K. Lu

Nanjing University of Science and Technology, Nan-ching, Jiangsu Sheng, China

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Publications (322)1013.53 Total impact

  • H.Y. Yi · F.K. Yan · N.R. Tao · K. Lu
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    ABSTRACT: The work hardening behavior of nanotwinned austenitic grains in a novel type of nanotwinned austenitic stainless steels was investigated. Multiple Shockley partial dislocation activities in the nanotwinned grains could trigger occurrence of stacking faults and strain induced martensitic transformation before necking, resulting in an increase in work hardening rate. Consequently, the fully recovered nanotwinned austenitic stainless steel exhibits a uniform elongation of ~ 13% at the strength of 950 MPa.
    No preview · Article · Mar 2016

  • No preview · Article · Jan 2016 · Science and Technology of Advanced Materials
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    ABSTRACT: Nano-twinned austenite grains were characterized in an austenitic stainless steel by using nanoindentation. The nano-twinned austenite grains exhibit identical elastic modulus with the micro-sized recrystallized austenitic grains. Nanoindentation hardness of the nano-twinned grains is about 4.5 GPa, ∼1.0 GPa higher than that of the recrystallized grains, but lower than that of the nano-sized grains with the comparable size owing to the presence of twinning partial dislocations.
    No preview · Article · Sep 2015 · Scripta Materialia
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    H.Y. Yi · F.K. Yan · N.R. Tao · K. Lu
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    ABSTRACT: Two types of austenitic stainless steel samples were prepared by means of dynamic plastic deformation followed by annealing: nanotwinned austenitic grains embedded in recrystallized austenite matrix and martensitic/austenitic duplex microstructures. Annealing at 923 K induced martensitic reversion while most nanotwinned grains are stable. An enhanced strength-ductility combination is observed in the annealed nanotwinned samples which exhibit a uniform elongation of similar to 21% and a yield strength of similar to 900 MPa, in contrast to a uniform elongation of similar to 12% with comparable strength in the martensitit/ austenitic samples.
    Full-text · Article · Sep 2015 · Materials Science and Engineering A
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    X.C. Liu · H.W. Zhang · K. Lu
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    ABSTRACT: A polycrystalline Ni (99.882% purity) bar sample was subjected to surface mechanical grinding treatment (SMGT) at ambient temperature. Gradient microstructures along depth from the treated surface were generated owing to a graded variation of strain and strain rates, including dislocation structures, submicron-sized structures, and nanostructures, respectively. In the subsurface layer of 10–80 μm deep, 2-dimensional laminated structures with low angle boundaries and strong deformation textures were formed of which the average thickness is ∼20 nm, one order of magnitude smaller than that of the ultrafine structures in Ni induced by conventional severe plastic deformation. The extraordinary grain refinement was ascribed to the high strain rates and high strain gradients that enhance accumulation of geometric necessary dislocations with a suppressed recovery dynamics. Deformation of the nano-laminated structures is governed by dislocation slip, and supplemented by deformation twining at the nanoscale, eventually leading to fragmentation into nano-sized equiaxed grains.
    Full-text · Article · Sep 2015 · Acta Materialia
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    ABSTRACT: Deformation twinning has rarely been observed in coarse grained Al and its alloys except under some extreme conditions such as ultrahigh deformation strain or strain rates. Here, we report that a significant amount of Σ3 deformation twins could be generated in a coarse-grained Al-7 Mg alloy by dynamic plastic deformation (DPD). A systematic investigation of the Σ3 boundaries shows that they are Σ3{112} type incoherent twin boundaries (ITBs). These ITBs have formed by gradual evolution from copious low-angle deformation bands through 〈111〉-twist Σ boundaries by lattice rotation. These findings provide an approach to generate deformation twin boundaries in high stacking fault energy metallic alloys. It is suggested that high solution content of Mg in the alloy and the special deformation mode of DPD played an important role in formation of the Σ and ITBs.
    Full-text · Article · Aug 2015 · Applied Physics Letters
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    H W Zhang · Z P Luo · N Hansen · K Lu
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    ABSTRACT: The structural heterogeneity of a polycrystalline Ni subjected to dynamic plastic deformation to a strain of 2.3 was characterized, and its influence on the structural coarsening behaviour during post annealing was investigated. Structural heterogeneity on the large scale manifests itself by formation of two types of layers: low misoriented regions (LMRs) and highly misoriented regions (HMRs). On the small scale, the heterogeneity was characterized by different distributions of boundaries and textures in each layer. LMRs contain only low angle boundaries and one dominating crystallographic orientation. In contrast HMRs contain both low and high angle boundaries (>15°) and the texture is mixed with close to the compression axis. During annealing, LMRs coarsen uniformly and recrystallization nucleation is difficult to form. In HMRs, the structural evolution is heterogeneous and recrystallization nuclei are readily formed. The importance of structural heterogeneity during structural design for high performance nanostructure was highlighted.
    Full-text · Article · Aug 2015 · IOP Conference Series Materials Science and Engineering
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    X. Chen · Z. Han · K. Lu
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    ABSTRACT: The sliding wear resistance of Cu-2.2 wt.% Al alloy can be remarkably enhanced by controlling subsurface dynamic recrystallization (DRX) process. The wear volume decreases from 3.1 × 107 to 0.9 × 107 μm3 when the DRX grain size increases from 0.28 to 0.62 μm induced by dynamic plastic deformation and subsequent annealing. The enhanced wear resistance stems from a wear mechanism transition from cracking and peeling-off of the fine-grained DRX layer to that of the topmost nanostructured mixing layer as DRX grains become coarser. © 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
    Full-text · Article · May 2015 · Scripta Materialia
  • H.W. Huang · Z.B. Wang · J. Lu · K. Lu
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    ABSTRACT: By means of surface mechanical rolling treatment (SMRT), a gradient nanostructured (GNS) surface layer was formed on AISI 316L stainless steel. The mean grain size is ∼30 nm in the topmost surface layer and increases with depth. Tension–compression fatigue measurements were performed on the SMRT sample under the stress-controlled mode. In comparison with the coarse-grained sample, the fatigue strength of the SMRT sample is significantly enhanced in both the low- and high- cycling fatigue regimes. Meanwhile, the fatigue ratio is evidently elevated with an increasing tensile strength in the SMRT sample. The initiation and growth of cracks, the cyclic deformation behaviors, as well as effects of strength and residual stresses, have been investigated to clarify the fatigue mechanism of the SMRT sample. The results emphasized the GNS surface layer enhances the fatigue property by suppressing the initiation of cracks and accommodating a remarkable cyclic plastic strain amplitude.
    No preview · Article · Apr 2015 · Acta Materialia
  • L.X. Sun · N.R. Tao · K. Lu
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    ABSTRACT: A bulk nanostructured CuCrZr alloy consisting of nanotwins and nanograins was prepared by dynamic plastic deformation at liquid nitrogen temperature. A tensile strength of 700 MPa and an electrical conductivity of 78.5% International Annealed Copper Standard are obtained in the nanostructured CuCrZr alloys processed by means of this one-step deformation without aging treatment. The reason for the increased strength without the sacrifice of its high electrical conductivity was discussed.
    No preview · Article · Apr 2015 · Scripta Materialia
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    X. G. Zheng · Y.- N. Shi · K. Lu
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    ABSTRACT: The performance of 2-Mercapto-5-benzimidazolesulfonic acid (MBIS) in a Watts bath in crack electro-healing was investigated. Potentiostatic and galvanostatic voltammetry, current efficiency measurements were performed for electrochemical investigation. The morphology of the healed crack indicates that the healing crystals grow in a controllable manner with the addition of MBIS under forced convection with the healing crystals fill preferentially in the crack tip to the crack sidewalls. No obvious defects were observed along the interface between the substrate and the healing crystals, which is attributed the much higher current efficiency of MBIS. Annual-ring like defects are observed but with a much longer width compared with PEI. The formation mechanism of annual ring is discussed. Possible approach to get defect-free crack healing is also prospected.
    Full-text · Article · Feb 2015 · Journal of The Electrochemical Society
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    ABSTRACT: By means of cold spray, a Zn-Al coating was successfully deposited on an interstitial-free (IF) steel sheet. The formation of interfacial compounds between the coating and the IF steel was studied during diffusion annealing at 400 °C. And its correlations with the stripping behaviors of the coating were investigated by using a three-point bending method. The results showed that Fe-Zn and Fe-Al-Zn compounds begin to form at the coating/substrate interface after an annealing duration of 60 min, and the stripping resistance increases slightly before that duration and then decreases significantly by further increasing annealing duration. The enhanced stripping resistance at the earlier stage might be due to the modifications of microstructure and deformation compatibility of the sprayed coating, while the decreased stripping resistance at the later stage is related to the high stress-concentration at the interface of the formed brittle Fe-Al-Zn phase and the Zn-Al coating.
    Preview · Article · Feb 2015 · Applied Surface Science
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    X. C. Liu · H. W. Zhang · K. Lu
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    ABSTRACT: Nanolaminated (NL) structure has been produced in an interstitial-free steel by means of surface mechanical grinding treatment. The NL structure is characterized by an average lamella thickness of similar to 20 nm and also exhibits a strong deformation texture. Various dislocation substructures and individual dislocations exist inside these lamellae from submicron size to a few nanometers. Due to this extraordinary grain refinement, the NL structure exhibits a record hardness of 5.3 +/- 0.6 GPa.
    Full-text · Article · Jan 2015 · Scripta Materialia
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    X. Chen · Z. Han · K. Lu
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    ABSTRACT: Dry sliding tribological properties and worn subsurface microstructures were investigated in Cu–Al alloys with Al concentrations of 0–2.2 wt%. It was found that the wear volume of Cu–Al alloys decreases with an increasing Al content below 0.5 wt%, and increases at higher Al contents above 0.5 wt%. For each sample, a worn subsurface layer is generated consisting of dynamic recrystallization (DRX) structures beneath the top nanostructured mixing layer (NML). DRX grain sizes decrease monotonically with an increasing Al content. As the DRX grain sizes are larger than 0.7 μm, the wear-off process is dominated by cracking and peel-off of the NML. For the samples with finer DRX grains, cracking takes place within the DRX layer, of which peeling-off becomes a dominant mechanism. Such a wear mechanism transition is in agreement with the quantitative correspondence between wear volume and DRX grain size, indicating that the minimum wear volume (i.e., the maximum wear resistance) exists at an average DRX grain size of about 0.7 μm.
    Full-text · Article · Dec 2014 · Wear
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    ABSTRACT: A novel type of duplex microstructure is generated in a single-phase austenitic steel (AISI 316L; X2CrNiMo19-12), consisting of plastically compliant recrystallized austenitic grains as the matrix containing coarse non-recrystallized grains with a nanotwinned austenitic (nt-c) structure as strengthening inclusions. This novel type of single-phase yet duplex microstructured steel exhibits an excellent combination of strength and ductility. We study the plastic co-deformation mechanisms between the nanotwinned and the recrystallized grains under tension using electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM). At tensile strains below 5%, the nt-c grains nearly deform homogeneously in conjunction with the surrounding statically recrystallized (SRX) grains without generating notable strain localization near their interfaces. The aniso-tropic plastic deformation of the nt-c grains with predominant shear parallel to the twin boundaries results in a higher dislocation density in the neigh-boring SRX grains. As the strain exceeds 12%, localized deformation occurs within the nt-c grains in the form of shear banding. A strain gradient is developed in the surrounding SRX grains as a function of distance from the nt-c/SRX interface. Deformation twinning is observed in the SRX grains near the nt-c grains, while away from nt-c grains dislocation slip dominates the deformation. The strengthening effect of the strong and ductile nt-c grains may offer a novel approach to strengthen austenitic steels and related alloys by generating a nanotwinned/recrystallized duplex microstructure.
    Full-text · Article · Dec 2014 · Acta Materialia
  • S. Guo · Z.B. Wang · L.M. Wang · K. Lu
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    ABSTRACT: By means of surface mechanical attrition treatment (SMAT), a gradient nanostructured surface layer was fabricated on a ferritic-martensitic (F-M) steel plate. Its aluminizing behaviors were investigated during a packed aluminization process and a subsequent diffusion annealing treatment at lower temperatures. In comparison with the initial sample, a much thicker Al5Fe2 layer was formed on the SMAT sample after the packed aluminization, with a growth constant of ~ 3 times higher at 600 °C. The transformation kinetics from Al5Fe2 phase into AlFe phase and α-(Fe,Al) solid solution are also enhanced in the subsequent annealing treatment at ~ 700 °C. The enhanced aluminizing kinetics originates from the increased atomic diffusivities by numerous grain boundaries and a higher concentration of vacancies in the nanostructured surface layer. With the determined growth kinetics, a duplex aluminizing process was demonstrated for achieving a gradient surface layer with lower-Al containing aluminides below the tempering temperature of F-M steel.
    No preview · Article · Nov 2014 · Surface and Coatings Technology
  • K Lu

    No preview · Article · Sep 2014 · Science
  • F.K. Yan · N.R. Tao · K. Lu
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    ABSTRACT: Dynamic plastic deformation followed by recovery annealing of an austenitic stainless steel results in the formation of a hierarchical microstructure consisting of nanotwinned austenitic grains (>55 vol.%) mixed with nanograins and dislocation structures. The sample exhibits a yield strength of 1055 MPa and a uniform elongation of ∼5.2% with a considerable work hardening. Such a remarkable tensile ductility originates from the intrinsic plasticity of the nanotwinned austenitic grains in which dislocation density is reduced after the recovery annealing.
    No preview · Article · Aug 2014 · Scripta Materialia
  • L.X. Sun · N.R. Tao · M. Kuntz · J.Q. Yu · K. Lu
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    ABSTRACT: Lamellar nanostructures were induced in a plain martensitic low-carbon steel by using dynamic plastic deformation at room temperature. The nanostructured steel was hardened after annealing at 673 K for 20 min, with a tensile strength increased from 1.2 GPa to 1.6 GPa. Both the remained nanostructures and annealing-induced precipitates in nano-scale play key roles in the hardening.
    No preview · Article · Aug 2014 · Journal of Materials Science and Technology -Shenyang-
  • T.H. Fang · N.R. Tao · K. Lu
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    ABSTRACT: With surface mechanical grinding treatment, a gradient nanograined (GNG) surface layer is produced on a bulk coarse-grained (CG) pure Cu, where the grain size increases gradually from 20 nm (topmost surface) to micrometer scale. Microhardness measurements of the GNG/CG sample after tension revealed that tension induces softening for grains smaller than 165 nm and induces hardening above this size. This critical size agrees with the strain-induced saturation grain size of Cu subjected to severe plastic deformation.
    No preview · Article · Apr 2014 · Scripta Materialia

Publication Stats

15k Citations
1,013.53 Total Impact Points


  • 2013-2015
    • Nanjing University of Science and Technology
      Nan-ching, Jiangsu Sheng, China
  • 1994-2015
    • Chinese Academy of Sciences
      • • Institute of Metal Research
      • • Shenyang National Laboratory for Materials Science
      • • Institute of Physics
      Peping, Beijing, China
  • 2005-2011
    • Université de Technologie de Troyes
      • LASMIS Laboratoire des Systèmes Mécaniques et d'Ingénierie Simultanée
      Troyes, Champagne-Ardenne, France
  • 2003-2008
    • Technical Institute of Physics and Chemistry
      Peping, Beijing, China
  • 2007
    • State Key Laboratory Of Transient Optics And Photonics
      Ch’ang-an, Shaanxi, China
  • 1987-2006
    • Academia Sinica
      • Institute of Physics
      T’ai-pei, Taipei, Taiwan