Prediction of fracture characteristic of particlereinforced alumina-based composites

Abstract

Residual microstresses in particle reinforced alumina/SiC and alumina/mullite composites were calculated. The results indicated that there existed a linear relation between matrix microstresses and the particle contents in the composites. The influence of stress state on crack propagating and grain boundary strengthening was analyzed. Ratios of grain boundary toughness to grain toughness of these composites were calculated in view of microstress analysis, and percentage of transgranular fracture (PTF) that increases with the microstress in the alumina matrix was then deduced. The relationship between microstructure, component, matrix microstresses, and PTF was established. Therefore, the fracture characteristic was predicted on basis of the particle content and distribution in addition to the microstructure of the composites. ceramic composite, alumina, microstress, fracture mode Particulate composites have the advantages of being isotropic, easier to be prepared and having more reliable mechanical properties compared with fiber composites and laminated 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] . We found that fracture mode transition was the underlying cause.Since the thermal expansion coefficient of alumina is higher than that of mullite, the residual stress states in alumina/mullite composites are such that the second phase particles are in approximately hydrostatic compression, and there are tensile hoop stresses in the surrounding matrix [9] , the stress states in an alumina/mullite composite are similar to those of an alumina/SiC composite [10] . The tensile stresses in the alumina matrix can facilitate crack propagating in it and therefore make its toughness decrease. In the meantime, the counterforces of particle compressive stresses can be passed to the grain boundaries, resulting in toughening. The change of grain and grain boundary toughness can in turn dramatically change the crack propagating and fracture behavior of these materials [11,12] . However, change of the grain and grain boundary toughness in the composites is determined not only by residual stress but also by matrix microstructure, second phase content, size and distribution, as reported by Shi et al. [13] and Taga et al. [14] .Kim et al. [15,16] has investigated the corresponding relation between the ratio of grain boundary toughness to grain toughness and fracture mode in monolithic alumina by 2D and 3D crack propagation modeling. This method can basical...

An experimental research on single discharge machining of insulating ceramics efficiently with high energy capacitor

“…Hence, they have been widely used in recent years in precision bearings, cutting tools, refractories, electronic components, and in the automotive, aerospace, and defense industries [1][2][3]. However, insulating ceramics are known as difficult-to-machine materials due to their beneficial properties such as high rigidity, high brittleness, and non-electrical conductivity [4].…”