Mechanical and thermal properties of multiwalled carbon-nanotube-reinforced Al₂O₃ nanocomposites

Multiwalled carbon nanotube (MWCNT)-reinforced Al₂O₃-matrix nanocomposites were obtained by wet ball milling composite powders and spark plasma sintering. The mechanical and thermal properties of the nanocomposites with five different MWCNT concentrations from 0 to 2.0 wt% were studied. Results show that the matrix grain sizes of the composites decreased after MWCNT addition. The hardness, bending strength, and fracture toughness of 0.5 wt% MWCNT nanocomposite are the highest, which are 35.7%, 55%, and 182% higher than those of monolithic alumina, respectively. Errors of fracture toughness values obtained by the single-edge notch beam method are significantly smaller than those measured by the direct crack measurement method. With the addition of MWCNTs, the thermal conductivity of the nanocomposites decreases gradually, reaching the minimum of 12 W/mK in 2.0 wt% MWCNT composite at 300 °C. The thermal conductivity decreased owing to the agglomeration of MWCNTs and changes in the porosity and grain size of the composite matrix. No distinct difference is observed in thermal expansion behaviours between the nanocomposites and monolithic Al₂O₃ owing to the low content of MWCNTs.