The influence of explosive-driven shock prestraining at 35 GPa and of high deformation on the structure/property behavio
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THE microstructural changes produced in austenitic stainless steels (SS’s) by the passage of shock waves and their attendant effects on mechanical properties and/or microstructure have been widely studied.[1–15] The strengthening of metals and alloys through the use of explosive shock waves has been known since the 1940’s and remains one of several processing procedures/strengthening mechanisms being explored to meet the demands for higher strength in bulk engineering materials.[1,16] The postshock mechanical behavior of a wide variety of materials as a function of the applied shock parameters has been reviewed previously.[1,17] Examples of the structure/property effects of shock-wave deformation on material response have been particularly well quantified for a large number of fcc metals such as copper, nickel, and aluminum and fcc alloys including brass and austenitic SS’s. In all of the previous literature studies, shock prestraining was accomplished using a “square-topped” impulse via flyerplate impact, either explosively driven or using a gas/powder launcher. During shock loading, a material is initially deformed by a compressive wave and then is released to ambient pressure and its nominal density and approximate “original” dimensions (excluding some small irreversible residual strain) by a rarefaction wave. Elastic and plastic deformation are applied in compressing the material to a higher density and then reversing the sign of loading, comprising a single load-reversal cycle akin to a Bauschinger loading cycle.[18] This high-strain-rate loading path leaves the specimen with a small measurable residual plastic strain, excluding radial release effects, but still retains a high density B.H. SENCER, Postdoc, S.A. MALOY, and G.T. GRAY III, Staff Members, are with Structure/Property Relations, Materials Science and Technology (MST-8), Los Alamos National Laboratory, Los Alamos, NM 87545. Contact e-mail: [email protected] Manuscript submitted November 1, 2004. METALLURGICAL AND MATERIALS TRANSACTIONS A
of deformation-induced defects in the microstructure.[17,26] The generation and storage of shock-induced defects is in response to the applied plastic-strain rate and volumetric compression of the atomic lattice during the shock-loading pulse. It has been shown that the microstructures created during shock loading strongly depend on the magnitude of the peak shock pressure and shock pulse duration.[1,17–22] The microstructures observed in shock-prestrained 304 SS using transmission electron microscopy (TEM) consist of deformation twinning and dislocations tangles for shock pressures above 15 GPa and, principally, stacking faults and dislocation tangles at lower shock pressures.[23] Materials possessing low-stacking-fault energies have been shown to deform by deformation twinning at very low shock pressures due to their restricted propensity to cross-slip.[23,24,25] In the current study, the mechanical properties and microstructural evolution of a direct high-explosive (HE)driven “Taylor wave” shock-prestrained,
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