Corrosion Resistance of Ni-Based WC/Co Coatings Deposited by Spray and Fuse Process Varying the Oxygen Flow

Abstract

In this work, the effect of oxygen flow variation in the corrosion behavior of Ni-based WC/Co coatings deposited by spray and fuse process was investigated. The coatings were deposited on gray cast iron substrates using a Superjet Eutalloy thermal spraying gun. The morphology of the coatings was analyzed using scanning electron microscopy. The crystallographic phases were registered by x-ray diffraction (XRD), the diffraction patterns show the crystalline phases of the powder components with principal reflections for Ni and WC, the increase in flame temperature, due to the oxygen flow variation, generated amorphization in the nickel and an important crystallization of the planes (111) and (222) of WC as well as the decarburization of WC in W2C and W metallic. The corrosion behavior was investigated at room temperature in a 3.5% w/w aqueous solution of NaCl via potentiodynamic polarization. Electrochemical corrosion test showed that the coatings deposited under neutral flame conditions with an oxygen flow of 12.88 SCFH evidenced higher corrosion resistance. The chemical composition of the coatings and corrosion areas were analyzed by particle-induced x-ray emission, this technique permitting the corroboration of the decarburization process of WC determined by XRD and the formation of Cl structures.