Deposition of single-crystal Ti 2 AlN thin films by reactive magnetron sputtering from a 2Ti:Al compound target

Single-crystal Ti 2 AlN (0001) thin films were grown on (111) oriented MgO substrates kept at 830 °C by ultrahigh vacuum dc reactive magnetron sputtering from a compound 2Ti:Al target in a mixed Ar/N 2 discharge. The effects of variations in the nitrogen partial pressure on the phase composition of the films were studied. Results from transmission electron microscopy, x-ray diffraction, and elastic recoil detection analysis show a narrow region for growth of Ti 2 AlN MAX phase with respect to the nitrogen content in the discharge. Perovskite Ti 3 AlN and intermetallic Ti 3 Al and TiAl phases dominate at nitrogen depletion. For overstoichiometric deposition conditions with respect to Ti 2 AlN, a phase mixture with NaCl-structured TiN is obtained. Epitaxial growth is observed with a layer-by-layer mode on the 0001 basal planes for all phases. A superstructure in the TiN phase is also observed along [111] with the repetition distance of 7.34 Å, most likely related to Al segregation. Nanoindentation shows that the film hardness increases from 11 to 27 GPa with increasing nitrogen content and corresponding phase transformations from Ti–Al intermetallics to Ti 3 AlN, Ti 2 AlN, and TiN.