Yttrium Oxide‐Mediated Interfacial Pinning in C@CoNi Composites for Ultra‐Broadband Microwave Absorption and Durable Tribological Performance

ABSTRACT The increasingly complex electromagnetic environment has imposed higher requirements on the electromagnetic protection capability and surface wear resistance of electronic packaging materials. In this work, different Y 2 O 3 contents were introduced to regulate the growth of CoNi, leading to progressive grain refinement and pronounced changes in its surface morphology. The resulting variations in electromagnetic response and microwave absorption performance were then systematically investigated. On this basis, a UV‐curable resin‐based C@CoNi‐Y composite packaging system was further constructed. With increasing Y 2 O 3 content, the CoNi grains are progressively refined, while their growth morphology on the carbon surface gradually evolves, accompanied by changes in the CoNi/Y 2 O 3 heterointerfaces and local structure. As a result, the optimized C@CoNi‐Y3 achieves a minimum reflection loss ( RL min ) of −74.22 dB at 1.72 mm and an maximum effective absorption bandwidth ( EAB max ) of 9.23 GHz at 1.56 mm. When incorporated into UV‐curable resin, the 9 wt.% C@CoNi‐Y composite film exhibits the lowest average friction coefficient of 0.16, 56.8% lower than that of neat resin. This work demonstrates that interfacial regulation mediated by Y 2 O 3 provides an effective strategy for modulating magnetic resonance behavior, optimizing impedance matching, and achieving broadband microwave absorption in rare‐earth‐modified absorbers.