Boron nitride nanotubes (BNNTs) are a unique class of light and strong tubular nanostructure
and are highly promising as reinforcing additives in ceramic materials. However, the mechanical
strength of BNNT-ceramic interfaces remains largely unexplored. Here we report the first direct
measurement of the interfacial strength by pulling out individual BNNTs from silica (silicon
dioxide) matrices using in situ electron microscopy techniques. Our nanomechanical
measurements show that the average interfacial shear stress reaches about 34.7 MPa, while
density functional theory calculations reveal strong bonded interactions between BN and silica
lattices with a binding energy of –6.98 eV nm−2
. Despite this strong BNNT-silica binding,
nanotube pull-out remains the dominant failure mode without noticeable silica matrix residues
on the pulled-out tube surface. The fracture toughness of BNNT-silica ceramic matrix
nanocomposite is evaluated based on the measured interfacial strength property, and substantial
fracture toughness enhancements are demonstrated at small filler concentrations.
