The cavitation-erosion phenomenon of chromium nitride coatings deposited using cathodic arc plasma deposition on steel

Abstract

The cavitation-erosion behavior of chromium nitride (CrN) coatings on AISI 4140 steel in fresh water and 3.5% NaCl solution has been investigated using an ultrasonic vibration system. The CrN coatings were deposited by cathodic arc plasma deposition (CAPD) with and without an intermediate layer of electroplated hard chrome, i.e. CrN/AISI 4140 and CrN/Cr/AISI 4140. The composition and structure of the CrN coatings have been studied using X-ray diffraction (XRD), using θ/2θ diffraction mode and Schulz reflection methods, which revealed a preferred orientation of CrN(220) for CrN/Cr/AISI 4140. The microstructure and crystalinity of the CrN coatings have been examined using cross-sectional transmission electron microscopy (XTEM). Both CrN/AISI 4140 and CrN/Cr/AISI 4140 coatings exhibited strong microcolumnar structures, however, the shape and grain size of the coatings were approximately the same. In addition to the microstructural investigations, cavitation-erosion tests were conducted under free corrosion conditions in fresh water and in chloride containing water. Subsequent electrochemical evaluation was made to elucidate the mechanism of cavitation-erosion. The resulting mechanical damage has been assessed using weight loss measurements and scanning electron microscopy (SEM) observations. Notwithstanding a significant improvement in the cavitation resistance of the coated specimens in fresh water and NaCl solution, the damage resulting from the cavitation-erosion in the 3.5% NaCl solution exhibited a higher weight loss than those in freshwater.