Spark plasma sintering of multi-, single/double- and single-walled carbon nanotube-reinforced alumina composites: Is it justifiable the effort to reinforce them?

Abstract Multi-walled carbon nanotube (MWCNT), single-double walled carbon nanotube (SDWCNT) and single-walled carbon nanotube (SWCNT) were dispersed for the first time into alumina matrix using conventional mixing/sonication for dispersion of pristine CNTs followed by spark plasma sintering (SPS) process. The resultant composites displayed an increase of the grain size, a decrease in fracture toughness from 8% to 40% over monolithic Al 2 O 3 and the hardness values did not change significantly with the addition of CNTs. In the light of the observed fracture surfaces in different CNT reinforced alumina composites, poor dispersion of these into ceramic matrix will lead to a decrease in fracture toughness. On the other hand, the lower ratio aspects, large surface areas of CNTs, as well as large grain size could be unfavorable to achieve high fracture toughness and the results are worse than for pure alumina questioning whether worth the effort to reinforce alumina with CNTs to obtain marginal improvement under the present conditions, although the literature has reported significant improvement of mechanical properties with alumina and other ceramics systems reinforced with CNTs, resulting from different testing techniques adopted.