Abstract
The indentation load-size effect (ISE) in Vickers hardness of Al₂O₃ and Al₂O₃ + SiC nanocomposites has been investigated using Meyer’s law, the proportional specimen resistance (PSR) model and the modified proportional specimen resistance (MPSR) model. The strongest ISE was found for alumina. It is suggested that the smaller ISE in the nanocomposites is associated with the large thermal residual stresses and pre-existing dislocations in these materials, both of which would help the initiation of plastic deformation. Both the PSR and MPSR models described the ISE well, but the MPSR model resulted in slightly lower true hardness values for all materials investigated. There was no evidence of an effect of machining stresses on the ISE.

Key words
nanocomposites, hardness, microstructure, residual stresses

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