Structure and mechanical properties of TiBN coatings fabricated by dc reactive sputtering technique

TiBN hard coatings were fabricated by dc reactive sputtering technique, using powders target, Ti (90 wt.%) and BN (10 wt.%), prepared by indirect reactive ball milling. The nitrogen flux was varied at 0, 5, 10, 15 and 20 sccm, respectively; while the argon flux was kept constant at 25 sccm. The effects of nitrogen flux on the structure and mechanical properties of these coatings were studied. The microstructure and phase composition of coatings were studied by means of X-ray diffraction and energy dispersive spectroscopy. The fractions of the relative phase were calculated from the chemical composition stoichiometry obtained by energy dispersive spectroscopy. X-ray diffraction and fractions of the relative phase measurements confirmed the presence of three mixtures phases, TiN, BN and TiB2, being dominant with 64.9% for sample M1. When the nitrogen flux increased, the mechanical properties decreased. This was due to the diminishments in TiB2 phase, to a minimum value of 25%, and the crystalline TiN phase changed completely in amorphous phase, leaving only the c-BN. The variations in nanohardness and elastic modulus values were to structural and chemical composition changes with the increase of nitrogen gas flow. The sample M1 presented the highest hardness (23.52 GPa) and strength (775.5 MPa).