Effect of shock-stress duration on the residual structure and hardness of nickel, chromel and inconel

Abstract

Sheet samples of pure nickel, chromel-A (80% Ni, 20% Cr) and inconel 600 (76% Ni, 16% Cr, 7% Fe) were simultaneously shock loaded in sandwich assemblies at a pressure of 250 kbar for shock-pulse durations of 0.5, 1.0 and 6.0 μsec utilizing a flying plate. The residual microhardness of all samples was observed to be increased by shock pulses in the range of approximately 0.5 – 2 μsec, to saturate at 2 μsec and to decrease in hardness in the range of 2 – 6 μsec. Examination of the residual substructures by transmission electron microscopy revealed a slight decrease in dislocation cell size in the range of 0.5 – 6 μsec, with a change in average dislocation density corresponding to the variations in residual hardness. Dislocation densities in the chromel-A and inconel 600 also corresponded to the residual hardness trend, and the deformation twin width was observed to vary from approximately 50 Å at 0.5 μsec to 150 Å at 6 μsec. The volume density of deformation twins did not vary appreciably in the same pulse-duration range. The results demonstrate an apparent interdependence of shock-stress amplitude and shock-stress duration in the effect of shock deformation on the residual structure and hardness of metals and alloys; that is, hardness can be increased by increasing the shock pressure at constant pulse duration or by increasing the pulse duration at a constant shock pressure.