The Corrosion Behavior of Cold Sprayed Zinc Coatings on Mild Steel Substrate
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aveen Manhar Chavan, B Kiran, A Jyothirmayi, P Sudharshan Phani, and G Sundararajan (Submitted March 18, 2012; in revised form December 19, 2012) Zinc and its alloy coatings have been used extensively for the cathodic protection of steel. Zinc coating corrodes in preference to the steel substrate due to its negative corrosion potential. Numerous studies have been conducted on the corrosion behavior of zinc and its alloy coatings deposited using several techniques viz., hot dip galvanizing, electrodeposition, metalizing or thermal spray etc. Cold spray is an emerging low temperature variant of thermal spray family which enables deposition of thick, dense, and pure coatings at a rapid rate with an added advantage of on-site coating of steel structures. In the present study, the corrosion characteristics of cold sprayed zinc coatings have been investigated for the first time. In addition, the influence of heat treatment of zinc coating at a temperature of 150 °C on its corrosion behavior has also been addressed.
Keywords
cold spray, corrosion, porosity, potentiodynamic polarization, zinc
1. Introduction Zinc and its alloy coatings have been used extensively on steel structures and components to protect them from corrosion and surface degradation in marine and aqueous environments (Ref 1-5). Most of the long-term test data collected over the years (Ref 4, 5) reveals that sprayed Zn coatings require certain ‘‘threshold thickness’’ for protection over a test span, both in as-coated and post-treated conditions. Also, for a given thickness Zn-Al alloy coatings perform better than Zn coatings (Ref 1, 4, 5). It has been very well documented that zinc provides sacrificial protection to steels in different aqueous media viz., basic NaOH, Na2SO4, and salty NaCl and also fairly well in dry conditions (Ref 6-10).Global estimates point out that nearly 60% of zinc produced is used by the galvanizing industry (Ref 5, 11). This bears testimony to the fact that zinc and its alloys are considered to be of paramount importance when it comes to protection of steel structures in harsh environments. There have been several commercial techniques to accomplish this task viz., hot dip galvanizing, electrogalvanizing, and electrodeposition (Ref 12-17). Other coating methods which have recently become popular are referred to as thermal spray coatings and include Naveen Manhar Chavan, B Kiran, A Jyothirmayi, P Sudharshan Phani, and G Sundararajan, International Advanced Research Centre for Powder Metallurgy & New Materials (ARCI), Hyderabad 500005, India. Contact e-mail: naveen.maestro@ gmail.com.
Journal of Thermal Spray Technology
viz., flame spray (Ref 18, 19), wire arc spray (Ref 20, 21), HVOF, and cold spray (Ref 22-27). In these techniques, zinc feedstock in the form of wires, rods, or powders are melted or softened and sprayed on the steel surface. These techniques are increasingly becoming popular since they also offer the advantage of on-site repair or refurbishment of steel structures unlike the workshop-based conventional processes
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