Under normal circumstances, monolithic diamond is pretty terrible at resisting impact, due to it being weak in certain planes, also known as cleavage planes.
To solve this, why don't we just make the diamonds smaller? They'd be much harder to hit on the cleavage plane that way, right?
What I had in mind was 50-80 nanometer diamond plates, arranged into a brickwork-like structure with an elastic polymer connecting them together. So, nacre but made from nanodiamonds instead of calcium carbonate.
Now, cleavage is present on the microscopic level (it arises from the "ideal" molecular structure of the crystal, not the deviations from it), so I don't know if it would work or if it would be better than boron carbide armor.
Would this diamond armor be able to resist firearms more effectively than either silicon carbide or boron carbide?