Strength and deformation are fundamental material responses to stress that are important to multiple scientific disciplines. The response of materials to thermodynamic conditions affects geologic and planetary processes and the structure, chemical behavior, and rheology of planetary interiors, as well as the outcome of accretionary impacts. These same properties are applied in defense science and are important industrially for the development of novel materials and the manufacture of strong tools and parts. In this dissertation, I determine the high-pressure strength, compression and deformation behavior of tungsten carbide, and solidified krypton and xenon – simple materials that exhibit very different strength and compression properties.Material properties are examined in this work with synchrotron radiation in the diamond anvil cell, which allows a variety of X-ray and complementary optical techniques to be used on materials under quasi-static stress loads. Synchrotron radiation is brilliant, tunable, and highly focused, allowing precision measurements of small samples. Pressure media may be used to minimize the effects of non-hydrostatic stress, or if non-hydrostaticity is required, the sample may be compressed without a medium. By using both the axial and radial diffraction geometries, materials may be probed under a range of stress conditions. Tungsten carbide is a hard, ultra-incompressible ceramic used widely in industry. The reported bulk modulus of WC was discrepant by more than 125 GPa. This is attributed to grain size dependence, though measurement techniques may also be important. Quasi-static compressive strength and deformation behavior of WC at high pressure have not been previously studied. I compressed bulk and nano-crystalline hexagonal WC to 66 GPa in the diamond anvil cell. Nano-WC is softer than bulk WC. Yielding at ~30 GPa is accommodated by prismatic slip up to 40-50 GPa, at which pressure pyramidal slip along a different direction also becomes activated. WC supports ~12-16 GPa differential stress, the difference between stress aligned with the load axis and stress in the direction of the gasket, at yielding but its strength is anisotropic and the (001) plane supports a ~68-70% higher differential stress at yielding. Solidified noble gases are prototypical solids that crystallize with simple structures and low strength. Heavy rare gas solids Ar, Kr, and Xe undergo a martensitic fcc-hcp phase transition as pressure is increased. At 300 K the metastable fcc phase persists over a wide pressure range. I compressed Kr and Xe in the diamond anvil cell to 115 GPa to determine phase equilibria, strength, and deformation. The phase transition progresses more quickly in Xe than in Kr. Both Kr and Xe crystallize as large fcc crystals and develop preferred crystallite orientation (texture) in the fcc and hcp phases. Xe peaks are highly textured and broad to at least 101 GPa. Non-hydrostaticity is observed at 15-20 GPa in both Kr and Xe and increases with pressure, with both materials supporting at least 5-7 GPa differential stress above 40 GPa. This work examines the strength, compression and deformation behavior of WC, Kr, and Xe, extremes in the range of possible mechanical responses to stress. Strength in WC is overestimated when determined by lattice strain due to plastic deformation and is anisotropic, possibly due to the position of C atoms blocking slip systems dislocation motion. Grain size may affect incompressibility. The phase transition progresses more slowly in both Kr and Xe than previously reported. Radial diffraction can reveal more about material properties than axial diffraction and may be especially useful when multiple phases are present because texture and stress orientation can bias axial patterns.
Read
