Efficient and Homogeneous Carbonitriding of High-Entropy Alloys by a Mechanochemical Process for Obtaining Coordinated Electromagnetic Matching

Optimizing the impedance matching via electromagnetic adjustment is considered an effective strategy to accomplish exceptional electromagnetic wave absorption (EMA) performance. Here, we report an efficient and green process to obtain the carbonitriding FeCoNiCr high-entropy alloys (HEAs) with flake-shaped morphology by using organic cyanide (Dicyandiamide, C 2 H 4 N 4 ) as nitrogen and carbon sources. The carbonitriding effects on the phase structure, magnetic properties, mechanical hardness, corrosion resistance, high-temperature oxidation resistance, and EMA performances were investigated systematically. The carbonitriding process optimized the impedance match by decreasing the dielectric constant via introducing the nonmetallic C and N. The #CN10 sample exhibited outstanding EMA performances with a minimum reflection loss of −32.3 dB at 7.89 GHz and a broad effective bandwidth of 4.46 GHz, which covered the majority of X-band. In addition, the carbonitriding FeCoNiCr HEAs had great mechanical properties, excellent corrosion resistance, and high-temperature oxidation resistance, indicating excellent adaptability to harsh environments as well as good EMA performances. This work provides a new idea for the preparation and design of carbonitriding EMA materials.