Hardness and adhesion properties of HfN/Si3N4 and NbN/Si3N4 multilayer coatings

HfN/Si3N4 and NbN/Si3N4 multilayer coatings are deposited onto a high speed tool steel substrate by reactive sputtering. Their mechanical properties are evaluated in terms of the dependence of hardness and adhesion strength on the sputter deposition process parameters. X-ray photoelectron spectroscopy analyses were performed to analyze the chemical states of the coatings. The hardness of both HfN/Si3N4 and NbN/Si3N4 multilayer coatings increase as the N2/Ar flux ratio increases up to 0.4 and then remain unchanged. The hardness of both multilayer coatings nearly do not change with annealing at low temperatures, but decrease at high temperatures over 800 °C because of oxidation. Post-annealing at low temperatures increases the adhesion strength of the multilayers, but high temperature annealing does not.