Structure and properties of the Si3N4 nitride ceramics with hard wear resistant coatings

The paper presents the investigation results of the multi-layer CVD coatings on the substrate from the Si3N4 nitride ceramics. Examination results are presented from the scanning electron microscope, test results of the adhesion of the coatings put down onto the substrate, as well as microhardness and roughness test results. Chemical composition examinations of the developed coatings were also carried out using the EDS X-ray dispersive energy spectrometer and the X-ray diffractometer. The Si3N4 inserts were multi-layer coated in the high-temperature CVD process with the combination of the TiC, Ti(C,N), Al2O3 and TiN coatings, which were further compared with the commercially available inserts of various manufacturers offering the combination of the CVD coatings of the Al2O3 + TiN type. It was demonstrated that all double- and multi-layer coatings were characterized by a very good adhesion to the substrate. The microhardness tests revealed that the insert with the TiN + Al2O3 coating had the highest hardness. It was found out also that roughness of the investigated specimens grows by about 0.3 μm on an average after putting down the coatings with the CVD method. Based on the metallographic examinations carried out it was found out that the multi-layer CVD coatings were uniformly put down onto the substrate and their particular layers adhere closely to each other. Results of the X-ray quantitative phase analysis confirm presence of phases originating from coatings and substrate. Analysis of the chemical composition – EDS – confirms presence of both titanium and aluminium, as well as of oxygen, carbon, and nitrogen in the investigated coatings and also of silicon and nitrogen in the investigated substrate.