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Metal matrix composites (MMCs) are a relatively new category of engineering materials, which provide tailorable properties to meet specific needs. Cryomilling, mechanical milling at cryogenic temperatures, was employed in this study to fabricate nanostructured metal matrix composite powder with nanocrystalline aluminum alloys as the matrix and particulate B 4 C as the reinforcement. Cryomilling provided an extremely low temperature for the processing of this composite, which prevented the formation of secondary phases that are detrimental to mechanical properties. A uniform distribution of B 4 C in the Al and a clean strong interface between them were achieved. The contamination that results from cryomilling was analyzed. The effects of the B 4 C addition and the process control agent (PCA) on the microstructure of the composite powder were investigated. Results indicate that these additives had significant, yet opposing, effects on powder yield; a slight effect on contamination, particle size, and particle morphology; and no detectable effect on grain size refinement in the matrix.

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