The influence of yield strength on the non-hydrostatic compression of elastically anisotropic polycrystals

The compression behavior of a foil of Ni3A1 in a pressure medium of NaCl has been studied by energy-dispersive X-ray diffraction in a diamond anvil cell. Increasingly non-hydrostatic conditions lead to a region of incompressibility starting at around 3 GPa and terminated by a discontinuity in the compressibility at 7 GPa. Strong line broadening indicating plastic deformation starts at 3 GPa and continues to above 7 GPa. Direct compression of a foil between the diamonds results in a strong divergence in lattice parameters calculated from different lattice spacings and a volume incompressibility terminated by a discontinuity in the compressibility. The divergence in lattice spacings calculated from multiple orders of reflections can be explained from the introduction of stacking faults. The trend with pressure of the divergence agrees with that of the line profiles suggesting that these are to a large extent due to stacking faults. Comparison with earlier results for Cu3Au in identical experiments shows that the shift to higher pressures of the features of the compression curve is due to the higher yield strength of Ni3Al