XPS and PAT Study on NiAl Phase Formed in a Superalloy by Pack Cementation

The NiAl phase prepared by pack cementation (PC) on a nickel base superalloy was investigated by X-ray photoelectron spectroscopy (XPS) and positron annihilation technique (PAT). The focus was on the effect of the solid solution of the alloying element from substrate on the binding energy of Ni (Al) 2p peaks and vacancy concentration of the NiAl phase formed in a superalloy. The results showed that the binding energy of Ni 2p peak of the NiAl phase grown in a superalloy was shifted by up to 0.55 eV at the temperature from 850 to 1050℃ towards higher energies and the binding energy of Al 2p peak by up to 1.09 eV in comparison with the NiAl phase formed in pure Ni. The positron lifetimes obtained from the NiAl phase formed in a superalloy were found to be markedly lower than the theoretical values, indicating the decrease in vacancy concentration. The variation of binding energies and vacancy concentration are possibly due to the solid solution of the alloying atoms from the substrate into the NiAl lattice.