Coefficient of friction and wear resistance of zirconia–MWCNTs composites

Composites of 3 mol% yttria-doped tetragonal zirconia (3Y-TZP) reinforced with multiwalled carbon nanotubes (MWCNT) up to 2 wt% content 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 addition of MWCNT content resulted in reduction of 3Y-TZP grain size from 174 to 148 nm. The effect of MWCNT on the friction coefficient (COF) was studied by performing nano- and macro-scratches using diamond Berkovich and Rockwell indenters, respectively. Moreover, the COF and the wear rate were also investigated in reciprocating sliding against a zirconia ball under a load of 5 N. The results showed that the COF decreased upon the increase in 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 very slightly for less than 1 wt% MWCNT, while it increases strongly for the addition of 2 wt% MWCNT under the conditions studied. The results were discussed in terms of material properties, scanning electron microscopy observations of the wear track and nanoindentation tests.