Outstanding Wear Resistance of Alumina–Carbon Nanotube Composites via “Near‐Ideal” Inter‐/Intragranular Reinforcement

ABSTRACT

Achieving consistent and the best possible improvement of the tribological properties of polycrystalline ceramics upon reinforcement with multiwalled carbon nanotubes (MWCNTs) is challenging because the MWCNTs tend to segregate along the matrix grain boundaries, leading to grain interiors being devoid of reinforcement, which also suppresses densification and degrades interfacial properties. Against this backdrop, aided by a sol–gel‐based processing (SG), Al ₂ O ₃ –2.5/5 vol% MWCNT composites have been developed, with the MWCNTs uniformly distributed as inter‐/intragranular reinforcement. This also facilitated a narrower‐cum‐finer grain size distribution, unlike the conventionally processed counterparts (BM), which have MWCNTs only along matrix grain boundaries. Together, this resulted in the SG composites exhibiting significantly reduced sliding wear rates (i.e., improved wear resistance) relative to monolithic Al ₂ O ₃ , viz., ∼90% and ∼82% reductions for the 2.5 and 5 vol% MWCNT‐containing SG composites, respectively, as compared to lesser reduction (by ∼68%) and rather increase in wear rate for the 2.5 and 5 vol% MWCNT‐containing BM composites, respectively, due to poor MWCNT distribution and concomitant inferior reinforcing efficacy for the latter. Worn surfaces reveal suppression of grain pull‐out and occurrence of crack bridging by MWCNTs in the case of SG composites, with the reinforcing “active” MWCNTs also getting more disordered post‐wear, as compared to the “inactive” MWCNTs in the BM counterparts.