Surface segregation and its relation to grain boundary segregation

Abstract

Equilibrium surface segregation concentrations have been measured for iron-tin alloys over the temperature range 500° to 850°C using Auger electron spectroscopy. The results are compared with the grain boundary segregation measurements reported earlier for these alloys, over the same temperature range, and also with the surface and grain boundary segregation data deduced from surface and interfacial energy measurements at 1420°C (Seah and Hondros 1973). The observations are all fully compatible with the theoretical predictions which incorporate the appropriate entropy terms. At low temperatures, in dilute solutions, it is found that the surface enrichment is approximately 130 times that at the grain boundary, whereas at 1420°C the ratio is only six. This difference, which will depend on the particular system considered, indicates that careful correlation experiments are required if surface segregation is to be used as a direct guide to grain boundary segregation. A second practical difference is that site competition between sulphur and tin is strongly evident on the surface but was not significant at grain boundaries (Seah and Hondros 1973).