High‐Temperature‐Resistant, Mechanically Stable FeCrNiAl/Al2O3 Thermally Sprayed Thick Ceramic Coatings for Stealth Applications over X‐Band

To avoid radar detection during tactical operations, engine exhaust zones of aircrafts are difficult to treat with rubber/resin‐based stealth coatings, due to their thermal and mechanical instability at high temperature (>1000 °C). Further, monolithic fabrication of thick ceramic coatings without any crack/rupture and stability of functional fillers at such high temperatures is an additional challenge in the development. To overcome these difficulties, for the first time, FeCrNiAl/Al 2 O 3 thick ceramic composite coatings are developed with excellent radar/microwave (MW) absorbing capability and good mechanical strength on the titanium alloy substrate using an in‐house developed gas flame‐spraying apparatus, without any cracks or deformations. The 50 wt% FeCrNiAl/Al 2 O 3 ceramic coating is found to have excellent reflection loss (RL) >−20 dB (99% MW absorption) over X‐band (8.2–12.4 GHz) frequencies with capability of tuning the absorption frequency at different thicknesses, while maintaining the RL values. This coating has tensile strength of more than 23 MPa, which may be advantageous for prolonged use on aircraft surfaces.