High-temperature oxidation behavior of the Crofer 22 APU steel coated with (La,Sr)(Co,Fe)O3 film prepared by pulsed laser deposition

Abstract

The La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF48) film was deposited on Crofer 22 APU ferritic stainless steel using the pulsed laser deposition (PLD) technique. The LSCF48 film with a thickness of about 1.1 μm was dense and homogeneous, with good adhesion to the metallic substrate. Transmission electron microscopy combined with the energy-dispersive X-ray spectroscopy studies showed that the stoichiometry of the target was precisely transferred to the film by pulsed laser deposition. Oxidation studies of bare Crofer 22 APU steel, and steel with the LSCF48 film were carried out in laboratory air at 1073 K under both isothermal and cyclic oxidation conditions. The calculated parabolic rate constant kp after oxidation for 200 h for the steel with LSCF48 film was approximately three times lower than the oxidation rate of the steel without surface modification. The oxide scale formed on Crofer 22 APU steel consisted of two layers: an inner layer built of chromia and an outer layer consisting of the Mn1.5Cr1.5O4spinel. In the case of the steel with LSCF48 film, the oxide scale was two times thinner and had a similar phase composition. In both cases, the presence of an internal oxidation zone with SiO2 and Al2O3 precipitates was observed. In addition, small amounts of spinel crystals were observed on the film surface. After 2400 h of oxidation at 1073 K under thermal cyclic conditions, the total mass gain was 1.04 mg · cm−2 and 0.67 mg · cm−2 for the respectively bare and coated substrate. The results indicated that the spallation of the oxide scale and/or the film did not occur. In both cases, the composition of the scales was similar to the scales formed on the samples after isothermal oxidation. Studies of the electrical properties show, that Crofer 22 APU steel with LSCF48 film deposited by PLD method meets criteria for the interconnector materials for intermediate-temperature solid oxide fuel cells applications.