Probing temperature-induced ordering in supersaturated Ti1 − xAlxN coatings by electronic structure

• The major peaks at the N K-edge of c-Ti0.35Al0.65N during spinodal decomposition are calculated.
• The N p–Ti d overlap is reduced during decomposition which may suggest N-depletion.
• Nitrogen is found to favor Al surrounding whereas N vacancies are attracted to Ti.

The ordering of supersaturated cubic titanium aluminum nitride (c-Ti0.35Al0.65N) coatings is probed from room temperature up to and above the point of spinodal decomposition, using Near Edge X-ray Absorption Fine-structure (NEXAFS) and first principles calculations. The measured and calculated nitrogen (N) K spectra suggest that unoccupied N p states hybridize with Ti d states. When temperature is raised the N p–Ti d overlap decreases, whereas hybridization between N p and Al p tends to increase. The observed spectral changes with temperature together with calculations of defect heat of formation suggest a depletion of N in the surroundings of Ti in c-Ti1 − xAlxN and/or in the formed c-TiN.