Dielectric Properties of Composites Containing Meltextracted Co-based Microwires

TL;DR

This study explores how melt-extracted Co-based microwires influence the microwave dielectric properties of epoxy composites, highlighting the effects of annealing and wire length on permittivity spectra and anisotropy.

Contribution

It introduces the use of combined current-modulation annealing (CCMA) to improve microwire properties and examines the impact of wire length and annealing on dielectric behavior.

Findings

Double-peak permittivity spectra linked to nanocrystallites and amorphous phases.

CCMA enhances wire anisotropy and reduces residual stress effects.

Wire length affects the presence of resonance peaks and spectral features.

Abstract

We have investigated the microwave properties of epoxy-based composites containing melt-extracted Co69.25Fe4. 25B13.5-xSi13Nbx (x=0, 1, 3) microwires of various length annealed using a so-called combined current-modulation annealing (CCMA) technique. The observation of a double-peak feature in the permittivity spectra is believed due to the coexistence of the amorphous phase and a small amount of nanocrystallites on the wires with a high Nb content. CCMA was found to be favorable for a better-defined circular anisotropy of microwires and had suppressed the highfrequency peak due to residual stress relief for the composite with 25 mm long wires. Neither the shift of resonance peak nor the characteristic double peak feature was detected for composites containing as-cast 15 or 35 mm long microwires.