Preparation and Microstructure of Carbon Nanotube-Toughened Alumina Composites

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Engineering ceramics have high stiffness, excellent thermostability and relatively low density, but their brittleness impedes their use as structural materials. Incorporating carbon nanotubes (CNTs) into a brittle ceramic might be expected to produce CNT/ceramic composites with both high toughness and high temperature stability. Until now, however, materials fabrication difficulties have limited research on CNT/ceramic composites. The mechanical failure of CNT/ceramic composites reported previously is primarily attributed to poor CNTs-matrix connectivity and severe phase segregation. The connectivity with, and uniform distribution within the matrix are essential structural requirements for the stronger and tougher CNT/ceramic composites. Here we show that a novel processing approach based on the precursor method for synthesis of Al2O3 and acid-treated multi-walled carbon nanotubes (MWCNTs) can diminish the phase segregation, and render MWCNT/Al2O3 composites highly homogeneous. Combined with mechanical interlock induced by the chemically modified MWCNTs, this approach leads to improved mechanical properties. Direct toughness measurements, using the single edge notched beam method, reveal that only 0.9 vol.% acid-treated MWCNT addition results in 25% increases in fracture toughness (5.90±0.27 MPa·m1/2).