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An extraordinary-performance gradient nanostructured hadfield manganese steel containing multi-phase nanocrystalline-amorphous core-shell surface layer by laser surface processing

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journal of Materials Science & Technology 2023年第3期134卷 209-222页

作者： Wanting Sun jiasi Luo Yim Ying Chan j.h.luan Xu-Sheng Yang Research Institute for Advanced Manufacturing Department of Industrial and Systems EngineeringThe Hong Kong Polytechnic UniversityHung HomHong KongChina hong Kong Branch of National Rail Transit Electrification and Automation Engineering Technology Research Center The Hong Kong Polytechnic UniversityHung HomHong KongChina Department of Materials Science and Engineering City University of Hong KongHong KongChina

Reducing grain size(i.***.increasing the fraction of grain boundaries)could effectively strengthen nanograined metals but inevitably sacrifices the ductility and possibly causes a strengthening-softening transition below a critical grain size.In this work,a facile laser surface remelting-based technique was employed and optimized to fabricate a∼600μm-thick heterogeneous gradient nanostructured layer on an austenitic hadfield manganese steel,in which the average grain size is gradually decreased from∼200μm in the matrix to only∼8 nm in the nanocrystalline-amorphous core-shell topmost surface.Atomic-scale microstructural characterizations dissected the gradient refinement processes along the gradient direction,i.***.transiting from the dislocations activities and twinning in sub-region to three kinds of martensitic transformations,and finally a multi-phase nanocrystalline-amorphous core-shell structural surface.Mechanical tests(e.***.nanoindentation,bulk-specimen tensile,and micro-pillar compression)were conducted along the gradient direction.It confirms a tensile strength of∼1055 MPa and ductility of∼10.5%in the laser-processed specimen.Particularly,the core-shell structural surface maintains ultra-strong(tensile strength of∼1.6 GPa,micro-pillar compressive strength of∼4 GPa at a strain of∼8%,and nanoindentation hardness of∼7.7 GPa)to overcome the potential strengthening-softening transition.Such significant strengthening effects are ascribed to the strength-ductility synergetic effects-induced extra work hardening ability in gradient nanostructure and the well-maintained dislocation activities inside extremely refined nanograins in the multi-phase nanocrystalline-amorphous core-shell structural surface,which are evidenced by atomic-scale observations and theoretical analysis.This study provides a unique hetero-nanostructure through a facile laser-related technique for extraordinary mechanical performance.

关键词： Laser surface processing hadfield manganese steel Gradient nanostructure Nanocrystalline-amorphous Martensitic transformation

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Cu-assisted austenite reversion and enhanced TRIP effect in maraging stainless steels

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journal of Materials Science & Technology 2022年第9期104卷 52-58页

作者： M.C.Niu K.Yang j.h.luan W.Wang Z.B.jiao School of Materials Science and Engineering University of Science and Technology of ChinaShenyang 110016China Shi-changxu Innovation Center for Advance Materials Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHong KongChina Department of Materials Science and Engineering City University of Hong KongHong KongChina The hong Kong Polytechnic University Shenzhen Research Institute ShenzhenGuangdongChina

Control of the formation and stability of reverted austenite is critical in achieving a favorable combination of strength,ductility,and toughness in high-strength steels.In this work,the effects of Cu precipitation on the austenite reversion and mechanical properties of maraging stainless steels were investigated by atom probe tomography,transmission electron microscopy,and mechanical tests.Our results indicate that Cu accelerates the austenite reversion kinetics in two manners:first,Cu,as an austenite stabilizer,increases the equilibrium austenite fraction and hence enhances the chemical driving force for the austenite formation,and second,Cu-rich nanoprecipitates promote the austenite reversion by serving as heterogeneous nucleation sites and providing Ni-enriched chemical conditions through interfacial segregation.In addition,the Cu precipitation hardening compensates the strength drop induced by the formation of soft reverted austenite.During tensile deformation,the metastable reverted austenite transforms to martensite,which substantially improves the ductility and toughness through a transformation-induced plasticity(TRIP)effect.The Cu-added maraging stainless steel exhibits a superior combination of a yield strength of~1.3 GPa,an elongation of~15%,and an impact toughness of~58 j.

关键词： Maraging stainless steel TRIP effect Austenite reversion Cu-rich nanoprecipitate

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hardness-thermal stability synergy in nanograined Ni and Ni alloys:Superposition of nanotwin and low-energy columnar boundary

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journal of Materials Science & Technology 2023年第6期137卷 123-131页

作者： F.h.Duan Y.Lin Q.Li j.h.luan j.Lu j.Pan Y.Li Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016China Laboratory of Nanomaterials&Nanomechanics Department of Mechanical EngineeringCity University of Hong KongHong KongChina State Key Laboratory of Material Processing and Die&Mould Technology and School of Materials Science and Engineering Huazhong University of Science and TechnologyWuhan 430074China Department of Materials Science and Engineering City University of Hong KongHong KongChina Centre for Advanced Structural Materials Greater Bay Joint DivisionShenyang National Laboratory for Materials ScienceCity University of Hong Kong Shenzhen Research InstituteShenzhen 518057China City U-Shenzhen Futian Research Institute Shenzhen 518045China

Refining grains into nanoscale can significantly strengthen and harden metallic materials;however,nanograined metals generally exhibit low thermal stability,hindering their practical applications.In this work,we exploit the superposition of the contribution of nanotwins,low-angle grain boundaries,and microalloying to tailor superior combinations of high hardness and good thermal stability in Ni and Ni alloys.For the nanotwinned Ni having a twin thickness of∼2.9 nm and grain size of 28 nm,it exhibits a hardness over 8.0 GPa and an onset coarsening temperature of 623 K,both of which are well above those of nanograined Ni.Re/Mo microalloying can further improve the onset coarsening temperature to 773 K without comprising hardness.Our analyses reveal that high hardness is achieved via strengthen-ing offered by extremely fine nanotwins.Meanwhile,the superior thermal stability is mainly ascribed to the low driving force for grain growth induced by the low-angle columnar boundary architecture and to the additional pinning effect on the migration of twin/columnar boundaries provided by minor Re/Mo solutes.The present work not only reveals a family of nanotwinned metals possessing the combination of ultra-high hardness and high thermal stability but also provides a strategy for tailoring properties of metallic materials by pairing low-angle grain boundaries and twin boundaries.

关键词： Nanotwin Thermal stability hardness Low-angle grain boundary Microalloying

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Achieving ultrahigh strength and ductility in high-entropy alloys via dual precipitation

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journal of Materials Science & Technology 2023年第35期166卷 67-77页

作者： j.M.Guo B.C.Zhou S.Qiu h.j.Kong M.C.Niu j.h.luan T.L.Zhang h.Wu Z.B.jiao Department of Mechanical Engineering Research Institute for Advanced ManufacturingThe Hong Kong Polytechnic UniversityHong KongChina The hong Kong Polytechnic University Shenzhen Research Institute Shenzhen 518057China Department of Materials Science and Engineering City University of Hong KongHong KongChina State Key Laboratory of Powder Metallurgy Central South UniversityChangsha 410083China

The strength-ductility trade-offhas been a longstanding dilemma in metallic materials.here we report an innovative approach to achieve a high strength-ductility synergy via dual precipitation of sheared and bypassed precipitates.(Ni_(2) Co_(2) FeCr)_(96-x) Al_(4) Nb_(x)(at.%)alloys strengthened by nanoscale L12 particles and Laves precipitates were selected as a model for this study,and their precipitate microstructures and mechanical properties were thoroughly investigated.The dual-precipitation-strengthened alloys exhibit a yield strength of more than 1400 MPa,an ultimate tensile strength of over 1800 MPa,and a uniform elon-gation of 18%,thus achieving a high strength-ductility synergy.Our analysis reveals that the nanoscale L1_(2) precipitates contribute to the strength via the particle shearing mechanism,whereas the Laves phase provides the strengthening through the Orowan bypass mechanism.The study of deformation microstruc-tures shows that the L1_(2) precipitates are sheared by stacking faults,which facilitates long-range disloca-tion gliding through the matrix.As a result,deformation induces the formation of hierarchical stacking fault networks and immobile Lomer-Cottrell locks,which effectively enhance the work hardening ca-pability and plastic stability,thereby resulting in a high ductility at high strength levels.Dislocations are piled-up against the interface between the Laves precipitates and matrix,which increases the work hardening capability at the early stages of plastic deformation but causes stress concentrations.The dual precipitation strategy may be useful for many other alloys for achieving superior mechanical properties for technological applications.

关键词： high-entropy alloy Dual precipitation Precipitation strengthening Deformation mechanism

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Enhanced helium ion irradiation tolerance in a Fe-Co-Ni-Cr-Al-Ti high-entropy alloy with L12 nanoparticles

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journal of Materials Science & Technology 2023年第12期143卷 169-177页

作者： Y.L.Zhao F.L.Meng T.Yang j.h.luan S.F.Liu G.M.Yeli W.T.Lin W.h.Liu X.j.Liu C.T.Liu j.j.Kai School of Materials Science and Engineering Harbin Institute of Technology(Shenzhen)Shenzhen 518055China School of Materials Science and Engineering Southern University of Science and TechnologyShenzhen 518055China Department of Materials Science and Engineering Mechanical Behavior Division of Shenyang National Laboratory for Materials ScienceCity University of Hong KongHong KongChina Department of Mechanical Engineering City University of Hong KongHong KongChina Institute of Nuclear&New Energy Technology Tsinghua UniversityBeijing 100084China

L12-strengthened high entropy alloys(hEAs)with excellent room and high-temperature mechanical prop-erties have been proposed as promising candidates as structural materials for advanced nuclear systems.however,knowledge about their radiation response is fairly limited.In the present work,a novel hEA with a high density of L12 nanoparticles was irradiated with he ion at 500°C.Transmission electron microscope(TEM)and atom probe tomography(APT)were employed to study the evolution of mi-crostructural stability and radiation-induced segregation.Similar to the single-phase FeCoNiCr hEA,the main microstructural features were numerous large faulted dislocation loops and helium bubbles.While the irradiation resistance of the present L12-strengthened hEA is much improved in terms of reduced bubble size,which could be attributed to the considerable he trapping efficiency of the coherent pre-cipitate/matrix interface and the enhanced capability of the interface for damage elimination when the matrix channel width is narrow.APT analysis revealed that an inverse-Kirkendall-mechanism-dominated radiation-induced segregation(RIS)occurs around bubbles,where a significant Co enrichment and Ni de-pletion can be clearly observed.In addition,the competing dynamics of ballistic mixing and elemental clustering that raised from the irradiation-enhanced diffusion in a highly supersaturated matrix,along with the low precipitation nucleation barrier due to the small lattice misfit,lead to a dynamical pre-cipitation dissolution and re-precipitation appears under irradiation.Such a promising phenomenon is expected to promote a potential self-healing effect and could in turn provide a sustainable irradiation tolerance over the operational lifetime of a reactor.

关键词： L12 nanoparticles high-entropy alloy helium bubble Phase stability Radiation-induced segregation

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Strategies for improving ductility of ordered intermetallics

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Progress in Natural Science:Materials International 2016年第1期26卷 1-12页

作者： Z.B.jiao j.h.luan C.T.Liu Center for Advanced Structural Materials Department of Mechanical and Biomedical Engineering College of Science and Engineering City University of Hong Kong

Ordered intermetallics possess attractive high-temperature properties; however, low ductility and brittle fracture limit their use as engineering materials in many cases. This paper provides a comprehensive review on the recent progress in the development of ductile ordered intermetallics and summarizes the strategies used to improve the tensile ductility of ordered intermetallics, including control of ordered crystal structures,engineering grain-boundary structure and chemistry, eliminating environmental embrittlement, microstructure optimization, control of phase stability, and promoting transformation-/twining-induced plasticity. The basic ideas and related mechanisms underlying these ductilizing strategies are discussed. In addition, a brief mention of the current use of intermetallic alloys for structural and corrosion applications is made.

关键词： Ordered intermetallics Ductility Ductilizing strategy Microstructure Alloy design

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Mode Switching and Consistency Control for Electric-hydraulic hybrid Steering System

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Automotive Innovation 2024年第1期7卷 166-181页

作者： Zhongkai luan Wanzhong Zhao Chunyan Wang College of Energy and Power Engineering 29 Yudao St.Nanjing 210016China

Electric-hydraulic hybrid power steering(E-hhPS)system,a novel device with multiple modes for commercial electric vehicles,is designed to realize both superior steering feel and high energy efficiency.however,inconsistent steering perfor-mance occurs in the mode-switching process due to different dynamic characteristics of electric and hydraulic components,which even threatens driving safety.In this paper,mode-switching strategy and dynamic compensation control method are proposed for the E-hhPS system to eliminate the inconsistency of steering feel,which comprehensively considers ideal assistance characteristics and energy consumption of the system.Then,the influence of disturbances on system stability is analyzed,and h_(∞)robust controller is employed to guarantee system robustness and stability.The experimental results dem-onstrate that the proposed strategy can provide a steering system with natural steering feel without apparent inconsistency and effectively minimize energy consumption.

关键词： hydraulic hybrid steering system Steering feel Consistency Mode switch Robust control

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In situ neutron diffraction unravels deformation mechanisms of a strong and ductile Fe Cr Ni medium entropy alloy

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journal of Materials Science & Technology 2022年第21期116卷 103-120页

作者： L.Tang F.Q.jiang j.S.Wróbel B.Liu S.Kabra R.X.Duan j.h.luan Z.B.jiao M.M.Attallah D.Nguyen-Manh B.Cai School of Metallurgy and Materials University of BirminghamB152TTUnited Kingdom Institute of Metal Research Chinese Academy of SciencesShenyang 110016China Faculty of Materials Science and Engineering Warsaw University of Technologyul.Wołoska 141Warsaw 02-507Poland State Key Laboratory for Powder Metallurgy Central South UniversityChangsha 410083China Rutherford Appleton Laboratory ISIS FacilityDidcot OX110QXUnited Kingdom Department of Materials Science and Engineering City University of Hong KongKowloonHong KongChina Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHung HomHong KongChina CCFE United Kingdom Atomic Energy AuthorityAbingdonOxfordshire OX143DBUnited Kingdom

We investigated the mechanical and microstructural responses of a high-strength equal-molar medium entropy FeCrNi alloy at 293 and 15 K by in situ neutron diffraction testing.At 293 K,the alloy had a very high yield strength of 651±12 MPa,with a total elongation of 48%±5%.At 15 K,the yield strength increased to 1092±22 MPa,but the total elongation dropped to 18%±1%.Via analyzing the neutron diffraction data,we determined the lattice strain evolution,single-crystal elastic constants,stacking fault probability,and estimated stacking fault energy of the alloy at both temperatures,which are the critical parameters to feed into and compare against our first-principles calculations and dislocation-based slip system modeling.The density functional theory calculations show that the alloy tends to form shortrange order at room temperatures.however,atom probe tomography and atomic-resolution transmission electron microscopy did not clearly identify the short-range order.Additionally,at 293 K,experimental measured single-crystal elastic constants did not agree with those determined by first-principles calculations with short-range order but agreed well with the values from the calculation with the disordered configuration at 2000 K.This suggests that the alloy is at a metastable state resulted from the fabrication methods.In view of the high yield strength of the alloy,we calculated the strengthening contribution to the yield strength from grain boundaries,dislocations,and lattice distortion.The lattice distortion contribution was based on the Varenne-Luque-Curtine strengthening theory for multi-component alloys,which was found to be 316 MPa at 293 K and increased to 629 MPa at 15 K,making a significant contribution to the high yield strength.Regarding plastic deformation,dislocation movement and multiplication were found to be the dominant hardening mechanism at both temperatures,whereas twinning and phase transformation were not prevalent.This is mainly due to the high stacking fault energy of the alloy as estimated to be

关键词： Medium entropy alloy Multi-component alloy Cryogenic temperature Neutron diffraction

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Thermal stability and deformation mechanisms in Ni-Co-Fe-Cr-Al-Ti-Nb-type nanoparticle-strengthened high-entropy alloys

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journal of Materials Science & Technology 2023年第36期167卷 171-183页

作者： j.X.hou j.Y.Zhang j.X.Zhang j.h.luan Y.X.Wang B.X.Cao Y.L.Zhao Z.B.jiao X.j.Liu W.W.Song P.K.Liaw T.Yang Department of Materials Science and Engineering Hong Kong Institute for Advanced StudyCity University of Hong KongHong KongChina School of Materials Science and Engineering Harbin Institute of Technology(Shenzhen)Shenzhen 518055China Department of Mechanical Engineering The Hong Kong Polytechnic UniversityHong KongChina Steel Institute RWTH Aachen UniversityAachen 52072Germany Institute of Materials Engineering University of KasselKassel 334125Germany Department of Materials Science and Engineering The University of TennesseeKnoxvilleTN 37996-2200USA City University of hong Kong China

The precipitate morphologies,coarsening kinetics,elemental partitioning behaviors,grain structures,and tensile properties were explored in detail for L1_(2)-strengthened Ni_(39.9)Co_(20)Fe_(15)Cr_(15)Al_(6)Ti_(4-x)Nb_(x)B_(0.1)(x=0 at.%,2 at.%,and 4 at.%)high-entropy alloys(hEAs).By substituting Ti with Nb,the spheroidal-to-cuboidal precipitate morphological transition,increase in the coarsening kinetics,and phase decomposition upon aging at 800°C occurred.The excessive addition of Nb brings about the grain boundary precipitation of an Nb-rich phase along with the phase decomposition from the L1_(2)to lamellar-structured D019 phase upon the long-term aging duration.By partially substituting Ti with Nb,the chemically complex and thermally stable L12 phase with a composition of(Ni_(58.8)Co_(9.8)Fe_(2.7))(Al_(12.7)Ti_(5.8)Nb_(7.5)Cr_(2.3))ensures the stable phase structure and clean grain boundaries,which guarantees the superb high-temperature mechanical properties(791±7 MPa for yielding and 1013±11 MPa for failure)at 700℃.Stacking faults(SFs)were observed to prevail during the plastic deformation,offering a high work-hardening capability at 700°C.An anomalous rise in the yield strength at 800℃was found,which could be ascribed to the multi-layered super-partial dislocations with a cross-slip configuration within the L1_(2)particles.

关键词： high-entropy alloys Coarsening kinetics Coherent precipitation strengthening Mechanical properties

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Effects of rare earth elements on inclusions, microstructure and impact toughness of spring steel

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journal of Iron and Steel Research(International) 2024年第4期31卷 933-944页

作者： Chun-lei hao Chao-yun Yang Peng Liu Yi-kun luan Bao-guang Sang Shenyang National Laboratory for Materials Science Institute of Metal ResearchChinese Academy of SciencesShenyang 110016LiaoningChina School of Mechanical Engineering and Automation Dalian Polytechnic UniversityDalian 116034LiaoningChina

Spring steel is an indispensable basic part manufacturing material in mechanical equipment,which is widely used in transportation tools such as automobiles,railways,construction machinery and other industries.The effects of rare earth(RE)on inclusions,microstructure,carbides and impact toughness of 50CrV spring steel were studied by means of optical microscope,scanning electron microscope,transmission electron microscope and impact tester.The results show that the addition of rare earth can modify the main MnS and Al_(2)O_(3) inclusions in steel to form spherical or near-spherical rare earth inclusions,and the size of inclusions is significantly reduced.In the quenched structure,the size of martensite slab becomes smaller and the structure is refined.After tempering,the carbide changes from sheet to ellipse,which makes it easier for spring steel to form stress concentration cracks under stress.VC becomes finer and more dispersed,which leads to better pinning of grain boundaries and smaller grain sizes.The impact toughness of 50CrV-RE spring steel increased from 21 to 41 j by 95%due to the improvement of inclusions,microstructure and carbides by rare earth.It is possible to improve the strength and toughness of spring steel for the improvement of railway running speed and the development of vehicle lightweight in China.

关键词： Rare earth-Spring steel Inclusion Microstructure Impact toughness

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