Synthesis and structure of nanocrystalline powders of ultrahard phases

The synthesis of ultrahard nanocrystalline phases is based on the occurrenc e of direct phase transformations in carbon and boron nitride at high press ures during shock compression. This survey examines the relationship betwee n features of the initial layered structures, the mechanisms of the direct transformations (martensitic, diffusional), and the actual structure of the ultrahard phases formed during shock compressions.