Strong strain hardening in nanocrystalline nickel.

Low strain hardening has hitherto been considered an intrinsic behavior for most nanocrystalline (NC) metals, due to their perceived inability to accumulate dislocations. In this Letter, we show strong strain hardening in NC nickel with a grain size of approximately 20 nm under large plastic strains. Contrary to common belief, we have observed significant dislocation accumulation in the grain interior. This is enabled primarily by Lomer-Cottrell locks, which pin the lock-forming dislocations and obstruct dislocation motion. These observations may help with developing strong and ductile NC metals and alloys.

[1]  P. Liaw,et al.  Deformation crossover: from nano- to mesoscale. , 2009, Physical review letters.

[2]  A. Cottrell LX. The formation of immobile dislocations during slip , 1952 .

[3]  F. Sansoz,et al.  Strengthening in Gold Nanopillars with Nanoscale Twins , 2007 .

[4]  Yonghao Zhao,et al.  Simultaneously Increasing the Ductility and Strength of Nanostructured Alloys , 2006 .

[5]  Ronald O. Scattergood,et al.  Ultrahigh strength and high ductility of bulk nanocrystalline copper , 2005 .

[6]  Phillips,et al.  Mesoscopic analysis of structure and strength of dislocation junctions in fcc metals , 2000, Physical review letters.

[7]  Wei Liu,et al.  High Tensile Ductility and Strength in Bulk Nanostructured Nickel , 2008 .

[8]  V. Bulatov,et al.  Connecting atomistic and mesoscale simulations of crystal plasticity , 1998, Nature.

[9]  Q. Wei Strain rate effects in the ultrafine grain and nanocrystalline regimes—influence on some constitutive responses , 2007 .

[10]  X. Liao,et al.  Retaining ductility , 2004, Nature materials.

[11]  H. Karnthaler,et al.  Weak-beam studies of composite dislocations and dislocations gliding on (001) planes in silver , 1981 .

[12]  Yuntian Zhu,et al.  Partial-dislocation-mediated processes in nanocrystalline Ni with nonequilibrium grain boundaries , 2006 .

[13]  K. Jacobsen,et al.  A Maximum in the Strength of Nanocrystalline Copper , 2003, Science.

[14]  Andrew G. Glen,et al.  APPL , 2001 .

[15]  H. Van Swygenhoven,et al.  Dislocation cross-slip in nanocrystalline fcc metals. , 2008, Physical review letters.

[16]  C. Koch Optimization of strength and ductility in nanocrystalline and ultrafine grained metals , 2003 .

[17]  Xiaolei Wu,et al.  Twinning and stacking fault formation during tensile deformation of nanocrystalline Ni , 2006 .

[18]  Simon R. Phillpot,et al.  Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation , 2002, Nature materials.

[19]  H. V. Swygenhoven,et al.  Preface to the viewpoint set on: mechanical properties of fully dense nanocrystalline metals , 2003 .

[20]  Subra Suresh,et al.  Mechanical behavior of nanocrystalline metals and alloys , 2003 .

[21]  S. G. Srinivasan,et al.  Formation mechanism of wide stacking faults in nanocrystalline Al , 2004 .

[22]  H. Van Swygenhoven,et al.  Stacking fault energies and slip in nanocrystalline metals , 2004, Nature materials.

[23]  Evan Ma,et al.  Tensile properties of in situ consolidated nanocrystalline Cu , 2005 .

[24]  R Madec,et al.  From dislocation junctions to forest hardening. , 2002, Physical review letters.

[25]  J. Hirth On Dislocation Interactions in the fcc Lattice , 1961 .

[26]  Vasily V. Bulatov,et al.  Dislocation multi-junctions and strain hardening , 2006, Nature.

[27]  Lei Lu,et al.  Ultrahigh Strength and High Electrical Conductivity in Copper , 2004, Science.

[28]  D. Wolf,et al.  Deformation-mechanism map for nanocrystalline metals by molecular-dynamics simulation , 2004, Nature materials.

[29]  Fenghua Zhou,et al.  High tensile ductility in a nanostructured metal , 2002, Nature.

[30]  W. Lomer A dislocation reaction in the face-centred cubic lattice , 1951 .

[31]  P. Franciosi,et al.  Latent hardening in copper and aluminium single crystals , 1980 .

[32]  P. Liaw,et al.  Strain-dependent deformation behavior in nanocrystalline metals. , 2008, Physical review letters.

[33]  Xiaolei Wu,et al.  Dislocations in nanocrystalline grains , 2006 .

[34]  P. Jackson,et al.  Latent Hardening and the Flow Stress in Copper Single Crystals , 1967 .

[35]  Y. Zhu,et al.  Inverse grain-size effect on twinning in nanocrystalline Ni. , 2008, Physical review letters.

[36]  K. Lu,et al.  Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale , 2009, Science.

[37]  Jens Lothe John Price Hirth,et al.  Theory of Dislocations , 1968 .