Cutting Reactive Foils Without Igniting Them (A Femtosecond Laser Machining Approach)

Abstract

Ni/Al nanostructured multilayer foils were machined with femtosecond pulse-length laser irradiation at various fluences. Scanning electron microscopy, back-scattered electron detection, and atomic force microscopy were used to characterize the resulting laser modified regions. We show that material removal at the micron scale is possible with no ignition of a self-propagation reaction emanating from the irradiated areas, a danger minimized by the fact that the extremely short time duration of the pulse produces negligible heat dissipation into the multilayer system. Nevertheless, initial AFM and BSE results give indication that multilayers may be intermixing and reacting locally in areas smaller than the laser beam diameter, though the exact ignition mechanism is still to be determined.

Reactive multilayers fabricated by vapor deposition: A critical review

“…However, the nanosecond-pulse ignition fluences are less than the nanosecond threshold fluence for removing Pt (~0.49 ± 0.026 J/cm 2 ; 3.06 × 10 18 eV/cm 2 ) [134]. Thus, one strategy for laser machining reactive multilayers involves femtosecond pulses [136].…”

Effects of Ultrashort Pulsed Direct Laser Writing on Ni/Al Reactive Multilayer Foils

“…Although the ablation thresholds for Ni, Al, and their intermetallic compounds [33][34][35] are within similar orders of magnitude, previous research [30] suggests layer-by-layer ablation of the individual Ni and Al double layers. Applying this consideration on the conducted single pass processing of Ni/Al at either 1 kHz or 5 kHz, a deviation in the development of the advancing cut edge morphology can be suggested.…”

“…This further limits the time frame for quantitative thermal diffusion [31]. Previous studies more focused on ignition thresholds have shown that is possible to cut through Co/Al multilayers [16] and remove a few layers of Ni/Al [30] without ignition of self-propagating reactions at higher fluences than the ones used in this work. According to the manufacturer of the Ni/Al multilayers used in this study, cutting using nanosecond (ns) lasers is also possible at high pulse rates (i.e., low pulse energy).…”

“…Modifying the morphology of the RMF by introducing through-holes, lines, and other cut-out shapes is therefore interesting for improving joining performance. USP laser micromachining of reactive multilayers has been demonstrated to be possible without ignition of a self-propagating reaction [10,16,30], making it a promising technique for modifying the shape of RMFs for tailored joining applications. Currently, it remains unclear to what extent the RMF microstructure is modified near the cut edge.…”