Failure during scratch testing of thick and thin CrN coatings examined using focused ion Beam

Hard CrN0.88 coatings of various thickness were deposited on hot work tool steel in an industrial Hauzer HC 750 PVD machine. The coatings were subjected to scratch testing with a diamond stylus. The failure occurring during scratch testing was examined with an optical microscope and dual beam scanning electron microscope/focused ion beam (SEM/FIB). Different types of failure were observed after scratch testing CrN coatings of different thicknesses. The thin coating breaks in small pieces. High applied load does not lead to complete coating removal, but pieces of coating are squeezed into the substrate. Cracking occurs outside of the scratch track without extensive chipping. The thick coating is completely removed during scratch testing at high applied load. Pronounced chipping occurs at the edge of the scratch track.