sounds like the modern "ceramic in a metal matrix" tank armor:
https://en.wikipedia.org/wiki/Chobham_armour
"The (pulverised) ceramic also strongly abrades any penetrator. Against lighter projectiles the hardness of the tiles causes a "shatter gap" effect: a higher velocity will, within a certain velocity range (the "gap"), not lead to a deeper penetration but destroy the projectile itself instead."
From the article on the material
"Water jets were also found to be ineffective because the curved surfaces of the ceramic spheres widen the jet, which substantially reduces its speed and weakens its cutting capacity."
Not just water jet, the ceramic/metal armor withstands even shaped charge jet :
"Because the ceramic is so brittle the entrance channel of a shaped charge jet is not smooth—as it would be when penetrating a metal—but ragged, causing extreme asymmetric pressures which disturb the geometry of the jet, on which its penetrative capabilities are critically dependent as its mass is relatively low. This initiates a vicious circle as the disturbed jet causes still greater irregularities in the ceramic, until in the end it is defeated. The newer composites, though tougher, optimise this effect as tiles made with them have a layered internal structure conducive to it, causing "crack deflection".[2] This mechanism—using the jet's own energy against it—has caused the effects of Chobham to be compared to those of reactive armour."