Microstructural characterization of Ti–TiN/CNx gradient-multilayered coatings

A good mechanical performance of carbon nitride (CNx)-based hard coatings grown onto steel components requires an optimal adhesion to the substrates. In the present work, the CNx films have been joined to the AISI M2 steel substrates through a Ti–TiN functionally gradient underlayer. Three types of Ti–TiN/CNx graded systems were deposited by means of magnetron sputtering technique in different growing conditions and the adhesion properties were evaluated by scratch tests. Chemical and structural characterization at the nanoscale for these systems were carried out by grazing incidence X-ray diffraction, transmission electron microscopy (TEM), energy dispersive X-ray analysis, energy filtered TEM and electron energy loss spectroscopy. This complete microcharacterization of the multilayered Ti–TiN/CNx systems coupled with the observed adhesion properties has allowed to identify relationships between the deposition conditions and the material chemistry and structure, in order to reach the desired coating performance. A gradual enrichment in nitrogen and nitride phases was detected from the metallic substrate to the CNx top layer affording higher critical load for delamination.