【摘要】：材料的宏觀性質(zhì)取決于微觀結(jié)構(gòu)。熔化作為生產(chǎn)大部分金屬材料的必要過程,目前的認識更多的關(guān)注在工藝尺度,而對微觀結(jié)構(gòu)及其與宏觀性能間關(guān)系的認識還不夠充分。實際金屬中往往存在大量納米級缺陷,如納米第二相、納米孔洞等,這些缺陷會對晶體結(jié)構(gòu)以及晶界等造成弱化、釘扎等不同效應(yīng),導(dǎo)致金屬的熱穩(wěn)定性、力學性能等宏觀性能發(fā)生變化。例如,金屬中存在于晶界處的納米第二相粒子可以釘扎晶界,阻礙晶粒長大,從而細化晶粒尺寸,提高力學性能。納米孔洞會造成晶格不穩(wěn)定,引發(fā)裂紋等缺陷的產(chǎn)生。因此,對金屬熔化過程的微觀結(jié)構(gòu)演化、金屬液與納米顆粒的界面作用等進行研究,有利于從微觀尺度認識金屬熔化和凝固的宏觀性能,建立微觀結(jié)構(gòu)與宏觀性能關(guān)系的科學定量描述。本文借助計算機工作站,運用Materials Studio對Fe-氧化物體系的熔化過程和Fe-氧化物凝固界面的結(jié)構(gòu)演化進行了分子尺度研究。具體如下:基于完美Fe晶體模型,采用擬合的Sutton-Chen勢對包含2000個Fe原子純Fe體系的升溫和熔化過程進行了分子動力學模擬。徑向分布函數(shù)(RDF)和均方位移(MSD)分析顯示,純Fe的升溫和熔化過程經(jīng)歷了α-Fe→γ-Fe→δ-Fe→液態(tài)Fe的相變過程。計算得到總能量、體積和微觀結(jié)構(gòu)(RDF、MSD)的變化規(guī)律反映了實際金屬的升溫和熔化特性。計算得到完美Fe晶體熔點(2285K)與實際金屬鐵熔點(1833K)的差異,反映了金屬表面、缺陷、晶界和測試條件等對實際金屬熔化的重要作用。對含有不同半徑缺陷(納米Al_2O_3顆粒、納米孔洞)純Fe體系的升溫和熔化過程進行了研究,結(jié)果表明:缺陷的存在明顯降低了純Fe的熔點,熔點的降低程度隨著缺陷尺寸的增大而增大,當缺陷的尺寸范圍在0.6—1.05nm時,純Fe熔點降低了179—450K,納米孔洞比納米顆粒對熔點的降低效果更為明顯。采用第一性原理模擬了Fe—氧化物界面原子間相互作用,研究表明:在氧化物(Al_2O_3、Ti_2O_3、ZrO_2和SiO_2)基底上隨Fe原子或Fe團簇的增多,體系的總能量與束縛能均降低,反映出Fe原子在基底上聚集是熱力學自發(fā)過程。對比不同氧化物體系的總能量、束縛能和界面結(jié)構(gòu)表明,氧化物與Fe的界面穩(wěn)定性ZrO_2Ti_2O_3Al_2O_3SiO_2;氧化物與Fe界面的結(jié)合力(吸附能力)Ti_2O_3Al_2O_3ZrO_2SiO_2;當Fe原子個數(shù)較多時,SiO_2與Fe體系出現(xiàn)了晶格漂移現(xiàn)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 偽-Fe 緯-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.
【學位授予單位】：遼寧科技大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TG111

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