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.
The paper deals with the determination of the characteristic strength and as well as the Weibull moduli and of the Si3N4+SiC micro/nanocomposite determined by the four-point bending test and the contact test using opposite spheres both applied to specimens of different size, respectively. Material failure in the bending and contact modes is caused by the presence of processing defects as fracture origins, and by the formation of cone cracks, respectively, where a stable growth of the cone cracks initiated during contact loading is assumed to be a reason of , . A microstructural analysis of the processing flaws, and a mathematical analysis of the propagation of the cone cracks regarding different dimensions of a specimen are also presented.
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