Ceramic materials are of technical and commercial interest due to their chemical, mechanical and thermal performance, leading ceramics to meet many engineering requirements. Alumina (aluminum oxide) is one of the primary representatives of this class of materials because of its high fracture toughness, hardness and density, which enable its use in the production of highly critical parts. One such application involves protection against abrasion and erosion wear. The wear properties of a ceramic can be improved not only by controlling its material characteristics but also by controlling the fabrication process, which defines the material's microstructure. Many studies of the effects of the microstructure on these properties have been published. The objective of this study was to review the effects of the microstructure on the erosive wear resistance of alumina-based ceramics. Four factors that control the erosive wear of alumina were identified: (i) the effects of dopants on the diffusivity of the grain boundaries, (ii) the fabrication route, (iii) the sintering mechanisms and (iv) the alumina grain size. The published experimental results related to these topics are described and provide a clear understanding of the erosive wear of alumina.

With the aim of improving the toughness of ceramic materials, laminated composites have been successfully developed since Clegg et al. (1990) inserted weak interfaces using very thin graphite layers between silicon carbide sheets and obtained a composite that exhibited non-catastrophic fracture characteristics. The weak interface must allow the crack to deviate either by deflection or delamination; in other words, the interface must exhibit a fracture resistance that is lower than that of the matrix layer. In parallel, ceramic laminated composites with strong interfaces were developed in which the residual tensile and compressive stresses appeared in alternate layers during cooling after sintering. These composites are prepared by stacking ceramic sheets produced by lamination or tape casting or by the sequential formation of layers by slip casting, centrifugation or electrophoretic deposition. The techniques may be combined to obtain a composite with the most adequate configuration. This work presents a review about the obtainment of multilayered ceramic composites as a toughening mechanism of ceramic plates.

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This work aims to evaluate the influence of a Li 2 O-ZrO 2 -SiO 2 -Al 2 O 3 (LZSA) glass-ceramic on the mechanical behavior of alumina. Composites were prepared from alumina with three different particle sizes and 7 to 21 vol% of an LZSA glass-ceramic composition (11.6Li 2 O-16.8ZrO 2 -68.2SiO 2 -3.4Al 2 O 3 ,). Specimens were obtained by uniaxial pressing. The optimum sintering temperature and holding time were found to be different for each composite. Structural characterization (bulk density and crystalline phases); mechanical characterization (flexure strength, elastic modulus, fracture toughness, and fracture energy); and microstructural analyses were carried out. Fine-grained alumina-based composite containing 21 vol% of glass-ceramic (1470 ºC and 3 h holding time, 2.0% porosity) showed a fracture toughness of 4.93 MPa·m 0.5 , an elastic modulus of 210 GPa, a fracture energy of 57 J·m -2 , and a flexural strength of 170 MPa, in very good agreement with values reported by the literature. An increase of 37-177% in the fracture energy due to 21 vol% LZSA addition in the alumina was achieved for the range of grain size obtained in this work. Even though the final composition included a glassy component, the observed mechanical properties confirmed the effectiveness of the crystalline phases that were formed from LZSA glass-ceramic in reducing the propagation of cracks. The results showed that the addition of the LZSA glass-ceramic improved the mechanical properties of alumina.

Fracture toughness enhancement of ceramic materials through multilayered ceramic composites has been developed since 1990. Toughening mechanisms are based mainly on delamination, deflection, bifurcation or crack arrest effect. Delamination and crack deflection occur by means of weak interfaces. Bifurcation (and deflection as well) and crack arrest effects are result of residual stresses arising from the thermal expansion coefficient mismatch or phase transformation on alternating layers. The main manufacturing methods of these composites are slip casting of two ceramic materials, and stacking and pressing of ceramic tapes obtained by tape casting or rolling technics, followed by suitable sintering process. This review aims to present general aspects of research performed around the theme so far. It is verified that occurs the enhancement of ceramic toughness and reliability with this technic, so it is possible to enlarge its range of application in engineering.