1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and...1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].展开更多
Additive manufacturing(AM)has revolutionized the production of metal bone implants,enabling unprecedented levels of customization and functionality.Recent advancements in surface-modification technologies have been cr...Additive manufacturing(AM)has revolutionized the production of metal bone implants,enabling unprecedented levels of customization and functionality.Recent advancements in surface-modification technologies have been crucial in enhancing the performance and biocompatibility of implants.Through leveraging the versatility of AM techniques,particularly powder bed fusion,a range of metallic biomaterials,including stainless steel,titanium,and biodegradable alloys,can be utilized to fabricate implants tailored for craniofacial,trunk,and limb bone reconstructions.However,the potential of AM is contingent on addressing intrinsic defects that may hinder implant performance.Techniques such as sandblasting,chemical treatment,electropolishing,heat treatment,and laser technology effectively remove residual powder and improve the surface roughness of these implants.The development of functional coatings,applied via both dry and wet methods,represents a significant advancement in surface modification research.These coatings not only improve mechanical and biological interactions at the implant-bone interface but also facilitate controlled drug release and enhance antimicrobial properties.Addition-ally,micro-and nanoscale surface modifications using chemical and laser techniques can precisely sculpt implant surfaces to promote the desired cellular responses.This detailed exploration of surface engineering offers a wealth of opportunities for creating next-generation implants that are not only biocompatible but also bioactive,laying the foundation for more effective solutions in bone reconstruction.展开更多
The remarkable mechanical properties exhibited by laminated structures have generated significant in-terest in the realm of additively manufactured laminated high-entropy alloys(HEAs).Despite this bur-geoning interest...The remarkable mechanical properties exhibited by laminated structures have generated significant in-terest in the realm of additively manufactured laminated high-entropy alloys(HEAs).Despite this bur-geoning interest,the nexus between process,structure,and properties within laminated HEAs remains largely uncharted.There is a vast space for investigating the effect of the typical heterogeneous interface on the macroscopic mechanical properties.This study focuses on the influence of the characteristic het-erogeneous interface on macroscopic mechanical properties of laminated HEAs,particularly anisotropy.Using the 3D-printed Fe_(50)Mn_(30)Co_(10)Cr_(10)-CoCrNi HEA as a model,we investigate the impact of interface geometry on mechanical characteristics.Tensile tests show that the reduced interface spacing increases yield strength.This laminated HEA displays significant anisotropy in strength and ductility,depending on the loading direction relative to the interface.Electron microscopic observations suggest that finer layer spacing enhances interface and dislocation strengthening,increasing yield strength.Anisotropic behaviors are confirmed to be mediated by interface orientation,explained in terms of deformation compatibility and crack development at the interface.This research offers fundamental insights into the relationship between heterogeneous interfaces and the mechanical properties in laminated HEAs.The knowledge is vital for designing,fabricating,and optimizing laminated HEAs through additive manufacturing,advancing their engineering applications.展开更多
Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal st...Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.展开更多
Spinal fusion is a commonly used technique to treat acute and chronic spinal diseases by fusion of the adjacent vertebrae, aiming at achieving stability and eliminating the mobility of the objective segment. While bon...Spinal fusion is a commonly used technique to treat acute and chronic spinal diseases by fusion of the adjacent vertebrae, aiming at achieving stability and eliminating the mobility of the objective segment. While bone autografts and allografts have been conventionally used for spinal fusion, limitations persist in achieving optimization of both good osteoinductive capacity and mechanical stability. In this study, additively manufactured Zn-Li scaffolds were developed and evaluated for their potential in spinal fusion. First, three scaffold structures (BCC, Diamond, and Gyroid) were designed and verified in vitro. Due to the smooth transition surfaces and uniform degradation behavior, the Gyroid Zn-Li scaffold demonstrated mechanical integrity during degradation and enhanced cellular proliferation compared to the other two scaffolds. Subsequently, Zn-Li scaffolds (Gyroid) were selected for posterolateral lumbar fusion (L4/L5) in rabbits. Following 12 weeks of implantation, the Zn-Li scaffolds demonstrated a moderate biodegradation rate and satisfactory biocompatibility. Compared to bone allografts, the Zn-Li scaffolds significantly improved osseointegration adjacent to the transverse processes, which led to enhanced segmental stability of the fused vertebrae post posterolateral lumbar fusion. Overall, the results show that the biodegradable Zn-Li scaffold holds substantial potential as the next-generation graft for spinal fusion.展开更多
Nickel-based superalloys are indispensable for high-temperature engineering applications,yet their additive manufacturing(AM)is plagued by significant cracking defects.This review investigates crack failure mechanisms...Nickel-based superalloys are indispensable for high-temperature engineering applications,yet their additive manufacturing(AM)is plagued by significant cracking defects.This review investigates crack failure mechanisms in AM nickel-based superalloys,emphasizing methodologies to evaluate crack sensitivity and compositional design strategies to mitigate defects.Key crack types—solidification,liquation,solid-state,stress corrosion,fatigue,and creep-fatigue cracks—are analyzed,with focus on formation mechanisms driven by thermal gradients,solute segregation,and microstructural heterogeneities.Evaluation frameworks such as the Rappaz-Drezet-Gremaud(RDG)criterion,Solidification Cracking Index(SCI),and Strain Age Cracking(SAC)index are reviewed for predicting crack susceptibility through integration of thermodynamic parameters,solidification kinetics,and mechanical properties.Alloy compositional design strategies are presented,including optimization of strengthening elements(Al,Ti),grain boundary modifiers(B,Zr,Re),and impurity control(C,O),which suppress crack initiation and propagation via microstructure refinement and enhanced high-temperature resistance.Computational approaches,such as thermodynamically assisted design,high-throughput experimentation,and machine learning,are highlighted for decoding complex composition-structure-property relationships.Challenges in modeling multi-scale defect interactions and developing unified frameworks for manufacturing-and service-induced cracks are outlined.This review underscores the necessity of integrated computational-experimental strategies to advance reliable AM of nickel-based superalloys,providing insights for defect prediction,alloy optimization,and process control.展开更多
The unit cell configuration of lattice structures critically influences their load-bearing and energy absorption performance.In this study,three novel lattice structures were developed by modifying the conventional FB...The unit cell configuration of lattice structures critically influences their load-bearing and energy absorption performance.In this study,three novel lattice structures were developed by modifying the conventional FBCCZ unit cell through reversing,combining,and turning strategies.The designed lattices were fabricated via laser powder bed fusion(LPBF)using Ti-6Al-4V powder,and the mechanical properties,energy absorption capacity,and deformation behaviors were systematically investigated through quasi-static compression tests and finite element simulations.The results demonstrate that the three modified lattices exhibit superior performance over the conventional FBCCZ structure in terms of fracture strain,specific yield strength,specific ultimate strength,specific energy absorption,and energy absorption efficiency,thereby validating the efficacy of unit cell modifications in enhancing lattice performance.Notably,the CFBCCZ and TFBCCZ lattices significantly outperform both the FBCCZ and RFBCCZ lattice structures in load-bearing and energy absorption.While TFBCCZ shows marginally higher specific elastic modulus and energy absorption efficiency than CFBCCZ,the latter achieves superior energy absorption due to its highest ultimate strength and densification strain.Finite element simulations further reveal that the modified lattices,through optimized redistribution and adjustment of internal nodes and struts,effectively alleviate stress concentration during loading.This structural modification enhances the structural integrity and deformation stability under external loads,enabling a synergistic enhancement of load-bearing capacity and energy absorption performance.展开更多
A novel Additive Manufacturing(AM)-driven concurrent design strategy based on the beam characterization model considering strength constraints is proposed.The lattice topology,radius size,Building Orientation(BO),and ...A novel Additive Manufacturing(AM)-driven concurrent design strategy based on the beam characterization model considering strength constraints is proposed.The lattice topology,radius size,Building Orientation(BO),and structural yield strength can be simultaneously adjusted by integrating the overall process-structure-performance relationship of the AM process into the optimization.Specifically,the transverse isotropic material model is adopted to describe the material properties induced by the layer-by-layer manner of additive manufacturing.To bolster lattice strength performance,the stress constraints and ratio constraints of lattice struts are employed.The Tsai-Wu yield criterion is implemented to characterize the lattice strut's strength,while the P-norm method streamlines the handling of multiple constraints,minimizing computational overhead.Moreover,the gradient-based optimization model is established,where both the individual struts diameters and BO can be designed,and the buckling-prone spatial struts are strategically eliminated to improve the lattice strength further.Furthermore,several typical structures are optimized to verify the effectiveness of the proposed method.The optimized results are quite encouraging since the heterogeneous lattice structures with optimized BO obtained by the strength-based concurrent method show a remarkably improved performance compared to traditional designs.展开更多
Maraging steels are known for their exceptional strength but suffer from limited work hardening and ductility.Here,we report an intermittent printing strategy to tailor the microstructure and mechanical properties of ...Maraging steels are known for their exceptional strength but suffer from limited work hardening and ductility.Here,we report an intermittent printing strategy to tailor the microstructure and mechanical properties of maraging 250 steel via tuning the thermal history during wire-arc directed energy deposition.By introducing a dwell time between adjacent layers,the maraging 250 steel is cooled below the martensite start temperature,triggering thermally-driven martensitic transformation during the printing process.Thermal cycling during subsequent layer deposition results in the formation of reverted austenite which shows a refined microstructure and induces elemental segregation between martensite and reverted austenite.The Ni enrichment in the austenite promotes stabilization of the reverted austenite upon cooling to room temperature.The reverted austenite is metastable during deformation,leading to strain-induced martensitic transformation under loading.Specifically,a 3 min interlayer dwell time produces a maraging 250 steel with approximately 8% reverted austenite,resulting in improved work hardening via martensitic transformation induced plasticity during deformation.Meanwhile,the higher cooling rate and refined prior austenite grains lead to substantially refined martensitic grains(by approximately fivefold)together with an increased dislocation density.With 3 min interlayer dwell time,the yield strength of the printed maraging 250 steel increases from 836 MPa to 990 MPa,and the uniform elongation is doubled from 3.2% to 6.5%.This intermittent deposition strategy demonstrates the potential to tune the microstructure of maraging steels for achieving strength-ductility synergy by engineering the thermal history during additive manufacturing.展开更多
In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructu...In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructural evolution during deposition and subsequent heat treatment was explained through multi-scale microstructural characterization techniques,and the impact of heat treatment on the strengthductility synergy of the deposited alloy was systematically compared.The results showed that the microstructure of the deposited sample was mainly composed of fine equiaxedα-Mg grains and Mg_(24)(Gd,Y)_(5) phase.The optimized solution heat treatment(450℃×2 h)had little effect on the grain size,but can effectively reduce the Mg_(24)(Gd,Y)_(5) eutectic phase on the grain boundary,resulting in a significant increase in elongation from 13.7% to 26.6%.After peak-aging treatment,the strength of the GW63K alloy increased to 370 MPa,which was significantly higher than the as-built state(267 MPa).The superior strength in this study is attributed to the refinement strengthening imparted by the fine microstructure inherited in the as-built GW63K alloy,as well as the precipitation strengthening due to the formation of dense β’precipitates with a pronounced plate-like aspect ratio.展开更多
The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipme...The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipment for aerospace,robotics,and other engineering applications.Additive manufacturing provides high design freedom which can further enhance the power density of integrated valve-controlled cylinders.However,there is a lack of effective design methods to guide the additive manufacturing of valve-controlled cylinders for more efficient hydraulic energy transmission.This study accordingly introduces an energy-saving design method based on additive manufacturing for integrated valve-controlled cylinders.The method consists of two main parts:(1)redesigning the manifold block to eliminate leakage points and reduce energy losses through integrated design of the valve,cylinder,and piping;(2)establishing a pressure loss model to achieve energy savings through optimized flow channel design for bends with different parameters.Compared to traditional valve-controlled cylinders,the integrated valvecontrolled cylinder developed from our method reduces the weight by 31%,volume by 55%,and pressure loss in the main flow channel by over 30%.This indicates that the design achieves both lightweight construction and improved hydraulic transmission efficiency.This study provides theoretical guidance for the design of lightweight and energy-efficient valve-controlled cylinders,and may aid the design of similar hydraulic machinery.展开更多
The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redu...The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redundant tensile testing on specimens prepared along diverse directions,this study proposes an instrumented indentation-based inverse identification method for the efficient characterization of additively manufactured materials.In the present work,a 3D finite element model of indentation test is first established for the printed material,for which an anisotropic material constitutive model is incorporated.We have demonstrated that the indentation responses are information-rich,and material anisotropy along different directions can be interpreted by a single indentation imprint.Subsequently,an inverse identification framework is built,in which an Euclidean error norm between simulated and experimental indentation responses is minimized via optimization algorithms such as the Globally Convergent Method of Moving Asymptotes(GCMMA).The developed method has been verified on diverse printed materials referring to either the indentation curve or the residual imprint,and the superiority of this latter over the former is confirmed by a better and faster convergence of inverse identification.Experimental validations on 3D printed materials(including stainless steel 316L,aluminum alloy AlSi10Mg,and titanium alloy TC4)reveal that the developed method is both accurate and reliable when compared with material constitutive behaviors obtained from uni-axial tensile tests,regardless of the degree of anisotropy among different materials.展开更多
High entropy alloys(HEAs),particularly CoCrNiFeMn system,have emerged as a transformative class of high-performance alloys due to their exceptional mechanical and functional properties.However,traditional manufacturin...High entropy alloys(HEAs),particularly CoCrNiFeMn system,have emerged as a transformative class of high-performance alloys due to their exceptional mechanical and functional properties.However,traditional manufacturing methods for HEAs are limited by inefficiencies and high costs,restricting their widespread applications.Additive manufacturing(AM),specifically laser powder bed fusion(LPBF),offers a promising alternative by enabling the fabrication of HEAs with unique microstructures and enhanced properties.This study investigates the thermal stability and mechanical performance of LPBF-printed CoCrNiFeMn HEA across a wide temperature range.The as-built LPBF HEA with a hierarchically heterogeneous microstructure,featured by columnar grains and ultrafine dislocation cellular structure,demonstrates exceptional thermal stability,with minimal hardness reduction and no apparent recrystallisation even after prolonged exposure to high temperatures(up to 1373 K),in stark contrast to the significant property degradation observed in conventionally processed HEAs.This stability is attributed to the unique dislocation cellular structures and the intrinsic thermal self-stabilizing effects induced by the LPBF process and the inhibition of recrystallisation due to the low stored energy and columnar grain morphology.The LPBF-fabricated HEA also exhibits outstanding strength-ductility synergy across a broad temperature spectrum,with cryogenic deformation enhancing both strength and ductility due to the activation of deformation twinning.At elevated temperatures,the alloy undergoes a slight reduction in strength but retains good ductility,except at 873 K,where a sharp decline in ductility is observed likely due to grain boundary decohesion and porosity-related crack initiation manifested by the cleavage fracture surface and the cracks at grain boundaries.These findings provide new insights into the temperature-dependent mechanical behavior of AM HEAs,highlight the critical role of dislocation cellular structures in achieving superior thermal and mechanical performance,and underscore the potential of additively manufactured HEAs with tailored microstructures for extreme environments.展开更多
Additive manufacturing(AM)of magnesium alloys is under intense research activity.Practical engineering applications demand the development of parts with adequate corrosion resistance for their safe use.It is imperativ...Additive manufacturing(AM)of magnesium alloys is under intense research activity.Practical engineering applications demand the development of parts with adequate corrosion resistance for their safe use.It is imperative to understand the corrosion mechanisms of AM-processed Mg alloys,their correlation with processing parameters,and microstructural aspects.The present review explores this topic.A thorough assessment of the current literature on the AM methods of Mg alloys was undertaken,focusing on the main corrosion mechanisms,and their correlation with the microstructure,process defects,post-processing operations,and alloy composition.The opportunities to enhance the knowledge in this field are discussed.展开更多
An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix comp...An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix composites(MMCs).However,the corrosion be-havior of stainless steel and cast WC/W_(2)C varies inversely across different pH levels,and the phenomenon of pitting corrosion in LPBF MMCs under varying pH conditions remains insufficiently explored.In LPBF 420+5wt%WC/W_(2)C MMCs,pits form adjacent to cast WC/W_(2)C in acidic and neutral environments,attributed to the presence of chromium-rich carbides and galvanic coupling effects.The dis-solution of the reinforced particles facilitates pit nucleation in alkaline conditions.Notably,in-situ reaction layers exhibit superior corro-sion resistance to the matrix or the reinforced particles across all pH levels.The distinct corrosion mechanisms influence the pitting corro-sion behavior,with the corrosion ranking based on critical pitting potential being neutral>alkaline>acidic,contrasting the observed kin-etics of pit growth(alkaline>acidic>neutral).展开更多
The rapid development of the space field has presented elevated requirements for the performance of lightweight structures under high-temperature conditions,while the additive manufacturing of aluminum alloy for aeros...The rapid development of the space field has presented elevated requirements for the performance of lightweight structures under high-temperature conditions,while the additive manufacturing of aluminum alloy for aerospace is faced with the problem of insufficient high temperature performance and cracking.To this end,we designed a novel Ti-and Ag-modified Al-Cu-Mg alloy using laser powder bed fusion,which showed a high mechanical performance with a tensile strength of 426 MPa at room temperature and 314 MPa at 200℃,greatly surpassing the majority of currently developed heat-resistant Al alloys.The micro structural observation demonstrated that Ti element facilitates the formation of coherent L1_(2)-Al_(3)Ti particles,thereby contributing to grain refinement,while Ag segregates to the grain boundaries and forms small Ag_(2)Al particles,which effectively enhance pinning effects.Additionally,Ag_(2)Al particles at high temperature significantly contribute to the superior performance in elevated temperature conditions of the designed alloy.Thus,this study has developed a novel alloy with Ag and Ti elements addition and clarified the crucial role of Ag and Ti elements in modifying additively manufactured Al alloy,laying a foundation for the application of lightweight heat-resistant components in the future.展开更多
The effects of post heat treatment on the microstructure,aging kinetics,and room/elevated temperature mechanical properties of additively manufactured Inconel 718 superalloy were investigated.Scanning electron microsc...The effects of post heat treatment on the microstructure,aging kinetics,and room/elevated temperature mechanical properties of additively manufactured Inconel 718 superalloy were investigated.Scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),and X-ray diffraction(XRD),as well as hardness,tensile,and creep testing were used for characterization.At temperatures higher than 1100°C,homogenization treatment resulted in the appearance of equiaxed grains by recrystallization and diminishing the dislocation density.The precipitation activation energy for the homogenized and aged condition was obtained as 203.2 kJ/mol,which was higher than the value of~160 kJ/mol for the as-built IN718 superalloy.Therefore,direct aging resulted in a faster aging response,which led to a significant improvement in tensile properties,as rationalized by the strengthening mechanisms.Direct aging treatment resulted in a higher elevated-temperature ultimate tensile strength(UTS)as well as the optimum creep life and the lowest minimum creep rate in comparison with other heat treatment routes,which were attributed to the presence of fine and uniformly dispersed strengthening precipitates in conjunction with the high dislocation density.展开更多
NiTi alloys fabricated by laser powder bed fusion(LPBF)additive manufacturing technology not only address the compositional instability resulting from complex processes but also solve the challenges of difficult machi...NiTi alloys fabricated by laser powder bed fusion(LPBF)additive manufacturing technology not only address the compositional instability resulting from complex processes but also solve the challenges of difficult machining of intricate aerospace structures.However,there are very few reports on the wear behavior of LPBF-NiTi alloys.In the present work,the effects of microstructure and thermal treatment,including heat treatment and frictional heat,on the wear behavior of LPBF-NiTi alloy and 100Cr6 ball were analyzed through a series of tribological experiments with different sliding speeds.As the average sliding speed increases(0.079–0.216 m/s),the wear rate of the as-built and heat-treated samples tends to decrease in the range of 2.69×10^(-3)–0.97×10^(-3)mm^(3)/m.Although the heat-treated LPBF-NiTi alloy is 46%harder than the as-built alloy is,the latter has a higher toughness(505 MJ/m^(3))and greater transformation strain of SIM(0.097).This leads to a coupling effect of heat treatment and sliding speed on the wear resistance.In addition,the wear track morphologies under different sliding speeds are asymmetric due to the 24% greater acceleration at the far end from the motor and the 2.15 mm deviation between the maximum speed position and the geometric center of the track.The wear modes of the as-built and heat-treated samples included adhesive,abrasive and delamination wear.Moreover,the wear morphologies and dominant wear modes change with the frictionally caused heat release induced by the sliding speed.展开更多
Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat excha...Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat exchangers.This research examines the mi-crostructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM(WAAM 308L)process.Tensile tests were conducted at room temperature(RT,25℃),300℃,and 600℃in as-built conditions.The microstructure con-sists primarily of austenite grains with retainedδ-ferrite phases distributed within the austenitic matrix.The ferrite fraction,in terms of fer-rite number(FN),ranged between 2.30 and 4.80 along the build direction from top to bottom.The ferrite fraction in the middle region is 3.60 FN.Tensile strength was higher in the horizontal oriented samples(WAAM 308L-H),while ductility was higher in the vertical ones.Tensile results show a gradual reduction in strength with increasing test temperature,in which significant dynamic strain aging(DSA)is observed at 600℃.The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of WAAM 308L at 600℃were(240±10)MPa,(442±16)MPa,and(54±2.00)%,respectively,in the horizontal orientation(WAAM 308L-H),and(248±9)MPa,(412±19)MPa,and(75±2.80)%,respectively,in the vertical orientation(WAAM 308L-V).Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300℃to a mixed ductile-brittle failure with intergranular facets at 600℃.The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions,offering crucial in-sights for its use in thermally resistant structural and industrial components.展开更多
Wire arc additive manufacturing(WAAM)is one of the most promising approaches to manufacturing large and complex metal components owing to its low cost and high efficiency.However,pores and coarse columnar grains cause...Wire arc additive manufacturing(WAAM)is one of the most promising approaches to manufacturing large and complex metal components owing to its low cost and high efficiency.However,pores and coarse columnar grains caused by thermal accumulation in WAAM significantly decrease the strength and increase the anisotropy,preventing the achievement of both high strength and isotropy.In this study,the strength and anisotropy of AlMg-Sc-Zr alloys were improved by regulating heat input.The results indicated that as the heat input increased from 60 to 99 J/mm,all the components had lower porosity(lower than 0.04%),the size of the Al_(3)(Sc_(1-x),Zr_(x))phases decreased,and the number density increased.The average grain size gradually decreased,and the grain morphologies transformed from coarse equiaxed grain(CEG)+fine equiaxed grain(FEG)to FEG owing to the increase in Al_(3)(Sc_(1-x),Zr_(x))phases with increasing heat input.After heat treatment at 325℃for 6 h,high-density dispersed Al_(3)Sc phases(<10 nm)precipitated.The alloy possessed the highest strength at 79 J/mm,ultimate tensile strength(UTS)of approximately 423±3 MPa,and in-plane anisotropy of approximately 4.3%.At a heat input of 99 J/mm,the in-plane anisotropy decreased to 1.2%and UTS reached 414±5 MPa.The reduction in the CEG prolonged the crack propagation path,which improved the UTS in the vertical direction and reduced the anisotropy.Theoretical calculations indicated that the main strengthening mechanisms were solid solution and precipitation strengthening.This study lays the theoretical foundations for WAAM-processed high-strength and isotropic Al alloy components.展开更多
基金supported by the National Natu-ral Science Foundation of China(Nos.52071262,52301197,and 52234009)the National Key Research and Development Program(No.2022YFB3404203)+3 种基金the Natural Science Basic Research Pro-gram of Shaanxi Province,China(No.2023-JC-QN-0421)the Re-search Fund of the State Key Laboratory of Solidification Processing(NPU),China(Nos.2024-ZD-06 and 2024-TS-06)the Fundamental Research Funds for the Central Universities(No.D5000240144)the Young Talent Fund of Xi’an Association for Science and Tech-nology(No.959202413014).
文摘1.Introduction As one of the most widely used additive manufacturing(AM)techniques,selective laser melting(SLM)is a laser-based layer-by-layer manufacturing process,which has relatively high fabrication resolution and can directly form complex metal parts.During SLM,the interaction of laser with metal powder forms a tiny melt pool.Following the rapid movement of the laser,the cooling rate of the melt pool can be as high as 105-106 K s−1[1].Such a fast cool-ing rate inhibits grain growth and element segregation in the alloy,leading to a notable enhancement in strength and toughness[2].Therefore,SLM enables unlimited possibilities in the fabrication of complex parts with high performance.To date,the most extensively researched Al alloys for SLM are Al-Si alloys,such as AlSi10Mg,Al-12Si,and AlSi7Mg[2-5].
基金supported by National Natural Science Foundation of China(Grant No.52275343)Natural Science Foundation of Zhejiang Province(Grant No.LY23E050003)Ningbo Youth Science and Technology Innovation Leading Talent Project(Grant No.2023QL021).
文摘Additive manufacturing(AM)has revolutionized the production of metal bone implants,enabling unprecedented levels of customization and functionality.Recent advancements in surface-modification technologies have been crucial in enhancing the performance and biocompatibility of implants.Through leveraging the versatility of AM techniques,particularly powder bed fusion,a range of metallic biomaterials,including stainless steel,titanium,and biodegradable alloys,can be utilized to fabricate implants tailored for craniofacial,trunk,and limb bone reconstructions.However,the potential of AM is contingent on addressing intrinsic defects that may hinder implant performance.Techniques such as sandblasting,chemical treatment,electropolishing,heat treatment,and laser technology effectively remove residual powder and improve the surface roughness of these implants.The development of functional coatings,applied via both dry and wet methods,represents a significant advancement in surface modification research.These coatings not only improve mechanical and biological interactions at the implant-bone interface but also facilitate controlled drug release and enhance antimicrobial properties.Addition-ally,micro-and nanoscale surface modifications using chemical and laser techniques can precisely sculpt implant surfaces to promote the desired cellular responses.This detailed exploration of surface engineering offers a wealth of opportunities for creating next-generation implants that are not only biocompatible but also bioactive,laying the foundation for more effective solutions in bone reconstruction.
基金supported by the National Natural Science Foundation of China(No.12272392 and 11790292)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB22040303)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2022020).
文摘The remarkable mechanical properties exhibited by laminated structures have generated significant in-terest in the realm of additively manufactured laminated high-entropy alloys(HEAs).Despite this bur-geoning interest,the nexus between process,structure,and properties within laminated HEAs remains largely uncharted.There is a vast space for investigating the effect of the typical heterogeneous interface on the macroscopic mechanical properties.This study focuses on the influence of the characteristic het-erogeneous interface on macroscopic mechanical properties of laminated HEAs,particularly anisotropy.Using the 3D-printed Fe_(50)Mn_(30)Co_(10)Cr_(10)-CoCrNi HEA as a model,we investigate the impact of interface geometry on mechanical characteristics.Tensile tests show that the reduced interface spacing increases yield strength.This laminated HEA displays significant anisotropy in strength and ductility,depending on the loading direction relative to the interface.Electron microscopic observations suggest that finer layer spacing enhances interface and dislocation strengthening,increasing yield strength.Anisotropic behaviors are confirmed to be mediated by interface orientation,explained in terms of deformation compatibility and crack development at the interface.This research offers fundamental insights into the relationship between heterogeneous interfaces and the mechanical properties in laminated HEAs.The knowledge is vital for designing,fabricating,and optimizing laminated HEAs through additive manufacturing,advancing their engineering applications.
基金supported by the National Natural Science Foundation of China(Nos.52101037,52401040 and 52171034)the Postdoctoral Fellowship Program of CPSF(No.GZB20230944)with the computational resources provided by LvLiang Cloud Comput-ing Center.
文摘Implementing additive manufacturing to NiTi(Nitinol)alloys typically enables a preferred<001>_(B2) tex-ture along the building direction.Unfortunately,this growth orientation always possesses a high criti-cal stress level to induce the martensitic transformation and experiences premature failure before the formation of martensite during tensile testing.By utilizing in situ characterization technologies,in this study,we demonstrate that by fabricating a NiTi sample with complete<001>_(B2) texture using wire-fed electron beam directed energy deposition,a sluggish martensitic transformation can be achieved to re-tard the initiation of fracture under tensile loading.To discern the origins of this tensile response,we combine experiments with molecular dynamics simulations to systematically analyze the micro-scale de-tails on how internal lattice defects can select the variety of martensite variants.Using both quasi in situ transmission electron microscopy analysis and calculations of the different atomic configurations,our results indicate that the pre-existing precipitates and accumulated dislocation defects,rather than columnar boundaries,can have a positive influence on the sluggish formation of variants that can cou-ple with plastic deformation within a much wider stress interval.Specifically,only the variant favored by both internal strain/stress fluctuations around local defects and external tensile load will overcome the high-energy transition barrier of<001>_(B2)-oriented tension to nucleate and grow sluggishly.The cur-rent findings not only show how the mechanical responses can be controlled in additively manufactured NiTi alloys with<001>_(B2) texture,but also regard this understanding to be a step forward in decoding the salient underlying mechanisms for the correlating texture,defects,and phase transformation of these functional materials.
基金supported by the National Natural Science Foundation of China(grant Nos.52301302,U22A20121,52175274,52111530042,and 5210010632)the China Postdoctoral Science Foundation(grant No.2023M732339)+1 种基金the Guangdong Basic and Applied Basic Research Foundation(Nos.2021A1515220086,2023A1515220095,and 2024A1515012042)the Beijing Natural Science Foundation(Grant No.L212014).
文摘Spinal fusion is a commonly used technique to treat acute and chronic spinal diseases by fusion of the adjacent vertebrae, aiming at achieving stability and eliminating the mobility of the objective segment. While bone autografts and allografts have been conventionally used for spinal fusion, limitations persist in achieving optimization of both good osteoinductive capacity and mechanical stability. In this study, additively manufactured Zn-Li scaffolds were developed and evaluated for their potential in spinal fusion. First, three scaffold structures (BCC, Diamond, and Gyroid) were designed and verified in vitro. Due to the smooth transition surfaces and uniform degradation behavior, the Gyroid Zn-Li scaffold demonstrated mechanical integrity during degradation and enhanced cellular proliferation compared to the other two scaffolds. Subsequently, Zn-Li scaffolds (Gyroid) were selected for posterolateral lumbar fusion (L4/L5) in rabbits. Following 12 weeks of implantation, the Zn-Li scaffolds demonstrated a moderate biodegradation rate and satisfactory biocompatibility. Compared to bone allografts, the Zn-Li scaffolds significantly improved osseointegration adjacent to the transverse processes, which led to enhanced segmental stability of the fused vertebrae post posterolateral lumbar fusion. Overall, the results show that the biodegradable Zn-Li scaffold holds substantial potential as the next-generation graft for spinal fusion.
基金supported by the Aero Engine Corporation of China[Grant No.HFZL2022CXY029]the Young Elite Scientists Sponsorship Programby CAST[2022QNRC001]the High Performance Computing Center of Central South University,and the Project Supported by State Key Laboratory of Powder Metallurgy,Central South University,Changsha,China。
文摘Nickel-based superalloys are indispensable for high-temperature engineering applications,yet their additive manufacturing(AM)is plagued by significant cracking defects.This review investigates crack failure mechanisms in AM nickel-based superalloys,emphasizing methodologies to evaluate crack sensitivity and compositional design strategies to mitigate defects.Key crack types—solidification,liquation,solid-state,stress corrosion,fatigue,and creep-fatigue cracks—are analyzed,with focus on formation mechanisms driven by thermal gradients,solute segregation,and microstructural heterogeneities.Evaluation frameworks such as the Rappaz-Drezet-Gremaud(RDG)criterion,Solidification Cracking Index(SCI),and Strain Age Cracking(SAC)index are reviewed for predicting crack susceptibility through integration of thermodynamic parameters,solidification kinetics,and mechanical properties.Alloy compositional design strategies are presented,including optimization of strengthening elements(Al,Ti),grain boundary modifiers(B,Zr,Re),and impurity control(C,O),which suppress crack initiation and propagation via microstructure refinement and enhanced high-temperature resistance.Computational approaches,such as thermodynamically assisted design,high-throughput experimentation,and machine learning,are highlighted for decoding complex composition-structure-property relationships.Challenges in modeling multi-scale defect interactions and developing unified frameworks for manufacturing-and service-induced cracks are outlined.This review underscores the necessity of integrated computational-experimental strategies to advance reliable AM of nickel-based superalloys,providing insights for defect prediction,alloy optimization,and process control.
基金supported by National Key Lab of Aerospace Power System and Plasma Technology Foundation of China(Grant No.APSPT202301002)National Natural Science Foundation of China(Grant No.52001038)Natural Science Foundation of Chongqing,China(Grant Nos.cstc2019jcyj-msxm X0787 and cstc2021jcyj-msxm X0011)。
文摘The unit cell configuration of lattice structures critically influences their load-bearing and energy absorption performance.In this study,three novel lattice structures were developed by modifying the conventional FBCCZ unit cell through reversing,combining,and turning strategies.The designed lattices were fabricated via laser powder bed fusion(LPBF)using Ti-6Al-4V powder,and the mechanical properties,energy absorption capacity,and deformation behaviors were systematically investigated through quasi-static compression tests and finite element simulations.The results demonstrate that the three modified lattices exhibit superior performance over the conventional FBCCZ structure in terms of fracture strain,specific yield strength,specific ultimate strength,specific energy absorption,and energy absorption efficiency,thereby validating the efficacy of unit cell modifications in enhancing lattice performance.Notably,the CFBCCZ and TFBCCZ lattices significantly outperform both the FBCCZ and RFBCCZ lattice structures in load-bearing and energy absorption.While TFBCCZ shows marginally higher specific elastic modulus and energy absorption efficiency than CFBCCZ,the latter achieves superior energy absorption due to its highest ultimate strength and densification strain.Finite element simulations further reveal that the modified lattices,through optimized redistribution and adjustment of internal nodes and struts,effectively alleviate stress concentration during loading.This structural modification enhances the structural integrity and deformation stability under external loads,enabling a synergistic enhancement of load-bearing capacity and energy absorption performance.
基金co-supported by National Key R&D Program of China(No.2022YFB4602003)Key Project of National Natural Science Foundation of China(No.12032018)+2 种基金Guangdong Basic and Applied Basic Research Foundation(No.2022A1515110489)National Natural Science Foundation of China-China Academy of General Technology Joint Fund for Basic Research(No.52375380)National Key Research and Development Program of China(No.2022YFB3402200)。
文摘A novel Additive Manufacturing(AM)-driven concurrent design strategy based on the beam characterization model considering strength constraints is proposed.The lattice topology,radius size,Building Orientation(BO),and structural yield strength can be simultaneously adjusted by integrating the overall process-structure-performance relationship of the AM process into the optimization.Specifically,the transverse isotropic material model is adopted to describe the material properties induced by the layer-by-layer manner of additive manufacturing.To bolster lattice strength performance,the stress constraints and ratio constraints of lattice struts are employed.The Tsai-Wu yield criterion is implemented to characterize the lattice strut's strength,while the P-norm method streamlines the handling of multiple constraints,minimizing computational overhead.Moreover,the gradient-based optimization model is established,where both the individual struts diameters and BO can be designed,and the buckling-prone spatial struts are strategically eliminated to improve the lattice strength further.Furthermore,several typical structures are optimized to verify the effectiveness of the proposed method.The optimized results are quite encouraging since the heterogeneous lattice structures with optimized BO obtained by the strength-based concurrent method show a remarkably improved performance compared to traditional designs.
基金the U.S.Army Research Laboratory under Cooperative Agreement Award No.HQ0034-15-2-0007the U.S.National Science Foundation(DMR-2207965).
文摘Maraging steels are known for their exceptional strength but suffer from limited work hardening and ductility.Here,we report an intermittent printing strategy to tailor the microstructure and mechanical properties of maraging 250 steel via tuning the thermal history during wire-arc directed energy deposition.By introducing a dwell time between adjacent layers,the maraging 250 steel is cooled below the martensite start temperature,triggering thermally-driven martensitic transformation during the printing process.Thermal cycling during subsequent layer deposition results in the formation of reverted austenite which shows a refined microstructure and induces elemental segregation between martensite and reverted austenite.The Ni enrichment in the austenite promotes stabilization of the reverted austenite upon cooling to room temperature.The reverted austenite is metastable during deformation,leading to strain-induced martensitic transformation under loading.Specifically,a 3 min interlayer dwell time produces a maraging 250 steel with approximately 8% reverted austenite,resulting in improved work hardening via martensitic transformation induced plasticity during deformation.Meanwhile,the higher cooling rate and refined prior austenite grains lead to substantially refined martensitic grains(by approximately fivefold)together with an increased dislocation density.With 3 min interlayer dwell time,the yield strength of the printed maraging 250 steel increases from 836 MPa to 990 MPa,and the uniform elongation is doubled from 3.2% to 6.5%.This intermittent deposition strategy demonstrates the potential to tune the microstructure of maraging steels for achieving strength-ductility synergy by engineering the thermal history during additive manufacturing.
基金Supported by the Industrial Collaborative Innovation Project of Shanghai(Grant No XTCX-KJ-2022-2-11)the National Natural Science Foundation of China(Grant No52073176)。
文摘In this work,the GW63K(Mg-6.54Gd-3.93Y-0.41Zr,wt.%)alloy wire was utilized as the feedstock material and the thin-walled component was fabricated using wire-arc additive manufacturing technology(WAAM).The microstructural evolution during deposition and subsequent heat treatment was explained through multi-scale microstructural characterization techniques,and the impact of heat treatment on the strengthductility synergy of the deposited alloy was systematically compared.The results showed that the microstructure of the deposited sample was mainly composed of fine equiaxedα-Mg grains and Mg_(24)(Gd,Y)_(5) phase.The optimized solution heat treatment(450℃×2 h)had little effect on the grain size,but can effectively reduce the Mg_(24)(Gd,Y)_(5) eutectic phase on the grain boundary,resulting in a significant increase in elongation from 13.7% to 26.6%.After peak-aging treatment,the strength of the GW63K alloy increased to 370 MPa,which was significantly higher than the as-built state(267 MPa).The superior strength in this study is attributed to the refinement strengthening imparted by the fine microstructure inherited in the as-built GW63K alloy,as well as the precipitation strengthening due to the formation of dense β’precipitates with a pronounced plate-like aspect ratio.
基金supported by the National Natural Science Foundation of China(No.52222503)the Natural Science Foundation of Zhejiang Province(No.LD22E050003),China.
文摘The integrated valve-controlled cylinder combines various control and execution components in hydraulic transmission systems.Its precise control and rapid response characteristics make it widely used in mobile equipment for aerospace,robotics,and other engineering applications.Additive manufacturing provides high design freedom which can further enhance the power density of integrated valve-controlled cylinders.However,there is a lack of effective design methods to guide the additive manufacturing of valve-controlled cylinders for more efficient hydraulic energy transmission.This study accordingly introduces an energy-saving design method based on additive manufacturing for integrated valve-controlled cylinders.The method consists of two main parts:(1)redesigning the manifold block to eliminate leakage points and reduce energy losses through integrated design of the valve,cylinder,and piping;(2)establishing a pressure loss model to achieve energy savings through optimized flow channel design for bends with different parameters.Compared to traditional valve-controlled cylinders,the integrated valvecontrolled cylinder developed from our method reduces the weight by 31%,volume by 55%,and pressure loss in the main flow channel by over 30%.This indicates that the design achieves both lightweight construction and improved hydraulic transmission efficiency.This study provides theoretical guidance for the design of lightweight and energy-efficient valve-controlled cylinders,and may aid the design of similar hydraulic machinery.
基金Supported by National Key R&D Program of China(Grant Nos.2022YFB4603101,2022YFB3402200)Key Project of NSFC of China(Grant No.92271205)Sichuan Provincial Science and Technology Program and Fundamental Research Funds for the Central Universities of China(Grant No.D5000230049).
文摘The accurate characterization of anisotropy for additively manufactured materials is of vital importance for both highperformance structural design and printing processing optimization.To avoid the repetitive and redundant tensile testing on specimens prepared along diverse directions,this study proposes an instrumented indentation-based inverse identification method for the efficient characterization of additively manufactured materials.In the present work,a 3D finite element model of indentation test is first established for the printed material,for which an anisotropic material constitutive model is incorporated.We have demonstrated that the indentation responses are information-rich,and material anisotropy along different directions can be interpreted by a single indentation imprint.Subsequently,an inverse identification framework is built,in which an Euclidean error norm between simulated and experimental indentation responses is minimized via optimization algorithms such as the Globally Convergent Method of Moving Asymptotes(GCMMA).The developed method has been verified on diverse printed materials referring to either the indentation curve or the residual imprint,and the superiority of this latter over the former is confirmed by a better and faster convergence of inverse identification.Experimental validations on 3D printed materials(including stainless steel 316L,aluminum alloy AlSi10Mg,and titanium alloy TC4)reveal that the developed method is both accurate and reliable when compared with material constitutive behaviors obtained from uni-axial tensile tests,regardless of the degree of anisotropy among different materials.
基金support from the Australian Centre for Microscopy and Microanalysis(ACMM)as well as the Microscopy Australian node at the University of Sydneysupport from the Australian Research Council under DP23010228,from The University of Sydney under the Robinson Fellowship Scheme and from The University of Sydney Nano Institute under the Kickstarter Funding and Student Ambassador Scholarshipsupport from the National Natural Science Foundation of China(Grant number 52274381).
文摘High entropy alloys(HEAs),particularly CoCrNiFeMn system,have emerged as a transformative class of high-performance alloys due to their exceptional mechanical and functional properties.However,traditional manufacturing methods for HEAs are limited by inefficiencies and high costs,restricting their widespread applications.Additive manufacturing(AM),specifically laser powder bed fusion(LPBF),offers a promising alternative by enabling the fabrication of HEAs with unique microstructures and enhanced properties.This study investigates the thermal stability and mechanical performance of LPBF-printed CoCrNiFeMn HEA across a wide temperature range.The as-built LPBF HEA with a hierarchically heterogeneous microstructure,featured by columnar grains and ultrafine dislocation cellular structure,demonstrates exceptional thermal stability,with minimal hardness reduction and no apparent recrystallisation even after prolonged exposure to high temperatures(up to 1373 K),in stark contrast to the significant property degradation observed in conventionally processed HEAs.This stability is attributed to the unique dislocation cellular structures and the intrinsic thermal self-stabilizing effects induced by the LPBF process and the inhibition of recrystallisation due to the low stored energy and columnar grain morphology.The LPBF-fabricated HEA also exhibits outstanding strength-ductility synergy across a broad temperature spectrum,with cryogenic deformation enhancing both strength and ductility due to the activation of deformation twinning.At elevated temperatures,the alloy undergoes a slight reduction in strength but retains good ductility,except at 873 K,where a sharp decline in ductility is observed likely due to grain boundary decohesion and porosity-related crack initiation manifested by the cleavage fracture surface and the cracks at grain boundaries.These findings provide new insights into the temperature-dependent mechanical behavior of AM HEAs,highlight the critical role of dislocation cellular structures in achieving superior thermal and mechanical performance,and underscore the potential of additively manufactured HEAs with tailored microstructures for extreme environments.
基金the Brazilian agency CNPq for the financial support (grant number 303604/2020-4)
文摘Additive manufacturing(AM)of magnesium alloys is under intense research activity.Practical engineering applications demand the development of parts with adequate corrosion resistance for their safe use.It is imperative to understand the corrosion mechanisms of AM-processed Mg alloys,their correlation with processing parameters,and microstructural aspects.The present review explores this topic.A thorough assessment of the current literature on the AM methods of Mg alloys was undertaken,focusing on the main corrosion mechanisms,and their correlation with the microstructure,process defects,post-processing operations,and alloy composition.The opportunities to enhance the knowledge in this field are discussed.
基金support from the National Natural Science Foundation of China(No.U22B2065)the Science&Technology Fundamental Resources Investigation Program(No.2022FY101300)+1 种基金the Guangdong Basic and Applied Basic Research Foundation,China(No.2023A1515110926)Fundamental Research Funds for Central Universities(No.FRF-TP-25-082).
文摘An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix composites(MMCs).However,the corrosion be-havior of stainless steel and cast WC/W_(2)C varies inversely across different pH levels,and the phenomenon of pitting corrosion in LPBF MMCs under varying pH conditions remains insufficiently explored.In LPBF 420+5wt%WC/W_(2)C MMCs,pits form adjacent to cast WC/W_(2)C in acidic and neutral environments,attributed to the presence of chromium-rich carbides and galvanic coupling effects.The dis-solution of the reinforced particles facilitates pit nucleation in alkaline conditions.Notably,in-situ reaction layers exhibit superior corro-sion resistance to the matrix or the reinforced particles across all pH levels.The distinct corrosion mechanisms influence the pitting corro-sion behavior,with the corrosion ranking based on critical pitting potential being neutral>alkaline>acidic,contrasting the observed kin-etics of pit growth(alkaline>acidic>neutral).
基金supported by the National Natural Science Foundation of China financially(No.U21B2073)the Hunan Innovation Platform and Talent Plan(No.2022RC3033)Jiangxi Provincial Natural Science Foundation(No.20224BAB204019)
文摘The rapid development of the space field has presented elevated requirements for the performance of lightweight structures under high-temperature conditions,while the additive manufacturing of aluminum alloy for aerospace is faced with the problem of insufficient high temperature performance and cracking.To this end,we designed a novel Ti-and Ag-modified Al-Cu-Mg alloy using laser powder bed fusion,which showed a high mechanical performance with a tensile strength of 426 MPa at room temperature and 314 MPa at 200℃,greatly surpassing the majority of currently developed heat-resistant Al alloys.The micro structural observation demonstrated that Ti element facilitates the formation of coherent L1_(2)-Al_(3)Ti particles,thereby contributing to grain refinement,while Ag segregates to the grain boundaries and forms small Ag_(2)Al particles,which effectively enhance pinning effects.Additionally,Ag_(2)Al particles at high temperature significantly contribute to the superior performance in elevated temperature conditions of the designed alloy.Thus,this study has developed a novel alloy with Ag and Ti elements addition and clarified the crucial role of Ag and Ti elements in modifying additively manufactured Al alloy,laying a foundation for the application of lightweight heat-resistant components in the future.
文摘The effects of post heat treatment on the microstructure,aging kinetics,and room/elevated temperature mechanical properties of additively manufactured Inconel 718 superalloy were investigated.Scanning electron microscopy(SEM),electron backscattered diffraction(EBSD),and X-ray diffraction(XRD),as well as hardness,tensile,and creep testing were used for characterization.At temperatures higher than 1100°C,homogenization treatment resulted in the appearance of equiaxed grains by recrystallization and diminishing the dislocation density.The precipitation activation energy for the homogenized and aged condition was obtained as 203.2 kJ/mol,which was higher than the value of~160 kJ/mol for the as-built IN718 superalloy.Therefore,direct aging resulted in a faster aging response,which led to a significant improvement in tensile properties,as rationalized by the strengthening mechanisms.Direct aging treatment resulted in a higher elevated-temperature ultimate tensile strength(UTS)as well as the optimum creep life and the lowest minimum creep rate in comparison with other heat treatment routes,which were attributed to the presence of fine and uniformly dispersed strengthening precipitates in conjunction with the high dislocation density.
基金the State Key Laboratory of Robotics Technology and Systems Open Research Project(No.SKLRS-2022-KF-10)The author X.H.Huang is grateful for the financial support provided by the China Scholarship Council(No.202106230079)。
文摘NiTi alloys fabricated by laser powder bed fusion(LPBF)additive manufacturing technology not only address the compositional instability resulting from complex processes but also solve the challenges of difficult machining of intricate aerospace structures.However,there are very few reports on the wear behavior of LPBF-NiTi alloys.In the present work,the effects of microstructure and thermal treatment,including heat treatment and frictional heat,on the wear behavior of LPBF-NiTi alloy and 100Cr6 ball were analyzed through a series of tribological experiments with different sliding speeds.As the average sliding speed increases(0.079–0.216 m/s),the wear rate of the as-built and heat-treated samples tends to decrease in the range of 2.69×10^(-3)–0.97×10^(-3)mm^(3)/m.Although the heat-treated LPBF-NiTi alloy is 46%harder than the as-built alloy is,the latter has a higher toughness(505 MJ/m^(3))and greater transformation strain of SIM(0.097).This leads to a coupling effect of heat treatment and sliding speed on the wear resistance.In addition,the wear track morphologies under different sliding speeds are asymmetric due to the 24% greater acceleration at the far end from the motor and the 2.15 mm deviation between the maximum speed position and the geometric center of the track.The wear modes of the as-built and heat-treated samples included adhesive,abrasive and delamination wear.Moreover,the wear morphologies and dominant wear modes change with the frictionally caused heat release induced by the sliding speed.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning(KETEP)and the Ministry of Trade,Industry&Energy(MOTIE)of the Republic of Korea program(No.RS-2025-02603127,Innovation Research Center for Zero-carbon Fuel Gas Turbine Design,Manufacture,and Safety).
文摘Wire arc additive manufacturing(WAAM)presents a promising approach for fabricating medium-to-large austenitic stainless steel components,which are essential in industries like aerospace,pressure vessels,and heat exchangers.This research examines the mi-crostructural characteristics and tensile behaviour of SS308L manufactured via the gas metal arc welding-based WAAM(WAAM 308L)process.Tensile tests were conducted at room temperature(RT,25℃),300℃,and 600℃in as-built conditions.The microstructure con-sists primarily of austenite grains with retainedδ-ferrite phases distributed within the austenitic matrix.The ferrite fraction,in terms of fer-rite number(FN),ranged between 2.30 and 4.80 along the build direction from top to bottom.The ferrite fraction in the middle region is 3.60 FN.Tensile strength was higher in the horizontal oriented samples(WAAM 308L-H),while ductility was higher in the vertical ones.Tensile results show a gradual reduction in strength with increasing test temperature,in which significant dynamic strain aging(DSA)is observed at 600℃.The variation in serration behavior between the vertical and horizontal specimens may be attributed to microstructural differences arising from the build orientation.The yield strength(YS),ultimate tensile strength(UTS),and elongation(EL)of WAAM 308L at 600℃were(240±10)MPa,(442±16)MPa,and(54±2.00)%,respectively,in the horizontal orientation(WAAM 308L-H),and(248±9)MPa,(412±19)MPa,and(75±2.80)%,respectively,in the vertical orientation(WAAM 308L-V).Fracture surfaces revealed a transition from ductile dimple fracture at RT and 300℃to a mixed ductile-brittle failure with intergranular facets at 600℃.The research explores the applicability and constraints of WAAM-produced 308L stainless steel in high-temperature conditions,offering crucial in-sights for its use in thermally resistant structural and industrial components.
基金supported by National Key Research and Development Program(Grant No.2024YFB4609700)the National Natural Science Foundation of China(Grant No.52374365)。
文摘Wire arc additive manufacturing(WAAM)is one of the most promising approaches to manufacturing large and complex metal components owing to its low cost and high efficiency.However,pores and coarse columnar grains caused by thermal accumulation in WAAM significantly decrease the strength and increase the anisotropy,preventing the achievement of both high strength and isotropy.In this study,the strength and anisotropy of AlMg-Sc-Zr alloys were improved by regulating heat input.The results indicated that as the heat input increased from 60 to 99 J/mm,all the components had lower porosity(lower than 0.04%),the size of the Al_(3)(Sc_(1-x),Zr_(x))phases decreased,and the number density increased.The average grain size gradually decreased,and the grain morphologies transformed from coarse equiaxed grain(CEG)+fine equiaxed grain(FEG)to FEG owing to the increase in Al_(3)(Sc_(1-x),Zr_(x))phases with increasing heat input.After heat treatment at 325℃for 6 h,high-density dispersed Al_(3)Sc phases(<10 nm)precipitated.The alloy possessed the highest strength at 79 J/mm,ultimate tensile strength(UTS)of approximately 423±3 MPa,and in-plane anisotropy of approximately 4.3%.At a heat input of 99 J/mm,the in-plane anisotropy decreased to 1.2%and UTS reached 414±5 MPa.The reduction in the CEG prolonged the crack propagation path,which improved the UTS in the vertical direction and reduced the anisotropy.Theoretical calculations indicated that the main strengthening mechanisms were solid solution and precipitation strengthening.This study lays the theoretical foundations for WAAM-processed high-strength and isotropic Al alloy components.
