Comparative Analysis of Microstructural Defects in Monocrystalline Copper:

Comparative Analysis of Microstructural Defects in Monocrystalline Copper:

Comparative Analysis of Microstructural Defects in Monocrystalline Copper: Shock
Compression Versus Quasi-isentropic Compression
H. Jarmakani, M. Meyers, M. Schneider, B. Cao and B. Kad, Materials Science and Engineering, UCSD, La Jolla, CA.
Mc Naney, J Nguyen, and D. Orilkowsi, Lawrence Livermore National Laboratory, Livermore, CA.
OBJECTIVES:
Understanding deformation mechanisms of [001] Cu
under various high-pressure and high-strain rate loading
conditions.
Microstructural characterization.
Develop constitutive models to determine slip-twinning
transition in Quasi-ICE and shock compression.

Shock: Instantaneous loading.
Quasi-ICE: Controlled ramped loading.

TWINNING THRESHOLD MODELING

QUASI-ICE VS. SHOCK

The Prenston-Tonks-Wallace (PTW) constitutive description is used to
determine critical twinning pressure in both shock and quasi-isentropic
conditions.
PTW equation takes into account both thermal activation regime and
dislocation drag regimes.
The instantaneous flow stress is given by:
Slices cut from
cylindrical samples

Cell size vs. pressure: quasi-ICE,
laser shock and flyer-plate

Dislocation cell size vs. distance from sample free surface:
Gas-gun ICE

s y

p

1
exp
s s 0 y ln 1 1 exp p

p
s 0 y

s y

s 0 y exp p s 1

0
y

Where s and yare work hardening saturation stress and yield stress, respectively.
s0 is the value of taken at zero temperature, , are the strain and work
hardening rate, respectively, and p is a dimensionless material parameter.

Thermal Activation Regime

Strain-rate regimes in shock and Quasi
ICE-Gas-Gun

s s0 s0 s erf T ln

y y0 y0 y erf T ln

Strong Shock Regime

s s0

y s0

Flow stress is normalized to shear modulus and twinning threshold
assumed to vary with pressure:

G T , P
T P
G0
0
T

Source: M.Pullington et al., Discovery.

DYNAMIC
COMPRESSION
METHOD

EXPERIMENTAL SETUP

Temperature rise in shock and ICE (gas-gun)

PRESSURE PROFILES

Hardness, Temp. vs. Peak Pressure: Gas-gun quasi-ice

Dislocation sell size vs. distance from sample free surface:
Laser shock

TRANSMISSION ELECTRON MICROSCOPY (TEM) OF KEY FEARURES AT:
50-60 GPA
Twinning at 52GPa

30-40 GPA
Dislocated laths at 34GPa

15-30 GPA
Stacking faults at 26GPa

GAS-GUN
QUASI-ICE

Flow stress vs. peak pressure: gas-gun modeling

~104 s-1

CONCLUSIONS AND FUTURE WORK

Twins/laths at 59GPa

Dislocation cells and stacking
faults at 24GPa

Dislocation cells at 18GPa

LASER
QUASI-ICE
~107 s-1

Micro-twins at 57GPa

Stacking faults at 30GPa

FLYER PLATE
IMPACT

~10

4

Flow stress vs. peak pressure: laser modeling

(Experimental data unavailable)

s-1
Micro-twins at 55GPa

Staking faults at 40GPa

Dislocation activity decreased away from impact surface in
all cases.
TEM revealed twinning at higher pressures, stacking faults
and dislocated laths at intermediate pressures and mostly
dislocation cells at relatively lower pressures.
Modeling revealed twinning threshold lower for higherstrain rate compression experiments and reasonable
agreement with experimental data.
Future work will incorporate nanocrystalline materials (e.g.
nc Ni and nc Ni%Fe).
Understanding deformation mechanisms in nc materials:
Dislocation interactions with grain boundaries.
Grain boundary sliding.
Pressure effects on hardness.
Twinning thresholds modeling.
Molecular dynamics (MD), specifically LAMMPS, will be
used to simulate and study shock and high-strain-rate
phenomena in nc materials and compare with experiments.
High strain rate phenomena in bulk metallic glasses
(BMGs) will also be integrated into study.

Dislocation cells at 20GPa

ACKNOWLEDGEMENT:
LASER
SHOCK

~10

9

s-1

This work was performed under the auspices of
the U.S. Department of Energy by University of
California, Lawrence Livermore National
Laboratory.

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