Experimental evidence of disordered crystalline premixing in sputter-deposited Ni(V)/Al multilayers

TL;DR

This study provides direct microscopic evidence of a disordered crystalline premixed phase at Ni(V)/Al interfaces, revealing its structural stability and composition changes upon annealing, which impacts the understanding of multilayer reactions.

Contribution

It is the first direct measurement of a disordered FCC premixed phase in Ni(V)/Al multilayers, challenging previous assumptions of amorphous interlayers and highlighting the role of electronic entropy.

Findings

Disordered FCC phase observed at interfaces via electron microscopy.

The phase remains crystalline after annealing at 135°C for 16 hours.

Lattice parameter shifts indicate an Al-rich composition.

Abstract

The sputter deposition of alternating layers of Ni(V) and Al forms a reactive multilayer known to undergo self-propagating formation reactions when ignited. The sequential deposition process leads to nm-scale premixing of reactants at each included interface which ultimately affects multilayer exothermicity. This work performs the direct measurement of a disordered face-centered cubic (FCC) solid solution premixed phase at the interfaces of Ni(V)/Al multilayers via scanning transmission electron microscopy. The crystallinity of the observed phase differs from previously reported a priori predictions of an amorphous interlayer. The disordered FCC phase retains its symmetry after annealing for 16 h at 135 C, but the lattice parameter shifts consistent with an Al-rich composition. The existence of a crystalline premix in Ni(V)/Al is attributed to the electronic contribution to the entropy of crystallization.