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
NiTiCu thin walls were produced by twin-wire arc additive manufacturing(T-WAAM)using commercial NiTi and Cu wires as the feedstock materials.This approach aims to solve the problems typically associated with large pha...NiTiCu thin walls were produced by twin-wire arc additive manufacturing(T-WAAM)using commercial NiTi and Cu wires as the feedstock materials.This approach aims to solve the problems typically associated with large phase transformation hysteresis in NiTi shape memory alloys.The microstructure,mechanical properties,and phase transformation behavior of the as-deposited NiTiCu alloy were comprehensively examined.The results re-vealed that the as-deposited NiTiCu alloy was well-formed,with its microstructure showed columnar,equiaxed,and needle-like grains,depending on the location within the deposited walls.The microhardness gradually in-creased from the first to the third layer.The Cu content was 20.80 at%,and Cu-based precipitates were formed in the as-deposited NiTiCu.The volume fractions and lattice parameters of the matrix and precipitates in the as-deposited NiTiCu material were analyzed using high-energy synchrotron X-ray diffraction.The martensitic phase was identified as a B19 crystal structure,and the as-deposited NiTiCu underwent a one-step B2-B19 phase transformation.The tensile strength and fracture strain were approximately 232 MPa and 3.72%,respectively.In particular,the addition of Cu narrowed the phase transformation hysteresis of the as-deposited NiTiCu alloy from 24.4 to 7.1◦C compared with conventional binary NiTi alloys.This study expands the potential of T-WAAM in modifying the phase transformation behavior of NiTi-based ternary alloys.展开更多
Dissimilar welding of NiTi and stainless steel(SS)for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds(IMCs)that are formed in the weld zone.In this work,Ni and Nb...Dissimilar welding of NiTi and stainless steel(SS)for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds(IMCs)that are formed in the weld zone.In this work,Ni and Nb interlayers were applied for the resistance spot welding(RSW)of NiTi and SS to replace the harmful Fe_(2)Ti phase and to restrict the mixing of dissimilar molten metals,respectively.Microstructural evolution and mechanical properties of the joints were investigated.It was shown that a conventional weld nugget was created in the absence of any interlayer in the welded joint suffering from traversed cracks due to the formation of brittle IMCs network in the fusion zone(FZ).By the addition of Ni from the interlayer,Fe_(2)Ti dominated weld nugget was efficaciously replaced by Ni_(3)Ti phase;however,the presence of the large pore and cracks reduced the effective joining area.The use of a Nb interlayer resulted in a fundamentally different joint,in which FZs at NiTi and SS sides separated by the unmolten Nb would suppress the mixing of dissimilar molten metals.Nb-containing eutectic structures with low brittleness formed at the interfaces,contributing to the enhancement of joint strength(increased by 38%on fracture load and 460%on energy absorption).A high-melting-point interlayer showed great potential to realize a reliable and high-performing RSWed NiTi-SS joint.展开更多
The use of non-destructive evaluation(NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/...The use of non-destructive evaluation(NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/structure. Among the several NDE techniques available, electrical conductivity measurements using eddy currents attract great attention owing to its simplicity and reliability. In this work, the electrical conductivity profiles of friction stir processed Ti6Al4 V, Cu, Pb, S355 steel and gas tungsten arc welded AISI 304 stainless steel were determined through eddy currents and four-point probe. In parallel, hardness measurements were also performed. The profiles matched well with the optical macrographs of the materials: while entering in the processed region a variation in both profiles was always observed. One particular advantage of electrical conductivity profiles over hardness was evident: it provides a better resolution of the microstructural alterations in the processed materials. Moreover, when thermomechanical processing induces microstructural changes that modify the magnetic properties of a material,eddy currents testing can be used to qualitatively determine the phase fraction in a given region of the material. A qualitative relation between electrical conductivity measurements and hardness is observed.展开更多
Immobilization devices may be a valuable aid to ensure the improved effectiveness of radiotherapy treatments where constraining the movements of specific anatomical segments is crucial. This need is also present in ot...Immobilization devices may be a valuable aid to ensure the improved effectiveness of radiotherapy treatments where constraining the movements of specific anatomical segments is crucial. This need is also present in other situations, specifically when the superposition of various medical images is required for fine identification and characterization of some pathologies. Because of their structural characteristics, existing head immobilization systems may be claustrophobic and very uncomfortable for patients, during both the modeling and usage stages. Because of this, it is important to minimize all the discomforts related to the mask to alleviate patients’ distress and to simultaneously guarantee and maximize the restraint effectiveness of the mask. In the present work, various head immobilization mask models are proposed based on geometrical information extracted from computerized tomography images and from 3D laser scanning point clouds. These models also consider the corresponding connection to a radiotherapy table, as this connection is easily altered to accommodate various manufacturers’ solutions. A set of materials used in the radiotherapy field is considered to allow the assessment of the stiffness and strength of the masks when submitted to typical loadings.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 National Natural Science Founda-tion of China(Grant No.52175292)Science and Technology Project of Sichuan Province(Grant Nos.23NSFJQ0064,2022YFQ0058)+2 种基金Guangdong Basic and Applied Basic Research Foundation(Grant No.2021B1515140048)JPO and JS acknowledge the funding by na-tional funds from Fundação para a Ciência e a Tecnologia(FCT),I.P.,within the scope of projects LA/P/0037/2020,UIDP/50025/2020,and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostruc-tures,Nanomodelling,and Nanofabrication-i3NDESY(Hamburg,Germany),a member of the Helmholtz Associa-tion HGF,for providing the experimental facilities.Part of this study was conducted at PETRA III.The research leading to this result was sup-ported by project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020.
文摘NiTiCu thin walls were produced by twin-wire arc additive manufacturing(T-WAAM)using commercial NiTi and Cu wires as the feedstock materials.This approach aims to solve the problems typically associated with large phase transformation hysteresis in NiTi shape memory alloys.The microstructure,mechanical properties,and phase transformation behavior of the as-deposited NiTiCu alloy were comprehensively examined.The results re-vealed that the as-deposited NiTiCu alloy was well-formed,with its microstructure showed columnar,equiaxed,and needle-like grains,depending on the location within the deposited walls.The microhardness gradually in-creased from the first to the third layer.The Cu content was 20.80 at%,and Cu-based precipitates were formed in the as-deposited NiTiCu.The volume fractions and lattice parameters of the matrix and precipitates in the as-deposited NiTiCu material were analyzed using high-energy synchrotron X-ray diffraction.The martensitic phase was identified as a B19 crystal structure,and the as-deposited NiTiCu underwent a one-step B2-B19 phase transformation.The tensile strength and fracture strain were approximately 232 MPa and 3.72%,respectively.In particular,the addition of Cu narrowed the phase transformation hysteresis of the as-deposited NiTiCu alloy from 24.4 to 7.1◦C compared with conventional binary NiTi alloys.This study expands the potential of T-WAAM in modifying the phase transformation behavior of NiTi-based ternary alloys.
基金Natural Sciences and Engineering Research Council of Canada(NSERC)Canada Research Chairs(CRC)+1 种基金K.Z.acknowledges support from China Scholarship Council(CSC)J.P.O.acknowledges funding by national funds from FCT-Fundação para a Ciência e a Tecnologia,I.P.,in the scope of the projects LA/P/0037/2020,UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures,Nanomodelling and Nanofabrication–i3N.
文摘Dissimilar welding of NiTi and stainless steel(SS)for multifunctional device fabrication is challenging due to the brittle nature of intermetallic compounds(IMCs)that are formed in the weld zone.In this work,Ni and Nb interlayers were applied for the resistance spot welding(RSW)of NiTi and SS to replace the harmful Fe_(2)Ti phase and to restrict the mixing of dissimilar molten metals,respectively.Microstructural evolution and mechanical properties of the joints were investigated.It was shown that a conventional weld nugget was created in the absence of any interlayer in the welded joint suffering from traversed cracks due to the formation of brittle IMCs network in the fusion zone(FZ).By the addition of Ni from the interlayer,Fe_(2)Ti dominated weld nugget was efficaciously replaced by Ni_(3)Ti phase;however,the presence of the large pore and cracks reduced the effective joining area.The use of a Nb interlayer resulted in a fundamentally different joint,in which FZs at NiTi and SS sides separated by the unmolten Nb would suppress the mixing of dissimilar molten metals.Nb-containing eutectic structures with low brittleness formed at the interfaces,contributing to the enhancement of joint strength(increased by 38%on fracture load and 460%on energy absorption).A high-melting-point interlayer showed great potential to realize a reliable and high-performing RSWed NiTi-SS joint.
基金the Portuguese Fundacao para a Ciência e a Tecnologia (FCT, I.P.) for its financial support via the project PEst-OE/EME/UI0667/2014Project Hi2TRUST, (Refa3335), supported by Fundo Europeu de Desenvolvimento Regional (FEDER)Programa Operacional Regional de Lisboa (Lisb@2020 and Portugal2020)
文摘The use of non-destructive evaluation(NDE) techniques for assessing microstructural changes in processed materials is of particular importance as it can be used to assess, qualitatively, the integrity of any material/structure. Among the several NDE techniques available, electrical conductivity measurements using eddy currents attract great attention owing to its simplicity and reliability. In this work, the electrical conductivity profiles of friction stir processed Ti6Al4 V, Cu, Pb, S355 steel and gas tungsten arc welded AISI 304 stainless steel were determined through eddy currents and four-point probe. In parallel, hardness measurements were also performed. The profiles matched well with the optical macrographs of the materials: while entering in the processed region a variation in both profiles was always observed. One particular advantage of electrical conductivity profiles over hardness was evident: it provides a better resolution of the microstructural alterations in the processed materials. Moreover, when thermomechanical processing induces microstructural changes that modify the magnetic properties of a material,eddy currents testing can be used to qualitatively determine the phase fraction in a given region of the material. A qualitative relation between electrical conductivity measurements and hardness is observed.
基金supported by the Project IPL/2016/Soft Imob/ISEL and Project LAETA—UID/EMS/50022/2019
文摘Immobilization devices may be a valuable aid to ensure the improved effectiveness of radiotherapy treatments where constraining the movements of specific anatomical segments is crucial. This need is also present in other situations, specifically when the superposition of various medical images is required for fine identification and characterization of some pathologies. Because of their structural characteristics, existing head immobilization systems may be claustrophobic and very uncomfortable for patients, during both the modeling and usage stages. Because of this, it is important to minimize all the discomforts related to the mask to alleviate patients’ distress and to simultaneously guarantee and maximize the restraint effectiveness of the mask. In the present work, various head immobilization mask models are proposed based on geometrical information extracted from computerized tomography images and from 3D laser scanning point clouds. These models also consider the corresponding connection to a radiotherapy table, as this connection is easily altered to accommodate various manufacturers’ solutions. A set of materials used in the radiotherapy field is considered to allow the assessment of the stiffness and strength of the masks when submitted to typical loadings.
