Dense protective layers are needed to reduce chromium-related degradation in SOFC stacks. In particular, atmospheric plasma sprayed (APS) Mn_1.0Co_1.9Fe_0.1O₄ (MCF) coatings demonstrated low degradation rates in stack tests. We show that short-term annealing in air induces crack healing within these coatings. Parallel to this effect, a phase transformation is observed originating from oxidation that proceeds by solid state-diffusion. The present contribution reveals the basic mechanisms of the microstructural and phase changes of coatings in long-term annealing tests of up to 10,000 h at 700 °C. The layer develops differently at the air-facing surface and in the bulk. Due to cation deficiency, oxidation is dominated by cation outward diffusion, leading to a Co-enriched surface layer. The bulk displays a fine distribution of the initial (rock salt) and the final (spinel) phases. Understanding the mechanisms leading to these irreversible changes enables predictions to be made concerning durable protectivecoatings in SOFCs.

需要密集的保护层以减少SOFC堆中与铬有关的降解。特别是常压等离子体喷涂（APS）Mn _1.0 Co _1.9 Fe _0.1 O ₄（MCF）涂层在堆叠测试中显示出较低的降解率。我们表明，空气中的短期退火会在这些涂层内引起裂纹愈合。与此效果平行地，观察到由于固态扩散而发生的氧化引起的相变。本贡献揭示了在700°C下长达10,000 h的长期退火测试中，涂层的微观结构和相变的基本机理。该层在面向空气的表面和整体中的发育不同。由于阳离子不足，氧化作用主要由阳离子向外扩散导致，导致Co富集的表面层。块体显示出初始（岩盐）阶段和最终（尖晶石）阶段的精细分布。