Strengthening in Boron Nitride Nanotube Reinforced Aluminum Composites Prepared by Roll Bonding

Abstract

Boron Nitride Nanotube (BNNT) is a promising reinforcement for developing strong and lightweight metal matrix composites due to its brilliant mechanical properties and excellent high‐temperature oxidation resistance. In this study, layered composites of aluminum and BNNT are fabricated by a multi‐step process comprising of hot pressing, rolling, and annealing. Less than 0.1 wt% of ultra‐long nanotubes (up to 200 μm in length) are used to induce superior strengthening. For achieving enhanced mechanical properties, nanotubes are de‐agglomerated and chemically dispersed in an aqueous solution before introducing between the layers of aluminum sheets. Application of pressure (up to 10 MPa) and temperatures (up to 300 °C) during rolling and hot pressing induces a bonding between aluminum sheets and nanotubes. Scanning electron microscopy reveals that the nanotubes survive these conditions, suggesting superior thermal and mechanical endurance of BNNT. The nanohardness and elastic modulus of the composites are found to improve by 52% and 17%, respectively, by merely 0.045 wt% BNNT addition. BNNT reinforced composites exhibit up to 13% improvement in ultimate tensile strength. The improvement in mechanical properties is ascribed to effective load transfer from the aluminum matrix to the long nanotubes via interfacial shear stress and enhancement of dislocation density.