The influence of the mutual interaction of alloying elements on microsegregation

From the condition for the thermodynamic equilibrium between the liquid and the solid at the solid-liquid interface a relation has been derived, indicating that the segregation coefficient of the element X in a ternary system Me-X-Y is a function of the concentration of the element Y: kYX= exp[NSY(εLXYkY ȡ εSXY) + ln kX. From analysis of this relation it follows that when the thermodynamic activity of the element X is increased due to additions of element Y, the direction of element X microsegregation changes above a critical concentration of the element Y; the segregation intensity of X increases with increasing intensity of Y segregation. When element Y reduces the thermodynamic activity of K, the segregation intensity of the latter also increases with increasing segregation intensity of Y, but the direction of its microsegregation does not change. Conclusions which follow from this theoretical analysis were verified experimentally using nickel alloys. Experimental results confirmed the change of segregation direction resulting from an interaction between atoms of alloying elements in the alloys. A dependence of the microsegregation intensity of element X on the concentration of element Y has also been confirmed.