Effect of annealing on microstructure, residual stress, and hardness of Al-Ti multilayered films

Al-Ti multilayered films (12 at.% Ti) with bilayer period of 16 nm were deposited by magnetron sputtering. The films were annealed in vacuum at 350 or 400 degreesC between 2 and 24 h. During annealing, a diffusion-controlled chemical reaction between Al and Ti layers led to AI,TI precipitation. Differential thermal analysis studies showed an exothermic reaction associated with AI,Ti formation, taking place between 320 and 390 degreesC, depending on the heating rate. The evolution of microstructure with annealing was examined with transmission electron microscopy and x-ray diffraction. The hardness and residual stress of the films in the as-deposited and annealed conditions were studied in relation to the microstructural changes on annealing.