British and German engineers have developed a material that they say is impervious to cutting or drilling.
Called Proteus, the revolutionary synthetic material is inspired not by diamonds and sapphires, the toughest natural materials known to man, but by the cellular skin of the grapefruit and the fracture resistant shells of the abalone mollusk.
Proteus is made from alumina ceramic spheres encased in a cellular aluminium, metallic foam structure, and works by turning back the force of a cutting tool on itself. In the tests performed by its inventors, Proteus could not be cut by angle grinders, drills or even high-pressure water jets.
There's more at the link.
Here's a video of an angle-grinder fitted with a cutting wheel, trying to get through a slab of the Proteus material.
That's really impressive. I wonder how Proteus would stand up to ballistic penetration? For example, if it were used as armor plate - or one layer within composite armor - on a tank, would an armor-piercing shell from another tank be able to penetrate it? What about the superheated metal jet from a missile's high-explosive warhead?
If this material can be successfully commercialized, it would seem to hold out all sorts of possibilities.