Temperature and dynamic in materials and its surfaces
Abstract
(1)Ferritic steels are very widely used engineering materials. Typical metallic alloying agents are Al, Cr, Mn, Co, and Ni, which often are used in combination to optimize the steel towards a desired property. Today, ab initio alloy theory plays an increasingly important role in the design of steels. We will characterize in this project the mechanical properties of ferritic steels, for example, their single- and polycrystalline elastic constants, solid-solution hardening, and the ductile-brittle behavior. Another considered important intrinsic mechanical descriptor is the ideal strength, which defines the upper limit of the attainable strength in tension or shear. In order to describe and predict the mechanical behavior under realistic external conditions, one has to consider the effect of temperature. Here, we will also model the evolution of essential mechanical properties as a function of temperature.
(2)The fundamental thermodyamic properties of surfaces are the surface energy and the surface stress. Both play an important role in the understanding of many aspects of surface science, e.g., surface reconstruction, surface alloying, self-assembly and mesoscopic pattern formation. Presently, there is no reliable mean to measure absolute surface stress. Both surface quantities have been theoretically studied for many metallic systems by means of first principles modeling in the recent past, albeit the results obtained are valid at T=0K. Within this project, we will study the temperature dependence of surface energy and surface stress of metallic materials by modeling the underlying temperature-induced excitations.
(3) Both Fe and Cr are 3d transition metals. These metals are in several ways difficult to describe using common density functional methods, and this is due to the strong Coulombic interaction between the electrons. One usually says that the electrons in these metals are "correlated". In recent years a merging of dynamical mean field theory, a theory that is highly successful in describing correlated systems, with density functional theory has been initiated. Part of this project aims at this kind of method development, with the goal of obtaining a better description of Fe and its alloys.
