Novel Fe-based amorphous and nanocrystalline powder cores for high-frequency power conversion

The present work demonstrates the high-frequency core loss performance of Fe-based amorphous and nanocrystalline powder cores, initially produced by gas atomised powder, consolidated using sieved particles <= 20 mu m, and isolated by a precise insulating layer of polymer to limit the inter- and intra-particle eddy currents to attain enhanced performance. The large glass forming ability (GFA) of the gas atomised powder, reflected by different glass forming instruments, such as the supercooled region (Delta T-x = 54 degrees C) and the reduced glass transition temperature (T-rg = 0.56), is consistent with the substantial amorphisation capability of the alloy. To the best of our knowledge, this is the first-ever report to reveal a large Delta T-x in the Finemet-type alloy powders, an essential parameter to gas-atomise the amorphous powders with significantly lower cooling rates compared to the melt-spun ribbons. Further, subsequent annealing of the amorphous powders, between the exothermic events guided by differential scanning calorimetry (DSC), lead to the growth of a fine nanocrystalline structure of grains <= 15 nm, thanks to the positive enthalpy of mixing of Cu with the constituents to act as a nucleation agent, to retain the excellent soft magnetic properties. The DC soft magnetic properties of the powders were significantly improved on thermal annealing, confirmed by hysteretic loops, quantified by reduced coercivity H-c < 1 Oe of annealed powders at < 575 degrees C, and attributed to the reduced magnetoelastic contribution due to zero/near-zero magnetostriction anisotropy, attained due to the homogenous nanocrystalline structure. The amorphous and nanocrystalline powder cores, consolidated by compression moulding, show ultra-high loss performance, due to the ultra-low coercivity attained on nanocrystallisation, and negligible eddy currents loss, owning to efficient insulation of small particles, for high-frequency power conversion applications, such as voltage regulator (VR), and resonant converters, in automotive industry and data storage centres.