Direct nanomechanical characterization of carbon nanotube - titanium interfaces

Interfacial interactions between carbon nanotubes (CNTs) and metal matrices play a critical role in the bulk mechanical properties of CNT-reinforced metal matrix nanocomposites (MMNC), but their load-transfer mechanisms remain not well understood. In this paper, we conduct single-nanotube pull-out studies with in situ scanning electron microscopy to quantify the mechanical strength of binding interfaces in carbon nanotube (CNT)-reinforced titanium (Ti) nanocomposites. Our nanomechanical pull-out measurements reveal a shear lag effect in the load transfer on the CNT-Ti interface. The interfacial shear strength and the maximum load-bearing capacity of the tested CNT-Ti interfaces are quantified to be about 37.8 MPa and 245 nN, respectively, both of which are substantially higher than the reported values for CNT-Al interfaces. Density functional theory calculations reveal that the experimentally observed strong CNT-Ti binding interface is attributed to strong chemisorption interactions of Ti atoms on CNT surfaces, albeit moderated by the weakening effect of the oxide layer. The research findings are useful to better understand the load transfer process on the tube-metal interface and the reinforcing mechanism of nanotubes, and ultimately contribute to the optimal design and performance of nanotube-reinforced MMNC.