Fabrication and mechanical properties of high-dispersion-treated carbon nanofiber/alumina composites

Abstract

High-dispersion-treated carbon nanofibers (CNFs) were used to fabricate uniformly-dispersed CNFs-alumina composites with enhanced mechanical properties. The treatment was effective in obtaining dense and uniform composites. The composites containing 0.40.8 wt % CNFs were densified to a relative density of more than 99% by vacuum sintering and subsequent hot isostatic pressing, and those containing 1.62.5 wt % CNFs were densified to full density by plasma activated sintering. The maximum bending strength of the composites (1050 MPa) was approximately the same as the bending strength of monolithic alumina (1079 MPa). The maximum fracture toughness of the composites was 5.9 MPa·m 0.5 , which was a 69% increase compared with the fracture toughness of monolithic alumina (3.5 MPa·m 0.5 ). Fracture toughness (K IC ) increased rapidly with a decrease in alumina grain size (G), and we found that the relationship could be expressed by the following equation: K IC = (k 1 /G 2 ) + k 2 (where k 1 and k 2 are constants).

Microstructure development and fracture toughness of acid-treated carbon nanofibers/alumina composites

“…It was reported in our previous paper 32) that because the number of bendings per CNF could increase with a decrease in average alumina grain size and the resistance for bridging and/or pull-out of the CNFs could be increased with an increase in the number of bendings per CNF, the fracture toughness of the HDTCNFs/alumina composites increased with a decrease in average alumina grain size. Because of the similar reason, the fracture toughness of the AT05-CNFs/alumina composites increased with a decrease in average alumina grain sizes and that of the AT5-CNFs/alumina composites increased with a decrease in average alumina grain sizes in the range of 1.62.8¯m.…”

“…Fracture toughness of the 0.42.5 wt % HDT-CNFs/alumina composite increased rapidly with a decrease in average alumina grain size. 32) Similarly, fracture toughness of the 0.4 wt % AT05-CNFs/alumina composite increased with a decrease in average alumina grain size. However, fracture toughness of the 0.4 wt % AT1-and AT5-CNFs/alumina composites increased with a decrease in average alumina grain sizes, showed the maximum value at average alumina grain sizes of 1.3 and 1.6¯m, respectively, and decreased as the average alumina grain sizes decreased further.…”

“…In order to compare with the acid-treated CNFs, the highdispersion-treated CNFs, 32) which had smaller amount of defect and hydrophobic surface compared to the acid-treated CNFs, were also used and were described as HDT-CNFs.…”

“…22) In order to fabricate the reliable CNTs/alumina composites with higher toughness and higher strength, the uniform dispersion of CNTs in the composites and the enhancement of interfacial compatibility between CNT and alumina grain have been required. 19) 31) In our previous study, 32) carbon nanofibers (CNFs), which are a kind of multi-walled CNTs (MWCNTs), were high-dispersiontreated in order to disentangle agglomerates of the CNFs. The high-dispersion-treatment is one of the mechanical dispersion technique using an ultra fine grinding machine which is similar to wet jet milling.…”

Influence of CNF content on microstructure and fracture toughness of CNF/alumina composites

“…With that aim in mind for alumina ceramics, we have combined the high-dispersion-treated carbon nanofibers (CNFs), which are a type of multi-walled CNTs, with alumina. 9) In the study, we found that the fracture toughness of the CNF/alumina composites increased with a decrease in the average alumina grain size of the composites, regardless of CNF content in the range of 0.42.5 wt %. 9) In these composites, CNFs were observed bending along alumina grain boundaries.…”