Characterization of the Effects of Boron and Phosphorus Additions to the Nickel-Based Superalloy 718

The effects of controlled additions of boron and phosphorus to Alloy IN-718 have been investigated by atom probe field ion microscopy and transmission electron rnicroscopy. Boron and phosphorous additions are known to improve the creep rupture properties of IN-718. Significant enrichments of boron, phosphorus and carbon were measured at the grain boundaries. Some fine phosphide precipitates were also observed at the grain boundaries. No enrichment of boron or phosphorus was observed at γ' or γ" interfaces. However, the boron and phosphorus additions did slightly increase the stability of the γ" precipitates after long term ageing at 704°C