Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys(HEAs)is challenging.The present work investigates the in-situ synthesis of Fe_(49.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)interstitial...Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys(HEAs)is challenging.The present work investigates the in-situ synthesis of Fe_(49.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)interstitial solute-strengthened HEA containing 0.5 wt.%Nb(hereafter referred to as iHEA-Nb)using laser melt-ing deposition(LMD),aiming at simultaneously activating multiple strengthening mechanisms.The effect of Nb addition on the microstructure evolution,mechanical properties,strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated.Multiple levels of het-erogeneity were observed in the LMD-deposited microstructure,including different grain sizes,cellular subgrain structures,various carbide precipitates,as well as elemental segregation.The incorporation of Nb atoms with a large radius leads to lattice distortion,reduces the average grain size,and increases the types and fractions of carbides,aiding in promoting solid solution strengthening,grain boundary strengthening,and precipitation strengthening.Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa,respectively,while maintaining the elongation over 30%.Deformation twins were generated in the tensile deformed samples,contributing to the occurrence of twinning-induced plasticity.This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date,demon-strating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments.In addition,single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA,the micromechanical prop-erties of grains with different orientations were significantly enhanced.展开更多
To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys,ATI 718Plus alloys with varying Al contents(1,3,and 5 wt%)were fabricated using the laser additive manufacturing...To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys,ATI 718Plus alloys with varying Al contents(1,3,and 5 wt%)were fabricated using the laser additive manufacturing and the effects of Al content on the microstructure and mechanical properties were systematically analyzed.The experimental and CALPHAD simulation results show that with the increase in Al addition,the freezing range of the alloys was lowered,but this has a paradoxical effect on the susceptibility of the alloy to hot-tearing and solid-state cracking.The addition of Al increased theγ′and Laves phase volume fractions and suppressed the precipitation of theηphase.Simultaneously improvingγ/γ′lattice misfits effectively promoted the transformation ofγ′phase from spherical to cubic.The precipitation of NiAl phase in the 5 wt%Al-added alloy was determined,the formation mechanism of NiAl phase was analyzed,and the solidification sequence of the precipitated phase in the alloy was summarized.In addition,with the increase in Al addition,the microhardness of the alloy increased gradually,the tensile strength increased at first and then decreased,but the plasticity deteriorated seriously.The insights gained from this study offer valuable theoretical guidance for the strategic compositional design of additively manufactured Ni-based superalloys destined for deployment under extreme conditions.展开更多
Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infue...Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.展开更多
Laser additive manufacturing(LAM)technology can overcome the limitations of conventional manufacturing and facilitate the integrated design and production of geometrically complex metal parts,making it widely applicab...Laser additive manufacturing(LAM)technology can overcome the limitations of conventional manufacturing and facilitate the integrated design and production of geometrically complex metal parts,making it widely applicable in industrial sectors such as biomedical,aerospace,and molding.This review provides an overview of the frontiers of LAM techniques,focusing on the progress made by our research group over the past two decades.It begins with the introduction of four critical types of advanced LAM techniques:large-scale,multimaterial,field-assisted,and LAM/subtractive hybrid manufacturing.Subsequently,coaxial and off-axial in situ monitoring techniques based on sensor installation are presented,along with an exploration of their integration with high-speed cameras,photodiodes,and other photoelectric sensors within the LAM equipment.Representative innovative designs incorporating small-angle and support-free structures,nonassembled structures,and porous structures are then introduced.Finally,a comprehensive summary is provided,along with a discussion of the development trends of LAM from both manufacturing and design perspectives.展开更多
The urgent need for integrated molding and sintering across various industries has inspired the development of additive manu-facturing(AM)ceramics.Among the different AM technologies,direct laser additive manufacturin...The urgent need for integrated molding and sintering across various industries has inspired the development of additive manu-facturing(AM)ceramics.Among the different AM technologies,direct laser additive manufacturing(DLAM)stands out as a group of highly promising technology for flexibly manufacturing ceramics without molds and adhesives in a single step.Over the last decade,sig-nificant and encouraging progress has been accomplished in DLAM of high-performance ceramics,including Al_(2)O_(3),ZrO_(2),Al_(2)O_(3)/ZrO_(2),SiC,and others.However,high-performance ceramics fabricated by DLAM face challenges such as formation of pores and cracks and resultant low mechanical properties,hindering their practical application in high-end equipment.Further improvements are necessary be-fore they can be widely adopted.Methods such as field-assisted techniques and post-processing can be employed to address these chal-lenges,but a more systematic review is needed.This work aims to critically review the advancements in direct selective laser sintering/melting(SLS/SLM)and laser directed energy deposition(LDED)for various ceramic material systems.Additionally,it provides an overview of the current challenges,future research opportunities,and potential applications associated with DLAM of high-perform-ance ceramics.展开更多
The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures.In this study,the inf...The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures.In this study,the influence of aging temperatures(600,700 and 800°C)on microstructure and mechanical properties of titanium alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si was investigated.The results indicate that after solid solution treatment at 970°C followed by water quenching,the alloy mainly consists of coarsening lamellar a phase in martensite α' matrix.Aging at 600°C will not change the size of primary lamellar α phase but lead to huge amount of secondary a phases(α_(s))generating with very fine microstructure.By increasing the aging temperature,the number of α_(s) decreases but with coarsened microstructures.When aged at 800°C,the width of the asphase reaches 350 nm,almost 7 times wider than that aged at 600°C.The changing size of α_(s) obviously influences the property of the alloy.The fine α_(s) leads to high strength and microhardness but low plasticity,and specimen aged at 700°C with suitable assize has the best comprehensive properties.展开更多
Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many meth...Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.展开更多
TA2/TA15 graded structural material（GSM） was fabricated by the laser additive manufacturing（LAM） process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The ...TA2/TA15 graded structural material（GSM） was fabricated by the laser additive manufacturing（LAM） process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The results show that the TA2 part of exhibiting near-equiaxed grains was Widmanst？tten α-laths microstructure. The TA15 part containing large columnar grains was fine basket-weave microstructure. The graded zone was divided into four deposited layers with 3000 μm in thickness. As the distance from the TA2 part increases, the alloy element contents and the β phase volume fraction increase, the α phase volume fraction decreases and the microstructure shows the evolution from Widmanst？tten α-laths to basket-weave α-laths gradually. The micro-hardness increases from the TA2 part to the TA15 part due to the solid solution strengthening and grain boundary strengthening.展开更多
The effect of heat treatments on laser additive manufacturing(LAM)Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy(TC17)was studied aiming to optimize its microstructure and mechanical properties.The as-deposited sample exhibits...The effect of heat treatments on laser additive manufacturing(LAM)Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy(TC17)was studied aiming to optimize its microstructure and mechanical properties.The as-deposited sample exhibits features of a mixed priorβgrain structure consisting of equiaxed and columnar grains,intragranular ultra-fineαlaths and numerous continuous grain boundaryα(αGB).After being pre-annealed inα+βregion(840°C)and standard solution and aging treated,the continuousαGB becomes coarser and the precipitate free zone(PFZ)nearby theαGB transforms into a zone filled with ultra-fine secondaryα(αS)but no primaryα(αP).When pre-annealed in singleβregion(910°C),allαphases transform intoβphase and the alloying elements distribute uniformly near the grain boundary.DiscontinuousαGB and uniform mixture ofαP andαS near grain boundary form after subsequent solution and aging treatment.The two heat treatments can improve the tensile mechanical properties of LAM TC17to satisfy the aviation standard for TC17.展开更多
Important progresses in the study of laser additive manufacturing on metal matrix composites(MMCs)have been made.Recent efforts and advances in additive manufacturing on 5 types of MMCs are presented and reviewed.The ...Important progresses in the study of laser additive manufacturing on metal matrix composites(MMCs)have been made.Recent efforts and advances in additive manufacturing on 5 types of MMCs are presented and reviewed.The main focus is on the material design,the combination of reinforcement and the metal matrix,the synthesis principle during the manufacturing process,and the resulted microstructures as well as properties.Thereafter,the trend of development in future is forecasted,including:Formation mechanism and reinforcement principle of strengthening phase;Material and process design to actively achieve expected performance;Innovative structure design based on the special properties of laser AM MMCs;Simulation,monitoring and optimization in the process of laser AM MMCs.展开更多
Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,...Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,the aspect ratio of melting pools of single-layer specimens increases and the columnar-to-equiaxed transition occurs.The originalβgrain size andαplate width of TC11−1.0Nd are significantly reduced compared with those of pure TC11 specimens.It is proposed that the evenly distributed fine Nd_(2)O_(3) precipitates of about 1.51μm are formed preferentially during rapid solidification of melting pool,and they serve as heterogeneous nucleation particles to refine the microstructure in the subsequent solidification and solid-state phase transformation.Due to the multiple effects of Nd on the microstructure,the ultimate tensile strength of TC11−1.0Nd increases,while the yield strength,ductility and microhardness decrease compared with those of pure TC11.展开更多
Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of las...Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of laser additive repaired(LARed)specimen were investigated.The results show that,cellular substructures are observed in the laser deposited zone(LDZ),rather than the typicalαlaths morphology due to lack of enough subsequent thermal cycles.The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure.The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode.The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of11.7%is lower.展开更多
Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys ...Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.%were prepared by laser additive manufacturing to examine their formability,microstructure,and mechanical properties.For single-track cladding layers,the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability.The alloy,Ti−5.96Al−1.94V−3.54Nb(wt.%),exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder.The microstructures of the bulk samples contained similar columnar β-phase grains,regardless of Nb content.These grains grew epitaxially from the Ti substrate along the deposition direction,with basket-weaveα-phase laths within the columnar grains.Theα-phase size increased with increasing Nb contents,but its uniformity decreased.Along the deposition direction,the Vickers hardness increased from the substrate to the surface.The Ti−5.96Al−1.94V−3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between theα-phase size and its content among the designed alloys.展开更多
From the perspective of biomechanics and forming technology,Ti−Fe−Zr−Sn−Y eutectic alloy was designed using a“cluster-plus-glue-atom”model,and then the alloy was prepared by laser additive manufacturing(LAM)on pure ...From the perspective of biomechanics and forming technology,Ti−Fe−Zr−Sn−Y eutectic alloy was designed using a“cluster-plus-glue-atom”model,and then the alloy was prepared by laser additive manufacturing(LAM)on pure titanium substrate.The mechanical properties of the alloy were evaluated using micro-hardness and compression tester,and the elastic modulus was measured by nanoindenter.The results show that the alloy exhibits a high hardness of HV(788±10),a high strength of 2229 MPa,a failure strain of 14%,and a low elastic modulus of 87.5 GPa.The alloy also has good tribological,chemical,forming,and biological properties.The comprehensive performances of the Ti64.51Fe26.40Zr5.86Sn2.93Y0.30 alloy are superior to those of the Ti70.5Fe29.5 eutectic alloy and commercial Ti−6Al−4V alloy.All the above-mentioned qualities make the alloy a promising candidate as LAM biomaterial.展开更多
In this study,α+βTi-Al-V-Mo-Nb alloys with the addition of multiple elements that are suitable for laser additive manufacturing(LAM)were designed according to a Ti-6Al-4V cluster formula.This formula can be expresse...In this study,α+βTi-Al-V-Mo-Nb alloys with the addition of multiple elements that are suitable for laser additive manufacturing(LAM)were designed according to a Ti-6Al-4V cluster formula.This formula can be expressed as 12[Al-Ti12](AlTi2)+5[Al-Ti14]((Mo,V,Nb)2Ti),in which Mo and Nb were added into the alloys partially instead of V to give alloys with nominal compositions of Ti-6.01Al-3.13V-1.43Nb,Ti-5.97Al-2.33V-2.93Mo,and Ti-5.97Al-2.33V-2.20Mo-0.71Nb(wt.%).The microstructures and mechanical properties of the as-deposited and heat-treated samples prepared via LAM were examined.The sizes of theβcolumnar grains andαlaths in the Nb-containing samples are found to be larger than those of the Ti-6Al-4V alloy,whereas Mo-or Mo/Nb-added alloys contain finer grains.It indicates that Nb gives rise to coarsenedβcolumnar grains andαlaths,while Mo significantly refines them.Furthermore,the single addition of Nb improves the elongation,whereas the single addition of Mo enhances the strength of the alloys.The simultaneous addition of Mo/Nb significantly improves the comprehensive mechanical properties of the alloys,leading to the best properties with an ultimate tensile strength of 1,070 MPa,a yield strength of 1,004 MPa,an elongation of 9%,and micro-hardness of 355 HV.The fracture modes of all the alloys are ductile-brittle mixed fracture.展开更多
Metallic implants are widely used in internal fixation of bone fracture in surgical treatment.They are mainly used for providing mechanical support and stability during bone reunion,which usually takes a few months to...Metallic implants are widely used in internal fixation of bone fracture in surgical treatment.They are mainly used for providing mechanical support and stability during bone reunion,which usually takes a few months to complete.Conventional implants made of stainless steels,Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion resistance.Such metallic implants will remain permanently inside the body after implantation,and a second surgery after bone healing is needed because the long-term presence of implant will lead to various problems.An implant removal surgery not only incurs expenditure,but also risk and psychological burden.As a consequence,studies on the development of biodegradable implants,which would degrade and disappear in vivo after bone reunion is completed,have drawn researchers’attention.In this connection,Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density,inherent biocompatibility,biodegradability and mechanical properties close to those of bone.However,the high degradation rate of Mg-based implants in vivo is the biggest hurdle to overcome.Apart from materials selection,a fixation implant is ideally tailor-made in size and shape for an individual case,for best surgical outcomes.Therefore,laser additive manufacturing(LAM),with the advent of sophisticated laser systems and software,is an ideal process to solve these problems.In this paper,we reviewed the progress in LAM of biodegradable Mg-based alloys for biomedical applications.The effect of powder properties and laser processing parameter on the formability and quality was thoroughly discussed.The microstructure,phase constituents and metallurgical defects formed in the LAMed samples were delineated.The mechanical properties,corrosion resistance,biocompatibility and antibacterial properties of the LAMed samples were summarized and compared with samples fabricated by traditional processes.In addition,we have made some suggestions for advancing the knowledge in the LAM of Mg-based alloys for biomedical implants.展开更多
The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by ...The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.展开更多
Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,...Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,microstructural evolution,and mechanical properties of SMCs was established.The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing.Particularly,the involved thermal cycling,which encompassed multiple layers,strongly affected the processing quality of SMCs.Sshaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs.However,due to large thermal stress,microcracks that were perpendicular to the building direction formed within the SMCs.By employing the checkerboard filling(CBF)hatching mode,the thermal stress arising during SLM can be significantly reduced,thus preventing the evolution of interlayer microcracks.The compressive properties of fabricated SMCs can be tailored at a high compressive strength(~3031.5 MPa)and fracture strain(~24.8%)by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode.This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input,e.g.,laser power and scanning speed.展开更多
The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the s...The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.展开更多
The synchronously periodic re-melting of molten pool was firstly introduced in additive manufacturing to promote the epitaxial growth of columnar structure using a novel quasi-continuous-wave(QCW)laser.The epitaxial g...The synchronously periodic re-melting of molten pool was firstly introduced in additive manufacturing to promote the epitaxial growth of columnar structure using a novel quasi-continuous-wave(QCW)laser.The epitaxial growth of columnar structure was intensified and the single-crystal-like sample with highly oriented "zigzag" columnar grains was produced.The modified molten-pool geometry and the synchronously high-frequency re-melting of the molten pool contribute to the formation of singlecrystal-like structure.This work reports a new route to promote the continuously epitaxial growth of dendrites for fabrication of single-crystal-like sample.展开更多
基金WZ acknowledges the China Scholarship Council for her PhD grant(CSC No.201906250212)YP acknowledges financial support by Samenwerkingsverband Noord-Nederland(SNN)within the pro-gram“3D Print Kompas”+8 种基金JPO and JS acknowledge Fundação para a Ciência e a Tecnologia(FCT-MCTES)for its financial support via the project UID/00667/2020(UNIDEMI)JPO acknowledges fund-ing by national funds from FCT-Fundação para a Ciência e a Tecnologia,I.P.,in the scope of the projects NosLA/P/0037/2020,UIDP/50025/2020,and UIDB/50025/2020 of the Associate Labo-ratory Institute of Nanostructures,Nanomodelling and Nanofabri-cation–i3N.JS acknowledges the China Scholarship Council for her PhD grant(CSC No.201808320394)The authors acknowledge DESY(Hamburg,Germany),a member of the Helmholtz Associ-ation HGF,for the provision of experimental facilities.Beamtime was allocated for proposal I-20210899 ECThe research leading to this result has been supported by the project CALIPSOplus un-der Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020SF acknowledges fi-nancial support from the National Natural Science Foundation of China(No.52105318 and 52311530340)"Chunhui Plan"Col-laborative Research Project of the Ministry of Education,China(HZKY20220023)This research was carried out under project number S17024o in the framework of the Partnership Program of the Materials Innova-tion Institute M2i(www.m2i.nl)the Netherlands Organization for Scientific Research(www.nwo.nl).
文摘Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys(HEAs)is challenging.The present work investigates the in-situ synthesis of Fe_(49.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)interstitial solute-strengthened HEA containing 0.5 wt.%Nb(hereafter referred to as iHEA-Nb)using laser melt-ing deposition(LMD),aiming at simultaneously activating multiple strengthening mechanisms.The effect of Nb addition on the microstructure evolution,mechanical properties,strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated.Multiple levels of het-erogeneity were observed in the LMD-deposited microstructure,including different grain sizes,cellular subgrain structures,various carbide precipitates,as well as elemental segregation.The incorporation of Nb atoms with a large radius leads to lattice distortion,reduces the average grain size,and increases the types and fractions of carbides,aiding in promoting solid solution strengthening,grain boundary strengthening,and precipitation strengthening.Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa,respectively,while maintaining the elongation over 30%.Deformation twins were generated in the tensile deformed samples,contributing to the occurrence of twinning-induced plasticity.This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date,demon-strating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments.In addition,single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA,the micromechanical prop-erties of grains with different orientations were significantly enhanced.
基金supported by the National Science and Technology Major Project(J2019-VI-0004-0144).
文摘To clarify the mechanism of the role of Al element in the additive manufacturing of Ni-based superalloys,ATI 718Plus alloys with varying Al contents(1,3,and 5 wt%)were fabricated using the laser additive manufacturing and the effects of Al content on the microstructure and mechanical properties were systematically analyzed.The experimental and CALPHAD simulation results show that with the increase in Al addition,the freezing range of the alloys was lowered,but this has a paradoxical effect on the susceptibility of the alloy to hot-tearing and solid-state cracking.The addition of Al increased theγ′and Laves phase volume fractions and suppressed the precipitation of theηphase.Simultaneously improvingγ/γ′lattice misfits effectively promoted the transformation ofγ′phase from spherical to cubic.The precipitation of NiAl phase in the 5 wt%Al-added alloy was determined,the formation mechanism of NiAl phase was analyzed,and the solidification sequence of the precipitated phase in the alloy was summarized.In addition,with the increase in Al addition,the microhardness of the alloy increased gradually,the tensile strength increased at first and then decreased,but the plasticity deteriorated seriously.The insights gained from this study offer valuable theoretical guidance for the strategic compositional design of additively manufactured Ni-based superalloys destined for deployment under extreme conditions.
基金supported by the National Key R&D Program of China(Grant No.2022YFB4600300)the National Natural Science Foundation of China(No.U22A20189,52175364)the China Scholarship Council(Grant No.202206290134)。
文摘Nd-Fe-B permanent magnets play a crucial role in energy conversion and electronic devices.The essential magnetic properties of Nd-Fe-B magnets,particularly coercivity and remanent magnetization,are significantly infuenced by the phase characteristics and microstructure.In this work,Nd-Fe-B magnets were manufactured using vacuum induction melting(VIM),laser directed energy deposition(LDED)and laser powder bed fusion(LPBF)technologies.Themicrostructure evolution and phase selection of Nd-Fe-B magnets were then clarified in detail.The results indicated that the solidification velocity(V)and cooling rate(R)are key factors in the phase selection.In terms of the VIM-casting Nd-Fe-B magnet,a large volume fraction of theα-Fe soft magnetic phase(39.7 vol.%)and Nd2Fe17Bxmetastable phase(34.7 vol.%)areformed due to the low R(2.3×10-1?C s-1),whereas only a minor fraction of the Nd2Fe14B hard magnetic phase(5.15 vol.%)is presented.For the LDED-processed Nd-Fe-B deposit,although the Nd2Fe14B hard magnetic phase also had a low value(3.4 vol.%)as the values of V(<10-2m s-1)and R(5.06×103?C s-1)increased,part of theα-Fe soft magnetic phase(31.7vol.%)is suppressed,and a higher volume of Nd2Fe17Bxmetastable phases(47.5 vol.%)areformed.As a result,both the VIM-casting and LDED-processed Nd-Fe-B deposits exhibited poor magnetic properties.In contrast,employing the high values of V(>10-2m s-1)and R(1.45×106?C s-1)in the LPBF process resulted in the substantial formation of the Nd2Fe14B hard magnetic phase(55.8 vol.%)directly from the liquid,while theα-Fe soft magnetic phase and Nd2Fe17Bxmetastable phase precipitation are suppressed in the LPBF-processed Nd-Fe-B magnet.Additionally,crystallographic texture analysis reveals that the LPBF-processedNd-Fe-B magnets exhibit isotropic magnetic characteristics.Consequently,the LPBF-processed Nd-Fe-B deposit,exhibiting a coercivity of 656 k A m-1,remanence of 0.79 T and maximum energy product of 71.5 k J m-3,achieved an acceptable magnetic performance,comparable to other additive manufacturing processed Nd-Fe-B magnets from MQP(Nd-lean)Nd-Fe-Bpowder.
基金supported by National Key R&D Program of China(Grant No.2022YFF0606000)National Natural Science Foundation of China(Grant No.U2001218)Guangdong Basic and Applied Basic Research Foundation(Grant No.2022B1515020064).
文摘Laser additive manufacturing(LAM)technology can overcome the limitations of conventional manufacturing and facilitate the integrated design and production of geometrically complex metal parts,making it widely applicable in industrial sectors such as biomedical,aerospace,and molding.This review provides an overview of the frontiers of LAM techniques,focusing on the progress made by our research group over the past two decades.It begins with the introduction of four critical types of advanced LAM techniques:large-scale,multimaterial,field-assisted,and LAM/subtractive hybrid manufacturing.Subsequently,coaxial and off-axial in situ monitoring techniques based on sensor installation are presented,along with an exploration of their integration with high-speed cameras,photodiodes,and other photoelectric sensors within the LAM equipment.Representative innovative designs incorporating small-angle and support-free structures,nonassembled structures,and porous structures are then introduced.Finally,a comprehensive summary is provided,along with a discussion of the development trends of LAM from both manufacturing and design perspectives.
基金the sponsorship of the following fund projects:the Guangdong Basic and Applied Basic Research Foundation,China(No.2023A1515110578)the Guangzhou Basic and Applied Basic Research Project,China(No.2024A04J00725)the Guangdong Academy of Sciences Project of Science and Technology Development,China(Nos.2022GDASZH-2022010107 and 2022GDASZH-2022010108).Dr.Zhao would particularly like to thank his wife,M.S.Guo,for her help with the language of the manuscript and for the encouragement of their newborn baby.
文摘The urgent need for integrated molding and sintering across various industries has inspired the development of additive manu-facturing(AM)ceramics.Among the different AM technologies,direct laser additive manufacturing(DLAM)stands out as a group of highly promising technology for flexibly manufacturing ceramics without molds and adhesives in a single step.Over the last decade,sig-nificant and encouraging progress has been accomplished in DLAM of high-performance ceramics,including Al_(2)O_(3),ZrO_(2),Al_(2)O_(3)/ZrO_(2),SiC,and others.However,high-performance ceramics fabricated by DLAM face challenges such as formation of pores and cracks and resultant low mechanical properties,hindering their practical application in high-end equipment.Further improvements are necessary be-fore they can be widely adopted.Methods such as field-assisted techniques and post-processing can be employed to address these chal-lenges,but a more systematic review is needed.This work aims to critically review the advancements in direct selective laser sintering/melting(SLS/SLM)and laser directed energy deposition(LDED)for various ceramic material systems.Additionally,it provides an overview of the current challenges,future research opportunities,and potential applications associated with DLAM of high-perform-ance ceramics.
基金financially supported by the Beijing Municipal Science and Technology Project(No.Z171100000817002)the Young Elite Scientist Sponsorship Program by CAST and the National Key Research and Development Program of China(No.2016YFB1100401)。
文摘The solid solution and aging treatment for conventional manufacturing processes might not be suitable for laser additive manufactured titanium alloys due to the different lamellar microstructures.In this study,the influence of aging temperatures(600,700 and 800°C)on microstructure and mechanical properties of titanium alloy Ti-6Al-2V-1.5Mo-0.5Zr-0.3Si was investigated.The results indicate that after solid solution treatment at 970°C followed by water quenching,the alloy mainly consists of coarsening lamellar a phase in martensite α' matrix.Aging at 600°C will not change the size of primary lamellar α phase but lead to huge amount of secondary a phases(α_(s))generating with very fine microstructure.By increasing the aging temperature,the number of α_(s) decreases but with coarsened microstructures.When aged at 800°C,the width of the asphase reaches 350 nm,almost 7 times wider than that aged at 600°C.The changing size of α_(s) obviously influences the property of the alloy.The fine α_(s) leads to high strength and microhardness but low plasticity,and specimen aged at 700°C with suitable assize has the best comprehensive properties.
基金Project(51771051)supported by the National Natural Science Foundation of ChinaProject(2021-MS-102)supported by the Natural Science Foundation of Liaoning Province,China+1 种基金Project(N2105021)supported by the Fundamental Research Funds for the Central Universities,ChinaProject(230032)supported by the National Training Program of Innovation and Entrepreneurship for Undergraduates,China。
文摘Large residual stresses would be generated in the laser additive manufactured(LAMed)structures after processing rapid and intense heating and cooling cycles with bad mechanical properties.Scholars have tried many methods to decrease the residual stress to prevent the structures from being broken and improve the mechanical properties.In this study,residual stress and mechanical properties of LAMed structures are analyzed,and the advanced measuring method,laser ultrasonic technique,is used to detect the residual stresses accumulated in the samples in time.The results show that when the solution temperature is less than T_(β)(992℃),the residual stress increases gradually with the increase of solution temperature,and when the temperature is more than T_(β)(992℃),Widmanstätten structure will significantly reduce the residual stress;the mechanical properties of the specimen decrease with the increase of the solution temperature,and the different cooling methods do not have much effect on the elastic properties of the specimen.Considering the residual stress and mechanical properties,the HT1 system used in this paper is the best.This study is of great significance for the reasonable suppression of residual stress and the regulation of mechanical properties of TC4 titanium alloy fabricated by laser additive manufacturing.
基金Project(2010CB731705)supported by the National Basic Research Program of China
文摘TA2/TA15 graded structural material（GSM） was fabricated by the laser additive manufacturing（LAM） process. The chemical composition, microstructure and micro-hardness of the as-deposited GSM were investigated. The results show that the TA2 part of exhibiting near-equiaxed grains was Widmanst？tten α-laths microstructure. The TA15 part containing large columnar grains was fine basket-weave microstructure. The graded zone was divided into four deposited layers with 3000 μm in thickness. As the distance from the TA2 part increases, the alloy element contents and the β phase volume fraction increase, the α phase volume fraction decreases and the microstructure shows the evolution from Widmanst？tten α-laths to basket-weave α-laths gradually. The micro-hardness increases from the TA2 part to the TA15 part due to the solid solution strengthening and grain boundary strengthening.
基金Project(BX201600010) supported by the National Postdoctoral Program for Innovative Talents of ChinaProject(2015QNRC001) supported by the Young Elite Scientist Sponsorship Program of China
文摘The effect of heat treatments on laser additive manufacturing(LAM)Ti-5Al-2Sn-2Zr-4Mo-4Cr titanium alloy(TC17)was studied aiming to optimize its microstructure and mechanical properties.The as-deposited sample exhibits features of a mixed priorβgrain structure consisting of equiaxed and columnar grains,intragranular ultra-fineαlaths and numerous continuous grain boundaryα(αGB).After being pre-annealed inα+βregion(840°C)and standard solution and aging treated,the continuousαGB becomes coarser and the precipitate free zone(PFZ)nearby theαGB transforms into a zone filled with ultra-fine secondaryα(αS)but no primaryα(αP).When pre-annealed in singleβregion(910°C),allαphases transform intoβphase and the alloying elements distribute uniformly near the grain boundary.DiscontinuousαGB and uniform mixture ofαP andαS near grain boundary form after subsequent solution and aging treatment.The two heat treatments can improve the tensile mechanical properties of LAM TC17to satisfy the aviation standard for TC17.
基金Supported by National Natural Science Foundation of China(Grant Nos.51775525,51605456)Beijing Nova Program(Grant No.Z201100006820094)from Beijing Municipal Science&Technology Commission.
文摘Important progresses in the study of laser additive manufacturing on metal matrix composites(MMCs)have been made.Recent efforts and advances in additive manufacturing on 5 types of MMCs are presented and reviewed.The main focus is on the material design,the combination of reinforcement and the metal matrix,the synthesis principle during the manufacturing process,and the resulted microstructures as well as properties.Thereafter,the trend of development in future is forecasted,including:Formation mechanism and reinforcement principle of strengthening phase;Material and process design to actively achieve expected performance;Innovative structure design based on the special properties of laser AM MMCs;Simulation,monitoring and optimization in the process of laser AM MMCs.
基金financially supported by the National Natural Science Foundation of China(Nos.51801009,52071005)the Youth Talent Support Program of Beihang University,China(No.YWF-21-BJ-J-1143)Shuangyiliu Fund of Beihang University,China(No.030810)。
文摘Single-layer and multilayer laser additive manufacturing(LAM)for TC11 alloy with different Nd additions was conducted and the effect of Nd addition on microstructure and properties was studied.With the addition of Nd,the aspect ratio of melting pools of single-layer specimens increases and the columnar-to-equiaxed transition occurs.The originalβgrain size andαplate width of TC11−1.0Nd are significantly reduced compared with those of pure TC11 specimens.It is proposed that the evenly distributed fine Nd_(2)O_(3) precipitates of about 1.51μm are formed preferentially during rapid solidification of melting pool,and they serve as heterogeneous nucleation particles to refine the microstructure in the subsequent solidification and solid-state phase transformation.Due to the multiple effects of Nd on the microstructure,the ultimate tensile strength of TC11−1.0Nd increases,while the yield strength,ductility and microhardness decrease compared with those of pure TC11.
基金Project(2016YFB11000100)supported by the National Key Technologies R&D Program,ChinaProject(KP201611)supported by Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject(51475380)supported by the National Natural Science Foundation of China
文摘Laser additive manufacturing technology with powder feeding was employed to repair wrought Ti17titanium alloy with small surface defects.The microstructure,micro-hardness and room temperature tensile properties of laser additive repaired(LARed)specimen were investigated.The results show that,cellular substructures are observed in the laser deposited zone(LDZ),rather than the typicalαlaths morphology due to lack of enough subsequent thermal cycles.The cellular substructures lead to lower micro-hardness in the LDZ compared with the wrought substrate zone which consists of duplex microstructure.The tensile test results indicate that the tensile deformation process of the LARed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and fracture in the laser repaired zone with a mixed dimple and cleavage mode.The tensile strength of the LARed specimen is slightly higher than that of the wrought specimen and the elongation of11.7%is lower.
基金the National Key Research and Development Program of China(No.2016YFB1100103)。
文摘Ti−Al−V−Nb alloys with the cluster formula,12[Al−Ti_(12)](AlTi_(2))+5[Al−Ti1_(4)](V,Nb)2Ti,were designed by replacing V with Nb based on the Ti−6Al−4V alloy.Single-track cladding layers and bulk samples of the alloys with Nb contents ranging from 0 to 6.96 wt.%were prepared by laser additive manufacturing to examine their formability,microstructure,and mechanical properties.For single-track cladding layers,the addition of Nb increased the surface roughness slightly and decreased the molten pool height to improve its spreadability.The alloy,Ti−5.96Al−1.94V−3.54Nb(wt.%),exhibited better geometrical accuracy than the other alloys because its molten pool height was consistent with the spread layer thickness of the powder.The microstructures of the bulk samples contained similar columnar β-phase grains,regardless of Nb content.These grains grew epitaxially from the Ti substrate along the deposition direction,with basket-weaveα-phase laths within the columnar grains.Theα-phase size increased with increasing Nb contents,but its uniformity decreased.Along the deposition direction,the Vickers hardness increased from the substrate to the surface.The Ti−5.96Al−1.94V−3.54Nb alloy exhibited the highest Vickers hardness regardless of deposition position because of the optimal matching relationship between theα-phase size and its content among the designed alloys.
基金Project(51371041)supported by the National Natural Science Foundation of China。
文摘From the perspective of biomechanics and forming technology,Ti−Fe−Zr−Sn−Y eutectic alloy was designed using a“cluster-plus-glue-atom”model,and then the alloy was prepared by laser additive manufacturing(LAM)on pure titanium substrate.The mechanical properties of the alloy were evaluated using micro-hardness and compression tester,and the elastic modulus was measured by nanoindenter.The results show that the alloy exhibits a high hardness of HV(788±10),a high strength of 2229 MPa,a failure strain of 14%,and a low elastic modulus of 87.5 GPa.The alloy also has good tribological,chemical,forming,and biological properties.The comprehensive performances of the Ti64.51Fe26.40Zr5.86Sn2.93Y0.30 alloy are superior to those of the Ti70.5Fe29.5 eutectic alloy and commercial Ti−6Al−4V alloy.All the above-mentioned qualities make the alloy a promising candidate as LAM biomaterial.
基金the National Key Research and Development Program of China(No.2016YFB1100103)the Key Discipline and Major Project of Dalian Science and Technology Innovation Foundation(No.2020JJ25CY004)。
文摘In this study,α+βTi-Al-V-Mo-Nb alloys with the addition of multiple elements that are suitable for laser additive manufacturing(LAM)were designed according to a Ti-6Al-4V cluster formula.This formula can be expressed as 12[Al-Ti12](AlTi2)+5[Al-Ti14]((Mo,V,Nb)2Ti),in which Mo and Nb were added into the alloys partially instead of V to give alloys with nominal compositions of Ti-6.01Al-3.13V-1.43Nb,Ti-5.97Al-2.33V-2.93Mo,and Ti-5.97Al-2.33V-2.20Mo-0.71Nb(wt.%).The microstructures and mechanical properties of the as-deposited and heat-treated samples prepared via LAM were examined.The sizes of theβcolumnar grains andαlaths in the Nb-containing samples are found to be larger than those of the Ti-6Al-4V alloy,whereas Mo-or Mo/Nb-added alloys contain finer grains.It indicates that Nb gives rise to coarsenedβcolumnar grains andαlaths,while Mo significantly refines them.Furthermore,the single addition of Nb improves the elongation,whereas the single addition of Mo enhances the strength of the alloys.The simultaneous addition of Mo/Nb significantly improves the comprehensive mechanical properties of the alloys,leading to the best properties with an ultimate tensile strength of 1,070 MPa,a yield strength of 1,004 MPa,an elongation of 9%,and micro-hardness of 355 HV.The fracture modes of all the alloys are ductile-brittle mixed fracture.
基金fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region(152131/18E).
文摘Metallic implants are widely used in internal fixation of bone fracture in surgical treatment.They are mainly used for providing mechanical support and stability during bone reunion,which usually takes a few months to complete.Conventional implants made of stainless steels,Ti-based alloys and CoCrMo alloys have been widely used for orthopedic reconstruction due to their high strength and high corrosion resistance.Such metallic implants will remain permanently inside the body after implantation,and a second surgery after bone healing is needed because the long-term presence of implant will lead to various problems.An implant removal surgery not only incurs expenditure,but also risk and psychological burden.As a consequence,studies on the development of biodegradable implants,which would degrade and disappear in vivo after bone reunion is completed,have drawn researchers’attention.In this connection,Mg-based alloys have shown great potentials as promising implant materials mainly due to their low density,inherent biocompatibility,biodegradability and mechanical properties close to those of bone.However,the high degradation rate of Mg-based implants in vivo is the biggest hurdle to overcome.Apart from materials selection,a fixation implant is ideally tailor-made in size and shape for an individual case,for best surgical outcomes.Therefore,laser additive manufacturing(LAM),with the advent of sophisticated laser systems and software,is an ideal process to solve these problems.In this paper,we reviewed the progress in LAM of biodegradable Mg-based alloys for biomedical applications.The effect of powder properties and laser processing parameter on the formability and quality was thoroughly discussed.The microstructure,phase constituents and metallurgical defects formed in the LAMed samples were delineated.The mechanical properties,corrosion resistance,biocompatibility and antibacterial properties of the LAMed samples were summarized and compared with samples fabricated by traditional processes.In addition,we have made some suggestions for advancing the knowledge in the LAM of Mg-based alloys for biomedical implants.
基金Projects(51105311,51475380)supported by the National Natural Science Foundation of ChinaProject(2013AA031103)supported by the National High-Tech Research and Development Program of China
文摘The microstructure, microhardness and tensile properties of laser additive manufactured (LAM) Ti?5Al?2Sn?2Zr?4Mo?4Cr alloy were investigated. The result shows that the microstructure evolution is strongly affected by the thermal history of LAM process. Primary α (αp) with different morphologies, secondary α (αs) and martensite α' can be observed at different positions of the LAMed specimen. Annealing treatment can promote the precipitation of rib-like α phase or acicular α phase. As a result, it can increase or decrease the microhardness. The as-deposited L-direction and T-direction specimens contain the same phase constituent with different morphologies. The tensile properties of the as-deposited LAMed specimens are characterized of anisotropy. The L-direction specimen shows the character of low strength but high ductility when compared with the T-direction specimen. After annealing treatment, the strength of L-direction specimen increases significantly while the ductility reduces. The strength of the annealed T-direction specimen changes little, however, the ductility reduces nearly by 50%.
基金the National Key Research and Development Program“Additive Manufacturing and Laser Manufacturing”(No.2016YFB1100101)the National Natural Science Foundation of China(No.51735005)+3 种基金the Basic Strengthening Program of Science and Technology(No.2019-JCJQ-JJ-331)the 5th Jiangsu Province 333 High Level Talents Training Project,China(No.BRA2019048)the 15th Batch of“Six Talents Peaks”Innovative Talents Team Program“Laser Precise Additive Manufacturing of Structure-Performance Integrated Lightweight Alloy Components”(No.TD-GDZB-001)and the 2017 Excellent Scientific and Technological Innovation Teams of Universities in Jiangsu“Laser Additive Manufacturing Technologies for Metallic Components”funded by Jiangsu Provincial Department of Education of China(No.51921003).Konrad Kosiba acknowledges the support from DFG under Grant No.KO 5771/1-1.
文摘Steel matrix composites(SMCs)reinforced with WC particles were fabricated via selective laser melting(SLM)by employing various laser scan strategies.A detailed relationship between the SLM strategies,defect formation,microstructural evolution,and mechanical properties of SMCs was established.The laser scan strategies can be manipulated to deliberately alter the thermal history of SMC during SLM processing.Particularly,the involved thermal cycling,which encompassed multiple layers,strongly affected the processing quality of SMCs.Sshaped scan sequence combined with interlayer offset and orthogonal stagger mode can effectively eliminate the metallurgical defects and retained austenite within the produced SMCs.However,due to large thermal stress,microcracks that were perpendicular to the building direction formed within the SMCs.By employing the checkerboard filling(CBF)hatching mode,the thermal stress arising during SLM can be significantly reduced,thus preventing the evolution of interlayer microcracks.The compressive properties of fabricated SMCs can be tailored at a high compressive strength(~3031.5 MPa)and fracture strain(~24.8%)by adopting the CBF hatching mode combined with the optimized scan sequence and stagger mode.This study demonstrates great feasibility in tuning the mechanical properties of SLM-fabricated SMCs without varying the set energy input,e.g.,laser power and scanning speed.
基金The authors are grateful for the financial supports from the project of Ministry of Industry and Information Technology of China(No.2019-00899-1-1)the Natural Science Foundation of Shaanxi Province,China(No.2021JM-060)Fundamental Research Funds for the Central Universities,China(No.3102019QD0409).
文摘The electrochemical dissolution and passivation of laser additive manufactured Ti6Al4V were investigated through Tafel polarization,potentiostatic polarization and AC impedance measurements.The results show that the solution treatment−aging(STA)process aggravates the element micro-segregation compared to the annealing process,leading to varied Al and V contents of the phases from different samples.It is proven that either Al-rich or V-rich condition can highly affect the electrochemical dissolution behaviors due to thermodynamical instability caused by element segregation.The dissolution rate in the metastable passivation process is controlled by the stability of the produced film that is affected by phases distribution,especially the difficult-to-dissolve phase.And then,the dissolution rate of the phases in the transpassivation region is consistent with the rank in the activation process because the dense film is not capable of being produced.Compared to the annealed sample,the higher dissolution rate of the STA sample is beneficial to the electrochemical machining(ECM)of Ti6Al4V.
基金supported financially by the National Natural Science Foundation of China(No.51875190)the Natural Science Foundation of Hunan Province(No.2020JJ5075)+3 种基金the Guangdong Basic and Applied Basic Research Foundation(No.2019A1515110274)the China Postdoctoral Science Foundation(No.2018M642973)the Science and Technology Planning Project of Hunan Province(No.2016JC2006)State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body at Hunan University(No.31875004)。
文摘The synchronously periodic re-melting of molten pool was firstly introduced in additive manufacturing to promote the epitaxial growth of columnar structure using a novel quasi-continuous-wave(QCW)laser.The epitaxial growth of columnar structure was intensified and the single-crystal-like sample with highly oriented "zigzag" columnar grains was produced.The modified molten-pool geometry and the synchronously high-frequency re-melting of the molten pool contribute to the formation of singlecrystal-like structure.This work reports a new route to promote the continuously epitaxial growth of dendrites for fabrication of single-crystal-like sample.
