Estudo comparativo das técnicas de fabricação e do comportamento de fratura de compósitos cerâmicos multicamadas à base de alumina

Abstract

Alumina is a ceramic material with interesting properties, having high hardness, good wear strength, good compressive strength and chemical stability at high temperatures, which led to its application in refractory plates in furnaces, thermal insulators, electronic components and prostheses for biomedical applications, among other components. However, its inherent brittleness becomes a limiting factor for advanced engineering applications, such as in the aerospace, biomaterials and nuclear industries. In this sense, an alternative to circumvent this issue and improve the reliability of ceramic materials is the construction of multilayer ceramic composites (CCMs). In order to analyze the fracture behavior of aluminabased CCMs, the influence of the composition, the main manufacturing methods, and the quantity, location and thickness of the layers that compose these materials were studied, based on a bibliographic review on the topic. This study sought to point out the most promising strategies for manufacturing ceramic alumina composites capable of absorbing higher values of fracture energy than alumina monoliths. The presence of internal interfaces separating the layers increases the distance coursed by the cracks that propagate in the material, through the mechanisms of deflection and bifurcation of cracks, in addition to delamination. The CCMs can be classified into two groups. Those with a weak interface deliver a significant gain in ductility, mainly due to the effect of delamination between the layers. The CCMs with a strong interface are built in such a way that residual stresses promote increased resistance to crack propagation. In both groups, controlling the thickness of the layers is essential to ensure the desired effects. The presence of residual compressive stress in some layers is capable of stopping the progress of the failure, requiring an increase in the imposed stress to continue the fracture process. This phenomenon promotes the effect of the threshold strength, which corresponds to a stress value at which the material does not fail under smaller stresses, regardless of the original size of the defect. This feature, combined with the promotion of noncatastrophic failures, allows the material to be applied with greater reliability in hightech industrial applications, such as structural, ballistic, thermal components and cutting tools. The study of the fracture behavior of the CCMs based on alumina indicated a tendency to increase the fracture toughness and ductility of these materials when compared to the alumina monolith.