Porosity-controlled electromagnetic performance and oxidation stability in atmospheric plasma-sprayed FeSiAl/CaO–B2O3–SiO2 composite coatings

Porosity is a characteristic feature of atmospheric plasma–sprayed (APS) coatings that strongly influences their physical and functional properties. However, studies on its effect on the electromagnetic (EM) performance and high-temperature stability of microwave-absorbing coatings (MACs) remain limited. In this work, FeSiAl/CaO–B 2 O 3 –SiO 2 composite coatings with different porosities were fabricated by adjusting powder feed rate (PFR). Microstructural evolution, EM properties, and isothermal oxidation behavior of prepared composite coatings were systematically investigated. Results show that increasing PFR reduces the extent to which particles are melted, leading to higher porosity due to the retention of unmelted particles. The increased porosity disrupted local conductive networks, altered the complex permittivity and permeability, and lowered the bonding strength of the coatings. Moreover, pores and cracks facilitated oxygen diffusion, accelerating oxidation and crack propagation at elevated temperatures. After high-temperature oxidation, the decrease in complex permittivity improved impedance matching and broadened the absorption bandwidth. These findings provide new insights into microstructure–property relationships of APS-deposited MACs and offer a strategy for tailoring the coating porosity to simultaneously optimize their EM absorption performance and high-temperature oxidation resistance.