THE INFLUENCE OF YIELD STRENGTH ON THE NONHYDROSTATIC COMPRESSION OF ELASTICALLY ANISOTROPIC POLYCRYSTALS

The compression behavior of a foil of Ni3Al in a pressure medium of Na Cl has been studied by energy-dispersive X-ray diffraction in a diamon d anvil cell. Increasingly nonhydrostatic conditions lead to a region of incompressibility starting at around 3 GPa and terminated by a disc ontinuity in the compressibility at 7 GPa. Strong line broadening indi cating plastic deformation starts at 3 GPa and continues to above 7 GP a. Direct compression of a foil between the diamonds results in a stro ng 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 introduc tion of stacking faults. The trend with pressure of the divergence agr ees with that of the line profiles suggesting that these are to a larg e extent due to stacking faults. Comparison with earlier results for C u3Au in identical experiments shows that the shift to higher pressures of the features of the compression curve is due to the higher yield s trength of Ni3Al.