Non-reactively sputtered TiN and TiB2 films:: influence of activation energy on film growth

An unbalanced d.c. magnetron sputtering unit was used to deposit titanium nitride and titanium boride films onto austenitic steel and molybdenum substrates using TiN and TiB2 targets. An external pair of Helmholtz coils was used to create an uniform axial magnetic field which allowed the ion/atom ratio incident at the growing film to be varied between 0.1 and 1.3. The characterization of the coatings was conducted by scanning electron microscopy, electron probe microanalysis and X-ray diffraction. The aim of this work was to investigate the effects of different activation energies on the film growth and the microstructure of two different hard materials with comparable melting points. The microstructure of the coatings was mainly influenced by the ion bombardment of the substrate, i.e. ion energy and ion intensity. In the case of TiN, single-phase stoichiometric TiN coatings were obtained. The columnar, porous structure of the films occurring at low ion bombardment was changed to a dense structure as the ion energy and the intensity were increased. At the same time the (111) preferred orientation changed to a mixed orientation. The highest hardness values (similar to 3000 HV0.01) were obtained at intensive ion bombardment. The TiB2 films exhibited a dense single-phase hexagonal TiB2 structure with (001) texture which altered to a mixed orientation as the energy of the incident ions was decreased. The Vickers microhardness of the coatings reached values similar to 6300 HV0.01. (C) 1997 Elsevier Science S.A.