Estudo de composições cerâmicas à base de alumina e vitrocerâmico do sistema LZSA para obtenção de estruturas multicamadas por tape casting

Abstract

Ceramic matrix composites have been developed in recent decades as an efficient way of improving the fracture toughness of ceramic materials. Multilayered ceramic composites have been highlighted by their relatively low cost and easy production. These composites are made of stacked layers of two different ceramic materials and present as toughening mechanism the crack path deviation layer by layer in the composite. In this work, compositions based on alumina and LZSA glass-ceramic (Li2O-ZrO2-SiO2-Al2O3) were studied to compose the layers in order to obtain multilayer composite with strong interfaces. Thus, compressive residual stresses in thin LZSA-based layers interspersed with Al2O3-based layers, under low tensile residual stress, were expected to obtain. The compositions were defined by factorial design, generating specimens by pressing that were sintered and characterized by determination of the coefficient of thermal expansion and modulus of elasticity. Three Al2O3-based compositions, in wt% (CA1: 100% Al2O3; CA2: 90% Al2O3 and 10% ZrO2; CA-PC: 90% Al2O3, 5% ZrO2 and 5% SiCwhisker) and three LZSA-based compositions (CF6: 70% LZSA, 10% Al2O3 and 20% SiCwhisker; CF8: 50% LZSA, 10% Al2O3, 20% TiO2 and 20% SiCwhisker; CF-PC: 75% LZSA, 5% Al2O3, 10% TiO2 and 10% SiCwhisker) were selected. Such compositions were designed to generate residual compressive stress in the LZSA-based layers (up to -32.35 MPa) and residual tensile stress on the Al2O3-based layers (at least 0.27 MPa). The tape casting technique was used to produce sheets of the selected compositions, using amounts of binders and plasticizers reported in the literature. The compositions were then prepared by tape casting obtaining homogenous, flexible ceramic sheets showing enough green strength to be handled. The alumina-based sheets thickness ranged between 130 and 210 μm, while LZSA-based sheets varied between 180 and 230 μm.