Synthesis of nanodiamond-reinforced aluminum metal composite powders and coatings using high-energy ball milling and cold spray

Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10 h, and a ND content of 10 wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46 GPa, a 210% increase over the pristine, untreated Al powder (1.10 GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.