K. Lu

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

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Publications (284)656.02 Total impact

  • [Show abstract] [Hide abstract]
    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 ∼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.
    Scripta Materialia. 01/2015; 95.
  • 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.
    Wear 12/2014; 320(s 1–2):41–50. · 1.86 Impact Factor
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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.
    Journal of Materials Science and Technology -Shenyang- 08/2014; · 1.20 Impact Factor
  • 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.
    Scripta Materialia 08/2014; s 84–85:31–34. · 2.82 Impact Factor
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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.
    Scripta Materialia 04/2014; 77:17–20. · 2.82 Impact Factor
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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.
    Surface and Coatings Technology 01/2014; · 1.94 Impact Factor
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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.
    Acta Materialia 01/2014; 81:487-500. · 3.94 Impact Factor
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    ABSTRACT: Heavy plastic deformation may refine grains of metals and make them very strong. But the strain-induced refinement saturates at large strains, forming three-dimensional ultrafine-grained (3D UFG) structures with random orientations. Further refinement of this microstructure is limited because of the enhanced mobility of grain boundaries. Very-high-rate shear deformation with high strain gradients was applied in the top surface layer of bulk nickel, where a 2D nanometer-scale laminated structure was induced. The strongly textured nanolaminated structure (average lamellar thickness of 20 nanometers) with low-angle boundaries among the lamellae is ultrahard and ultrastable: It exhibits a hardness of 6.4 gigapascal--which is higher than any reported hardness of the UFG nickel--and a coarsening temperature of 40 kelvin above that in UFG nickel.
    Science 10/2013; 342(6156):337-40. · 31.20 Impact Factor
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    ABSTRACT: Cyclic deformation was studied in Cu samples with a gradient nanograined (GNG) surface layer. Compared with the coarse-grained sample, the Cu samples with a GNG surface layer exhibit a greatly enhanced fatigue limit under stress-controlled cyclic deformation. The cyclic deformation induced an abnormal grain coarsening that initiated from the subsurface layer and grew along 45° to the stress axis toward the top surface layer, where the fatigue cracks were formed.
    Scripta Materialia 05/2013; 68(10):801–804. · 2.82 Impact Factor
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    ABSTRACT: A surface layer with a gradient decrease in twin density has been produced in a Fe–Mn austenitic steel, which corresponds to a gradient drop in hardness from 5.3 GPa in the top surface to 2.2 GPa in the coarse grained core. The dependence of hardness on the twin thickness was determined, showing a weaker strengthening effect of twin boundaries than that of conventional grain boundaries in this alloy. Superior strength–ductility synergy was observed in tensile tests of the gradient nanotwinned layer.
    Scripta Materialia 01/2013; 68(1):22–27. · 2.82 Impact Factor
  • B. Yao, Z. Han, K. Lu
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    ABSTRACT: Bulk nanostructured Cu sample with nano-scale twin bundles embedded in nano-sized grains was synthesized by using dynamic plastic deformation (DPD) technique. Dry sliding tribological properties of the DPD Cu and the coarse grained (CG) Cu samples were investigated under liquid nitrogen temperature (LNT) in comparison with room temperature (RT) conditions. Experimental results show that the wear volume under LNT was much larger than that under RT for both sets of Cu samples. The DPD Cu sample exhibits almost same wear volume compared with the CG Cu when sliding at LNT, which is quite different from the enhanced wear resistance for the DPD Cu sample sliding at RT. A similar steady worn subsurface structure was formed for two Cu samples, which was constituted by heavily deformed nanostructured mixing layer (NML) and ultra-fine grained dynamic recrystallization (DRX) layer. Comparing with the worn subsurface structure at RT, lower sliding temperature could effectively suppress grain growth within the DRX layer, resulting in a cracked NML and extremely fine grains in the DRX layer. When sliding at LNT, quick propagation of cracks from NML into DRX layer and flaking rate of NML are determining the wear process which results in a high wear rate.
    Wear. 01/2013; 301(s 1–2):608–614.
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    ABSTRACT: We examined the pre-emptive analgesic effect of a cyclooxygenase (COX)-2 inhibitor in a rat surgical pain model and characterised the changes in cutaneous COX-2 around a surgical site. Thermal hyperalgesia and mechanical allodynia were tested in the rats for three days after incision and skin tissues were collected for analysis of COX-2. There was decreased expression of cutaneous COX-2 one day after surgical incision. Pre-incision injection of the COX-2 inhibitor significantly inhibited expression of COX-2 and also reduced thermal hyperalgesia (but not mechanical allodynia) compared with the post-incision COX-2-inhibitor injection group, one day after incision.
    Anaesthesia 07/2012; 67(11):1225-1231. · 3.49 Impact Factor
  • K. Lu, Lei Lu
    Scripta Materialia. 06/2012; 66(11):835–836.
  • Bin Yao, Zhong Han, Ke Lu
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    ABSTRACT: The wear properties of ultrafine-grained (UFG) Cu samples of different purities were investigated in comparison with the coarse-grained (CG) Cu. The UFG Cu samples, prepared by means of plastic deformation via quasi-static compression, exhibit an enhanced wear resistance relative to the CG Cu samples. For both the UFG and the CG Cu samples, wear volumes increase at higher purities. A steady state worn subsurface structure was formed in each sample after sliding for 60 min, consisting of a heavily deformed nanostructured mixing layer (NML) on top of a continuous dynamic recrystallization (DRX) layer. A pronounced correlation is identified that wear volume increases monotonically with an increasing grain size of the DRX layer. The impurity level of the Cu samples has an obvious influence on the DRX grain sizes, which in turn determines the wear resistance of the Cu samples.
    Journal of Materials Science & Technology. 06/2012; 28(6):481–487.
  • L. Lu, Z.S. You, K. Lu
    Scripta Materialia. 06/2012; 66(11):837–842.
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    ABSTRACT: A novel strategy for strengthening austenite steels is introduced by using the unique strengthening effect of nanoscale twins. Austenite grains containing multiple nanoscale twins can be strengthened to a yield strength of a few GPa with very high work-hardening rates. Compared with the conventional dual-phase steels, several austenite steels strengthened by using ultra-strong nanotwinned austenite grains exhibit a superior strength–ductility synergy. Perspectives on future development of the nanotwinned austenite steels and the nanotwin strengthening strategy are presented.
    Scripta Materialia 06/2012; 66(11):878–883. · 2.82 Impact Factor
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    ABSTRACT: Stochastic, discontinuous flow is ubiquitous in the plastic deformation of small-volume metallic materials. We have identified a size-strengthening effect on the stress to initiate the jerky plastic yielding in nanoscale volumes of copper single crystals, subjected to nanoindentation in different orientations. Such a nanoscale size effect arises due to the stochastic nature of dislocation sources, in contrast to the microscale size effect often attributed to plastic strain gradients. The jerky response can result from the activation of either surface or bulk heterogeneous dislocation sources, as governed by the distribution and resistance of dislocation locks. Implications concerning the deformation mechanism in materials with flow defect-limited characteristics are discussed.
    Acta Materialia 05/2012; 60(8):3302–3309. · 3.94 Impact Factor
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    ABSTRACT: An austenitic Fe–25Mn steel with a low stacking fault energy was subjected to dynamic plastic deformation (DPD) followed by thermal annealing. The as-DPD sample is structurally characterized by a mixed nanostructure consisting of nanosized grains with an average size of 43 nm and bundles of nanoscale twins (with an average twin/matrix lamella thickness of 5 nm), as well as some dislocation structures, which exhibits a high yield strength of about 1470 MPa but a limited tensile ductility. Thermal annealing leads to static recrystallization (SRX) of the nanostructures forming a hierarchical structure of nanotwinned grains embedded in microsized SRX grains, owing to the higher thermal stability of the nanotwinned bundles than that of nanosized grains. With an increasing number of SRX grains the yield strength and ultimate tensile strength drop while the tensile ductility increases. The calculated yield strength of the nanotwinned grains is about 1.5 GPa, much lower than that determined from Hall–Petch strengthening extrapolated to the nanoscale. Work hardening rates of the nanotwin grains, comparable with that of the microsized grains, are higher than that of the original coarse grained sample. The micrograined austenitic Fe–Mn samples strengthened by nanotwinned grains exhibit enhanced strength–ductility synergy in comparison with the deformed samples. A combination of a 977 MPa yield strength with a uniform elongation of 21% is achieved in the annealed samples, well above that of the deformed samples.
    Acta Materialia. 05/2012; 60(9):4027–4040.
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    ABSTRACT: Average microstructural parameters and the extent of microstructural heterogeneity in nickel deformed at a high strain rate have been characterized quantitatively and compared to those after compression at a quasi-static strain rate. The microstructure in the high strain rate sample was found to be more refined and less heterogeneous than that in the sample compressed at a low strain rate. The greater refinement in the former sample was achieved due to subdivision by a high frequency of finely spaced low-angle boundaries.
    Scripta Materialia. 03/2012; 66(6):335–338.

Publication Stats

4k Citations
656.02 Total Impact Points

Institutions

  • 2014
    • Nanjing University of Science and Technology
      Nan-ching, Jiangsu Sheng, China
  • 1996–2014
    • Chinese Academy of Sciences
      • • Shenyang National Laboratory for Materials Science
      • • Institute of Metal Research
      Peping, Beijing, China
  • 1994–2013
    • Northeast Institute of Geography and Agroecology
      • • Shenyang National Laboratory for Materials Science
      • • Institute of Metal Research
      Beijing, Beijing Shi, China
  • 2009–2010
    • Technical University of Denmark
      • National Laboratory for Sustainable Energy
      Copenhagen, Capital Region, Denmark
  • 2006–2008
    • The Hong Kong Polytechnic University
      • Department of Mechanical Engineering
      Hong Kong, Hong Kong
  • 2007
    • University of Queensland 
      • School of Mechanical and Mining Engineering
      Brisbane, Queensland, Australia
    • State Key Laboratory Of Transient Optics And Photonics
      Ch’ang-an, Shaanxi, China
  • 1998–2004
    • Johns Hopkins University
      • Department of Materials Science and Engineering
      Baltimore, MD, United States
  • 2003
    • Dalian Maritime University
      Lü-ta-shih, Liaoning, China
  • 2001–2003
    • Université de Technologie de Troyes
      Troyes, Champagne-Ardenne, France
  • 1999
    • University of Wisconsin, Madison
      • Department of Materials Science and Engineering
      Madison, MS, United States
  • 1987–1998
    • Academia Sinica
      T’ai-pei, Taipei, Taiwan
  • 1997
    • Toyohashi University of Technology
      • Faculty of Engineering
      Toyohashi, Aichi-ken, Japan