Effect of modulation structure on the laser-ignited self-propagating behavior of Ti/Al multilayer films

Self-supporting Ti/Al (1:1 atomic ratio) multilayer films with different modulation structures were prepared using magnetron sputtering method and a sacrificial layer process. These films were ignited by single pulse irradiation for their self-propagating reactions. The ignition fluence thresholds were determined and their microstructures were observed using scanning and transmission electron microscope. Propagation velocity was characterized by high speed photography. Differential scanning calorimetry and X-ray diffraction were used to analyze reaction processes and products. Results indicated that all measured ignition thresholds (6-17 J/cm²) are above typical ablation thresholds for metals under laser irradiation. With decreasing modulation period, the ignition threshold decreases and the propagation velocity increases. In contrast, when the premixed thickness was a substantial fraction of modulation period, higher ignition fluences were required and reduced propagation speeds were obtained. For a given thickness of multilayers, the modulation structure with larger modulation period and smaller period numbers released more heat. Typically, the self-propagating reaction ignited by pulsed laser yielded one kind of product TiAl intermetallics.