Multilayer materials have demonstrated to provide an efficient mechanism for toughening by deflection of a propagating crack by weak interlayers. Therefore, the aim of this work is to study the colloidal processing of 8 mol% yttria stabilized zirconia (8YSZ) based laminates by intercalating thin layers of graphene enriched with 8YSZ, and to evaluate the advantages of such multilayered structure in the propagation of cracks induced by indentation.Green tapes of 8YSZ and graphene-oxide with YSZ were obtained by aqueous tape casting and sintered in one-step by spark plasma sintering at 1400 ºC.Microindentation results showed that the indentation cracks propagate within the horizontal direction within the ceramic layer, but in the cross-sectional direction the presence of the GO-rich layers stops the cracks without deflection or bifurcation. The hardness and elastic modulus values were higher than 17.6GPa and 230 GPa, respectively, and similar for all layers.
Introduction8 mol% yttria stabilized zirconia (8YSZ) has been extensively used as an electrolyte because of its low electronic and high oxide ion conductivity over wide ranges of temperature and oxygen partial pressure, as well as excellent chemical stability under reduced and oxidized atmospheres at a high temperature. These properties make 8YSZ a powerful material for applications as oxygen sensors and solid oxide fuel cells [1][2][3][4][5]. The basic structure of a solid oxide fuel cell (SOFC) comprises at least three layers of ceramics or cermet:i.e., electrolyte, anode and cathode layers [6,7]. The electrolyte is a dense ceramic, typically yttria stabilized zirconia (YSZ) or gadolinium doped ceria (CGO), whereas the electrodes must be porous and can be either a ceramic or a cermet. Typical anode materials are Ni-YSZ and Ni-CGO while LSM (La, Sr, produced by different techniques, such as tape casting and screen printing, which are the most suitable to produce large surfaces and fast, low cost mass production. Because of the multi-layer nature of the cells, any mismatch in the free sintering kinetics of the individual layers leads to stress and distortion during the sintering process [13][14][15]. Hence, the electrolyte layer must have high fracture strength and toughness, good thermal conductivity and a thermal expansion coefficient similar to that of the other components. Fully stabilized zirconia has not the excellent mechanical properties that partially stabilized zirconia has so that the development of strengthening mechanisms is strongly desired to meet the requirements of SOFCs.The main reinforcing mechanisms for zirconia ceramics are those based on the phase transformation of zirconia from tetragonal to monoclinic induced by mechanical stresses, and the use of composites with second phase particles, whiskers, platelets or fibers and, more recently, the development of ceramic matrix nanocomposites is receiving great attention [16][17][18][19]. The use of such nanocomposites has shown to significantly enhance the mechanical properties even at high tempe...