Corrosion behaviour of MoSx-based coatings deposited onto high speed steel by magnetron sputtering

Abstract

Abstract MoSx-based films were deposited using magnetron sputtering from a pure MoS2 target. Alloying was accomplished by “co-deposition” from separate targets onto substrates having a two-fold rotation. An additional experiment had also a Cr+-ion etch for surface preparation, followed by a Cr adhesion layer, made using a Cr target mounted on a cathodic arc evaporation source. MoSx and Al- and Ti-alloyed MoSx coatings have been deposited onto high speed steel (HSS) and glass substrates for corrosion investigations. The coatings were characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, hardness and adhesion measurements. The corrosion behaviour of the samples was electrochemically measured by open-circuit-potential (OCP) measurements and by potentiodynamic corrosion tests in 0.8 M NaCl solution (pH 7). Additionally the MoSx-based coatings on HSS have been exposed to salt spray tests. The corrosion investigations revealed that the addition of Al and Ti to MoSx shifts the open-circuit-potential of about 80 to 110 mV to lower values, i.e. the alloying elements make the MoSx coating a little bit less noble. In agreement with the OCP measurements, the corrosion potential Ecorr in potentiodynamic corrosion tests was the highest for non-alloyed MoSx coatings on HSS substrates. After the potentiodynamic corrosion tests, a strong corrosive attack could be observed for all coated samples. In salt spray tests the lowest number of corrosion pits was found for the MoSx–Al (Cr+) coating on HSS.