Comparison of valence-band structures of NiAl alloy containing Cr and Ti: Photoelectron spectrum and first-principles calculations

The effect of additions of Cr and Ti on the valence-band structures of NiAl alloys was investigated by a combination of photoelectron spectroscopy and first-principles calculations. The measurement of the ultraviolet photoelectron spectra (UPS) demonstrated that the Ni-d band centroid simultaneously moved towards higher energy by 5.26 eV as Ti and Cr were added. The charge transfer from Ti to Ni made the covalent bonding of the NiAl-Ti alloy become stronger due to the ionicity contribution from the Ni-Ti interactions. The Ni-Cr interactions reduced the directionality of the Ni-Al bonds, resulting in a uniform charge density. This meant that the covalent bonding present in the NiAl-Cr alloy exhibited some metallic bonding characteristics.