The segregation of impurities at the (110) surface of an Fe–10 at. % single crystal

Abstract

Measurement of the nonequilibrium surface concentration in a Fe–10 at. % Si (110) sample as an function of temperature reveals specific interrelated segregation behavior. A review of the initial processes in this single crystal shows the existence of certain interactions. In agreement with work on the other ternary systems, evidence has been found that carbon and silicon show a repulsive interaction in the segregation process. At lower temperatures the surface free energy favors the carbon and above a transition temperature, the silicon on the surface. On the other hand, silicon and phosphorus cosegregate, which is indicative of an attractive interaction. This has the effect that much less phosphorus is available for segregation to the surface or grain boundaries than in a pure Fe–P system. The LEED pattern for the silicon covered surface is the same as for a 1% Si sample viz. a c(7×1) superstructure with reference to the c(a×(2a)1/2) surface net, where a is the unit cell parameter in the [001] direction. Elongation of the spot in one direction indicates a change of order in the [001] direction in agreement with the silicon island formation. The pattern of the phosphorus covered surface shows a maximum surface coverage by phosphorus in good agreement with the observed value as determined by AES.

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

“…For higher concentrations island formation of Si was assumed [7,8]. Investigations by STM have recently shown, that Si first forms a c(lx3) structure with a surface coverage of 33%.…”

Grain boundary segregation and intergranular fracture in Ferrite containing Mo, Si or Al

“…The kinetics of the segregation are thus described by J (11) where F=4 for grain boundaries and 1 for the free surface, Xb(t) is the boundary content at time t, b is the solute bulk diffusivity and f is related to the atom sizes of the solute and matrix, b and a respectively, by f=a3b 2. For short times equation (11) approximates to (12) Equations (11) and (12) are, in fact, limited extremes of a general problem. In practice, [3 is constant only for dilute systems with low segregation levels.…”

“…In all these cases, interfacial segregation phenomena are suspected to play a significant role. Repulsion or cosegregation at surfaces or grain boundaries between Si and impurities has been reported in Fe-Si alloys [10][11][12][13][14][15][16][17][18]. Aluminum decreases the activity of carbon in ferrite and increases it in cementite, both effects acting to retard cementite precipitation [19].…”

Anomalous Sulfur Segregation Kinetics Governed by MnS Precipitation Reaction and {110} Annealing Texture Development in Al-free and 0.1% Mn–Added 3% Si–Fe Alloys

“…The pre-annealed strips were heated up to 1 200°C with heating rates of 50, 400 and 10 800°C/h (i.e., isothermal annealing at 1 200°C) under the same vacuum or in the same dry hydrogen and subsequently finalannealed at the temperature for 12 h. All the heat treatments were performed without any MgO coating in a quartz tube with the inner and outer diameters of 29 and 33 mm that is enclosed by a three-zone tube furnace. There are several studies [15][16][17][18][19] reporting surface segregation behaviors of solutes in the 3% Si-Fe alloy strips. Due to the active evaporation of solutes at a higher temperature that attacks the electron gun, most of these studies were performed in-situ below 1 000°C in AES (Auger electron spectroscope).…”

“…There are several studies [15][16][17][18][19] reporting surface segregation behaviors of solutes in the 3% Si-Fe alloy strips. Due to the active evaporation of solutes at a higher temperature that attacks the electron gun, most of these studies were performed in-situ below 1 000°C in AES (Auger electron spectroscope).…”