SEM images of (a) vapor-deposited and (b) mechanically processed Al/Ni multilayer composites. Note that while the bilayer spacing in the vapor-deposited foil remains constant, the mechanically processed material contains a broad distribution of bilayer spacings.
(a) Schematic depicting coarse and fine spatial distributions of bilayer spacings in dual-bilayer foils. The two bilayer spacings are denoted by and , and the bilayer section thicknesses (regions of constant bilayer spacing) are given by and . Note the thin intermixed region between individual Al and Ni layers. (b) A SEM image of a cross-section fracture surface showing an abrupt change from a small bilayer spacing to a large bilayer spacing. Note that the thick dark layer is a local defect due to a stage malfunction during deposition.
DSC traces of single-bilayer foils with various bilayer spacings. Note vertical offsets for clarity.
Plot of measured heat of reaction vs for single-bilayer foils and vs for dual-bilayer foils.
DSC traces of single- and dual-bilayer foils. The top two traces are for single-bilayer foils with bilayer spacings of 20 and 79 nm. The third trace is an average of the first two DSC traces plotted for comparison with the fourth trace, that of a dual-bilayer foil with 19 and 74 nm bilayer spacings. Note vertical offsets for clarity.
Comparison of experimental and simulated reaction velocities vs bilayer spacing for Al/Ni multilayer foils with a single-bilayer spacing.
Plot of measured reaction velocity vs average bilayer spacing, comparing experimental data from dual-bilayer foils plotted using two different averaging techniques (number average and volume average) with experimental data from single-bilayer foils and simulation data.
Comparison of experimental and simulated reaction velocities of dual-bilayer foils vs volume averaged bilayer spacing, displaying the differences in the behaviors of coarse and fine bilayer spacing distributions. Data from simulations and a smooth curve depicting experimental velocities for single-bilayer foils are shown for comparison.
Plot of estimated critical section thickness vs for stoichiometric Al/Ni, Al/Hf, Al/Zr, Ni/Ti, and Ni/Zr multilayers. This type of analysis can be used to determine when reaction velocities in mechanically processed materials will deviate from those predicted using average reactant spacings.
Experimental reaction velocities of dual-bilayer foils vs volume averaged bilayer spacing, displaying the differences in the behaviors of foils with one bilayer spacing less than 19 nm (the bilayer spacing marking the peak in velocity in Fig. 6) and those with both bilayer spacings equal to or greater than 19 nm. Data from simulations and a smooth curve depicting experimental velocities for single-bilayer foils are shown for comparison. Note that the plotted data are from foils having a fine spatial distribution of reactant spacings.
List of bilayer spacings for each bilayer section (, ), reaction velocity of each section (, ), total foil thickness , distribution of bilayer spacings (thickness of each bilayer section and whether one of the sections had a period in the prepeak region), and simulated and experimental reaction velocities (, ) for each dual-bilayer foil.
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