Nanomechanical Characterization of Boron Nitride Nanotube—Metal Interfaces

Boron nitride nanotubes (BNNTs) are promising reinforcing fillers for cutting-edge metal-matrix nanocomposite (MMNC) technology due to their ultrahigh strength, large surface-to-volume ratios, exceptional thermal stability, and low density. The reinforcing mechanism in BNNT-reinforced MMNCs critically depends on efficient load transfer at the nanotube-metal interface. However, the understanding of interfacial load transfer on BNNT-metal interfaces remains elusive, posing a major scientific challenge in the development of BNNT-reinforced MMNC technology. In this study, we investigate the mechanical strengths of interfaces formed by individual BNNTs with aluminum or titanium matrices using in situ scanning electron microscopy nanomechanical single-nanotube pull-out techniques. By pulling out individual nanotubes from metal matrices with atomic force microscopy force sensors inside a high-resolution scanning electron microscope, the pull-out force and the embedded tube length were measured with resolutions of a few nano-Newtons and nanometers, respectively. The load transfer at the nanotube-metal interface is found to follow a shear lag behavior, and the nanotube-metal interfacial strength is significantly affected by metal oxidation. These research findings are crucial for better understanding load transfer at the nanotube-metal interface and the reinforcing mechanism of nanotube-reinforced metal nanocomposites.