Study Of Diffusion Related Properties Of Fe-Al System

Diffusion is associated with the random thermal motion of atoms. These thermal motions can change the macroscopic concentration distribution. The investigation of diffusion can provide valuable information about the atomic structure of materials and the defects within them. Diffusion is closely related to the precipitation, annealing and creep of materials. Iron and aluminum are important industrial materials. They are widely used in construction, motor vehicle and aerospace. Study the diffusion properties about Fe and Al can contribute to understand the micro mechanism of diffusion, and it’s important for improving the properties of materials. This paper performs molecular dynamics (MD) simulations for the self-diffusion of Fe and Al with EAM potentials. The results agree well with theoretical results and experimental values. Confirm that the self-diffusion of Fe and Al are controlled by vacancy mechanism. The main results of this thesis are as follows:Minimize the energy of Fe and Al with different vacancies and self-interstitials to find the most stable structure. And nudged elastic band (NEB) method has been used to calculate the potential barrier of vacancy and interstitial in iron and aluminum. Vacancy jumps to the nearest neighbor atoms site is the most probable jump mechanism during self-diffusion, which require the least activation energy, The diffusion coefficient calculated from molecular dynamics (MD) simulations for self-diffusion of Fe and Al are agree well with the experimental values.Beside vacancy and self-interstitial, impurity atom is also an inevitable defect in materials. Boron can improve the hardness of Fe and the conductivity of Al. It also plays an important role in improving the brittleness Fe-Al intermetallics. The diffusion of boron in iron and aluminum has been calculated. The boron atoms occupy substitutional positions of iron and aluminum in lattice structure, respectively. The procedure of boron diffusion is carried out by jumping to nearest neighbor vacancies. The existence of boron atom also affects the formation energy of neighbor vacancies. Formation energy of vacancy, which is nearest neighbor of impurity boron atom, is higher than formation energy of vacancy in pure iron, while the formation energy of vacancy, which is the second nearest neighbor of boron atom, is lower than that of pure iron. However, both of the formation energies of vacancy near the boron in aluminum are lower than that in pure aluminum.The interdiffusion of Fe-Al interface has been simulated by MD method. The results indicate that iron atoms diffuse into aluminum, and the numbers of diffusing atoms become more and go further as temperature increases. At the same temperature, aluminum atoms diffuse faster than iron atoms, but only few of them diffuse into iron due to the higher migration energy.