Shock Deformation of Inconel 600 Alloy: Effect of Fine Coherent Precipitates on Explosive-Shock Hardening

Abstract

Sheet samples of pure nickel and Inconel 600 alloy (76% Ni, 16% Cr, 7% Fe) containing a fine precipitate were simultaneously shock loaded in sandwich assemblies at pressures of 50, 100, 150, 200, and 370 kbar by a planar pulse of roughly 2-μsec duration explosively initiated by a flying plate. The residual microhardness of the nickel was observed to saturate above 300 kbar while that for Inconel continued to increase steadily. Examination of the nickel substructures by transmission electron microscopy revealed a steadily decreasing cell size with increasing shock pressure; with almost no evidence of deformation twins at 370 kbar. The Inconel substructure was characterized by planar dislocation arrays which included an increasing concentration of dipoles and elongated loops to 200 kbar; while at 370 kbar deformation twins having an average thickness of 150 Å and occupying 19% of the volume were observed. The coherent precipitates in the Inconel matrix were observed to become incoherent at pressures above 50 kbar, with the concomitant production of dislocation tangles and loops at the particle-matrix interface. The precipitates were observed to enhance shock hardening by acting as sources for dislocation dipoles and elongated loops.

Repeated Shock Loading of Nickel and Stainless Steel

“…3 and 4. Although selective twinning in (001) in fcc metals predicted by Cowan (5) was observed earlier in shock-loaded copper (21), earlier investigations of shock-loaded nickel (20,22,23) failed to reveal this phenomenon. The reason for this seems to be that in some earlier studies (22,23) the grain size was too small to promote twinning [as described recently by Greulich and Murr (10)], and there may have been differences in the texture of the previously shocked nickel sheet (a preponderance of (110) and other higher index orientations), coupled with errors in indexing (001) twinned regions as a result of deviations in the foil surfaces in the electron microscope.…”