 6.90×10^(-7) mm^(3)·(N·m)^(−1) at 600℃.These results indicate that the application of additive manufacturing to fabricate RHEAs with superior wear resistance at high temperatures paves the way for the development of functional coatings designed to withstand extreme conditions.
基金financial supports from the National Natural Science Foundation of China (No.52305440)the Natural Science Foundation of Changsha City (Nos.kq2208272,kq2208274)+1 种基金the Tribology Science Fund of the State Key Laboratory of Tribology in Advanced Equipment (SKLTKF22B09)the National Key Research and Development Program of China (2022YFB3706902)。
文摘Under the laser directed energy deposition(LDED)process,the rapid melting and solidification usually lead to the emergence of pores and coarse columnar dendrites,which in turn compromise the properties of the deposited alloys.This study introduced in-situ ultrasonic rolling(UR)as an innovative method to enhance the corrosion resistance of LDED specimens,and the microstructural characteristics and their correlation with corrosion resistance were deeply investigated.The findings reveal that the LDED-UR specimen exhibits a reduction in both the fraction and size of pores.Under the influence of severe plastic deformation generated by LDED-UR process,fully equiaxed grains appear with a reduced average size of 28.61μm(compared to63.98μm for the LDED specimen with columnar grains).The electrochemical corrosion resistance of the LDED-UR specimen is significantly enhanced compared to the LDED specimen.This enhanced corrosion resistance can be attributed to the low fraction of small-sized pores,the fine and uniformly distributed Cr-enriched ferrite phase,and the formation of a compact and thick passive film due to dense grain boundaries.The insight of the correlation between microstructure and corrosion behavior opens up a new pathway to enhance the corrosion resistance of LDED specimens.
基金supported in part by the National Natural Science Foundation of China(62273255,62350003,62088101)the Shanghai Science and Technology Cooperation Project(22510712000,21550760900)+1 种基金the Shanghai Municipal Science and Technology Major Project(2021SHZDZX0100)the Fundamental Research Funds for the Central Universities
文摘Dear Editor,This letter is concerned with the problem of time-varying formation tracking for heterogeneous multi-agent systems(MASs) under directed switching networks. For this purpose, our first step is to present some sufficient conditions for the exponential stability of a particular category of switched systems.
基金financially supported by the National Natural Science Foundation of China[Grant No 52305341,U2341253,52371019]the Basic Scientific Research Project of Liaoning Provincial Education Department[JYTQN2023003].
文摘Grain size and texture can be controlled to improve the strength and ductility of magnesium rare-earth(Mg-RE)alloys by alloying.Directed energy deposition-arc(DED-arc)is a typical sub-rapid solidification process that contributes to the modification of the microstructure.In this paper,a series of novel Mg-3.0Nd-0.2Zn-0.3Zr-xCe(NZ30K-xCe)alloys with different Ce contents(0,0.1,0.3,0.5 wt.%)were prepared by DED-arc.The results show that the experimental alloys have lower porosity(≤0.11%).After adding 0.1 wt.%Ce,the average grain size decreases from 98.9±5.7μm to 49.8±1.0μm,and the texture is significantly weakened.Further additions of Ce(0.3 and 0.5 wt.%)do not lead to significant alterations in the average grain size and texture intensity when compared with the NZ30K-0.1Ce alloy.Grain refinement is related to the constitutional supercooling,and the texture weakening is connected to the solid solubility of Ce in the Mg matrix.The ultimate tensile strength and elongation of NZ30K-0.1Ce alloy are 37.2% and 61.3% higher than those of NZ30K alloy.Grain refinement and texture weakening are the reasons for the better strength-ductility of NZ30K-0.1Ce alloy.
基金supported by the Fund from the Science and Technology Department of Henan Province,China(Grant Nos.222102210233 and 232102210064)the National Natural Science Foundation of China(Grant Nos.62373169 and 72474086)+5 种基金the Young and Midcareer Academic Leader of Jiangsu Province,China(Grant No.Qinglan Project in 2024)the National Statistical Science Research Project(Grant No.2022LZ03)Shaanxi Provincial Soft Science Project(Grant No.2022KRM111)Shaanxi Provincial Social Science Foundation(Grant No.2022R016)the Special Project for Philosophical and Social Sciences Research in Shaanxi Province,China(Grant No.2024QN018)the Fund from the Henan Office of Philosophy and Social Science(Grant No.2023CJJ112).
文摘Recent advances in statistical physics highlight the significant potential of machine learning for phase transition recognition.This study introduces a deep learning framework based on graph neural network to investigate non-equilibrium phase transitions,specifically focusing on the directed percolation process.By converting lattices with varying dimensions and connectivity schemes into graph structures and embedding the temporal evolution of the percolation process into node features,our approach enables unified analysis across diverse systems.The framework utilizes a multi-layer graph attention mechanism combined with global pooling to autonomously extract critical features from local dynamics to global phase transition signatures.The model successfully predicts percolation thresholds without relying on lattice geometry,demonstrating its robustness and versatility.Our approach not only offers new insights into phase transition studies but also provides a powerful tool for analyzing complex dynamical systems across various domains.
基金supported by the National Natural Science Foundation of China(22101039,22471027,22311530679)the Science Fund for Creative Research Groups of the National Natural Science Foundation of China(22021005)the Fundamental Research Funds for the Central Universities(DUT24LK004).
文摘Metal-organic frameworks(MOFs)have garnered widespread attention due to their designability and diversity[1].Customization has always been a pursuit of chemists and materials scientists[2].Topology provides a means of abstracting the complex structures of MOFs by identifying and classifying the fundamental building units and connection patterns,simplifying the understanding of MOF structures[3].
基金Supported by Houston Methodist DeBakey Heart and Vascular Center Grant.
文摘BACKGROUND Significant gaps in guideline-directed medical therapy(GDMT)for heart failure(HF)stem from shortages of cardiologists and advanced HF providers,as well as a lack of optimal HF management knowledge among hospitalists.This study compared the impact of optimal medical therapy in HF(OMT-HF)certification on GDMT implementation and patient outcomes between an intervention group(IG)of hospitalists and a standard-of-care comparison group(SOC-CG).METHODS This study was implemented from November 2022 to May 2023.Hospitalized car-diology patients with HF and left ventricular ejection fraction≤40%were rando-mized to IG or SOC-CG.Exclusion criteria included patients in cardiogenic shock,unable to consent,or at high risk.Follow-up was at 30 days post-discharge.Diffe-rences between groups were analyzed using Fisher’s exact test for categorical va-riables and Wilcoxon rank-sum or unpaired t-test for continuous variables.Chan-ges in Minnesota Living with Heart Failure Questionnaire(MLWHFQ)scores were evaluated using a paired t-test.RESULTS IG patients had lower readmission rates[9(42.85%)vs 11(17.46%),P=0.03]and a decreased trend in mortality 30-day post discharge.IG patients also showed greater mean improvements in total(-27.03±24.59 vs-5.85±23.52,P<0.001),physical(-13.8±12.3 vs-2.71±11.16,P<0.001)and emotional(-4.76±8.10 vs-1.42±5.98)dimensions on the MLWHFQ compared to SOC-CG,however,change in emotional dimension did not reach statistical significance.CONCLUSION Hospitalist OMT-HF certification may lead to better 30-day outcomes in hospitalized HF patients including quality of life,mortality and readmission rates.Larger prospective studies are warranted to validate these findings.
基金supported by Natural Science Foundation of Shandong Province(Grant No.ZR202212010161)Natural Science Foundation of Qingdao(Grant No.23-2-1-83-zyyd-jch)+1 种基金Guangdong Basic and Applied Basic Research Foundation(Grant No.2023A1515110116)the National Natural Science Foundation of China(Grant No.52405359).
文摘Wire-fed laser-arc directed energy deposition(Wire-fed LA-DED)Technol.improves production speed while maintaining high quality and is particularly suited for manufacturing large,complex aluminum or titanium alloy components.The geometry of the weld bead(height and width)is influenced by multiple intricate parameters and variables during the manufacturing process.Accurately predicting the weld bead shape enables precise control over the surface flatness of the part,helping to prevent defects such as lack of fusion.This significantly reduces dimensional redundancy,enhances printing efficiency,and optimizes material usage.In this study,a quadratic regression prediction model for weld bead geometry was developed using the response surface methodology(RSM),with predictions generated through several machine learning models.These models included the back-propagation neural network(BPNN),support vector regression(SVR),multi-output support vector regression(MOSVR),extreme learning machine(ELM),and a differential evolution-optimized MOSVR(DE-MOSVR)model.Grid search and cross-validation techniques were utilized to identify the optimal parameters for each model to achieve the best predictive performance.A comparison of these models was conducted,followed by an evaluation of their generalization capabilities using an additional 20 sets of test data.The most accurate predictive model was selected based on a comprehensive assessment.The results showed that the DE-MOSVR model outperformed the others,achieving mean squared error,root mean squared error,mean absolute error,and R^(2) values for width(height)predictions of 0.0411(0.0041),0.2028(0.0639),0.1671(0.0550),and 0.9434(0.9433),respectively.It demonstrated the smallest deviation in the validation set,with mean deviations of 1.97% and 1.68%,respectively.The model we developed was validated through the production of prototype parts,providing valuable reference and guidance for predicting and modeling weld bead morphology in the Wire-fed LA-DED process.
基金supported by the National Natural Science Foundation of China(52475320).
文摘Here we fabricate LA103Z Mg-Li alloy via wire-arc directed energy deposition(WA-DED),and subsequent aging treatment is employed to improve its mechanical property.Results show that a typical dual-phase microstructure is formed upon WA-DED,consisting of α-Mg,β-Li,AlLi and Li_(2)MgAl,with negligible porosity,and the core-shell Li_(2)MgAl/AlLi composite particles are also generated.After aging treatment,the microstructure is slightly coarsened,together with the precipitation of nano-sized D0_(3)-Mg_(3)Al particles,as well as the dissolution and the mergence of α-Mg phases.Negligible strength and ductility anisotropies are found for the as-deposited alloy.Significant strength increment is achieved via aging treatment,and the ultimate strength increases by~20%(~34 MPa),reaching 200±1 MPa.Both as-deposited and aged alloys show acceptable uniform elongation,with a transgranular fracture mode.Precipitation strengthening enabled by nano-sized D0_(3)-Mg_(3)Al precipitates is primarily responsible for the strength increment mediated by aging treatment.Grain refinement strengthening and solid solution strengthening provide additional contributions to the improved strength.Our work thus offers an applicable additive manufacturing pathway for the efficient and safety-guaranteed fabrication of Mg-Li alloy components with decent mechanical property.
基金the financial support provided by the industrial grant(No.G1006320).
文摘Ti and its alloys have been broadly adopted across various industries owing to their outstanding proper-ties,such as high strength-to-weight ratio,excellent fatigue performance,exceptional corrosion resistance and so on.Additive manufacturing(AM)is a complement to,rather than a replacement for,traditional manufacturing processes.It enhances flexibility in fabricating complex components and resolves machin-ing challenges,resulting in reduced lead times for custom designs.However,owing to distinctions among various AM technologies,Ti alloys fabricated by different AM methods usually present differences in mi-crostructure and defects,which can significantly influence the mechanical performance of built parts.Therefore,having an in-depth knowledge of the scientific aspects of fabrication and material properties is crucial to achieving high-performance Ti alloys through different AM methods.This article reviews the mechanical properties of Ti alloys fabricated by two mainstream powder-type AM techniques:powder bed fusion(PBF)and directed energy deposition(DED).The review examines several key aspects,en-compassing phase formation,grain size and morphology,and defects,and provides an in-depth analysis of their influence on the mechanical behaviors of Ti alloys.This review can aid researchers and engi-neers in selecting appropriate PBF or DED methods and optimizing their process parameters to fabricate high-performance Ti alloys for a wide range of industrial applications.
基金supported by the 2022 MTC Young Individual Research Grants(Grant No.M22K3c0097)the Singapore Research,Innovation and Enterprise(RIE)2025 PlanSingapore Aerospace Programme Cycle 16(Grant No.M2215a0073)。
文摘Lightweight aluminum(Al)alloys have been widely used in frontier fields like aerospace and automotive industries,which attracts great interest in additive manufacturing(AM)to process high-value Al parts.As a mainstream AM technique,laser-directed energy deposition(LDED)shows good scalability to meet the requirements for large-format component manufacturing and repair.However,LDED Al alloys are highly challenging due to their inherent poor printability(e.g.low laser absorption,high oxidation sensitivity and cracking tendency).To further promote the development of LDED high-performance Al alloys,this review offers a deep understanding of the challenges and strategies to improve printability in LDED Al alloys.The porosity,cracking,distortion,inclusions,element evaporation and resultant inferior mechanical properties(worse than laser powder bed fusion)are the key challenges in LDED Al alloys.Processing parameter optimizations,in-situ alloy design,reinforcing particle addition and field assistance are the efficient approaches to improving the printability and performance of LDED Al alloys.The underlying correlations between processes,alloy innovation,characteristic microstructures,and achievable performances in LDED Al alloys are discussed.The benchmark mechanical properties and primary strengthening mechanism of LDED Al alloys are summarized.This review aims to provide a critical and in-depth evaluation of current progress in LDED Al alloys.Future opportunities and perspectives in LDED high-performance Al alloys are also outlined.
基金supported by the National Natural Science Foundation of China(51975112,52375412)Fundamental Research Funds for Central Universities(N2203011)。
文摘Additive manufacturing provides achievability for the fabrication of bimetallic and multi-material structures;however,the material compatibility and bondability directly affect the parts’formability and final quality.It is essential to understand the underlying printability of different material combinations based on an adapted process.Here,the printability disparities of two common and attractive material combinations(nickel-and iron-based alloys)are evaluated at the macro and micro levels via laser directed energy deposition(DED).The deposition processes were captured using in situ high-speed imaging,and the dissimilarities in melt pool features and track morphology were quantitatively investigated within specific process windows.Moreover,the microstructure diversity of the tracks and blocks processed with varied material pairs was comparatively elaborated and,complemented with the informative multi-physics modeling,the presented non-uniformity in mechanical properties(microhardness)among the heterogeneous material pairs was rationalized.The differences in melt flow induced by the unlike thermophysical properties of the material pairs and the resulting element intermixing and localized re-alloying during solidification dominate the presented dissimilarity in printability among the material combinations.This work provides an in-depth understanding of the phenomenological differences in the deposition of dissimilar materials and aims to guide more reliable DED forming of bimetallic parts.
基金National Natural Science Foun-dation of China(Nos.52275374,52205414)Xiaomi Founda-tion through the Xiaomi Young Scholar Program,the Key Research and Development Projects of Shaanxi Province(No.2023-YBGY-361)+2 种基金as well as the Young Elite Scientists Sponsorship Program by CAST(No.2021QNRC001)State Key Laboratory for Mechan-ical Behavior of Materials(NO.20212311)as well as the Xi’an Jiaotong University Basic Research Funds for Freedom of Explo-ration and Innovation-Student Programs(NO.xzy022023066).
文摘Investigations on the fabrication of large-size lightweight Mg alloy components by wire-arc directed en-ergy deposition(DED)are steadily flourishing.Nevertheless,most of these components still suffer from inferior performance due to internal defects and inherent columnar grains.Herein,external ultrasound fields with different powers were successfully introduced into the wire-arc DED of AZ31 Mg alloy.The microstructure,defects,and mechanical properties of the fabricated components were carefully charac-terized and compared.The results show that the external ultrasound fields lead to decreased porosity,complete columnar to equiaxed transition(CET),and enhanced performance.Consequently,the UA90 samples exhibited a remarkable increase of~30%,~45%,and~189%in yield strength,ultimate tensile strength,and elongation,respectively.The dominant mechanisms of enhanced strength-ductility synergy were analyzed in detail.This study thus sheds new light on wire-arc DED of Mg alloy components with excellent performance via external ultrasound fields.
基金The study was supported by the National Natural Science Foundation of China(No.52105396).The authors thank the State Key Laboratory of Materials Processing and Die&Mould Technology,and the Analytical&Testing Center,Huazhong University of Science&Technology for the extensive experiments.
文摘Directed energy deposition-arc(DED-Arc)technology has the advantages of simple equipment,low manufacturing cost and high deposition rate,while the use of DED-Arc has problems of microstructure inhomogeneity,position dependence of macroscopic mechanical properties and anisotropy.Therefore,it is necessary to carry out a subsequent heat treatment to improve its microstructure uniformity,mechanical properties and superelasticity.In this investigation,the DED-Arc 15-layer NiTi alloy thin-walled parts with the solution treatment at different process parameters were studied to analyze the effects of solution heat treatment on microstructure,phase composition,phase transformation,microhardness,tensile and superelasticity.The temperature range of solution treatment is 800-1050℃,and the treatment time range is 1-5.5 h.The results show that after solution treatment at 800℃/1 h,the content of precipitated phase decreases,the grain is refined,the microhardness increases,and the mechanical properties in the 0°direction are improved.The strain recovery rate after 10 tensile cycles has increased from 37.13%(as-built)to 49.25%(solid solution treatment).This research provides an effective post treatment method for high-performance DED-Arc NiTi shape memory alloys.
