Solid state formation of Ti4AlN3 in cathodic arc deposited (Ti1−xAlx)Ny alloys

Reactive cathodic arc deposition was used to grow substoichiometric solid solution cubic c-(Ti _1−xAl _x)N _y thin films. The films were removed from the substrate and then heated in an argon environment to 1400 °C. Via solid state reactions, formation of MAX phase Ti ₄ AlN ₃ was obtained. Additional phases such as Ti ₂AlN, c-TiN, w-AlN, Al ₅Ti ₂ and Al ₃Ti were also present during the solid state reaction. Ti ₄AlN ₃ formation was observed in samples with an Al metal fraction x < 0.63 and a nitrogen content 0.4 < y < 0.6. Regardless of the initial composition, formation of Ti ₄AlN ₃ started in Ti ₂AlN crystal plates in the temperature range between 1200 and 1400 °C. Accompanying the onset of Ti ₄AlN ₃ was the presence of an intermediate structure identified as Ti ₆Al ₂N ₄, consisting of alternating layers of intergrown Ti ₂AlN and Ti ₄AlN ₃ phases with a half-unit-cell stacking. We suggest that the formation of Ti ₄AlN ₃ occurred via intercalation of aluminum and nitrogen along the basal plane accompanied by a simultaneous detwinning process. In addition we propose that this formation mechanism can be used to obtain MAX phases of high n order.