Effect of character of grain boundaries on non-equilibrium segregation of B in a nickel base superalloy

Boron was observed to segregate heterogeneously to the grain boundaries of Inconel 718 during cooling from the solution heat treatment temperature. That is, in the same area only a few grain boundaries were segregated while others were not. The examination of a water-quenched Inconel 718 by SEM, orientation imaging microscopy based on electron back scatter diffraction, and by SIMS suggested the heterogeneity in segregation of B to be due to the variation in the character of different GBs. It was found that the high angle random boundaries were invariably segregated with B, high Σ CSL boundaries were occasionally segregated, and low Σ CSL and low angle boundaries were seldom segregated. A direct correlated between segregation of B on GBs and their liquation during thermal cycling was also observed. (orig.)