Corrosion properties of HVOF cermet coatings with bond coats in an aqueous chloride environment

WC-17Co coatings with Ni-5Al bonding layers were deposited on Al-7075 by HVOF spraying. The top-coat consisted of layers comprising tungsten carbide particles embedded in a Co(W,C) matrix of varied composition. The coated specimens were subjected to potentiodynamic polarization in 3.5% aqueous NaCl at 25, 35 and 45 degrees C. The coatings exhibited pseudopassivity caused by the oxidation of tungsten, carbon and possibly cobalt. Chronoamperometric measurements indicated that the inhomogeneous binder composition induced active corrosion processes taking place simultaneously with pseudopassivity. Cyclic polarization suggested that the coatings were not susceptible to pit corrosion in the temperature range of 25-45 degrees C. The likely "critical pitting" temperature of the coatings was 60 degrees C. Higher testing temperatures led to lower corrosion potentials and faster corrosion kinetics. (C) 2007 Elsevier B.V. All rights reserved.Thin Solid Film

High Temperature Sliding Wear of Co-Based Plasma Sprayed Coatings for Aeronautical Applications

Abstract Co-based alloys are used extensively in applications requiring good wear resistance, corrosion and heat resistance. This paper presents the wear data of Co-based plasma sprayed coatings for aeronautical applications at temperatures up to 750 deg C, evaluated in a pin-on-disk unit. Investigation of the coating structure and the wear mechanisms revealed the processing-structure-functionality relationships. The analysis of the tribological results was supported by structure, microhardness and X-ray diffraction studies of the coatings. An SEM examination of the wear marks revealed the predominantly active wear mechanisms in each case. Paper includes a German-language abstract.</jats:p