Analysis of materials exposed to ultra-high shock pressure

摘要

A spherical shock-recovery system was used to study materials behavior under ultra-high pressure conditions. The samples were recovered intact and subjected to metallurgical analysis and scanning electron microscopy. The first sample was a one-inch diameter solid steel sphere. As reported previously, inspection of the shocked sphere upon recovery revealed a large void at its center. Analysis with SEM revealed areas of sub micron porosity near the void. The porous structure of the material at the center of the sample indicates melting and vaporization followed by rapid cooling. Additionally, two samples consisting of different compositions of nanograde nickel powder and buckeyballs were shock loaded. One of these samples contained fifty wt% nanograde nickel while the other sample contained eighty wt% nanograde nickel. Upon shock loading, both samples solidified, forming a solid coating on the inside surface of the containment vessel. The formed microstructures are lamellar, made up of light and dark layers. The hardness exhibited by these samples is substantially higher than the hardness values recorded for nickel alloys. The CTH hydrocode was used to simulate the shock-recovery experiments. CTH predicted the pressure to exceed 700 GPa at the center of the solid steel sphere during shock loading. The pressure was predicted to reach about 350 GPa in the nickel-buckeyball samples during shock loading.