TiN hard coatings deposited on high-speed steel substrates by reactive direct current magnetron sputtering

We report on TiN hard coatings deposited on high-speed steel substrates by reactive dc sputtering in an Ar/N2 atmosphere. The sputter parameters lie within the technically interesting coating conditions; i.e., substrate preheating temperatures of 200 or 450 °C, adequate particle scattering by a sputter pressure of 1.3 Pa, and bias voltages of −250 V. With increasing power density on the target the Thornton-model columnar film structure vanishes and the fracture cross sections of the layers are almost structureless. Transmission electron microscopy investigations revealed grain sizes of 15–30 nm or less; and bimodal grain size distributions were not observed. An assessment of the dislocation densities resulted in about 1012 cm−2. At high bias voltages the incorporation of argon in the film comes up to 1 at. % and the compressive residual macrostresses are about 11 GPa.