Cyclic stress-strain response and dislocation substructure evolution of nickel

The cyclic stress-strain response and substructure evolution of initially annealed pure nickel (high stacking fault energy FCC material) were studied by accomplishing full-reversed tension-compression tests at room temperature over a large range of constant plastic strain amplitudes. Both single crystals oriented for single slip and polycrystals with two grain sizes, 24 μ m and 290 μm were studied.; Detailed analyses of the cyclic stress-strain responses (including hardening curve, shape of hysteresis loop, loop shape parameter and second derivative response) of deformed nickel specimens were performed to reveal the characteristics associated with the specific dislocation structures that form. Distinct substructure evolution is characterized by the change of the dislocation structures from low plastic strain amplitude to high plastic strain amplitude. Vein structures at low plastic strain amplitude will give way to PSB structures at intermediate plastic strain amplitude. These PSBs structures are replaced by the well-developed cell structures at high plastic strain amplitude. These dislocation structures were studied using transmission electron microscopy (TEM) and surface observation analysis. In addition a preliminary study of the magnetostriction effect on the cyclic deformation behavior of nickel was also accomplished.; The major goal of this study was to provide a connection between macroscopically observed cyclic stress-strain responses and the underlying substructure evolution, thereby providing a fundamental understanding of the mechanisms of microstructural influences on cyclic plasticity behavior of nickel.