Soft magnetic composite obtained by interface reaction upon spark plasma sintering using double-coated Al-permalloy (Ni71.25Fe23.75Al5) composite particles

Abstract

Soft magnetic composite with oxide matrix (mainly alumina) have been prepared by reactive sintering of double-coated Al-permalloy (Ni71.25Fe23.75Al5 wt. %) composite particles. Nanocrystalline Al-permalloy powder have been first superficially oxidized by immersion in HCl solution. Upon oxidizing a thin layer of a mixture of oxides is formed. The Ni71.25Fe23.75Al5@oxide particles have been homogenised with Fe₂O₃ nanoparticles to obtain double layer coated particles. The as-obtained double coated particles have been densified at 900 °C by spark plasma sintering. Upon sintering, reactions at the interface between the metallic part of the particles and the double-layer of oxides occurs. Al atoms diffused to the particles' outer layer and reacted with the oxides layers, resulting mainly alumina. The microstructure is consisting of metallic Ni-based clusters embedded in alumina matrix. The alumina layer is continuous offering a high electrical resistivity. The interface between the metallic and oxide layer was analysed and discussed. The powder has been characterised by scanning electron microscopy (SEM), X-ray microanalyses (EDX), X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FTIR) and the sintered composite compacts by SEM and from magnetic and electric point of views. The characteristics of powder and compacts are discussed and corelated with the process and interface reactions.