Development of pressureless sintered and hot‐pressed CNT/alumina composites including mechanical characterization

Abstract A process for the production of carbon nanotube (CNT)/alumina composites on the basis of an aqueous suspension and without any extensive pretreatment was developed. Pressureless sintering and hot‐pressing of the nanocomposites were extensively researched and optimized. The influence of varying CNT contents, different alumina powders, sintering temperature and pressure on mechanical properties were investigated. Optimal hot‐pressing conditions are specified at 1550°C, 15 min dwell time, and 80 MPa applied pressure. Dense nanocomposites up to 3 wt.% and 0.5 wt.% CNT content were achieved by hot‐pressing and pressureless sintering, respectively. Furthermore, a 20% increase in hardness for CNT contents below 1.0 wt.% was detected, which is independent from the applied force and the alumina matrix. A highly anisotropic fracture toughness at increased CNT contents was detected by an indentation‐based method. The developed process provides a possibility to produce CNT/alumina composites with improved mechanical properties under reasonable effort, which could also be used for industrial production.