Fabrication Of Al/Ti Reactive Multilayer Films And Their Reaction Characteristics

Nano-scale reactive multilayer film is a novel kind of energetic material which is generally prepared by alternatively depositing two or more materials that can intermix with each other. Upon energy pulse, the film can react exothermically and the reaction region can self-propagate at a fixed velocity. The multilayer films have been utilized in joining and SHS industry widely. Besides, these materials can be potentially used in ignition.In this thesis, Al/Ti multilayer films were prepared using magnetron sputtering deposition, and the individual layer thicknesses of aluminum and titanium of the films varied from 10 nm to 240 nm, while the overall thicknesses of the multilayer films ranged from 7 to 17μm. SEM and XRD characterization showed that the multilayer films had a layered structure and consisted of aluminum and titanium.The reaction mechanism of as-deposited Al/Ti multilayer films was investigated by DTA and XRD analysis. Results show that the reaction process consists of two stages, the first reaction stage takes place at around 440℃-550℃, which relates to formation of TiAl₃, and the second stage at around 650℃-700℃, which corresponds to the formation of AlTi. Furthermore, in the first reaction stage, titanium diffuses into aluminum to form TiAl₃ until aluminum is completely consumed.The propagating velocity of reaction waves in multilayer films is a key parameter to characterize the multilayer films. Earlier studies had shown that the propagating velocity depends mainly on the individual layer thickness. Current mathematical models assumed the layer thickness ratio of the constituents to be 1:1, which limited the usage of the model to one special case. In this work, an extended model accounting for the multilayer films that have alternating layers with different thicknesses was presented. The propagating velocities of reaction waves in Al/Ni, Al/Ti multilayer films were calculated using the extended model and the calculated results show better agreement with the experimental data than that of earlier models.Furthermore, the propagating velocity of as-deposited Al/Ti multilayer films was investigated both experimentally and theoretically. Results show that there is a critical layer thickness which lies at around 25 nm. Below this critical thickness, the reaction propagating velocity quickly drops, and in this regime the intermixing is regarded as reaction controlled. While above that critical value, a reciprocal dependence of the propagating velocity on the layer thickness was observed, in this regime, the intermixing can be viewed as diffusion controlled. Moreover, a novel igniter incorporating Al/Ti reactive multilayer film was designed. Such igniters consist of several key components: ceramic or glass electrode plug substrate, a heating layer, an insulating layer, and the energy source layer. A prototype of such igniters was fabricated. The igniting ability of such igniters is as good as or even overmatches that of the igniters incorporating Ti/B multilayer films through firing tests. In addition, the heating layer resistance should be set at around 2Ω. To achieve a resistance of about 2Ω, the depositing time for titanium films was about 8 hours.