Dry sliding wear characteristics of carbon nanotube/alumina nanocomposites under a sharp pyramidal indenter

Hot-pressed multiwalled carbon nanotube (MWCNT)/alumina (Al2O3) nanocomposites offered improved flexural strength (σ4-FS), hardness (HV) and fracture toughness (KIC-SENB) over pure Al2O3. While HV and σ4-FS of nanocomposites improved by 8-10%, KIC-SENB of 0.13 wt% CNT/Al2O3 nanocomposite (~7.45 MPa m0.5) was ~1.3 and ~2.1 times higher than hot-pressed and pressureless sintered Al2O3, respectively. Unlubricated sliding wear experiments at 1-20 N normal load (FN) under a sharp pyramidal indenter revealed enhanced resistance to catastrophic failure and wear of nanocomposites over pure Al2O3. At FN=20 N, the lowest wear rate (WR≈0.02 mm3/N m) of 0.07 wt% CNT/Al2O3 nanocomposite was found to be ~50% lower than that of monolithic Al2O3. Scratch tests on ground and polished samples revealed notable changes in WR and wear mode as a function of surface roughness (Ra). Wear mode maps indicated that while in ground specimens the primary mechanism was excessive flake formation, severity of flake formation reduced significantly in polished samples and turned toward powder formation and/or ploughing due to effective indenter tip/specimen surface interaction in absence of stochastic surface irregularities present in ground samples. Present study indicated that for characteristic wear analysis of CNT/Al2O3 nanocomposites, Ra should be ≤100 nm.