Influence Of Magnetic Field On Evolution Of Modulated Microstructure And Magnetic Properties Of Fe-Cr-Co Alloy

In this paper the modulated microstructure and magnetic properties of the Fe-25Cr-12Co-1Si alloy were studied by experiments. The modulated microstructure were investigated by transmission electron microscopy (TEM) and M?ssbauer spectrometry in early and late stage of spinodal decomposition, microstructures of the alloy isothermally treated at 647oC without magnetic field, with low magnetic field and high magnetic field, and under different isothermal treatment conditions were observed by TEM. And the evolution of modulated microstructure in binary alloy treated with magnetic field was simulated using phase-field method.Microstructure observation shows that high magnetic field accelerates the spinodal decomposition. The interphases ofα1 phase particles of the alloy treated with a 12T magnetic field are clear, and the orientation of particles is not along the direction of the external magnetic field (Hext). Theα1 phase particles in the alloy treated without magnetic field and with low magnetic fields have no obvious shape. When the alloy was treated at 647oC for 1h with different magnetic field intensities (Hint), the uniformity of theα1 phase particles orientation is increased with increasing Hint, the volume fraction ofα1 phase particles are the highest for the alloy treated with a 12T magnetic field.Microstructure observation shows that the coarsening trend ofα1 phase particles is the same when the alloy was treated without magnetic field and with low magnetic field. After the alloy was isothermally treated at 647oC for more than 15h in a 12T magnetic field, theα1 phase particles about 12nm in diameters are observed. The modulated structure in the alloy is greatly affected by isothermal treatment conditions, and the morphology ofα1 phase particles is much different in different treatment conditions. Microstructure of the alloy could be controlled by the thermo-magnetic treatment conditions.The results of M?ssbauer spectrum analyses show that high magnetic field enhances the interaction between the atoms of iron and cobalt, accelerate the spinodal decomposition of the alloy, broadens the magnetic sextet, increases the average hyperfine field intensity () of the alloy. When the alloy was treated with 0, 0.8T and 12T magnetic fields, the average hyperfine field intensity () of the alloy keeps the same in the early and late stage of spinodal decomposition, which are about 256kOe, 256kOe and 293kOe, respectively.The simulation results of a binary alloy show that the modulated structure elongates along the direction of external magnetic field, and the coarsening process is very complex. High magnetic field was found to accelerate the decomposition at early stage but hinder the coarsening process. The compositions in the modulated two phases were modified under ultra-high magnetic field, leading to the increase of volume fraction of ferromagnetic phase. The high magnetic field accelerates the spinodal decomposition, decreases the spinodal wave length, and refines the spinodal microstructure.The magnetic properties and of the alloy all increase during ageing progress, and the volume fraction ofα1 phase particles increases. The magnetic properties of the alloy treated with high magnetic field obviously increase. When the alloy was treated at 647oC for 1h, the magnetic properties increase with increasing Hint. When the alloy was treated at 647oC for 1h to 21h in external magnetic field with different intensities, the alloy treated with a 12T magnetic field gets the best magnetic properties. The magnetic properties of the alloy treated without and with low magnetic fields decrease obviously with increasing isothermal time.The magnetic properties of the alloy are mainly decided by the composition ofα1 andα2 phases. The high magnetic field changes the local structure of the alloy, including the atoms arrangement, the exchange of atoms and electrons, which leads to the change of compositions and magnetic moment ofα1 andα2 phases. Based on the single-domain particle theory, the effect ofα1 phase morphology on magnetic properties was discussed, including volume fraction and aspect ratio.