Corrosion Resistance of 304L SS Spray Coated with Zirconia Nanoparticles

Abstract

Grain boundary character modification employing thermo-mechanical processing in type 304L stainless steel S K Pradhan and S Mandal Abstr act. Influence of substrate temperature on corrosion (in 3.5% NaCl) and wear resistance of nanostructured zirconia thin film coated 304L SS substrates are studied by electrochemical and nano-indentation methods. This analysis shows 304L SS substrate spray coated with nanostructured zirconia at substrate temperature closer to the boiling point of the spray solvent ethanol exhibited good corrosion and wear resistance behaviour. This is because of the compressive stress developed during film fabrication at lower substrate temperature (~50 °C) and hence constrains the indentation plasticity, which leads to higher indentation load than the bare 304L SS. Key words: Zirconia nanoparticles, Spray coating, Corrosion resistance Intr oductionCorrosion is one of the most serious problems faced by industries. Metals normally corrode on exposure to environment and lose its useful properties. Consequently, metal components used in industries have to be repaired or replaced constantly. Though corrosion is inevitable, the rate of corrosion of metals can be reduced by proper choice of material combination [1], using corrosion inhibitors [2] or by surface modification [3] and protective coatings [4]. For instance, stainless steel is widely used for making oil field valves, chemical process equipment, aircraft fittings, fasteners, pump shafts, compressor impeller, nuclear reactor components, gears, paper mill equipment etc., because of its excellent mechanical and corrosion resistance properties. However, in chloride environments at elevated temperatures, austenitic stainless steels are prone to intergranular corrosion due to precipitation of chromium as chromium carbide (Cr 23 C 6 ) at grain boundaries. This process of precipitation requires large amount of chromium and hence the chromium from the adjacent region diffuse resulting in the formation of chromium-depleted zone. This zone is anodic to the unaffected grains and consequently becomes a preferential site for corrosion attack or crack propagation under tensile stress.Presently various coating techniques such as oxidation of an evaporated metal film [5,6], reactive and non-reactive sputtering techniques [7], chemical vapor deposition [8], physical vapour deposition [9] and sol-gel coating [10] are employed to fabricate surface protective coatings for ferrous and non-ferrous alloys. Nevertheless, fabrication of nanocomposite coatings with required proportion of nanostructures like nanoparticles and nanorods of other elements by the above