Measurement of Impurity Concentration at Grain Boundaries after Recrystallization

Abstract:

Impurity segregation at grain boundaries in polycrystalline alloys is known to have a tremendous impact on the material properties such as grain boundary mobility, cohesion... But direct measurement of grain boundary chemistry is quite complex and there are few results concerning polycrystals. In this paper we present an indirect method to measure segregationmisorientation dependence on polycrystalline Ni-S alloys using 3D reconstruction of etch grooves. Samples of Ni-S alloy (1 ppm at) have been cold rolled at respectively 0.3 and 0.9 Von Mises equivalent strain and then annealed at 455°C to promote recrystallization. Then they have been etched near the transpassive potential to form etch grooves, whose geometry depends on the sulfur segregation level. It is found that the sulfur concentration at grain boundary decreases significantly when the driving force for grain boundary migration (i.e. the initial strain) increases, as predicted by solute drag theory.