Mechanical and corrosion performance of multilayer ceramic coatings deposited on an austenitic stainless steel using plasma spray

Abstract

This research investigated consecutive multilayer thermal barrier coatings, including $\hbox {Ni}_{3}\hbox {Al}$–$\hbox {Al}_{2}\hbox {O}_{3}$–$\hbox {Al}_{2}\hbox {O}_{3}/\hbox {MgO}$, produced by plasma spray with outer layer thicknesses of 50, 100 and $150\,\upmu \hbox {m}$ deposited on an AISI 316 stainless steel. X-ray diffraction, scanning electron microscopy, Rockwell-B hardness measurements, pin-on-disk wear test and potentiodynamic polarization test were performed to evaluate the specimens. The results revealed that the structure of the produced coatings was completely crystalline. An increase in the coating thickness formed a smooth surface and a low degree of roughness and promoted grain growth. According to the Hall–Petch equation, the degree of hardness decreased from 99 to 92 HRB, and the friction coefficient decreased from 1.25 to 0.6 because of low surface roughness. An adherence test performed with a Brinell hardness test showed that an increase in the layer thickness improved the coating adherence coefficient ($\hbox {d}p/\hbox {d}r$) from 0.083 to $0.118\,\hbox {kg}\,\upmu \hbox {m}^{-1}$. The corrosion test results indicated that the increase in the coating thickness caused a decrease in corrosion current density from 1.1 to $0.008\,\hbox {mA}\, \hbox {cm}^{-2}$.