Abstract Shock compaction of metallic as well as ceramic materials has been a subject of active research during the last three decades because the process has the inherent capability of retaining the original grain sizes in most materials. Despite advancements in the understanding of the processes and mechanisms of compaction, the process has not yet attained commercial success. Although the basic compaction criterion has been determined, every experimental anomaly has resulted in a new model for shock compaction. Shock compression of metallic materials has been understood to a greater degree than those of ceramic materials, possibly due to the knowledge of the behavior of metallic materials above and close to melting temperatures. Some single phase ceramic materials have been compacted well in recent work. Optimum conditions for achieving such compaction are being researched. With the advent of nanocrystalline materials, a closer scrutiny of previous work and the various aspects of shock-compression mechanisms is required to ascertain the applicability of existing theories for nanometer-sized materials. In this paper, various aspects of compaction of fine grained materials will be reviewed and the criterion for compaction of microcrystalline and nanocrystalline powders that yield well bonded compacts with high mechanical properties for various applications will be discussed. Nanocrystalline diamond composites are of special interest, due to the extreme properties of diamond itself, and the possibility of improving the property in polycrystalline materials due to reduction in grain size. For this material, where issues of phase transformations are also involved, results of recent compaction experiments and its microstructural characterization will be presented.
Vasant S. Joshi (Sun,) studied this question.