The evolution of microstructure, micromechanical and magnetic properties of FeCoNiSi alloys solidified under high pressure

Abstract

A comprehensive study has been conducted on the effects of high-pressure solidification (HPS) on the evolution of microstructures, micromechanical properties, and magnetic properties of FeCoNiSi alloys. As solidification pressure increases(up to 7GPa), FeCoNiSi alloy's columnar grain changes into an equiaxed grain, and the grain size and Ni-rich precipitates are significantly refined. Furthermore, HPS facilitates the conversion of in-coherent matrix/precipitates interface of alloy solidified under atmospheric pressure into semi-coherent, which reduces the pinning effect of phase boundaries on the motion of the magnetic domains and enhances the exchange coupling between matrix and precipitates. As FeCoNiSi alloy solidifying under 7GPa, the maximum magnetic permeability (μ m ) is significantly increased (from 52,600 to 113,000), the inherent coercivity is decreased by 29.5%, and the saturation magnetic polarization( Js ) is increased by 21%. In addition, the high temperature magnetic properties of FeCoNiSi alloys are improved by HPS. Furthermore, HPS produces compressive stress in both the precipitates and matrix, which significantly improved the modulus of precipitates and matrix (i.e. from 171GPa to 215 GPa in matrix),as well as microhardness (i.e. from 5.46 GPa to 10.65 GPa in matrix). Based on the results of these studies, HPS is capable to improve the comprehensive properties of magnetic alloys significantly. • The J s and μ max (H MC ) of FeCoNiSi alloy are increased (decreased) by 21% and 114% (29.5%) after solidified under 7GPa. • HPS produces compressive stress in the precipitates and matrix and significantly improved the modulus and microhardness. • HPS refine the microstructure of FeCoNSi alloy and result in the semi-coherent interface. • The semi-coherent interface enhances the exchange coupling effect between precipitates and matrix.