Oxidation weakens interfaces in carbon nanotube reinforced titanium nanocomposites: An in situ electron microscopy nanomechanical study

Abstract

The interfacial binding interactions in fiber–reinforced metal matrix nanocomposites (MMNC) are involved with sophisticated physico-chemical​ phenomena that are sensitive to their commonly encountered high-temperature processing and/or working environments. The resulting interfacial load transfer characteristics, which play a vital role in achieving the anticipated bulk mechanical properties enhancements, remain elusive. Here we investigate the effect of thermal processing on the interfacial strength of carbon nanotube (CNT) reinforced titanium (Ti) nanocomposites by conducting in situ nanomechanical single-nanotube pull-out measurements inside a high resolution scanning electron microscope. Our nanomechanical measurements reveal that thermal annealing at 400 °C for two hours results in a 40% decrease of the interfacial load-carrying capacity. The measurements were analyzed using a micromechanics shear-lag model, and the results show that the thermal annealing reduces the maximum interfacial shear strength by about 42% from about 231MPa to about 135 MPa. The observed weakening of the CNT–Ti interface caused by thermal annealing is attributed to the formation of newly grown titanium oxide on the CNT–Ti binding interface. The findings reported here are useful to better understand the impact of thermal processing on the reinforcing efficiency of nanotubes in metal matrices, which is essential to the design and manufacturing of nanotube-reinforced MMNC with superior high-temperature performance.