【作者】 王丽；

【导师】 王强；

【作者基本信息】 东北大学 ， 材料加工工程， 2014， 硕士

【摘要】 颗粒粗化是半固态加工、液相合成、难混溶合金凝固、沉淀强化、液相烧结、夹杂物控制等多种材料制备过程的核心问题。深入理解颗粒粗化过程的基本规律有利于对颗粒粗化过程进行有效控制、改善材料的微观组织进而提高性能。本文将强磁场施加到液/固二元体系中半固态等温处理过程,以期通过强磁场控制液相中颗粒的粗化行为。本文进行了亚共晶Mn-Sb合金的半固态等温处理实验,研究了合金的微观组织演变,考察了MnSb颗粒的尺寸变化及其分布,分析了强磁场的作用机制。主要研究结果如下：(1)随着保温时间的延长,0T和1T磁场下经半固态等温处理的合金中MnSb枝晶经历了碎化、球化和粗化的过程,形成了MnSb颗粒与共晶组织共存的组织；4、8、11.5T磁场下在半固态等温处理初期的合金的淬火组织中出现了初生MnSb相、初生Sb相和共晶组织共存的特殊组织；随着保温时间的延长,合金重新转变为MnS颗粒分布在MnSb/Sb共晶基体的组织：(2)半固态等温处理过程中出现的特殊组织是由于强磁场通过洛伦兹力抑制对流、未熔断枝阻碍对流及MnSb相磁化引起磁场梯度变化而导致Mn溶质富集所引起的；(3)MnSb初生相粗化动力学符合,noc t的粗化规律,0T和1T磁场条件下颗粒粗化方程n值大约为3,颗粒分布曲线与LSW理论下的稳态分布趋近,颗粒粗化机制为扩散控制,随着磁场强度增加到11.5T,颗粒粗化速率增大,粗化方程n值增加到4,颗粒分布曲线偏离LSW理论。(4)强磁场作用下,磁极间的相互作用引起颗粒接触和合并以及MnSb相被磁化引起局部磁场梯度变化而导致Mn溶质浓度分布发生变化是引起颗粒粗化偏离LSW理论的主要原因。更多还原

【Abstract】 Coarsening process is the core issues of materials processing like semi-solid processing, liquid synthesis, immiscible alloy solidification, precipitation strengthening, liquid-state sintering, inclusions control and so on. A good understanding of the basic laws of particles coarsening process is beneficial of controlling particles coarsening processing and changing the micro structure of materials to improve its performance effectively. A high magnetic field is applied to the a liquid/solid binary system in semi-solid state during isothermal annealing in this paper, hoping to control the coarsening behavior of particles in the liquid phase through a high magnetic field. In this study, the experiment of isothermal annealing in semi-solid state in high magnetic fields of hypoeutectic Mn-Sb alloy were carried out. The microstructure evolution of the alloy and particles size and distribution of MnSb were investigated. the action mechanism of high magnetic fields was analysed.The main findings are as follows:(1) With the extension of the holding time, MnSb dendrites in the alloy specimens after isothermal annealing in semi-solid state at OT and 1T experienced fragmentation, globalization and the coarsening process and formed the microstructure in which MnSb particles and MnSb/Sb eutectic structure coexisted. A special microstructure in which MnSb particles, the primary Sb and eutectic structure coexisted were formed in the alloy after quenching of isothermal annealing in semi-solid state at the magnetic field of 4,8,11.5T. With the extension of the holding time, the microstructure transformed into a distribution of MnSb particles in MnSb/Sb eutectic matrix.(2) The special microstructure appeared after isothermal annealing in semi-solid state is due to convection suppression caused by Lorentz force and the dendrite arm. Besides, the solute accumulation of Mn caused by the local magnetic field gradients induced by the magnetized MnSb particles is another reason for the appearance of this structure.(3) The coarsening kinetics of MnSb primary phases corresponds to Y " ∝ t. The average size of MnSb particles at the magnetic field of OT and 1T increases with annealing time t as t1/3, as predicted by LSW theory. The size distribution of MnSb particles under this condition resemble the steady-state distribution of LSW theory. The particles coarsening at the magnetic field of OT and 1T is mainly diffusion controlled. The average size of particles at the magnetic field of 11.5T increases with annealing time t as t1/4. Particle coarsening rate increased.The size distributions of the MnSb particles at 11.5T deviates from the LSW theory.(4) The contact and mergence caused by the magnetic interaction between the particles and the change of Mn solute concentration caused by local magnetic field gradients induced by the magnetized MnSb particles is the main reasons for the deviation of particles size distribution from LSW theory.更多还原