In this research paper, a routing problem of undirected networks has been solved. The problem was to determine the optimal routes of a telecommunication network. A heuristic approach has been adopted,due to the specif...In this research paper, a routing problem of undirected networks has been solved. The problem was to determine the optimal routes of a telecommunication network. A heuristic approach has been adopted,due to the specific uature of the problem.The problem is only concerned withdistant(remote) nodes of the network which are indirectly linked through a single intermediate node.To determine the optimal routes,the devised heuristic has been coded in FORTRAN language. Forthe validation of developed heuristic,it has been implemented on two sample networks. Finally, ithas been applied to the actual(gived) network. The achieved results have proved its application insepcific networking problem. It can also enhance the effective utilization of available resources.展开更多
Consensus control of multi-agent systems is an innovative paradigm for the development of intelligent distributed systems.This has fascinated numerous scientific groups for their promising applications as they have th...Consensus control of multi-agent systems is an innovative paradigm for the development of intelligent distributed systems.This has fascinated numerous scientific groups for their promising applications as they have the freedom to achieve their local and global goals and make their own decisions.Network communication topologies based on graph and matrix theory are widely used in a various real-time applications ranging from software agents to robotics.Therefore,while sustaining the significance of both directed and undirected graphs,this research emphases on the demonstration of a distributed average consensus algorithm.It uses the harmonic mean in the domain of multi-agent systems with directed and undirected graphs under static topologies based on a control input scheme.The proposed agreement protocol focuses on achieving a constant consensus on directional and undirected graphs using the exchange of information between neighbors to update their status values and to be able to calculate the total number of agents that contribute to the communication network at the same time.The proposed method is implemented for the identical networks that are considered under the directional and non-directional communication links.Two different scenarios are simulated and it is concluded that the undirected approach has an advantage over directed graph communication in terms of processing time and the total number of iterations required to achieve convergence.The same network parameters are introduced for both orientations of the communication graphs.In addition,the results of the simulation and the calculation of various matrices are provided at the end to validate the effectiveness of the proposed algorithm to achieve consensus.展开更多
The undirected power graph <i>P</i>(<i>Z<sub>n</sub></i>) of a finite group <i>Z<sub>n</sub></i> is the graph with vertex set G and two distinct vertices u a...The undirected power graph <i>P</i>(<i>Z<sub>n</sub></i>) of a finite group <i>Z<sub>n</sub></i> is the graph with vertex set G and two distinct vertices u and v are adjacent if and only if <i>u</i> ≠ <i>v</i> and <img src="Edit_3b1df203-9ff2-4c13-93d1-4bba568eae54.png" width="40" height="20" alt="" /> or <img src="Edit_094c8f88-deb6-4f41-825a-ba91c0306ae8.png" width="40" height="20" alt="" />. The Wiener index <i>W</i>(<i>P</i>(<i>Z<sub>n</sub></i>)) of an undirected power graph <i>P</i>(<i>Z<sub>n</sub></i>) is defined to be sum <img src="Edit_348337df-b9c2-480d-9713-ec299a6fcd4e.png" width="110" height="25" alt="" /> of distances between all unordered pair of vertices in <i>P</i>(<i>Z<sub>n</sub></i>). Similarly, the edge-Wiener index <i>W<sub>e</sub></i>(<i>P</i>(<i>Z<sub>n</sub></i>)) of <i>P</i>(<i>Z<sub>n</sub></i>) is defined to be the sum <img src="Edit_e9b89765-f71e-4865-a0c5-c688710ff0c6.png" width="60" height="25" alt="" /> of distances between all unordered pairs of edges in <i>P</i>(<i>Z<sub>n</sub></i>). In this paper, we concentrate on the wiener index of a power graph <img src="Edit_dff0cd99-eb11-4123-a437-78cbbd8ebf96.png" width="40" height="20" alt="" />, <i>P</i>(<i>Z<sub>pq</sub></i>) and <i>P</i>(<i>Z<sub>p</sub></i>). Firstly, we obtain new results on the wiener index and edge-wiener index of power graph <i>P</i>(<i>Z<sub>n</sub></i>), using <i>m,n</i> and Euler function. Also, we obtain an equivalence between the edge-wiener index and wiener index of a power graph of <i>Z<sub>n</sub></i>.展开更多
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
A kernel in a directed graph D=(V,A)is a set K of vertices of D such that no two vertices in K are adjacent and for every vertex v in V\K there is a vertex u in K,such that(v,u)is an arc of D.It is well known that the...A kernel in a directed graph D=(V,A)is a set K of vertices of D such that no two vertices in K are adjacent and for every vertex v in V\K there is a vertex u in K,such that(v,u)is an arc of D.It is well known that the problem of the existence of a kernel is NP-complete for a general digraph.Bang-Jensen and Gutin pose an interesting problem(Problem 12.3.5)in their book[Digraphs:Theory,Algorithms and Applications,London:Springer-Verlag,2000]:to characterize all circular digraphs with kernels.In this paper,we study the problem of the existence of the kernel for several special classes of circular digraphs.Moreover,a class of counterexamples is given for the Duchet kernel conjecture(for every connected kernel-less digraph which is not an odd directed cycle,there exists an arc which can be removed and the obtained digraph is still kernel-less).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
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
The inherent hysteresis of NiTi alloy samples is one of the key factors limiting their elastocaloric cooling performance.However,reducing hysteresis often leads to a decrease in adiabatic temperature change(ΔT_(ad)),...The inherent hysteresis of NiTi alloy samples is one of the key factors limiting their elastocaloric cooling performance.However,reducing hysteresis often leads to a decrease in adiabatic temperature change(ΔT_(ad)),thereby hindering the application of NiTi alloys in the refrigeration field.Here,NiTi alloys with alternating high-Ni and low-Ni content were fabricated by tailoring heat input during the wire-arc directed energy deposition(DED)process,which modifies the Ni concentration gradient and enables the modulation of the elastocaloric cooling performance of NiTi alloys.The coefficient of performance of material(COP_(mat))of the high-Ni NiTi alloy samples is relatively high,but theirΔT_(ad) during deformation is lower.On the other hand,the low-Ni NiTi alloy samples,while exhibiting higherΔT_(ad),show poorer stability during cycling.Due to the synergistic effect of the microstructures in the high-Ni and low-Ni region,a favorable combination of low cyclic hysteresis and highΔT_(ad) were achieved in the composite NiTi samples.Additionally,the composite NiTi samples also demonstrate excellent cyclic stability,with a degradation rate of only 4%during the cycling process under a 2%strain condition.This study proposes a feasible approach for regulating the elastocaloric effect of NiTi alloys,paving the way for additive manufacturing to prepare elastocaloric cooling materials.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
The fabrication of Invar/MnCu functionally graded material(FGM)through directed energy deposition(DED)can satisfy the demands for precision devices in aerospace,providing lightweight properties and integrating thermal...The fabrication of Invar/MnCu functionally graded material(FGM)through directed energy deposition(DED)can satisfy the demands for precision devices in aerospace,providing lightweight properties and integrating thermal stability and vibration damping capabilities.However,basic research on Invar/MnCu FGM is still lacking,hindering its potential applications.To address this gap,this study was conducted using mixed powders and consistent process parameters to print experiments for Invar/MnCu FGM and homogeneous samples.Phases,microstructures,compositions,and thermal expansion properties were thoroughly examined.Three types of defects were detected in the Invar/MnCu FGM sample:unmelted Invar 36 powders,cracks,and pores.The mechanism of unmelted powders was deeply discussed,attributing it to material properties influencing laser absorptivity,the required time for melting powder,and effects on solidus temperature.The mechanism of cracks was also discussed,attributing it to theγ-Fe dendritic structure causing low melting point metal to form an intergranular liquid film,harmful secondary phases mismatched with the terminal alloy,and obvious tensile stresses during the DED process.Additionally,an effective strategy was proposed to reduce defects in Invar/MnCu FGM.After optimization,the specimens exhibited excellent tensile properties,with a yield strength of 262±5 MPa,an ultimate tensile strength of 316±7 MPa,and an elongation of 3%±1%.This research provides valuable references and insights for subsequent work,offering robust support for better understanding and designing other FGM.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
In this study,we demonstrate the direct in-situ synthesis of NiTi alloys with tunable chemical com-position(Ni/Ti atomic ratio)and corresponding thermomechanical response.This synthesis is achieved by regulating the f...In this study,we demonstrate the direct in-situ synthesis of NiTi alloys with tunable chemical com-position(Ni/Ti atomic ratio)and corresponding thermomechanical response.This synthesis is achieved by regulating the feeding speed ratio of pure Ni and Ti wires during the additive manufacturing pro-cess based on dual-wire-feed electron beam directed energy deposition(EB-DED)technology.Under ap-propriate process conditions,the resulting NiTi alloys exhibit a controllable evolution around the near-equiatomic composition and display a typical columnar grain morphology characteristic of additively manufactured NiTi alloys.With an increase in Ni content(shifting from Ti-rich to Ni-rich),the second phase particles present in the samples change from Ti-rich phase(Ti_(2) Ni)to Ni-rich phases(such as Ni4 Ti3 and Ni3 Ti_(2)).The phase transformation temperatures gradually decrease with increasing Ni content,and the predominant matrix phase transitions from martensite to austenite.The as-built NiTi alloy exhibits a typical tensile curve with a good tensile elongation of 11%,fabricated under suitable composition and microstructure conditions.This result surpasses values reported in current in-situ synthesized NiTi alloys through additive manufacturing methods.Moreover,it almost reaches the levels achieved by additively manufactured NiTi alloys using pre-alloyed raw materials.Furthermore,this study reports,for the first time in the field of in-situ synthesized NiTi alloys,a good tensile shape memory effect,achieving an im-pressive recovery rate of up to 70%under a tensile strain of 6%.This investigation provides a meaningful theoretical perspective and technical strategy for the integrated customization of NiTi alloy components in structure,composition,and function.This low-cost and high-efficiency approach is particularly attrac-tive for the preparation of functional graded,large-scale and disposable NiTi components.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
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
Laser directed energy deposition(LDED)is an emerging branch of metal-based additive manufacturing(AM)processes,offering unprecedented capabilities for high-performance fabrication with complex geometries and near-net ...Laser directed energy deposition(LDED)is an emerging branch of metal-based additive manufacturing(AM)processes,offering unprecedented capabilities for high-performance fabrication with complex geometries and near-net shapes.This technology is gathering increasing attention from industries such as biomedical,automotive,and aerospace.However,achieving consistent part quality and desired material properties is challenging due to intricate processing parameters and potential process defects such as dynamic melt-pool behavior and localized heat accumulation.This paper reviews recent advances in on-line quality control,focusing on in-situ measurement and closed-loop control for efficient assurance of LDED-fabricated parts.The quality principles,encompassing accuracy and material performance,are summarized to lay a foundation for understanding the mechanisms of quality defects and influencing factors.This review explores and thoroughly compares advancements in indirect process measurements,such as optical,thermal,and acoustic monitoring with direct quality measurements,including laser-line scanning and operando synchrotron X-ray imaging.Depending on the sensing techniques,this paper highlights a hierarchical control strategy for adaptive parameter regulation on intra-layer and inter-layer scales.The requirements and performance of various state-of-the-art controllers are critically compared to indicate their suitable applications.The importance of machine learning in detecting process anomalies and predicting build quality based on sensory signals is also outlined.Future directions are proposed towards adaptive,automated,and intelligent quality control,with a focus on multi-modal monitoring,physics-informed neural networks for interpretable analysis,and multi-objective control applications.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
文摘In this research paper, a routing problem of undirected networks has been solved. The problem was to determine the optimal routes of a telecommunication network. A heuristic approach has been adopted,due to the specific uature of the problem.The problem is only concerned withdistant(remote) nodes of the network which are indirectly linked through a single intermediate node.To determine the optimal routes,the devised heuristic has been coded in FORTRAN language. Forthe validation of developed heuristic,it has been implemented on two sample networks. Finally, ithas been applied to the actual(gived) network. The achieved results have proved its application insepcific networking problem. It can also enhance the effective utilization of available resources.
文摘Consensus control of multi-agent systems is an innovative paradigm for the development of intelligent distributed systems.This has fascinated numerous scientific groups for their promising applications as they have the freedom to achieve their local and global goals and make their own decisions.Network communication topologies based on graph and matrix theory are widely used in a various real-time applications ranging from software agents to robotics.Therefore,while sustaining the significance of both directed and undirected graphs,this research emphases on the demonstration of a distributed average consensus algorithm.It uses the harmonic mean in the domain of multi-agent systems with directed and undirected graphs under static topologies based on a control input scheme.The proposed agreement protocol focuses on achieving a constant consensus on directional and undirected graphs using the exchange of information between neighbors to update their status values and to be able to calculate the total number of agents that contribute to the communication network at the same time.The proposed method is implemented for the identical networks that are considered under the directional and non-directional communication links.Two different scenarios are simulated and it is concluded that the undirected approach has an advantage over directed graph communication in terms of processing time and the total number of iterations required to achieve convergence.The same network parameters are introduced for both orientations of the communication graphs.In addition,the results of the simulation and the calculation of various matrices are provided at the end to validate the effectiveness of the proposed algorithm to achieve consensus.
文摘The undirected power graph <i>P</i>(<i>Z<sub>n</sub></i>) of a finite group <i>Z<sub>n</sub></i> is the graph with vertex set G and two distinct vertices u and v are adjacent if and only if <i>u</i> ≠ <i>v</i> and <img src="Edit_3b1df203-9ff2-4c13-93d1-4bba568eae54.png" width="40" height="20" alt="" /> or <img src="Edit_094c8f88-deb6-4f41-825a-ba91c0306ae8.png" width="40" height="20" alt="" />. The Wiener index <i>W</i>(<i>P</i>(<i>Z<sub>n</sub></i>)) of an undirected power graph <i>P</i>(<i>Z<sub>n</sub></i>) is defined to be sum <img src="Edit_348337df-b9c2-480d-9713-ec299a6fcd4e.png" width="110" height="25" alt="" /> of distances between all unordered pair of vertices in <i>P</i>(<i>Z<sub>n</sub></i>). Similarly, the edge-Wiener index <i>W<sub>e</sub></i>(<i>P</i>(<i>Z<sub>n</sub></i>)) of <i>P</i>(<i>Z<sub>n</sub></i>) is defined to be the sum <img src="Edit_e9b89765-f71e-4865-a0c5-c688710ff0c6.png" width="60" height="25" alt="" /> of distances between all unordered pairs of edges in <i>P</i>(<i>Z<sub>n</sub></i>). In this paper, we concentrate on the wiener index of a power graph <img src="Edit_dff0cd99-eb11-4123-a437-78cbbd8ebf96.png" width="40" height="20" alt="" />, <i>P</i>(<i>Z<sub>pq</sub></i>) and <i>P</i>(<i>Z<sub>p</sub></i>). Firstly, we obtain new results on the wiener index and edge-wiener index of power graph <i>P</i>(<i>Z<sub>n</sub></i>), using <i>m,n</i> and Euler function. Also, we obtain an equivalence between the edge-wiener index and wiener index of a power graph of <i>Z<sub>n</sub></i>.
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.
文摘A kernel in a directed graph D=(V,A)is a set K of vertices of D such that no two vertices in K are adjacent and for every vertex v in V\K there is a vertex u in K,such that(v,u)is an arc of D.It is well known that the problem of the existence of a kernel is NP-complete for a general digraph.Bang-Jensen and Gutin pose an interesting problem(Problem 12.3.5)in their book[Digraphs:Theory,Algorithms and Applications,London:Springer-Verlag,2000]:to characterize all circular digraphs with kernels.In this paper,we study the problem of the existence of the kernel for several special classes of circular digraphs.Moreover,a class of counterexamples is given for the Duchet kernel conjecture(for every connected kernel-less digraph which is not an odd directed cycle,there exists an arc which can be removed and the obtained digraph is still kernel-less).
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 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financially supported by the National Natural Science Foundation of China(Nos.52275374 and 52205414)the Key Research and Development Projects of Shaanxi Province(No.2023-YBGY-361)+1 种基金the Xi’an Jiaotong University Basic Research Funds for Freedom of Exploration and Innovation-Student Programs(No.xzy022024099)the Taihu Lake Innovation Fund for the School of Future Technology of Xi’an Jiaotong University.
文摘The inherent hysteresis of NiTi alloy samples is one of the key factors limiting their elastocaloric cooling performance.However,reducing hysteresis often leads to a decrease in adiabatic temperature change(ΔT_(ad)),thereby hindering the application of NiTi alloys in the refrigeration field.Here,NiTi alloys with alternating high-Ni and low-Ni content were fabricated by tailoring heat input during the wire-arc directed energy deposition(DED)process,which modifies the Ni concentration gradient and enables the modulation of the elastocaloric cooling performance of NiTi alloys.The coefficient of performance of material(COP_(mat))of the high-Ni NiTi alloy samples is relatively high,but theirΔT_(ad) during deformation is lower.On the other hand,the low-Ni NiTi alloy samples,while exhibiting higherΔT_(ad),show poorer stability during cycling.Due to the synergistic effect of the microstructures in the high-Ni and low-Ni region,a favorable combination of low cyclic hysteresis and highΔT_(ad) were achieved in the composite NiTi samples.Additionally,the composite NiTi samples also demonstrate excellent cyclic stability,with a degradation rate of only 4%during the cycling process under a 2%strain condition.This study proposes a feasible approach for regulating the elastocaloric effect of NiTi alloys,paving the way for additive manufacturing to prepare elastocaloric cooling materials.
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 the National Key Research and Development Program of China(Nos.2022YFB4600300 and 2022YFB4600301)the National Natural Science Foundation of China(No.52175364)+1 种基金the ND Basic Research Funds of NPU(G2022WD)the Research Fund of the State Key Laboratory of Solidification Processing(NPU),China(No.2023-QZ-04).
文摘The fabrication of Invar/MnCu functionally graded material(FGM)through directed energy deposition(DED)can satisfy the demands for precision devices in aerospace,providing lightweight properties and integrating thermal stability and vibration damping capabilities.However,basic research on Invar/MnCu FGM is still lacking,hindering its potential applications.To address this gap,this study was conducted using mixed powders and consistent process parameters to print experiments for Invar/MnCu FGM and homogeneous samples.Phases,microstructures,compositions,and thermal expansion properties were thoroughly examined.Three types of defects were detected in the Invar/MnCu FGM sample:unmelted Invar 36 powders,cracks,and pores.The mechanism of unmelted powders was deeply discussed,attributing it to material properties influencing laser absorptivity,the required time for melting powder,and effects on solidus temperature.The mechanism of cracks was also discussed,attributing it to theγ-Fe dendritic structure causing low melting point metal to form an intergranular liquid film,harmful secondary phases mismatched with the terminal alloy,and obvious tensile stresses during the DED process.Additionally,an effective strategy was proposed to reduce defects in Invar/MnCu FGM.After optimization,the specimens exhibited excellent tensile properties,with a yield strength of 262±5 MPa,an ultimate tensile strength of 316±7 MPa,and an elongation of 3%±1%.This research provides valuable references and insights for subsequent work,offering robust support for better understanding and designing other FGM.
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the State Key Laboratory of Tribology in Advanced Equipment(Project code:SKLT2022C20)Postdoc Matching Fund Scheme of The Hong Kong Polytechnic University(Project code:1-W283)+3 种基金Research Institute of Advanced Manufacturing at The Hong Kong Polytechnic Univer-sity(PolyU)(Project code:CD9E,CD8Y)PolyU Research and Inno-vation Office(Project code:BBR5)Departmental General Research Fund of the Department of Industrial and Systems Engineering of The Hong Kong Polytechnic University(Project code:G-UAKX)the funding support for the State Key Laboratories in Hong Kong from the Innovation and Technology Commission of the Govern-ment of the Hong Kong Special Administrative Region,China.
文摘In this study,we demonstrate the direct in-situ synthesis of NiTi alloys with tunable chemical com-position(Ni/Ti atomic ratio)and corresponding thermomechanical response.This synthesis is achieved by regulating the feeding speed ratio of pure Ni and Ti wires during the additive manufacturing pro-cess based on dual-wire-feed electron beam directed energy deposition(EB-DED)technology.Under ap-propriate process conditions,the resulting NiTi alloys exhibit a controllable evolution around the near-equiatomic composition and display a typical columnar grain morphology characteristic of additively manufactured NiTi alloys.With an increase in Ni content(shifting from Ti-rich to Ni-rich),the second phase particles present in the samples change from Ti-rich phase(Ti_(2) Ni)to Ni-rich phases(such as Ni4 Ti3 and Ni3 Ti_(2)).The phase transformation temperatures gradually decrease with increasing Ni content,and the predominant matrix phase transitions from martensite to austenite.The as-built NiTi alloy exhibits a typical tensile curve with a good tensile elongation of 11%,fabricated under suitable composition and microstructure conditions.This result surpasses values reported in current in-situ synthesized NiTi alloys through additive manufacturing methods.Moreover,it almost reaches the levels achieved by additively manufactured NiTi alloys using pre-alloyed raw materials.Furthermore,this study reports,for the first time in the field of in-situ synthesized NiTi alloys,a good tensile shape memory effect,achieving an im-pressive recovery rate of up to 70%under a tensile strain of 6%.This investigation provides a meaningful theoretical perspective and technical strategy for the integrated customization of NiTi alloy components in structure,composition,and function.This low-cost and high-efficiency approach is particularly attrac-tive for the preparation of functional graded,large-scale and disposable NiTi components.
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 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 by Royal Academy of Engineering(IF2223B-125)Royal Society(IECR3213107)。
文摘Laser directed energy deposition(LDED)is an emerging branch of metal-based additive manufacturing(AM)processes,offering unprecedented capabilities for high-performance fabrication with complex geometries and near-net shapes.This technology is gathering increasing attention from industries such as biomedical,automotive,and aerospace.However,achieving consistent part quality and desired material properties is challenging due to intricate processing parameters and potential process defects such as dynamic melt-pool behavior and localized heat accumulation.This paper reviews recent advances in on-line quality control,focusing on in-situ measurement and closed-loop control for efficient assurance of LDED-fabricated parts.The quality principles,encompassing accuracy and material performance,are summarized to lay a foundation for understanding the mechanisms of quality defects and influencing factors.This review explores and thoroughly compares advancements in indirect process measurements,such as optical,thermal,and acoustic monitoring with direct quality measurements,including laser-line scanning and operando synchrotron X-ray imaging.Depending on the sensing techniques,this paper highlights a hierarchical control strategy for adaptive parameter regulation on intra-layer and inter-layer scales.The requirements and performance of various state-of-the-art controllers are critically compared to indicate their suitable applications.The importance of machine learning in detecting process anomalies and predicting build quality based on sensory signals is also outlined.Future directions are proposed towards adaptive,automated,and intelligent quality control,with a focus on multi-modal monitoring,physics-informed neural networks for interpretable analysis,and multi-objective control applications.
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.
