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In situ x-ray synchrotron diffraction experiments were carried out on nickel-based high-strength superalloys under pressure to understand their deformation mechanism using a diamond anvil cell (DAC). Radial x-ray diffraction determines the room-temperature equations of state and yield strengths of binary Ni3Al alloy and 500 ppm boron-doped Ni3Al to pressures of 20 and 46 GPa, respectively. Crystallographic preferred orientations observed in these superalloys due to anisotropic stress field in DAC indicate the onset of plastic deformation. Inverse pole figure analysis reveals that the underlying deformation mechanisms change from an octahedral slip to a simultaneous activation of octahedral and cube slips upon doping with boron. The yield-strength values were found to increase with pressure and are comparable to those determined from axial diffraction experiments. The results indicate that the yield strength of Ni3Al:B is about 0.5 GPa higher (at pressures below 20 GPa) due to grain boundary strengthening by boron. It is shown that due to high elastic anisotropy of Ni3Al alloy, the yield-strength estimations from diffraction experiments strongly depend on the micromechanical model used to convert the measured elastic strains into stresses. [ABSTRACT FROM AUTHOR]

High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of ∼15-25 GPa; the discrepancies are may be due to the effects of texturing. [ABSTRACT FROM AUTHOR]

The ac resistance measurements on the trigonal (α-) phase of ZrMo2O8 and HfMo2O8 carried out up to 5 GPa using the toroid anvil apparatus are reported. The ac resistance data in both the materials are found to be strongly frequency dependent and show a transition between two power law regimes with a crossover frequency (ωc) near 1 kHz. For both the compounds slope changes and anomalies are observed in the ac resistance data at the structural transition pressures. The activation volumes at room temperature are obtained by analyzing the ac conductance data in terms of the pressure dependent activation volume model. The main conduction mechanism at 12 Hz is believed to be the diffusion of oxygens ions, whereas hopping of point defects is responsible for ac conductuance above 33 kHz. At 1 KHz, a crossover from hopping to diffusion of point defects is observed at the α-δ (monoclinic) phase transition pressure. [ABSTRACT FROM AUTHOR]

Presents a study which focused on the variation of the effective ablation pressure with thickness of laser irradiated thin gold foils. Experimental details; Results and their interpretation with the radiation model; Computation of shock pressures.

Focuses on a study which investigated the effect of impedance mismatch on shock-pressure enhancement in laser-irradiated layered targets by numerical simulation of the history of shock generation. Impedance mismatch in layered targets; Description of the model; Test of the model and study of layered targets.