Hardness evaluation of thin ceramic coatings on tool steel

Six samples of cold work tool steel were used as substrates for physical and chemical vapour deposition coatings. Three of them were made of a powder metallurgy steel called Vanadis-4, the other three were Carmo steel. Both are commercial Swedish tool steels. TiN and CrN coatings were deposited onto both steels using physical vapour deposition. The TiC coating was deposited onto Vanadis-4 and a TiC/CrC composite coating was deposited onto Carmo using chemical vapour deposition. The area law of mixture model was used to estimate the hardnesses of the investigated coatings. These values were reasonably close to the experimental coating hardnesses measured at 10 or 25 g load which were still affected by substrate deformation. The increase in coating thickness due to the rougher substrate surface caused an increase in coating hardness. The shape and behaviour of lateral cracking in the indentation impressions for different coatings was studied.