Study of ceramic compositions based on alumina and LZSA glass-ceramic for obtaining multilayer structures by 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% SiC_whisker) and three LZSA-based compositions (CF6: 70% LZSA, 10% Al₂O₃ and 20% SiC_whisker; CF8: 50% LZSA, 10% Al₂O₃, 20% TiO₂ and 20% SiC_whisker; CF-PC: 75% LZSA, 5% Al₂O₃, 10% TiO₂ and 10% SiC_whisker) 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.

Keywords:
multilayer ceramic composite; alumina; LZSA glass-ceramic; residual stresses; tape casting