Effects of functionally graded TiN layer and deposition temperature on the structure and surface properties of TiCN coating deposited on plasma nitrided H13 steel by PACVD method

The poor adhesion of nitride coatings to steel substrates is one of the main challenges for industrial applications. In this study, plasma nitriding process and TiN functional intermediate layer were used in order to increase the adhesion of TiCN coating to the hot worked steel H13 substrate and also to improve its mechanical properties. The functionally graded nanostructured TiCN coating was deposited using pulsed-DC plasma-assisted chemical vapor deposition (PACVD) method. The coatings microstructural and mechanical properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), optical microscopy (OM), Rockwell-C indentation, micro hardness and ball-on-disk tests. The results showed that peaks of TiN and TiCN phases existed in the XRD pattern and the size of their crystallites is about 7 nm. Carbon and nitrogen contents in the TiCN coating gradually increased from the substrate to its surface. The functional coating prepared at 475 °C had higher adhesion to the substrate in comparison with those deposited at 450 and 500 °C. The high adhesion led to reduction of radial and peripheral cracks within the coating. Decrease in the friction coefficient and lost volume during ball-on-disk tests indicated that the wear resistance of the functional coating deposited at 475 °C was 78% higher than that of the other coatings.