Boron Segregation at grain boundaries in Co-9Al-9W-0.005B alloy

In this project we work on correlative atomic structural and compositional investigations on Co and CoNi-based superalloys as a part of SFB/Transregio 103 project “Superalloy Single Crystals”. The task is to image the boron segregation at grain boundaries in the Co-9Al-9W-0.005B alloy.

Boron is an essential solute element for improving the grain boundary strength in several high temperature metallic alloys especially in Ni- and Co-base superalloys. Boron leads to the formation of borides and precipitate depleted zones around the grain boundaries and alters the bond strength among the grains directly. The Co-9Al-9W-0.005B alloy exhibits good mechanical properties due to enhanced grain boundary strength gained from an optimized boron content. Further increase in boron leads to the formation of a precipitate depleted zones around the grain boundaries that deteriorates the mechanical properties.

This work requires site specific preparation of atom probe specimens from a grain boundary. The sequence of experiments involve transmission kikuchi diffraction (TKD) analysis on the tip to confirm the presence of a grain boundary followed by APT.