Enhanced broad-frequency electromagnetic-wave absorption and environmental stability of carbonitrided high-entropy alloys via a green mechanochemical approach

High-entropy alloys (HEAs) are important candidates for efficient electromagnetic-wave absorbing (EMA) materials, but the further design of HEA absorbers with harmonized impedance matching and excellent environmental stability remains a major challenge. In this study, a novel carbonitriding process based on a mechanochemical method is employed to prepare carbonitrided FeCoNiMn HEAs by utilizing a cyano-compound (C3H2N2) as a source of C and N. The introduction of C and N effectively optimizes the permittivity of FeCoNiMn HEAs, achieving the equilibrium of electromagnetic matching and thus improving the EMA performances (especially the bandwidth). The carbonitrided FeCoNiMn HEAs exhibit significant reflection loss (RL) and absorption capability. FeCoNiMnM0.04 achieves a minimum RL of -65.8 dB at 3.44 GHz. FeCoNiMnM0.08 achieves an ultra-broad effective absorption bandwidth (EAB) of up to 7.76 GHz at 1.62 mm, covering the entire Ku-band. In addition, the carbonitrided FeCoNiMn HEAs exhibit excellent corrosion resistance and good mechanical properties, ensuring their suitability for harsh environments. This study highlights the potential of carbonitrided HEAs prepared using a cyano-compound as highly efficient EMA materials, and provides a reference for optimizing the electromagnetic matching of HEAs.