Investigation of the diamond machinability of newly developed hard coatings

Presently, coatings of electroless nickel are used for diamond turning mold s for injection molding of optical lenses. We have investigated the diamond machinability of substoichiometric hard nitride coatings (TiNx, TiAlNx. an d CrNx). These coatings have a superior hardness compared to electroless ni ckel suggesting an improved wear resistance of molds with optical surface q uality. In the case of CrNx and TiAIN(x), high tool wear occurred, even aft er small cutting distances, and the surfaces showed a roughness larger than R-a = 0.5 mu m. A considerably higher surface quality was obtained on TiNx coatings. The best results (R-a = 15 nm) were achieved with a nitrogen con tent of x = 0.03. As a first application, a mold for a diffractive optical element was machined using this newly developed substoichiometric titanium nitride deposit. (C) 2000 Elsevier Science Inc. All rights reserved.