NONHYDROSTATIC COMPRESSION OF ELASTICALLY ANISOTROPIC POLYCRYSTALS - II - DIRECT COMPRESSION AND PLASTIC-DEFORMATION

The effects of nonhydrostatic conditions on the compression behavior o f elastically anisotropic polycrystals have been studied by energy-dis persive x-ray diffraction of a foil of Cu3Au compressed directly betwe en diamond anvils. A volume expansion between 0.3 and 1 Cpa is explain ed to result from the introduction of dislocations. A volume incompres sibility accompanied by saturation in stress, strain, and the stacking fault probability between 1 and 2 GPa is due to work hardening. A com plete pressure cycle, including repressurization after pressure releas e, and the compression of Cu3Au previously deformed by filing demonstr ate that mutual repulsion between lattice defects also contributes to the volume incompressibility. The pressure region of incompressibility terminates at a discontinuity which occurs when the yield strength of the plastically deformed material is exceeded. The compression above this point is elastic and isotropic. The yield strength is estimated f rom the offset of the measured compression curves from the hydrostat.