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Title: Deformation of nanocrystalline materials at ultrahigh strain rates - microstructure perspective in nanocrystalline nickel

Abstract

Nanocrystalline materials with grain sizes smaller than 100 nm have attracted extensive research in the past decade. Due to their high strength, these materials are good candidates for high pressure shock loading experiments. In this paper, we investigated the microstructural evolutions of nanocrystalline nickel with grain sizes of 10-50 nm, shock-loaded in a range of pressures (20-70 GPa). A laser-driven isentropic compression process was applied to achieve high shock-pressures in a timescale of nanoseconds and thus the high-strain-rate deformation of nanocrystalline nickel. Postmortem transmission electron microscopy (TEM) examinations reveal that the nanocrystalline structures survive the shock deformation and that dislocation activity is the prevalent deformation mechanism when the grain sizes are larger than 30 nm, without any twinning activity at twice the stress threshold for twin formation in micrometer-sized polycrystals. However, deformation twinning becomes an important deformation mode for 10-20 nm grain-sized samples.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
893573
Report Number(s):
UCRL-PROC-220628
TRN: US200625%%409
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: Presented at: 8th International Conference on Mechanical and Physical Behavior of Materials Under Dynamic Loading (Dymat 2006), Dijon, France, Sep 11 - Sep 15, 2006
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; COMPRESSION; DEFORMATION; DISLOCATIONS; GRAIN SIZE; MICROSTRUCTURE; NICKEL; POLYCRYSTALS; STRAIN RATE; TRANSMISSION ELECTRON MICROSCOPY; TWINNING

Citation Formats

Wang, Y, Bringa, E, Victoria, M, Caro, A, McNaney, J, Smith, R, and Remington, B. Deformation of nanocrystalline materials at ultrahigh strain rates - microstructure perspective in nanocrystalline nickel. United States: N. p., 2006. Web.
Wang, Y, Bringa, E, Victoria, M, Caro, A, McNaney, J, Smith, R, & Remington, B. Deformation of nanocrystalline materials at ultrahigh strain rates - microstructure perspective in nanocrystalline nickel. United States.
Wang, Y, Bringa, E, Victoria, M, Caro, A, McNaney, J, Smith, R, and Remington, B. Mon . "Deformation of nanocrystalline materials at ultrahigh strain rates - microstructure perspective in nanocrystalline nickel". United States. doi:. https://www.osti.gov/servlets/purl/893573.
@article{osti_893573,
title = {Deformation of nanocrystalline materials at ultrahigh strain rates - microstructure perspective in nanocrystalline nickel},
author = {Wang, Y and Bringa, E and Victoria, M and Caro, A and McNaney, J and Smith, R and Remington, B},
abstractNote = {Nanocrystalline materials with grain sizes smaller than 100 nm have attracted extensive research in the past decade. Due to their high strength, these materials are good candidates for high pressure shock loading experiments. In this paper, we investigated the microstructural evolutions of nanocrystalline nickel with grain sizes of 10-50 nm, shock-loaded in a range of pressures (20-70 GPa). A laser-driven isentropic compression process was applied to achieve high shock-pressures in a timescale of nanoseconds and thus the high-strain-rate deformation of nanocrystalline nickel. Postmortem transmission electron microscopy (TEM) examinations reveal that the nanocrystalline structures survive the shock deformation and that dislocation activity is the prevalent deformation mechanism when the grain sizes are larger than 30 nm, without any twinning activity at twice the stress threshold for twin formation in micrometer-sized polycrystals. However, deformation twinning becomes an important deformation mode for 10-20 nm grain-sized samples.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Apr 10 00:00:00 EDT 2006},
month = {Mon Apr 10 00:00:00 EDT 2006}
}

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  • The mechanical response of a pearlitic UHCS-1.3C steel deformed at approximately 4000 s{sup -1} to large strains ({var_epsilon} = -0.9) has been studied. Failure, at both the macroscopic and the microscopic levels has been evaluated, and the ability of the material to absorb energy in compression has been examined. Failure occurred by the development of a shear band. However before failure, extensive buckling of the carbide plates was observed and the UHCS-1.3C material exhibited significant potential for compressive ductility and energy absorption due to the distributed buckling of these plates. Strain localization during adiabatic shear band development resulted in themore » formation of austenite. Subsequent cooling produced a divorced-eutectoid transformation with associated deformation, which resulted in a microstructure consisting of 50 to 100 nm sized grains. The stress-strain behavior within the shear band has also been determined. The results are used to critically evaluate the maximum shear stress criterion of shear band development. New criteria for the development of shear bands are developed based on a strain energy concept.« less
  • Abstract not provided.
  • The strain rate sensitivity of materials is measured through a combination of quasistatic, Hopkinson bar, and pressure-shear experiments. The pressure-shear technique has largely been limited to strain rates of order 1E6 1/s. Recent advances in laser and magnetically driven ramp loading have made it possible to achieve significantly higher rates, 1E5-1E8 1/s, under uniaxial strain compression. Strength in these experiments can be calculated by comparing the loading response to the hydrostatic (pressure-density) response of the material for the same density and temperature [Fowles, 1961]. This must be done accounting for the heating due to plastic work in the experiments. Experimentalmore » uniaxial strain data for aluminum for strain rates up to 1E8 1/s are examined and compared with existing data. The results are consistent with conventional views of the strain rate sensitivity of aluminum. However, when one considers the higher mean stress (pressure) present in the uniaxial strain experiments and, to a lesser extent, the pressure-shear experiments, one finds the material remains rate insensitive to about 1E7 1/s, two orders of magnitude higher than previously thought. Important caveats about determining strength in this manner will be discussed, and recommendations for future work will be made.« less