Prediction of fracture strength in Al₂O₃/SiC_pceramic matrix nanocomposites

Abstract

Based primarily on a recent publication [S.M. Choi, H. Awaji, Sci. Tech. Adv. Mater. 6 (2005) 2-10.], where the dislocations around the nano-sized particles in the intra-granular type of ceramic matrix nanocomposites (CMNCs) were modeled, dislocation activities in Al 2 O 3 /SiC p CMNCs were discussed in relation to the processing conditions. The dislocations around the nano-sized particles, caused by the thermal mismatch between the ceramic matrix and nano-sized particles, were assumed to hold out the effect of Orowan-like strengthening, although the conventional Owowan loops induced by the movement of dislocations were unlikely in the ceramic matrix at room temperature. A model involving the yield strength of metal matrix nanocomposites (MMNCs), where the Owowan strengthening effect was taken into consideration, was thus modified and extended to predict the fracture strength of the intra-granular type of CMNCs without and with annealing. On the basis of the characteristics of dislocations in the CMNCs, the load-bearing effect and Orowan-like strengthening were considered before annealing, while the load-bearing effect and enhanced dislocation density strengthening were taken into account after annealing. The model prediction was found to be in agreement with the experimental data of Al 2 O 3 /SiC p nanocomposites reported in the literature. r

Pop-in characteristic induced by nanoindentation in ZrB2-SiC composites

“…These sessile dislocations restrict the movement of both these movable dislocations and the newly formed dislocations. Therefore, they would form loop-like configuration around the nanofillers [19], which is similar to the Orowan loops formed around the nanoparticles in metal matrix nanocomposites when the dislocations by-pass these nanoparticles on the slip plane. Such a dislocation configuration leads to an assumption that the Orowan-type strengthening the effect might be operative.…”

Spherical indentation with multiple partial unloading for assessing the mechanical properties of ZrB2–SiC composites

“…This is due to BNNTs and BNNPs exhibit much smaller coefficient of thermal expansion (CTE) values than those of ZrB 2 ($ 6.7 Â 10 À 6 K À 1 ) and SiC ($ 4.3 Â 10 À 6 K À 1 ) [27], respectively. Moreover, theoretical analysis has shown the highly localized residual stresses in the vicinity of these nanofillers would be larger enough to create the dislocations [28,29]. Therefore, the pre-existing dislocations would form in the close vicinity of these BNNTs and/or BNNPs in the ZrB 2 -SiC composites during the process cooling from the processing temperature.…”

“…These sessile dislocations restrict the movement of both these movable dislocations and the newly formed dislocations resulting from fracture process when a crack tip approaches this area. These pre-existing dislocations are therefore considered to form loop-like configuration around the nanofillers [28], which is similar to the Orowan loops formed around the nanoparticles in metal matrix nanocomposites when the dislocations by-pass these nanoparticles on the slip plane. Such a dislocation configuration leads to an assumption that the Orowan-type strengthening effect might be operative [28], and the resistance to plastic deformation associated with Orowanloop-like configuration increases with the added content of BNNTs-BNNPs, leading to an increase in strain-hardening exponent.…”

“…These pre-existing dislocations are therefore considered to form loop-like configuration around the nanofillers [28], which is similar to the Orowan loops formed around the nanoparticles in metal matrix nanocomposites when the dislocations by-pass these nanoparticles on the slip plane. Such a dislocation configuration leads to an assumption that the Orowan-type strengthening effect might be operative [28], and the resistance to plastic deformation associated with Orowanloop-like configuration increases with the added content of BNNTs-BNNPs, leading to an increase in strain-hardening exponent. On the other hand, it is worth to note that the volume fraction of BNNPs is $ 60% in the mixture of BNNTs-BNNPs [12].…”

Mechanism of nucleation and growth of directionally crystallized alloys of the B4C–MeB2 system

“…Employing directional crystallization of the boride systems enables fabrication of highpurity self-reinforced composites consisting of a ceramic matrix reinforced by ceramic inclusions. The composites have superior mechanical properties compared to individual borides [10][11][12][13][14][15][16][17][18].…”