Solid state reaction of Fe/Ti nanometer-scale multilayers

The Fe/Ti multilayers 19.0 nm thick with alternating Fe and Ti sublayers thickness ratio of 1:1 were deposited by direct current magnetron sputtering. The Fe/Ti multilayers were in situ submitted to thermal vacuum annealing at the temperatures ranging from 250 °C to 450 °C for the annealing time of 1 h. Structural evolution of Fe/Ti multilayers was detected by X-ray diffraction and high resolution transmission electron microscopy. The diffraction peaks of α-Fe (110) and broaden α-Ti (002) were obtained without any additional diffraction peaks when the Fe/Ti multilayers were annealed at the lower temperatures of 250 °C and 350 °C, which suggested the formation of the solid solution of Fe with Ti due to interdiffusion between Fe and Ti sublayers during the thermal annealing. At the higher annealing temperature of 450 °C, the precipitation of intermetallic FeTi carried out in the Fe–Ti solid solution. The mixture of intermetallic FeTi and α-Fe phase presented in the extended Fe sublayer of the Fe/Ti multilayers. Three distinct exothermic peaks were characterized in the differential scanning calorimetry traces of the Fe/Ti multilayers 19.0 nm thick heated from 25 °C to 630 °C at the four heating rates of 10–40 °C/min. The activation energy for the three peaks is 1.04 eV, 1.43 eV and 1.49 eV, respectively, corresponding to the formation of the Fe–Ti solid solution, the nucleation and growth of the intermetallic FeTi, respectively.