Grain boundary segregation in the Ni-base alloy 182

Abstract

Grain boundary segregation is often considered to play a role in the various types of intergranular failures observed in austenitic alloys. However, there has been little direct study of this segregation because it is usually very difficult to obtain intergranular fracture in these alloys in the high vacuum required for surface analysis. This paper reports an Auger electron spectroscopy study of grain boundary segregation in the nickel-base Alloy 182. This alloy was used because it would easily fracture along its grain boundaries in high vacuum and because it has a very complex microstructure, as do many nickel-base alloys used in engineering applications. Furthermore, the alloy is widely used as a weld filler metal to join nickel-base alloys to one another or to stainless steels. Phosphorus was found to be the only impurity element that segregated to the grain boundaries. There was considerable variability in segregation from grain boundary to grain boundary and also on a single grain facet. It is suggested that these variations arise primarily from variations in grain boundary structure, in the density and types of precipitates in a grain boundary, and in the consequent variety of precipitate matrix interfaces present at the grain boundary. It is also suggested that quantitative Auger analysis on such a material would be very difficult.