Formation of Ti2AlN phase after post-heat treatment of Ti–Al–N films deposited by pulsed magnetron sputtering

Ti–Al–N films with different compositions were prepared by varying the nitrogen flow rate using pulsed magnetron sputtering and subsequently annealed in air at 700 °C. The microstructure and microhardness of the films were investigated before and after heat treatment. The XRD results indicate that no Ti2AlN MAX phase occurs in all the as-deposited films. Ti2AlN phases could be acquired only after annealing via solid state reaction. The formation condition of Ti2AlN phase is strongly dependent on the film composition. It has been found that the nitrogen concentration in the films plays a key role for the phase formation, and the critical value is in the range of 22.5–29.6 at.%. The fractured cross-section SEM images show that all the as-deposited films exhibit a fine columnar morphology. The annealed films with Ti2AlN phase components change the morphology from columnar to fine equiaxed polycrystalline. In addition, the microhardness of the films containing Ti2AlN phase is also explored, which is within the range of 18–24 GPa.