Metal Passivation Strengthens the Interface in Titanium Composites Reinforced With Boron Nitride Nanotubes

We investigate the interfacial interaction in titanium metal matrix composites (MMCs) reinforced with boron nitride nanotubes (BNNTs) through in situ scanning electron microscopy nanomechanical pullout experiments. The measurements reveal a stronger interface formed by Ti with BNNTs than carbon nanotubes (CNTs). Density functional theory (DFT) calculations reveal that the observed interfacial strength is attributed to covalent bonding formed on the metal surface that is partially oxidized due to passivation. Moreover, the composite interface maintains its strength even after prolonged thermal annealing in air, which is in stark contrast to the substantial degradation that occurs on the composite interface with CNTs. The complex interplay of metal passivation on the interfacial interaction and reinforcement opens a new avenue of exploiting metal passivation as an innovative active self-strengthening mechanism for nanotube-reinforced MMCs.