SEM and XRD Characterization of Ni-Hf Alloys at Low Hf Concentration

The alloying and phase formation in Ni-Hf samples with 0.2-, 2-, and 5-at.% Hf were studied by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase (fcc structure) where the excess Ni atoms are present in the form of Ni or Ni-rich segregations in the sample containing 5-at.% Hf. The sample with 2-at.% Hf is characterized by the presence of the two phases present in the 5-at.% sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2-at.% Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X-ray absorption fine structure spectroscopy (EXAFS).