Significant decrease in interfacial energy of grain boundary through serrated grain boundary transition

Abstract

The mechanism of serrated grain boundary formation and its effect on liquation behaviour have been studied in a wrought nickel-based superalloy – Alloy 263. It was newly discovered that grain boundaries are considerably serrated in the absence of γ ′-phase or M₂₃C₆ at the grain boundaries. An electron energy-loss spectroscopy study suggests that serration is triggered by the discontinuous segregation of C and Cr atoms at grain boundaries for the purpose of relieving the excessive elastic strain energy. The grain boundaries serrate to have specific segments approaching one {111} low-index plane at a boundary so that the interfacial free energy of the grain boundary can be decreased, which may be responsible for the driving force of the serration. The serrated grain boundaries effectively suppress grain coarsening and are highly resistant to liquation due to their lower wettability resulting from a lower interfacial energy of the grain boundary.

Keywords:

• Ni-based superalloys
• grain boundary serration
• grain boundary energy
• grain boundary segregation
• wetting

Acknowledgements

The authors acknowledge the financial support of MKE (Ministry of Knowledge Economy), Account No. UCN615-2848.C, and UCN248-284845.C, which made this work possible. Also, this paper was supported by research funds of Changwon National University in 2012.