The morphology and phase composition of nanocrystalline powders of aluminum and carbon in the form of cluster diamonds are investigated. It is found that the hot compaction of the C-Al powder mixture is accompanied by the formation of an Al 4 C 3 phase that has a highly disperse structure. The average crystallite size in hot-compacted materials is 40 nm for the metal matrix and 30 nm for aluminum. It is shown that as the carbon fraction in the initial powder mixture rises, the volume of the threshold space in hot-compacted materials increases.