【作者】 孙学银；

【导师】 甄良；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 博士

【摘要】 本文对Fe-25Cr-12Co-1Si合金在磁场作用下调幅组织演化以及磁场处理对合金磁性能影响进行了试验研究。采用透射电子显微镜(TEM)和穆斯堡尔谱仪对合金调幅分解前期、后期的显微组织和局域结构进行了观察和分析。研究了合金在无外磁场条件、低磁场和强磁场中647oC等温处理后调幅组织的粗化行为,以及合金在不同等温处理条件下调幅组织的变化。采用相场模拟的方法对二元合金在低磁场和强磁场作用下的调幅分解以及组织的演化进行了模拟。组织观察结果表明,强磁场加快了合金调幅分解的进行。合金在12T磁场中得到了界面清晰的α1相粒子,其分布并没沿外磁场方向明显取向;合金在无外磁场条件和低磁场中相应条件下未得到明显的α1相粒子形貌。在647oC保温1h时,随着外磁场强度的升高,α1相粒子体积份数随之增加,在12T磁场中获得α1相粒子体积份数最高。合金调幅组织α1相粒子在无外磁场条件和低磁场中粗化规律基本一致。合金调幅组织形貌受等温处理条件的影响,不同等温处理条件下获得的α1相粒子形貌有着显著的差异。通过控制磁场处理条件可实现合金微观组织的控制。穆斯堡尔谱分析结果表明,强磁场增强了Fe、Co原子间的交互作用,加速了原子的扩散过程,促进了合金调幅分解。强磁场导致了合金穆斯堡尔谱谱线1、6峰间距的宽化,提高了合金平均超精细场强度。合金在无外磁场条件、0.8T低磁场和12T强磁场中得到的平均超精细场强度<H>在调幅分解前期和后期基本保持不变,其值分别为256kOe、256kOe和293kOe左右。二元合金相场模拟结果发现,在外磁场下调幅分解组织沿外场方向伸长,并有着非常复杂的粗化过程。强磁场可以促进调幅分解但却阻碍后期粗化的进行,它能改变分解两相成分,并使强磁性相体积分数增加。强磁场加速了调幅分解,减小了调幅波长,细化了调幅组织。合金磁性能与平均超精细场强度在回火过程中不断增加,α1相粒子体积份数也不断提高。在不同强度磁场中经647oC等温处理1h获得的磁性能随着磁场强度的增强而增大。在不同强度磁场中于647oC进行1~21h等温处理后,相应条件下在12T磁场中合金获得的磁性能最佳,在低磁场和无外磁场条件下合金的磁性能随着时间的延长显著下降。合金磁性能的变化主要是由α1和α2两相成分变化所引起的。强磁场处理改变了合金局域结构,包括原子的占位排布、原子间以及电子间的交互作用,因而改变了两相的成分以及磁矩结构。以单畴粒子理论为基础,讨论了α1相形貌因素对磁性能的影响,指出α1相粒子的体积分数、长径比等均为造成磁性能变化的因素。更多还原

【Abstract】 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 (<H>) of the alloy. When the alloy was treated with 0, 0.8T and 12T magnetic fields, the average hyperfine field intensity (<H>) 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 <H> 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.更多还原