Spark Plasma Sintered 3Y-TZP/CNT composites

Sammanfattning: Composites of 3 mol% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2 wt% have been produced using spark plasma sintering (SPS). The theoretical densities of the studied composites were found to be between 99.4 and 97.4 %. The average grain size of the composites was decreasing with addition of MWCNT content from 174 to 148 nm. The effect of MWCNTs on the mechanical properties of 3Y-TZP has been investigated. A novel method was used for the calculation of the true fracture toughness and reported for the first time in this type of composites. It was based on producing a shallow surface sharp notch machined by ultra-short pulsed laser ablation on single edge V-notch beam specimens. Indentation fracture toughness was measured using Vickers indentation and it was found to be increasing with the addition of MWCNT content while the true fracture toughness is hardly increasing. It was concluded that the increase in the resistance to indentation cracking of the composites cannot be associated to higher true fracture toughness. Moreover, nanoindentation was measured using Berkovich nanoindenter where the contact hardness and elastic modulus were determined by Oliver-Pharr method. It was found that both properties decrease with the addition of MWCNTs.Additionally, the effect of MWCNT on the tribological properties of 3Y-TZP was also investigated. The friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Furthermore, the COF and the wear rate were determined in reciprocating sliding where a zirconia ball was used as a counterpart under dry conditions using a load of 5 N and sliding distance of 100 m. The COF was found to be decreasing with increasing MWCNT content. However, in macro-scratch testing, there was a critical load over which brittle fracture sets in and its value decreases as the MWCNT content increases. The wear resistance was found to be decreasing slightly for less than 1 wt% MWCNT, while it increased strongly for the addition of 2 wt. % MWCNT under the conditions studied.