Electrical discharge approach for large-scale and high-thermostability FeCoNi Kovar alloy microwave absorbers covering the low-frequency bands

Abstract

Good thermal stability and low thermal expansion are critical challenges for magnetic microwave absorbers in engineering applications. Herein, we develop a low-cost and large-scale electrical discharge method to design a high-thermostability FeCoNi Kovar alloy microwave absorber to address the low-frequency absorption issue. The spherical fine FeCoNi (FCN) powders are achieved from thermal ablation of bulk alloys by this technique, which possesses a dual-peak size distribution and gives the strongest RL value at − 40 dB at a frequency of 10.8 GHz with a qualified frequency bandwidth of 5.7 GHz from 8.2 to 13.9 GHz. To exceed Snoek’s limit, the ball-milling method is applied to flatten FCN powders. Increasing the ball-milling time from 12 h to 36 h, the microwave attenuation shifts to a lower frequency band. FCN-36 powders achieve a maximum RL value of − 50.1 dB at 3 GHz. Good conductive loss among the overlapped flaked powders with a papillated surface, well dielectric loss caused by interface and dipolar polarization between the oxide coating layer and metal bases, smaller grain size, and the natural resonance contributes to enhancing the electromagnetic wave energy conversion. The research demonstrates a new inspiration toward the preparation of metallic microwave absorbers on scale large scale and provides novel alloy powders for microwave absorption in the low-frequency range.