First-principles investigation of titanium doping into beta-SiAlON crystal in TiN-SiAlON composites for EDM applications

Following the experimental work on the incorporation of titanium into beta-SiAlON crystal in TiN-SiAlON composites for electrical discharge machining (EDM) applications, Ti doping mechanisms in beta-Si6-z AlzOzN8-z have been systematically investigated by means of density functional theory based formation energy calculations. A series of calculations, performed considering the random distributions of Ti-O/N, Al-O/N, and Si-O/N bonds in beta-Si6-z TizOzN8-z crystal, showed that the structures with enriched Ti-O and Si-N bonds have lower formation energy than those of Ti-N and Si-O bonds. In addition, it was determined that there is a notable difference between the average bond lengths of Ti-X and Al-X (X=O, N). Electronic structure calculations demonstrated that there is no correlation between either the z values or the number of Ti-O bonds and the one-electron band gap. However, in the case of beta-Si6-z AlzOzN8-z, there was a decreasing trend regarding the energy on one-electron band gap with respect to increasing z values. (C) 2015 Published by Elsevier B.V.