Grain-boundary corrosion of nickel-based alloy by synchrotron radiation technology

The spatial distribution and chemical speciation of tellurium (Te) at the grain boundary (GB) of nickel (Ni)-based alloys are crucial for investigating the tellurium corrosion mechanism. In this work, corrosion products along GBs were investigated by synchrotron-radiation-based microprobe techniques, including micro-X-ray fluorescence, micro-X-ray diffraction and micro-X-ray absorption near-edge structure (μ-XANES), for the first time. A gradually decreasing tendency in the concentration of tellurium from the GB area into the grains was identified, together with the presence of GB corrosion products in the form of nickel telluride (Ni₃Te₂), as well as nickel–tellurium solid solution. Moreover, both the µ-XANES results and density functional theory results confirmed that the impurity tellurium atoms in the nickel–tellurium solid solution tend to bond with their neighboring nickel atoms through weak covalent interactions, due to the hybrid state of tellurium 2p–nickel 4s. Such an unstable antibonding character from the nickel–tellurium combination is believed to play a key role in weakening the structural stability of nickel-based alloys. The efficient analysis of the tellurium corrosion mechanism based on these feasible synchrotron radiation characterizations will inspire more pertinent experimental investigations.