多级纳米金属的力学性能-卢柯

1、Mechanical properties of hierarchical nanostructured metals 多级纳米金属的力学性能,卢 柯 中国科学院金属研究所， 沈阳材料科学国家（联合）实验室,“钱学森讲座报告” 中国科学院力学研究所, 2013-09-12,Increased strength Reduced ductility Reduced work-hardening,Nano-grained materials: strong but brittle,C.C. Koch et al MRS Bull. (1999),nm,Trade-off of strength an

2、d ductility,Processing-induced porosities Processing-induced contamination Strain localization Lack of strain hardening,Why brittle under tension?,Homogeneous nano-grained metals, Fully dense samples Clean samples ? (early necking) ? (uniform deformation),Hierarchical (heterogeneous) nanostructures,

3、Hierarchical nanostructured materials,Strain delocalization Acta Mater. (2008),Dislocation-TB interactions in fcc metals,Z.H. Jin, Acta Mater. (2008),Plan-view TEM images: edge-on TBs,Polycrystalline Cu with nano-scale twins,Synthesis: pulsed electrodeposition (PED),Tensile properties of PED nano-tw

4、inned Cu,Strength AND ductility increase hand-in-hand !,Lu, et al, Science, (2004), 6x10-3 s-1,Dislocation-TB interaction: 3 modes,Dislocation slip-transfer,Threading dislocations,Twinning partials,T. Zhu & HJ Gao, Scripta Mater., 2012,Hard-I,Hard-II,Soft,Slip systems: twinned FCC metals,Z.S. You et

5、 al, Acta Mater., 2013,Columnar grains with nano-twins in Cu,DC electrodeposition,Strong 111 out-of-plane texture,L. Lu et al, Acta Mater., 2011,Twin thickness effects in nt-Cu,L. Lu et al, Acta Mater., 2011,Hardness of Ag thin films with NTs,X.H. Zhang, et al, Acta Mater., 2011,Strength of Cu nanow

6、ires with NTs,J. Greer, HJ Gao, et al, Nature Nanotech., 2012,Strength of Au nanowires with NTs,S. Mao et al, Nature Comm., 2013,Cubic BN with NTs: harder than diamond,nt-cBN,Y.J. Tian, et al, Nature, 2013,Ductility and work-hardening: nt Cu,Lu, et al, Science, (2009),- Dominated by twinning partial

7、s - GB/TB intersections: nucleation sites,Hard-I and Hard-II TB-lattice dislocation interactions,Soft Twinning partials nucleation & slip,Nano-twinned Cu: Maximum strength,L. Lu, et al, Science, (2009),HJ. Gao, et al, Nature, (2010),100 nm,5 nm,b,Nano-twinned Cu: ultrahigh work-hardening,L. Lu, et a

8、l, Science, (2009),Deformed cg-metals: 10141015m-2,r 5x1016m-2,Nano-twinned Cu vs nano-grained Cu,K. Lu, L. Lu, S. Suresh, Science, (2009), RT, LNT Strain rate: 102103 s-1 Strain of each impact: 0.1,W.S. Zhao, et al Scripta Mater. (2006),Y.S. Li, et al, Acta Mater. (2008),Dynamic plastic deformation

9、 (DPD),Bulk samples: Nano-scale deformation twins,DPD Cu: nano-sized grains & nano-scale twins,Cross-sectional TEM,e = 2.1,Y.S. Li, et al, Acta Mater. (2008),Deformation map: Cu alloys,Y. Zhang, et al, (2011),T/M lamellar spacing 15 nm,DPD CuAl4.5 wt.% (=1.47),Strength & toughness: increase hand-in-

10、hand,Hierarchical nanostructured metals,Dislocation-TB interactions Dislocation slip in T/M lamellae Dislocation nucleation at TB/GB junctions,Plastic deformation mechanism,Nano-twinned materials,High strength Ductility & work-hardening Toughness High electrical conductivity Enhanced e-migration res

11、istance ,RT,Nano-twinned Cu alloys: strong & conductive,Bulk nt-Cu,?,Thin foil nt-Cu,Nano-twins: suppress diffusion at GBs in Cu,NTs slow down grain-boundary and surface electro-migration by one order of magnitude.,Turbo disc superalloys with nano-twins,NiCo-base superalloy TMW 675 725 oC,H. Harada

12、group, NIMS Japan,Y. Yuan, et al, Adv. Eng. Mater. (2011),Hierarchical nanostructured materials,Strain delocalization & strain-hardening,Ductility drops more significantly than strength gain,Steels: strength-ductility trade-off (Banana curve),Strain localization at interfaces Work-hardening rates dr

13、op sharply,Nano-twinned grains: a reinforcing “phase” ?,Single-phased Reinforcement: strong & deformable Elastically homogeneous Plastically heterogeneous,Austenitic steels strengthened by nano-twinned austenitic (nt-g) grains,Lu K, et al, Scripta Mater. (2012),Polycrystalline coarse grains,Nano-twi

14、n strengthened austenitic steels,g,Strain rate: 102103 s-1 Each impact: e 0.1,Dynamic plastic deformation (DPD),W.S. Zhao, et al Scripta Mater. (2006),Y.S. Li, et al, Acta Mater. (2008),Thermal stability: DPD 316L stainless steels,Yan FK, et al, Acta Mater. (2012),Nano-grains: 33 nm/100 nm NT: l=23

15、nm,730 oC/20 min,750oC for 45min, Micro-grained + 10% NT Micro-grained + 2% NT CG (D100 mm),Nano-twinned 316L steel: tensile tests,Rule-of-mixture: NT: sy 2.0 GPa,High work-hardening rates,Nano-twinned 316L stainless steels,Corrosion resistance: unchanged !,Nano-twinned austenitic steels,Enhanced st

16、rength-ductility synergy Enhanced ductility at a comparable strength,Lu K, et al, Scripta Mater. (2012),“iso-phase composite”,02 mm,26 mm,6 mm,Vertical to TBs,e=0.5%,Vertical to TBs,e=0.5%,crystal zone axis：100,crystal zone axis：110,Vertical to TBs,e=0.5%,Recrystallized grains：101012 m-2,e =5.0%,Nan

17、o-twinned 316L austenitic steels,Nano-twinned grains: a reinforcing “phase” !,Single-phased Reinforcement: strong & deformable Elastically homogeneous Plastically heterogeneous,Austenitic steels strengthened by nano-twinned austenitic (nt-g) grains,Lu K, et al, Scripta Mater. (2012),Nt-g grains may

18、act as a “strong phase” to reinforce soft austenite, resulting in a better strength-ductility synergy. A unique “iso-phase composite” structure without generating obvious strain localization at interfaces at low strains, higher work-hardening rates. Strain anisotropy develops around nt-g grains at h

19、igh strains. Properties and performance to be explored: corrosion, fatigue, creep, thermal stability,Hierarchical nanostructured materials,Strain delocalization & strain-hardening,Z.G. Suo, et al. APL (2005),Strain localization induced failure,Suppression of strain localization by a ductile substrat

20、e,10% elongation without crack,Tensile ductility of Cu films on a polymer substrate,Interface de-bonding Strain localization Failure,Gradient nano-grained layer on a coarse-grained substrate an ideal structure,To suppress strain localization To eliminate debonding,Large tensile plastic strain in nan

21、o-grained metals ?,No interface !,Surface mechanical grinding treatment (SMGT),Gradient nano-grained surface layer,Fang TH, et al, Science (2011),WC/Co,K. Lu & J. Lu, J. Mater. Sci. Tech. (1999),Surface mechanical attrition treatment (SMAT),Li, Tao & Lu, Scripta Mater. (2008),Ra 0.2 mm,SMGT Tensile

22、bar sample (Cu),GNG surface layer of SMGT tensile sample,GNG surface layer of SMGT tensile sample,SMGT sample: grain size and microhardness,Unit: GPa,D100 nm,GNG surface layer,Tensile stress-strain curves: GNG/CG vs CG,(top 50 mm thick),CG Cu,SMGT Cu,Tensile samples: surface morphology,Strength-duct

23、ility: GNG/CG vs deformed CG,F4.5,F6,eT=0%,10%,33%,Tensile bar sample: Cross-sectional TEM view,Topmost layer,Tensile bar sample: Cross-sectional view,Tensile sample: grain size vs strain,Mechanically-driven GB migration (grain growth),Softening vs hardening: a saturated grain size,Plastic deformati

24、on mechanism,Mechanically-driven GB migration (grain growth),Coupling GB motion (J. Cahn 2006), indentation Weertman 2004 (Cu), Minor 2004 (Al) compression Pan 2007, Weertman 2008 (Ni, Cu) tensile Hemker 2006,2009 (Al), Fan 2006 (Fe-Ni) MD simulation Schiotz 2004,Al,Gianola et al 2006,Hierarchical nanostructured metals,Nano-grained: mechanically-driven GB migration (softening) Coarse-grained: dislocation slip (hardening),Pl