Intragranular Particle Residual Stress Strengthening of Al₂O₃–SiC Nanocomposites

Abstract

Al2O3/SiC ceramic nanocomposites were fabricated from nanocrystalline Al2O3 (10 nm in diameter) and SiC (15 nm in diameter) powders, and a theoretical model of intragranular particle residual stress strengthening was investigated. The SiC nanoparticles in the Al2O3 grains create a normal compressive stress at the grain boundaries and a tangential tensile stress in the Al2O3 grains, resulting in the “strengthening” of the grain boundaries and “weakening” of the grains. The model gives a good explanation of the experimental results of the authors and others which are difficult to be explained by the existing strengthening models, i.e. the maximum strength is normally achieved at about 5 vol% of SiC particles in the Al2O3–SiC ceramic nanocomposites. According to the model, there exists an optimum amount of SiC for strengthening, below which the grain boundaries are not fully “strengthened” and the fracture is mainly intergranular, above which the grains are “weakened” too much and the fracture is mainly transgranular, and at which the fracture is a mixture of intergranular and transgranular.

Prediction of fracture strength in Al2O3/SiCpceramic matrix nanocomposites

“…4 with different volume fractions of SiC nanoparticles, where the following data reported recently by Sun et al [26] are used: It should be pointed out that while the above analysis exhibits a fairly good agreement with the experimental results reported in the literature [9][10][11]24,26], the dislocation activities in the CMNCs are different from those in the precipitation-hardened metallic materials. For example, unlike aluminum alloys and nickel-based sueralloys, the dislocations in ceramics can hardly move on the slip plane and be stopped by the barrier to form the conventional Orowan loops at room temperature.…”

“…late-reinforced alumina nanocomposites tested at room temperature, where the error bars were based on the range given in Ref. [26].…”

Prediction of fracture characteristic of particlereinforced alumina-based composites

“…As a typical two-phase particulate composite, alumina/SiC nanocomposite has been intensively investigated since its excellent mechanical properties and wear resistance were discovered [1][2][3] . The tremendous improvement of properties in the ceramic composite is relevant to fracture mode transition, as generally believed, though the main reason is still in dispute [4][5][6] . An alumina/mullite composite with flexural strength and wear resistance bettered by 21% and 3 times, respectively, than monolithic alumina, was recently fabricated by utilizing the high-temperature metastable character of silicon carbide [7,8] .…”

Microstructural design for mechanical and electrical properties of spark plasma sintered Al2O3–SiC nanocomposites

“…Al 2 O 3 -SiC composites are usually sintered by hot pressing (HP) of powder mixtures [7,8]. Although the simultaneous heating and uniaxial pressure applied facilitates the densification of these composites, high temperatures up to 1800 • C are usually required.…”