Influence of Lanthanum Coatings on a Model 330 Alloy (Fe–35Ni–18Cr–2Si) Oxidation at High Temperatures

Abstract

The influence of a lanthanum sol–gel coating on chromia scale adherence has been studied on the 330 alloy (Fe–35Ni–18Cr–2Si) oxidized at 900 °C, in air. Argon annealing of lanthanum sol–gel coatings were performed at various temperatures. Kinetic results show that lanthanum sol–gel coatings lead to a lower oxidation rate compared to blank specimens. On blank 330 specimens scale spallation is observed after cooling to room temperature. On the non-annealed sol–gel coated specimen and the argon annealed specimens at 600, 800 or 1,000 °C, the oxide scale formed at 900 °C is adherent after 48 h isothermal oxidation. The adherent oxide scales are convoluted, resulting from a mixed anionic + cationic diffusion process in the chromia scale. Thermal cycling tests on lanthanum the sol–gel coated specimen show that the oxide scale remains adherent after 250 cycles. It is concluded that argon annealing of the lanthanum sol gel coating is not necessary to improve the scale adherence.