In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

Abstract

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum-an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

Femtosecond X-Ray Diffraction Studies of the Reversal of the Microstructural Effects of Plastic Deformation during Shock Release of Tantalum

“…As has been shown in [43] under [110] compression in these samples, the shock-induced shear stress is relieved by either slip on {112} 111 system or {112} twinning. Since the material is laterally confined, in order to preserve the geometry of uniaxial compression, both slip and twinning induce crystal lattice rotations [31,43,50] about [110] which can be directly related to the amount of shear stress relieved.…”

“…The relative intensity of these spots provide a measure of the degree of twinning within the sample, which has been found to maximize at a volume fraction of order 30% between shock pressures of 50 and 150 GPa [43]. Figure 2c shows a diffraction pattern during release after a passage of 75 GPa shock, which on compression generates large amounts of twinning, with the diffraction associated with the twins marked both under compression, and where they would be expected to appear under release.…”

“…By bringing the x-ray beam in at an angle to the compression axis of the fiber textured target we are able to directly monitor lattice rotation and twinning. Such a geometry does not produce full Debye-Scherrer (DS) rings, but distinct arcs on each ring, the azimuthal position of which provides direct information on the orientation of the planes with respect to the shock direction, [48] and which previously enabled the observation of lattice rotation due to slip and twinning under shock compression [43]. The texture direction is aligned with the sample's normal, and we define angles χ between the sample's normal and the normals to the lattice planes producing the diffraction spots, and denote by χ 0 such angles for the ambient unshocked material.…”

“…The technique of in situ XRD to study shock-compressed materi-als has been developed over several years utilizing a number of different shock drivers and x-ray sources, including diodes [24][25][26][27], laser-produced-plasmas [28][29][30][31][32][33] and 3 rd generation synchrotrons [34][35][36][37]. More recently, with the advent of 4 th generation light sources such as the Linac Coherent Light Source (LCLS) single-shot 100-fs diffraction patterns can be obtained from laser-shocked crystals, providing lattice-level information on a timescale shorter than even the fastest phonon period [38][39][40][41][42][43].…”

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

“…In addition to accessing extreme thermodynamic states, shock-wave experiments are ideally suited to examine condensed-matter changes in real time (picosecondnanosecond timescales). Although the majority of past studies have involved continuum measurements (e.g., impedance matching and wave profiles) [1][2][3][4]7,8], recent experimental advances are providing real-time microscopic information through in situ, x-ray diffraction (XRD) measurements, including new insights into phenomena such as shock-induced structural transformations [9][10][11] and deformation twinning [12,13].…”