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.