AbstractThe changes in composition of the grain boundary regions in Nimonic PE16, which occur during heat treatment and on neutron irradiation, are described. The results show that the composition of these regions is sensitive to heat treatment variables, bulk composition, and irradiation. In particular, molybdenum has a strong tendency to segregate to grain boundaries both on cooling from solution treatment and on aging. The non-equilibrium segregation which occurs on cooling increases with increasing boron content of the alloy. Chromium also segregates to grain boundaries under these conditions, though there is no dependence on boron content. Aging at 700°C causes molybdenum and chromium to segregate to grain boundaries until the onset of precipitation of M23C6, M6C, and Laves phase causes a decrease in the concentrations of these elements. The effects of neutron irradiation are dependent on the boron content of the alloy.MST/1336