Tribology: Diamonds are forever - Or are they?

The amorphous layer formed on the contact surface of diamonds results from the protruding crystal atoms that pluck each other off the opposing surfaces during polishing. This process builds up an amorphous carbon layer whose thickness is determined by how difficult it is to pluck an atom off the neighboring diamond surfaces. The amorphous, diamond-like carbon (DLC) material composing the layer is itself quite hard. Using atomic potentials previously derived to describe the fracture of carbon bonds, Pastewka and colleagues demonstrated good quantitative agreement with the dependence of experimental wear rates on crystal orientation and polishing direction. When surfaces are sufficiently rough, however, friction suddenly becomes substantial. Both friction and wear are very sensitive to the conditions at the sliding interface. This sensitivity results from the fact that the load-supporting contacts that compose the interface are both discrete and relatively few in number.