Real-Time Observation of Stacking Faults in Gold Shock Compressed to 150 GPa

Abstract

A microscopic-level understanding of the high-pressure states achieved under shock compression, including comparisons with static compression, is a long-standing and important scientific challenge. Unlike hydrostatic compression, uniaxial strains inherent to shock compression result in plastic deformation and abundant lattice defects. At high pressures (>50 GPa), the role of shock-induced deformation and defects remains an open question. Because of the nanosecond time scales in shock experiments, real-time in situ observations of shock-induced lattice defects have been challenging. Here, we present synchrotron x-ray diffraction measurements on laser-shock-compressed gold that provide the first unambiguous in situ measurements of stacking faults (SFs), likely formed by partial dislocations, during shock compression. SF abundance increases monotonically with shock compression up to 150 GPa, where SFs comprise almost every 6th atomic layer. Our results show that SFs play an important role in the plastic deformation of face-centered-cubic metals shocked to high stresses, providing a quantitative benchmark for future theoretical developments.

Fingerprinting shock-induced deformations via diffraction

“…9 b). Note that these stacking faults not only broadened but also shifted the spots/peaks 25 . Excluding the role of pressure, the presence of stacking faults in the FCC phase would shift {111} and {200} peaks to higher and lower 2θ values, respectively 44 .…”

“…However, researchers have just begun to harness high-speed X-ray diffraction to detail an experimental shock response in real-time 22 , 23 . Over just the last five years, this approach has resolved a long-standing controversy over the phase transformations of shocked graphite 24 , connected stacking faults to the plastic deformation of shocked Au 25 , tracked the twins and slip in shocked Mg 23 , 26 , demonstrated the pressure dependence of slip and twining for Ta 8 , and elucidated the phase transformation of BCC Fe 27 . Moreover, researchers have just begun to harness high-speed electron diffraction for even finer spatial resolution 28 – 31 .…”

Slip competition and rotation suppression in tantalum and copper during dynamic uniaxial compression

“…al. suggests that the fault fraction at this pressure should be closer to 4% [80], which implies that a considerably greater fraction of the plastic strain is in reality mediated by full slip. One could then ask whether the dominant slip directions being of the type 011 rather than 112 substantively alters the implications of the model.…”

Femtosecond Diffraction and Dynamic High Pressure Science

“…To date the laser-compression hutch has been used to study a number of compressed metals to pressures as high as 383 GPa. [69][70][71][72][73] .…”

“…This comes about as a stacking fault looks like a thin sheet of hcp material embedded in the fcc lattice, and as such each fault introduces a phase difference between the x-rays and bulk fcc material. Indeed, an analysis of x-ray line shifts and line profiles has allowed stacking fault densities to be measured in laser-shocked gold at pressures up to 150 GPa using 100 psec pulses of x-rays from a synchrotron source 71 .…”