Grain refinement in a copper alloy by shaped charge explosion

It is proposed that the microcrystal transformation process of the Cu-Sn-P alloy in the shaped charge is interpreted by the homogeneous nucleation (i.e., rotational-mode) mechanism of dynamic recrystallization. Complex lattice structure and serious lattice distortion exist in the alloy, and these factors reduce dislocation slip. The deformation flow of the alloy at high-strain and high-strain-rate may be produced by rigid glide among the atoms, besides partly by dislocation slip when the external load is in excess of its theoretical yield stress. The deformation flow due to rigid glide is similar to the solid-liquid phase transformation since the glide affects the bonding. This means that the alloy may be "liquefied" under the action of the shock stress, and the "liquid" lies in undercooled if it is below its melting point. According to the preliminary calculation, a high undercooling appears under the experimental conditions. The high undercooling results in occurrence of the more nuclei, and this may be reason why the crystals of the alloy are refined in the shaped charge. The annealing twins present in a part of grains of the shocked specimen are the evidence for migration recrystallization. This phenomenon is possibly consistent with the third mixed-mode mechanism proposed by Meyers et al., that is, once this microcrystalline structure is formed by the rotational-mode mechanism, it remains stable by being subjected to migration recrystallization.