Matching of TiN coating structures by plasma nitriding of substrates

Abstract

The influence of plasma nitriding of samples made of steel grades DIN S 6-5-2 and DIN X38CrMoV5 1 on the subsequent growth of TiN coatings has been investigated. Plasma nitriding has been performed in a laboratory plasma nitriding unit with a continuous dc current supply and precise control of all process parameters during treatment. A strong influence of the plasma nitriding of substrates on the structure and other properties of deposited TiN coatings was found. The properties of the composite plasma nitrided/coated layer were analysed by SEM, optical microscopy, the scratch test method, kalotest and X-ray spectroscopy. The surface microhardness as well as the microhardness distribution over metallographic cross-sections of the samples were also measured. It was found that coating-to-substrate adhesion, structure, morphology and texture of the TiN are affected by plasma nitriding of the substrates. In all experiments the critical load as defined by the scratch test method was increased due to plasma nitriding prior to coating. The preferred orientation of the film growth is very pronounced. After plasma nitriding of the substrate, the intensity of the line 220 is increased relative to the 110 line intensity. The influence of the base substrate material on the TiN coating properties is also evident. After plasma nitriding, the structure, morphology and topography of the coatings are less dependent on the steel grade of the substrate. This is not completely true with respect to preferred orientation of the coating.