Molecular Scale Simulations Of Melting And Solidification Interface Of Fe-oxide System

The macroscopic properties of materials depend on the microstructure.Melting is the necessary process for producing most of metal materials.The current understanding of melting is on the process scale,while the microstructure and its relationship with the macro mechanical properties are not understood clearly.There are many nano-scale defects in the actual metal,such as nano-second phase,nano-pores.These defects have different impact on the crystal structure and grain boundary,such as pinning and weakening,rusulting in the changes of metal thermal stability and mechanical properties.For example,the grain boundaries can be pinned by the nano-sized second-phase particles,which hinders grain growth,thereby refining the grain size and improving the mechanical properties.Nano-pores can cause lattice instability,cracks and other defects.Therefore,the microstructure evolution of metal melting process and the interaction between molten metal and nanoparticles are studied,which is helpful to understand the macroscopic properties of metal melting and solidification from microcosmic scale,and to establish a scientific and quantitative description of the relationship between microstructure and macroscopic properties.In this paper,the melting process of Fe-oxide system and the structural evolution of Fe-oxide solidification interface were studied by means of Materials Studio and computer station.Details as follows:Based on the perfect Fe crystal model,the heating and melting processes of pure Fe system containing 2000 Fe atoms was simulated by the molecular dynamics method using the fitted Sutton-Chen potential.Radial distribution function?RDF?and mean square displacement?MSD?show that the heating and melting processes of pure Fe undergo the transformation process of ?-Fe ? ?-Fe ? ?-Fe ? liquid Fe.The variations of the calculated total energy,volume and microstructure?RDF,MSD?reflect the heating and melting characteristics of the real metal.The difference of the melting point between the calculated perfect Fe crystal and the actual metal iron reflects the importance of the metal surface,defects,grain boundaries and test conditions on the melting of the actual metal.The heating and melting processes of pure Fe system with different radius defects?nano-Al₂O₃ particles,nano-pores?were studied.The results show that the existence of defects decrease the melting point of pure Fe remarkably,and the decrease of melting point increases as the sizes of defects increase.When the size of the defects is in the range of 0.6-1.05 nm,the melting points of pure Fe decrease by179-450 K.The effect of nano-pores on the melting point is more obvious than that of nano-particles.The interfacial interactions of the Fe-oxide were simulated by first-principles method.The results show that the total energy and binding energy decrease with theincrease of Fe atoms or Fe clusters on the oxide?Al₂O₃,Ti₂O₃,ZrO₂ and SiO₂?substrates,reflecting that the aggregation of Fe atoms on the substrates is thermodynamically spontaneous.The total energy,binding energy and interface structure of different oxide systems are compared,which show that the interface stabilities of oxides?ZrO₂,Ti₂O₃,Al₂O₃ and SiO₂?and Fe are decreasing gradually.The binding forces of oxides?Ti₂O₃,Al₂O₃,ZrO₂ and SiO₂?and Fe are decreasing gradually.When the number of Fe atoms is large,the system of SiO₂ and Fe exhibits lattice drift.