Non-hydrostatic Conditions in High-pressure Devices: Analysis of Plastic Deformation with EDX

The effect of different pressure devices and pressure media on the compression behavior of elastically anisotropic polycrystals (Cu3Au, Ni3Al) is investigated with energy-dispersive X-ray diffraction (EDX) correlating information from both line profiles and line positions. Plastic deformation due to stacking faults leads to a volume incompressibility preceded at high ratios of non-hydrostatic to hydrostatic stresses by a volume increase due to introduction of dislocations. A discontinuity in the compressibility at the transition back from plastic to elastic compression is due to the yield strength of the plastically deformed material and corresponds to the Hugoniot elastic limit. The compression of a fully plastically deformed material is elastic and isotropic, independent of the presence and type of pressure medium. The yield strength of the samples is estimated from the offset to the hydrostat of the compression curve above the discontinuity in the compressibility