Boron trapping at dislocations in an additively manufactured polycrystalline superalloy

Abstract

Segregation of solutes at dislocations in a nickel-based superalloy produced by laser powder bed fusion was investigated. Transmission electron microscopy has shown a high dislocation density present in the as-built microstructure, which was significantly reduced after a subsolvus heat-treatment, but not completely removed. Atom probe tomography revealed segregation of boron at dislocations in the γ matrix in the as-built state. Such segregation was observed for dislocations both in the interdendritic and dendritic core region, but also for dislocations close to grain boundaries. Molybdenum, carbon and tungsten were also found to segregate at dislocations in the γ matrix. After the subsolvus heat treatment, the segregation behaviour of dislocations remaining in the γ matrix is not altered. Boron, molybdenum and tungsten were found to segregate at dislocations but at higher amounts compared to those in the as-built state. Ramifications of boron trapping at dislocations in additively manufactured superalloys are briefly discussed.