Statistical analysis of mechanical properties of pressureless sintered multiwalled carbon nanotube/alumina nanocomposites

Mechanical properties of pressureless sintered 0.15–1.2 vol.% multiwalled carbon nanotube reinforced alumina matrix nanocomposites have been analyzed using the 2-parameter Weibull statistics. Electron microscopy and phase analysis of nanocomposites sintered at 1700 °C for 2 h in Argon revealed existence of interpenetrating network of nanotubes in alumina, formation of thin interface resembling stoichiometric aluminum monoxycarbide and matrix grain refinement by nanotubes. Statistical analyses indicated that with increasing Vickers hardness testing load (4.9–19.6 N) and flexural strength measurement temperature (room temperature to 1100 °C), Weibull modulus of nanocomposites increased significantly suggesting improved consistency at higher load and temperature. The highest Weibull moduli were obtained for nanocomposites containing either 0.15 or 0.3 vol.% nanotube which were ∼40% and ∼15% higher than single phase alumina for hardness and strength, respectively, supporting the specimen size effect on reliability of present brittle ceramic matrix nanocomposites. Superior mechanical reliability of nanocomposites over pure alumina was primarily attributed to the presence of structurally intact nanotubes forming effective interface region to ensure proper load sharing, matrix grain refinement, and especially, at higher testing load and temperature, overall averaging effect of flaws to yield higher Weibull moduli.