Study On The Interfical Structure Of Iron-oxide And Solidification Mechanism Of Pure Iron

The macroscopic properties of materials depend on the microstructure, as we all know, with the development of the society, people’s requirements for materials are also increasing, with all kinds of functional materials, especially for metal materials, which has become an indispensable part of social development.Solidification- as the most important and common process for obtaining metal materials, is very important to understand the mechanism of solidification process,and to understand the solidification mechanism. In recent years, with the development of calculation technology, the theory of solidification and the continuous development of multiple disciplines, we have a new understanding on the mechanism of metal solidification process. Based on the two-step nucleation theory, with the aid of computer workstation and the simulation software(Accelrys Materials Studio 7.0, MS), we have calculated the thermodynamics and kinetics of liquid iron solidification process, then, the solid oxide – liquid iron interface structure evolution process was simulated to explore the mechanism of solidification process, which can be summarized as:Firstly, the GULP molecular dynamics program is used to simulate the cooling dynamics of a liquid containing 2000 Fe atoms. The results show that the solidification process of the system is composed of a liquid disordered structureâ†' a local short-range order and a long range disorder(cluster) â†' ordered structure in larger region â†' ordered crystal structures.Secondly, the thermodynamic properties of Fe clusters(Fe)n, with the atomic number n=2-10, are calculated by the first principles of quantum mechanics program, DMol3. Through the analysis of entropy(S), enthalpy(H), zero point energy(E(0K)) and heat capacity at a constant pressure(Cp) changes with temperature, and the atomic number. The results showed that:(1) Cp, H, S of Fe clusters(Fe)n were increased with the increase of temperature, and increases with the increase of the atomic number N, furthermore, vibration free energy(Gv)decreased with the temperature increases, and the Gv curve shows two-two cross between 100-300 K, indicating the change of selectivity stability phenomenon in this range of Fe clusters;(2) With the increase of the atomic number, zero point energy E(0K) decreased, which indicated that the larger clusters are more stable than small clusters at 0K;(3) In the whole process, the changes ofthermodynamic properties of clusters with the atomic number is large relatively,indicating that there may exist size dependent effect between thermodynamic properties of Fe clusters and atomic number.Thirdly, in the establishment of the iron- oxide interface system, the relationship between the atomic number and oxide species is simulated. The simulation results show that the total energy and binding energy of the system can be reduced at the whole process. The stability of the α-Al2O3 surface layer is significantly affected by the growth of Fe clusters(Fe)n on the surface of α-Al2O3.A drift phenomenon appeared with the atomic number in the clusters close to a number(n>3), which indicated the larger clusters can hardly combined with theα-Al2O3 substrate, at the same time, the same phenomenon does not appear on the titanium dioxide substrate.Finally, we have done a pure iron melting and solidification process DSC analysis experimentally, from which the view of the phase transition temperature and our knowledge of the phase transition temperature is not large and the approximate phase change information can be obtained.