Strengthening And Toughening Of Feal Electron Theory

Iron-aluminides are considered as potential candidates for medium and high temperature structural applications in a wide range of mechanical and magnetic industries. They present excellent resistance to oxidation and corrosion, low densities, high melting points, good mechanical properties at high temperatures, and low raw material cost. However the application of these alloys at room temperature is limited by their low ductility. It was until 1970!s that the above mentioned major limitation may be alleviated through the addition of alloy elements, thermomechanical treatments, which resulted in the research interests all over the world.Using the Empirical Electron Theory of Solids and Molecules (EET), the strengthening and toughening mechanisms of FeAl was studied at the electronic level.It is of great value to improve the properties of material through the understanding of electronic structure and bonding character. In this paper the valence electron structure of B2-ordered FeAl is calculated based on EET theory. The hybrid states of Fe and Al atom for ordered FeAl was then determined in accordance with experimental data. The analysis of embrittlement for FeAl intermetallic compound was carried out. The approach to the toughening of FeAl was proposed. For the convenience of comparison, the valence electron structure of NiAl with the same structure as B2-ordered FeAl was also presented. It's noted that all the calculation is based on the perfectly B2-ordered FeAl or NiAl without considering the actual conditions including the order degreee and site preference under various processing instances.In terms of disordering effect on the strengthening and toughening FeAl, the dependance of the lattice constant for disordered Fe-Al as a function of the Al content was initially set up. Magnetic moments of Fe as a function of the numberN of Fe nearest neighbors for disordered FeAl were calculated by applying Jaccrino-Walker model and mean atom model. It is found that the mean magnetic moments of Fe atom as a function of the number N of Fe nearest neighbors for disordered FeAl is 1.41 μb, which is much larger than the experimental datum (0.65μB), but slightly small than other theoretical calculation result (1.65μb). The discrepancy between theoretical value and experimental one is presumably due to the degree of ordering, in that the theoretical value resulted from ideally disordered FeAl, while the experimental value is from partly ordered FeAl. The difference between experiment value and theoretical value also shows that the magnetic moments for FeAl intermetallic compound may be elevated through disordering. And the enhancement of the magnetic moments for FeAl may be ascribed to a local environment effects on the magnetic moment of the Fe atom for Fe-Al alloy, which indicates that the more nearest neighbors Al atom, the more local environment effects.With respect to reinforcement by composites, the electron density of low index crystal planes for FeAl and transition metal carbides was firstly computed. It is found that the electron density along the interface (110)FeAl//(100)MC is basically consistent under first order approximation. According to Cheng-Liu model, the number of atomic states σ along the interface (110)FeAl//(100)Mc was determined. The mechanical properties of FeAl/MC composites may be increased through properly selecting processing, such as in-situ technique, to achieve more (110)FcAl//(100)mc interfaces in composites, thus strengthening and toughening FeAl intermetallic compound. This theoretical method may be used in other ceramic/intermetallics composites.