Papers by Keyword: Layered Ceramics

Abstract: Layered ceramics are foreseen as possible substitutes for monolithic ceramics due to their attractive mechanical properties in terms of strength reliability and toughness. The different loading conditions to which ceramic materials may be subjected in service encourage the design of tailored layered structures as function of their application. The use of residual stresses generated during cooling due to the different thermal strain of adjacent layers has been the keystone for the improvement of the fracture response of many layered ceramic systems, e.g. alumina-zirconia, alumina-mullite, silicon nitride-titanium nitride, etc. In this work, the fracture features of layered ceramics are addressed analysing two multilayered structures, based on the alumina-zirconia system, designed with tailored compressive residual stresses either in the external or internal layers. Contact strength and indentation strength tests have been performed to investigate the response of both designs to crack propagation. The experimental findings show a different response in terms of strength and crack growth resistance of both designs. While layered structures with compressive stresses at the surface provide a better response against contact damage compared to monoliths, a flaw tolerant design in terms of strength and an improved toughness through energy release mechanisms is achieved with internal compressive stresses. The use of layered architectures for automotive or biomedical applications as substitutes for alumina-based ceramics should be regarded in the near future, where reliable ceramic designs are needed.

Abstract: A simple analytical model of residual stresses far from edges in symmetrical planar functionally graded material (FGM) is presented. The model is based on elastic plate theory and neglects the influence of edges and free surfaces. The results are compared to analytical model of laminar ceramics and to finite element model of FGM. The influence of various geometrical and material parameters on the internal stress state is discussed.

Abstract: The present contribution summarizes the recent results in the field of high temperature properties of layered ceramics and thermal barrier coatings (TBC), mainly as regards their thermal shock resistance and creep characteristics. The thermal shock and creep behavior of layered ceramics are discussed with the main focus on the influence of layered composition and interlayer boundary on the creep behavior of the composite. In the last part the high temperature deformation and creep of TBC’s are discussed.