Laser-induced shock compression of monocrystalline copper: characterization and analysis
Introduction
Askaryon and Morez [1] demonstrated in 1963 that shock pulses could be generated in metals from laser-pulse induced vaporization at the surface. The use of surfaces covered by a laser-transparent overlay was introduced by Anderholm [2]; this enabled the confinement of the vapor products resulting in an increase of the peak pressure of the shock incident on the metal. Shock amplitudes as high as those generated by explosives or planar impact devices could be generated with a basic difference: the duration of the shock pulse was in the nanosecond range. Fairand et al. [3] and Clauer et al. [4] used these laser-induced shock pulses to modify the microstructure of engineering alloys, increasing their strength and fatigue resistance.
Simultaneous shock compression and X-ray diffraction experiments were introduced by Johnson et al. [5] and continued by Zaretsky et al. [6]. Wark et al. [7] used laser-generated X-rays to produce shock compression at the Nova laser facility. These shock compression experiments on silicon monocrystals were coupled with X-ray diffraction that successfully measured the compression both perpendicular (Laue) and parallel (Bragg) to the shock propagation direction. The X-rays that generated the shock pressure were created by eight laser beams focused into an internally shielded hohlraum [8], and the X-rays used for X-ray diffraction were provided by two lasers incident on a separate metal foil.
The use of simultaneous shock compression and X-ray diffraction offers a very attractive means of observing the distortions in the lattice as it is being compressed. These measurements are essential to unravel the mechanisms of plastic deformation in shock compression. A number of proposals for dislocation generation in shock compression have been advanced over the years [9], [10], [11], [12], [13], [14], but none of them have been critically tested.
This paper describes a series of experiments carried out on copper single crystals at the Omega ICF (Inertial Confinement Fusion) Facility, University of Rochester. Some of these experiments were carried out to record the simultaneous Bragg and Laue diffraction, while others were carried out to shock compress and then recover the sample for post-mortem analysis of the plastic deformation microstructure. The initial shock amplitudes varied from approximately 10 to 60 GPa and pulse durations were on the order of 5 ns, one order of magnitude lower than earlier shock laser experiments (20–100 ns) and two orders of magnitude lower than plate impact experiments (0.1–0.2 μs). Thus, these experiments explore a new regime of shock compression. In this paper, we describe laser recovery experiments and the deformation substructures generated, and compare these observations with analytical predictions.
Section snippets
Experimental techniques
For the recovery experiments, single crystals of Cu with a [100] orientation were obtained from Goodfellow in the form of disks with 2.0–3.0 mm diameter and 1 mm thickness. They were mounted into foam-filled recovery tubes shown in Fig. 1(a). Foam with a density of 50 mg/cm3 was used to decelerate the samples for recovery.
The shock amplitude at the surface of the Cu crystal can be obtained from the laser energy and the computed values (using hydrocode calculations). Results are shown in Fig. 2.
Experimental results and discussion
Copper has been the object of numerous shock recovery experiments and its response is fairly well understood. It has a stacking-fault energy of 57±8 mJ/m2. The shock-induced structure consists of dislocation cells up to a critical pressure. At higher pressures, twinning is prevalent. For single crystals, De Angelis and Cohen [15] found that the crystal twinning stress was 14 GPa, for the shock wave propagating along [100] while it was 20 GPa for [111]. This is consistent with the findings by
Analysis
The dislocations are envisioned to be generated as loops and this is supported by Fig. 13 (two-dimensional schematic representation). The edge (positive and negative) components of the loops are shown. The sheared area (within the loop) is indicated by a thinner line connecting the positive and negative edge dislocations. Whereas one of the loop legs moves towards the shock front, the other (opposite) is repelled from the front. Xu and Argon [24] calculated the activation energy for loop
Conclusions
It is demonstrated that laser-driven shock compression experiments can provide unique information on the processes of defect generation at high strain rates. The results indicate that all critical processes of defect generation operate at the shock front. The pulse duration in the current experiments was on the order of nanoseconds, two orders of magnitude lower than plate impact experiments. Nevertheless, the substructures observed by transmission electron microscopy are very similar. The
Acknowledgements
Research supported by the Department of Energy Grants DEFG0398DP00212 and DEFG0300SF2202, and by the US Army Research Office MURI Program.
References (37)
Acta Met
(1962)Scripta Met
(1978)Mech of Matls
(1986)- et al.
Acta Met.
(1963) - et al.
Acta Met
(1964) Scripta Met
(1978)J Mech Phys Solids
(1992)- et al.
J Mech Phys Sol
(1992) - et al.
Matls Sci and Eng
(1991) - et al.
Acta Mater
(1997)
Acta Mat
JETP Lett
Appl Phys Lett
Appl Phys Lett
Phys Rev Lett.
J Appl Phys
Phys Rev B
Cited by (245)
Role of micro-alloying element in dynamic deformation of Mg-Y alloys
2024, International Journal of Mechanical SciencesFormation of microbands in copper under loading by spherically converging shock waves
2023, Materials CharacterizationComparative numerical study of rate-dependent continuum-based plasticity models for high-velocity impacts of copper particles against a substrate
2023, International Journal of Impact EngineeringDynamic deformation of Al under shock loading
2022, Computational Materials Science