Cubic boron nitride (cBN) films with a thickness of more than 2 mum on silicon and up to 0.8 pint on tungsten carbide substrates were prepared by reactive rf sputtering, in an Ar/N-2 discharge, using an electrically conducting toron carbide (B4C) target. The increase in cBN film thickness was reached with a process including: a boron carbide interlayer with a variable thickness; and a subsequent gradient layer consisting of B, C and N. First, the boron carbide layer was deposited i a pure Ar discharge followed by a graded interlayer, which was conducted by continuously replacing Ar by N, gas. Structure and composition of the films were investigated by: IR spectroscopy; TEM and SEM; as well as by SIMS. Tribological and mechanical properties of relatively thick (similar to 1 mum) and long time stable films were investigated in detail. Quantities like: friction coefficients against different materials; abrasive wear rates; as well as hardness; Young's modulus; or surface tension data of cBN films were determined. The hardness measured with a nano-indentation technique was approximately 65 GPa and corresponds to the known cBN bulk value. Abrasive wear rates were clearly lower than for hard coating materials like TiN. Furthermore, results concerning process transfer to technically relevant substrates like tungsten carbide (WC-Co) will be presented.