Fe-氧化物体系熔化与凝固界面的分子尺度模拟
发布时间：2018-10-11 06:46
【摘要】：材料的宏观性质取决于微观结构。熔化作为生产大部分金属材料的必要过程,目前的认识更多的关注在工艺尺度,而对微观结构及其与宏观性能间关系的认识还不够充分。实际金属中往往存在大量纳米级缺陷,如纳米第二相、纳米孔洞等,这些缺陷会对晶体结构以及晶界等造成弱化、钉扎等不同效应,导致金属的热稳定性、力学性能等宏观性能发生变化。例如,金属中存在于晶界处的纳米第二相粒子可以钉扎晶界,阻碍晶粒长大,从而细化晶粒尺寸,提高力学性能。纳米孔洞会造成晶格不稳定,引发裂纹等缺陷的产生。因此,对金属熔化过程的微观结构演化、金属液与纳米颗粒的界面作用等进行研究,有利于从微观尺度认识金属熔化和凝固的宏观性能,建立微观结构与宏观性能关系的科学定量描述。本文借助计算机工作站,运用Materials Studio对Fe-氧化物体系的熔化过程和Fe-氧化物凝固界面的结构演化进行了分子尺度研究。具体如下:基于完美Fe晶体模型,采用拟合的Sutton-Chen势对包含2000个Fe原子纯Fe体系的升温和熔化过程进行了分子动力学模拟。径向分布函数(RDF)和均方位移(MSD)分析显示,纯Fe的升温和熔化过程经历了α-Fe→γ-Fe→δ-Fe→液态Fe的相变过程。计算得到总能量、体积和微观结构(RDF、MSD)的变化规律反映了实际金属的升温和熔化特性。计算得到完美Fe晶体熔点(2285K)与实际金属铁熔点(1833K)的差异,反映了金属表面、缺陷、晶界和测试条件等对实际金属熔化的重要作用。对含有不同半径缺陷(纳米Al_2O_3颗粒、纳米孔洞)纯Fe体系的升温和熔化过程进行了研究,结果表明:缺陷的存在明显降低了纯Fe的熔点,熔点的降低程度随着缺陷尺寸的增大而增大,当缺陷的尺寸范围在0.6—1.05nm时,纯Fe熔点降低了179—450K,纳米孔洞比纳米颗粒对熔点的降低效果更为明显。采用第一性原理模拟了Fe—氧化物界面原子间相互作用,研究表明:在氧化物(Al_2O_3、Ti_2O_3、ZrO_2和SiO_2)基底上随Fe原子或Fe团簇的增多,体系的总能量与束缚能均降低,反映出Fe原子在基底上聚集是热力学自发过程。对比不同氧化物体系的总能量、束缚能和界面结构表明,氧化物与Fe的界面稳定性ZrO_2Ti_2O_3Al_2O_3SiO_2;氧化物与Fe界面的结合力(吸附能力)Ti_2O_3Al_2O_3ZrO_2SiO_2;当Fe原子个数较多时,SiO_2与Fe体系出现了晶格漂移现象。
[Abstract]:The macroscopic properties of the material depend on the microstructure. Melting is a necessary process for the production of most metallic materials. At present, more attention is paid to the technological scale, but the understanding of the microstructure and the relationship between the microstructure and the macroscopic properties is not enough. There are many nanometer-scale defects in real metals, such as nano-second phase, nano-pore and so on. These defects will weaken the crystal structure and grain boundary, and lead to different effects such as pinning, resulting in the thermal stability of the metal. Mechanical properties and other macro properties change. For example, the nanocrystalline second phase particles in metals can be pinned to the grain boundaries, which hinders the grain growth, thus refining the grain size and improving the mechanical properties. Nanocrystalline holes will cause lattice instability and lead to cracks and other defects. Therefore, the study of the microstructure evolution of metal melting process and the interface between liquid metal and nanoparticles is beneficial to the understanding of the macroscopic properties of metal melting and solidification from the micro scale. A scientific quantitative description of the relationship between microstructure and macroscopic performance is established. In this paper, the melting process of Fe- oxide system and the structure evolution of Fe- oxide solidification interface have been studied on a molecular scale by means of computer workstation and Materials Studio. The main results are as follows: based on the perfect Fe crystal model, the molecular dynamics simulation of the heating and melting process of the pure Fe system containing 2000 Fe atoms was carried out by using the fitted Sutton-Chen potential. The radial distribution function (RDF) and mean square shift (MSD) analysis show that the heating and melting processes of pure Fe undergo the phase transition process of 伪-Fe 纬-Fe 未-Fe. The variations of total energy, volume and microstructure (RDF,MSD) reflect the heating and melting characteristics of metals. The difference between the melting point of perfect Fe crystal (2285K) and the actual melting point of iron (1833K) is obtained, which reflects the important effect of metal surface, defect, grain boundary and test conditions on the melting of actual metal. The heating and melting process of pure Fe system containing different radius defects (nanometer Al_2O_3 particles, nano pores) was studied. The results showed that the existence of defects significantly reduced the melting point of pure Fe. The melting point decreases with the increase of the size of the defect. When the size of the defect is in the range of 0.6-1.05nm, the melting point of pure Fe decreases by 179-450 K, and the effect of nano-pore is more obvious than that of nano-particle. First-principle simulation of the interatomic interaction between Fe- oxides has been carried out. The results show that the total energy and binding energy of the system decrease with the increase of Fe atoms or Fe clusters on the oxide (Al_2O_3,Ti_2O_3,ZrO_2 and SiO_2) substrates. It is shown that the aggregation of Fe atoms on the substrate is a thermodynamic spontaneous process. Compared with the total energy, binding energy and interface structure of different oxide systems, Interfacial Stability of oxide and Fe the binding ability of ZrO_2Ti_2O_3Al_2O_3SiO_2; oxide to Fe interface Ti_2O_3Al_2O_3ZrO_2SiO_2; when the number of Fe atoms is more SiO_2 and Fe system appear lattice drift phenomenon.
【学位授予单位】：辽宁科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG111
本文编号：2263242
[Abstract]:The macroscopic properties of the material depend on the microstructure. Melting is a necessary process for the production of most metallic materials. At present, more attention is paid to the technological scale, but the understanding of the microstructure and the relationship between the microstructure and the macroscopic properties is not enough. There are many nanometer-scale defects in real metals, such as nano-second phase, nano-pore and so on. These defects will weaken the crystal structure and grain boundary, and lead to different effects such as pinning, resulting in the thermal stability of the metal. Mechanical properties and other macro properties change. For example, the nanocrystalline second phase particles in metals can be pinned to the grain boundaries, which hinders the grain growth, thus refining the grain size and improving the mechanical properties. Nanocrystalline holes will cause lattice instability and lead to cracks and other defects. Therefore, the study of the microstructure evolution of metal melting process and the interface between liquid metal and nanoparticles is beneficial to the understanding of the macroscopic properties of metal melting and solidification from the micro scale. A scientific quantitative description of the relationship between microstructure and macroscopic performance is established. In this paper, the melting process of Fe- oxide system and the structure evolution of Fe- oxide solidification interface have been studied on a molecular scale by means of computer workstation and Materials Studio. The main results are as follows: based on the perfect Fe crystal model, the molecular dynamics simulation of the heating and melting process of the pure Fe system containing 2000 Fe atoms was carried out by using the fitted Sutton-Chen potential. The radial distribution function (RDF) and mean square shift (MSD) analysis show that the heating and melting processes of pure Fe undergo the phase transition process of 伪-Fe 纬-Fe 未-Fe. The variations of total energy, volume and microstructure (RDF,MSD) reflect the heating and melting characteristics of metals. The difference between the melting point of perfect Fe crystal (2285K) and the actual melting point of iron (1833K) is obtained, which reflects the important effect of metal surface, defect, grain boundary and test conditions on the melting of actual metal. The heating and melting process of pure Fe system containing different radius defects (nanometer Al_2O_3 particles, nano pores) was studied. The results showed that the existence of defects significantly reduced the melting point of pure Fe. The melting point decreases with the increase of the size of the defect. When the size of the defect is in the range of 0.6-1.05nm, the melting point of pure Fe decreases by 179-450 K, and the effect of nano-pore is more obvious than that of nano-particle. First-principle simulation of the interatomic interaction between Fe- oxides has been carried out. The results show that the total energy and binding energy of the system decrease with the increase of Fe atoms or Fe clusters on the oxide (Al_2O_3,Ti_2O_3,ZrO_2 and SiO_2) substrates. It is shown that the aggregation of Fe atoms on the substrate is a thermodynamic spontaneous process. Compared with the total energy, binding energy and interface structure of different oxide systems, Interfacial Stability of oxide and Fe the binding ability of ZrO_2Ti_2O_3Al_2O_3SiO_2; oxide to Fe interface Ti_2O_3Al_2O_3ZrO_2SiO_2; when the number of Fe atoms is more SiO_2 and Fe system appear lattice drift phenomenon.
【学位授予单位】：辽宁科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG111
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