Hello nice people!
Metal Matrix Composites (MMC) mix ceramic powder, nanotubes, other small things with a matrix of metal like magnesium, aluminium, titanium, iron alloys. The goal is to increase the stiffness, the compression resistance, have a small density, and hopefully keep a decent tensile resistance and toughness.
I haven't searched for long, but apparently they use a single range of particle size, to about 40% volume filing factor. Though, a suspension becomes quickly a slurry, and with about 40% volume of solid particles, it doesn't flow any more. I understand that particles touch an other as their arrangement isn't optimum, so they immobilize the suspension, and more particles create cracks.
A solution is already know and may apply to MMC. Concrete uses three very different ranges of particle sizes: pebbles, than grit to fill the voids between the pebbles, then sand to fill the voids between the pieces of grit. In this way, the liquid fraction is much smaller when concrete is mixed, and it still flows.
It is my hope that, by using several very different particle size ranges in MMC, a higher volume fraction can be used, and as the metal is still contiguous, the MMC retains a decent tensile resistance and toughness.
Marc Schaefer, aka Enthalpy