An experimental and theoretical study of surface segregation in a Fe-6at.%Si bicrystal

Abstract

Abstract. The analysis of segregation phenomena in bicrystals is an important step for the understanding of combined effects of the elementary diffusion processes involved in the segregation in polycristalline SYstems. The segregation of Si and P in a Fe-6at.%Si bicrystal with a (100) and (110) surface has been investigated by means of AES (Auger electron spectroscopy). For these experiments the technique of a linearly increased temperature has been applied. Significant differences between the segregation kinetics at the two surfaces of the sample have been found on the one hand for the maximum coverage of P and on the other hand for the high temperature behaviour of Si. Additionally, model calculations based on the KTBIM (kinetic tight binding Ising model) have been performed to qualitatively describe the experimental results. It is shown, that the striking differences between the segregation behaviour at the two differently oriented surfaces can be explained by different segregation energies of P, whereas Si plays a minor role due to its relatively small segregation energy.Key words: Auger electron spectroscopy, iron, surface segregation, single crystal surfaces.as for surface segregation. Therefore, the knowledge of surface segregation is an important step to explain interface segregation phenomena. In this work the evolution of surface concentrations of Si, P, C, S, N and O on a Fe-6at.%Si bicrystal with a (100) and a (110) oriented surface have been measured by means of AES and SAM (scanning Auger microscopy) in order to gain data for a mathematical description of the surface segregation behaviour of Si and P and the interaction with grain boundary segregation. Measurements were performed by using the method of temperature programmed segregation [23.Additionally, the results are compared with a theoretical model for the segregation kinetics using the KTBIM under consideration of the surface structure which is formed by the segregands.Interface segregation of impurities such as Si and P can drastically change the material properties of iron and steel especially in connection with high temperatures and large temperature gradients during the production and use of the material. Segregation is determined by a complex combination of several diffusion mechanisms such as bulk diffusion, grain boundary diffusion and surface diffusion. To investigate the segregation phenomena a bicrystal is often used as a simple model system, which consists of two single crystals with a grain boundary between them perpendicular to the plain surface. As pointed out by [1] grain boundary segregation can be explained by using the same models * Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday ** To whom correspondence should be addressed ExperimentalThe measurements were performed using a Fe-6at.%Si bicrystal which contained a phosphorus concentration of about 70 ppm. The sample was metallographically polished before introducing it into a Perkin-Elmer 25-260 Auger spectrometer (beam energ...