MICROSTRUCTURAL ASPECTS OF HYPERVELOCITY IMPACT CRATERING AND JETTINGIN COPPER

Light and transmission electron microscopy techniques have been applie d in observations of hypervelocity impact craters in two different cop per targets: a 38 mu m grain size mill-processed target, and a 763 mu m grain size annealed target, the smaller grained target being impacte d with a 1100 aluminium sphere and the larger grained target being imp acted with a soda-lime glass sphere, at velocities near 6 km s(-1). Bo th target craters exhibited dynamic recrystallization near the crater wall. The jetting associated with these two craters was very different . Considerably more plastic flow and a larger rim characterized the la rger grained target. No significant melt-related phenomena were observ ed either near the crater wall or in the jetted rim for either crater. Consequently, the principal features of crater formation involve extr eme plastic flow in the solid state. Microbands were observed to occur profusely in a zone below the smaller grained mill-processed target c rater while more profuse and extremely long, unidirectional bundles of microbands (which were coincident with traces of {111} planes) occurr ed below the annealed larger grained target crater. These observations attest to the dominant and unique role played by deformation microban ds in cratering in copper, because essentially no deformation twins we re observed in either target.