Abstract
The scientific interest in the investigation of nitride composites as protecting materials in tool and machining industries intensively increases. The good oxidation resistance of CrN single-layer films and high melting point, good chemical and thermal resistance of ZrN compound are motive factors for designing of multilayer composites composed of these metal nitrides. The suggested advantages of ZrN/CrN multilayer coatings as structural materials are the high-temperature resistance, high density and extreme hardness compared to the metal-nitride systems. Experimental ZrN/CrN multilayer coatings were deposited on AISI 321 steel substrates by using a cathodic arc evaporation device equipped with two high-purity metal Cr and Zr targets. Structural, chemical and morphological characteristics together with mechanical properties of multilayer composites were analyzed by X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Vickers hardness tester. SEM analysis revealed an increase of roughness and concentration of the droplets on the surface of the coatings when negative bias potential decreased to -70 V. The results of data obtained from the X-ray analysis showed (200) and (111) plane for ZrN and Cr2N phases as the most intense. The peak positions of ZrN were shifted towards lower diffraction angles comparing with bulk values and indicated a decrease of the inter-planar distance and formation of compressive stresses. The calculated lattice strain values in the ZrN were higher than those of the CrN, indicated a greater presence of dislocations and defects in the lattice of ZrN. The averaged crystallite sizes in ZrN and CrN layers were 11-14 and 7-12 nm, respectively. The maximum value of the Vickers microhardness was found to be 6600HV0.01 that is 2.1 and 1.8 times greater than the corresponding values of binary CrN and ZrN coatings.