Patent ID: 7255084

Claim:
A piston for an internal combustion motor, comprising: a) a skirt having a surface; b) the surface being at least partially polished and thereafter coated with a coating, the coating having a hardness of greater than 8 GPa, the hardness being an indentation modulus as measured by an indenter, and having a coefficient of friction of less than 0.20, the coefficient of friction being as measured in a ball on disk test according to ASTM G 99 ; c) the surface of the skirt having a flat surface morphology and having at least partially a ten-point mean roughness Rz of less than 1.0; d) the surface of the skirt having at least partially an arithmetical mean roughness Ra of less than 0.15; e) the coating being selected from the group consisting of diamond-like carbon coatings, diamond-like nanocomposite coatings, wolfram carbide coatings, and a combination thereof; f) an intermediate tie layer being present between the polished surface and the coating; and g) the intermediate tie layer being selected from a group consisting of diamond-like nanocomposite coatings, doped diamond-like coatings, doped diamond-like nanocomposite coatings, TiN coatings, Ti (C,N) coatings, SiN coatings, CrN coatings, wolfram carbide coatings, and a combination thereof.