CHARACTERISATION AND EVALUATION OF THE CORROSION BEHAVIOUR OF MODIFIED HVOF SPRAYED WC BASED COATINGS DEPOSITED ON AISI 1020 MILD STEEL SUBSTRATES

摘要

Traditionally the use of hard chrome plating has been applied to specific regions of the aircraft, such as the landing gear, in order to improve the surface hardness, wear and erosion resistance. However, due to restrictions imposed on the use of these coatings, alternatives are being sought as replacements for hard chrome. Of particular interest are modified tungsten carbide (WC) based Cermet coatings. While these types of coatings are known for their superior hardness and wear resistance, little is known about the corrosion resistance. In this study, three WC based composite coatings, containing various combinations of nickel (Ni), cobalt (Co), Chromium (Cr) and chromium carbide (Cr{sub}2C{sub}3), (WC-12Ni, WC-20Cr{sub}2C{sub}3-7Ni and WC-10C0-4Cr), were deposited onto AISI 1020 mild steel substrates using high velocity oxy fuel (HVOF) technology. Salt spray tests and potentiodynamic scans in a saline environment were conducted on the coatings. Characterization of the coating structure, composition and morphology, was carried out, prior to and after corrosion testing, using optical microscopy, scanning electron microscopy and EDX elemental analysis. The results of the salt spray tests and potentiodynamic studies revealed high levels of porosity and the presence of micro-cracks were observed within the coatings. These factors were considered to be predominantly responsible for the poor corrosion performance exhibited by all three coatings.