Deposition and microstructure of PVD TiN-NbN multilayered coatings by combined reactive electron beam evaporation and DC sputtering

Well-adherent TiN/NbN multilayer coatings were deposited on high speed steel and cemented carbide substrates in a high vacuum coating equipment using a reactive hybrid deposition process consisting of a combination of electron beam evaporation (Ti) and D.C. magnetron sputtering (Nb). Homogeneous TiN and NbN layers as well as four different multilayer TiN/NbN coatings with periodicity 500/500 nm (TiN/NbN), 100/10, 10/100 and 10/5 nm were deposited. Analytical techniques including X-ray diffraction, transmission electron microscopy, Rutherford backscattering spectroscopy and Auger electron spectroscopy were used to characterise the phase composition, microstructure and the chemical composition of the coatings. In addition the microhardness was determined. The phase of the homogeneous TiN and NbN coatings as well as for individual TiN and NbN layers in the multilayer coatings was predominantly the cubic NaCl-structure. In addition the 10/5 coating was found to have a superlattice structure. All coatings showed a dense, columnar microstructure and were slightly overstoichiometric. The highest hardness (approximate to 3400 HV) was found for the 10/5, 10/100 and the single layered NbN coating.