Abstract Nitric acid oxidation has been used to fabricate insulation coatings of the FeSiAl soft magnetic composites (SMCs). Growth mechanism of the coatings obtained with varied HNO3 concentration has been systematically studied based on careful analysis of the coating thickness, microstructure and composition. The oxidation process for the powders reacted with 10 wt% HNO3 corresponds to the steady-state passivation, while pitting corrosion occurs with raised HNO3 concentration of 30 wt%. Origin of the pitting corrosion has been analyzed based on the point defect model. Evolution of the coatings has been revealed under different growth conditions and correlated to the magnetic performance of the SMCs. The samples oxidized with 10 wt% HNO3 mainly form a thin and compact oxidation layer with dominating Al2O3, AlO(OH) and a small amount of Fe3O4, while increased HNO3 concentration (30 wt%) gives rise to mixed Al2O3, AlO(OH), Fe2O3 and Fe3O4 in the thicker coating layers. Enhanced magnetic performance of the FeSiAl SMCs can be achieved by optimized thickness and composition of the coatings (μe = 180.4, Pcv = 327.2 mW/cm3 for the SMCs oxidized by 10 wt% HNO3 and μe = 157.3, Pcv = 241.2 mW/cm3 via oxidization by 30 wt% HNO3 for 5 min).

中文翻译：

---

通过 HNO 3 氧化制备 FeSiAl 软磁复合材料的微观结构、生长机制和磁性能的相关性

摘要 硝酸氧化已被用于制备 FeSiAl 软磁复合材料 (SMCs) 的绝缘涂层。基于对涂层厚度、微观结构和成分的仔细分析，系统研究了用不同 HNO3 浓度获得的涂层的生长机制。粉末与 10 wt% HNO3 反应的氧化过程对应于稳态钝化，而点腐蚀发生在 HNO3 浓度升高至 30 wt% 时。基于点缺陷模型分析了点腐蚀的成因。涂层在不同生长条件下的演变已被揭示，并与 SMC 的磁性能相关。样品经 10 wt% HNO3 氧化后，主要形成薄而致密的氧化层，以 Al2O3、AlO(OH) 和少量 Fe3O4 为主，而增加 HNO3 浓度 (30 wt%) 会在较厚的涂层中产生混合的 Al2O3、AlO(OH)、Fe2O3 和 Fe3O4。FeSiAl SMC 的增强磁性能可以通过优化涂层的厚度和成分来实现（μe = 180.4，Pcv = 327.2 mW/cm3，对于被 10 wt% HNO3 氧化的 SMC 和 μe = 157.3，Pcv = 241.2 mW/cm3 通过30 wt% HNO3 氧化 5 分钟）。