Reactive wetting and filling of boron nitride nanotubes by molten aluminum during equilibrium solidification

Interactions between long boron nitride nanotube (BNNT) fibrils and molten aluminum (Al) pool are probed in this study to assess the feasibility of fabricating composite materials by solidification route. BNNTs were found to survive high temperature and reactive conditions present in molten aluminum. Very limited interfacial reaction was observed, resulting in the formation of AlN, AlB2 and AlB10 in trace amounts. AlN was the principal reaction product, resulting in improved interfacial wetting. Calculations based on surface energies revealed improved work of interfacial adhesion due to AlN formation. BNNTs were found to be well integrated in the aluminum matrix, signifying AlN induced excellent wetting. We also report capillarity-induced high temperature filling of BNNT by molten Al. The filling was promoted by AlN formation. In addition, formation of B-rich AlB10 phase inside the nanotube was observed. Nanotube filling by metal and subsequent reaction to form nano-ceramic phases is expected to alter mechanical properties of the cast Aluminum-BNNT composites. This study establishes the suitability of solidification route for developing high strength Al-BNNT composites in future.