J. Ceram. Sci. Technol., 09 [1] 69-78 (2018) DOI: 10.4416/JCST2017-00077 available online at: http://www.ceramic-science.com © 2018 Göller Verlag Mechanical Behaviour of Zirconia-Toughened Alumina Laminates with or without Y-PSZ Intermediate Layers M.D. Barros 1 , P.L. Rachadel 1 , M.C. Fredel 1 , R. Janssen 2 , D. Hotza *3 1 Department of Mechanical Engineering, Federal University of Santa Catarina (UFSC), 88040 – 900, Florian ´ opolis, SC, Brazil 2 Institute of Advanced Ceramics, Hamburg University of Technology (TUHH), Denickestrasse 15, D-21073 Hamburg, Germany 3 Department of Chemical Engineering, Federal University of Santa Catarina (UFSC), 88040 – 900, Florian ´ opolis, SC, Brazil received September 21, 2017; received in revised form October 23, 2017; accepted November 15, 2017 Abstract Zirconia-toughened alumina (ZTA) laminates with 5 vol% (95A) and 30 vol% (70A) of yttria-partially stabilized zirconia (Y-PSZ), as well as laminated composites with thick ZTA layers and thin Y-PSZ layers were developed and processed by means of tape casting followed by co-firing. The addition of 5 vol% Y-PSZ led to grain refinement, higher densification and an increase in mechanical properties compared to those of pure alumina. In contrast, the addition of 30 vol% Y-PSZ refined the alumina grains and formed clusters of zirconia. However, it promoted lower densification when compared to pure alumina and 95A. Nevertheless, mechanical strength increased in the 70A composites owing to the zirconia toughening mechanism. Laminated composites with intermediate Y-PSZ layers have shown thermal residual stresses after sintering as a result of the different coefficients of thermal expansion (CTE) of the components and higher performance in mechanical behaviour owing to compressive stresses in ZTA layers and to the zirconia toughening mechanism present in Y-PSZ thin layers and in ZTA with 30 vol% thick layers. Keywords: ZTA, Y-PSZ, laminated composites, tape casting I. Introduction Ceramic matrix composites (CMC) are developed to overcome the brittleness and low reliability of monolithic ceramic materials. The main advantages of these materials include high strength at high temperatures, low weight and flaw tolerance. Oxide/oxide composites additionally offer good stability against corrosive and oxidative envi- ronments. Although CMCs are promising thermostruc- tural materials, their application is limited by the absence of adequate reinforcements, processing difficulties, dura- bility and cost 1, 2 . Zirconia-toughened alumina (ZTA) was designed to sub- stitute alumina in applications where higher fracture re- sistance is needed. This material consists of an alumina matrix in which zirconia particles are embedded. Mechan- ical properties as flexural strength, fracture toughness and fatigue resistance are enhanced mainly due to stress- induced zirconia phase transformation 3–6 . The transfor- mation of tetragonal zirconia into monoclinic zirconia results in volume expansion (∼ 4 %) that acts contrary to crack propagation due to compressive stresses around the crack tip. Enhanced mechanical properties are directly re- lated to the amount of zirconia added 7, 8 . Another mech- anism responsible for improved mechanical behaviour in ZTA is microcracking. Volume expansion causes tan- * Corresponding author: d.hotza@ufsc.br gential stresses around transformed particles and induces crack nucleation in a matrix. The crack propagates un- til a transformed zirconia particle is found and then it is deflected, becoming a ramified crack. Transformability of zirconia depends on grain size, stabilizer type and amount, and sintering parameters. Internal residual stresses gener- ated by different coefficients of thermal expansion may also affect the mechanical properties of ZTA 9 – 11 . In this context, interfaces, brittle layers and residual stresses present in laminated ceramics can be used in an at- tempt to oppose crack growth and/or to develop a thresh- old strength 12 – 18 . This behaviour offers the opportunity for tailoring the mechanical properties based on stacking of layers of different thickness and composition in a suit- able sequence 19 . Laminated composites can be manufac- tured by means of different processing routes, such as tape casting 18, 20, 21 , dip coating 22 , spin coating 23 , sequential slip casting 19, 24 , electrophoretic deposition (EPD) 25, 26 and colloidal techniques. Combined processing can be also used, such as tape casting with dip coating 27 , tape casting with EPD 16 , or tape casting with EPD and dip coating 28 . Drastic increases in strength and especially in fracture toughness at room temperature have been achieved in alu- mina/zirconia laminar composites owing to various crack- shielding phenomena related to the presence of the lay- ers (delamination, crack deflection, etc.) 19 . In particular,