Feasibility studies on the deposition of thick CrN coatings by sputtering process

Chrome plating is routinely being used in piston rings in the automobile industry. However, as the emission norms are getting tightened, the working surface temperature of top piston rings needs to be increased. Consequently wear increases and hence the need for better wear resistant coatings on piston rings. We have identified sputter deposited CrN as a suitable replacement for hard chrome for piston rings. CrN coatings were deposited on steel, silicon and other substrates using a reactive DC magnetron sputtering process. As CrN exists in different phases (i.e., cubic-CrN and hexagonal-Cr2N), process parameters were optimized to achieve single phase of CrN with varying hardness values. The basic properties of CrN such as: structure, mechanical properties, thermal stability, oxidation resistance and corrosion behavior have been studied in detail using X-ray diffraction, nanoindentation, atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray analysis, micro-Raman spectroscopy, potentiodynamic polarization, etc. For a comparison, we have also evaluated the properties of TiN coatings. Cubic-CrN coatings with different thicknesses (about 1.5, 3, 4.5, 6 and 10 m) have also been deposited on various steel samples for wear measurements.\ud We are in a position to deposit CrN coatings with a maximum thickness of approximately 10 m on steel substrates in the existing planar magnetron sputtering system. New sputtering facility has also been developed to coat full piston rings. \u