Corrosion behavior of Al1.8Cr0.2O3solid solution-based atmospheric plasma sprayed Al2O3- Cr2O3coatings in saline environment

Abstract

This work investigates the corrosion behavior of atmospheric plasma sprayed Al<inf>2</inf>O<inf>3</inf> - Cr<inf>2</inf>O<inf>3</inf> coatings produced by spraying Al<inf>2</inf>O<inf>3</inf> - Cr<inf>2</inf>O<inf>3</inf> powder mixtures having 2–6 wt% Cr<inf>2</inf>O<inf>3</inf> in it. The resulting coatings with Al<inf>2</inf>O<inf>3</inf>, Al<inf>1.8</inf>Cr<inf>0.2</inf>O<inf>3</inf>, and Cr<inf>2</inf>O<inf>3</inf> phases are exposed to NaCl salt spray environment for various durations. The coatings are characterized by XRD, TEM, XPS, SEM, and EDS techniques. Those are also analyzed electrochemically using Tafel curves obtained from Linear Sweep Voltammetry (LSV) tests. The micro-hardness and porosity of the coatings are estimated by using a Vickers microhardness tester and image analysis technique, respectively. The salt accumulated on the coating surface increases the average surface roughness (R<inf>a</inf>) significantly. With an increase in time, the weight of all the samples increases due to corrosion. The metastable γ-Al<inf>2</inf>O<inf>3</inf> and Al<inf>1.8</inf>Cr<inf>0.2</inf>O<inf>3</inf> solid solution phases of the coatings chemically react with the salt to form corrosion products and influence the corrosion effects. The Al<inf>1.8</inf>Cr<inf>0.2</inf>O<inf>3</inf> phase forms Cr-based compounds, which act as protective layers and reduce further corrosion. Till 48 h, the corrosion products decrease coating porosity by sealing the defects up to a certain extent. With further increase in time, the overall coating porosity is increased due to the formation of new cracks in the brittle corrosion products. Having the lowest porosity and the highest amount of stable α-Al<inf>2</inf>O<inf>3</inf>, the coating with 4 wt% Cr<inf>2</inf>O<inf>3</inf> shows the highest corrosion resistance, which is confirmed by the electrochemical test. A meagre amount of Cr<inf>2</inf>O<inf>3</inf> added to the Al<inf>2</inf>O<inf>3</inf> feedstock improves the corrosion resistance of the coating remarkably. © 2026 Elsevier Ltd and Techna Group S.r.l. All rights are reserved, including those for text and data mining, AI training, and similar technologies.