J Mater Sci(2006)41:7425-7436 DOI10.1007/10853-0060808y Oxide ceramic laminates with highly textured a-alumina interlayers: I. Texture control and laminate formation Ming wei· Dan Zhi· David G. Brandon Received: 18 August 2005/ Accepted: 29 November 2005/Published online: 20 September 2006 +Business media. Lle Abstract Three kinds of texture-reinforced oxide component, could be used to tailor electronic and ceramic laminates with strongly bonded interfaces have structural properties and obtain some of the singl been fabricated. All three were based on highly textured crystal anisotropy. Such texture could be used to a-alumina interlayers, but each with a different oxide reduce thermal expansion mismatch, and hence the laminate matrix and a correspondingly different ther- risk of microcracking 1, while texture control offers a mal mismatch between the textured interlayers and the useful alternative to aligned second-phase reinforce- matrix. Alginate-based, aqueous gel casting was used to ment [2]. Most recently, it has been reported that the produce a flexible tape for all the compositions studied. formation of texture in a-alumina can effectively lower The highly textured alumina(TA) interlayers were the residual stress and make the stress distribution derived from gel-cast tapes containing aligned alumina narrower 3]. In general, processing to develop texture seed platelets. It has been found that the strongest in ceramics differs significantly from the conventional texture derived from g1 vol of the seed platelets in powder processing of dense, fine-grained and equiaxed the gelled precursor tape. Using the March-Dollase microstructures. Textured ceramics have been fabri model for texture analysis, the oriented volume frac- cated by several techniques: sinter-forging [4, hot- tion in the highly textured interlayers was estimated to pressing [5], slip-casting [6], gel-casting in a magnetic vary from 60 to 80% field 1,7,8, and, most commonly, by templating using seeded grain growth [2, 9-13]. Textured micro- tructures have been reported in a single-phase iron titanate ceramic laminate, containing a predetermine Introduction configuration of the textured and non-textured layer In a conventional ceramic the anisotropic single crystal The design of ceramic composites with layered properties are averaged in the isotropic, randomly macrostructures is also receiving considerable research oriented polycrystal. Texturing a polycrystalline attention because they exhibit decreased sensitivity material, by controlling the orientation distribution of surface defects and have demonstrated non-cata- crystallites with respect to the coordinate system of a strophic failure in some laminate systems [14-16 key feature in multilayer ceramic systems is the ability to deflect propagating cracks and two different mechanisms of crack deflection have previously been of Materials Science and metall employed. Propagating cracks can be deflected either Cambridge, Cambridge CB along weak interfaces with adjacent layers [14, 15]or wei@@gmail.com into layers exhibiting residual biaxial compressive D. G. Brandon stress[17-19. Essentially, the first mechanism depends epartment of Materials Engineering, Technion-Israel on matrix/interface strength ratio and has had varying degrees of success. However, controlling the strength 2 SpringerAbstract Three kinds of texture-reinforced oxide ceramic laminates with strongly bonded interfaces have been fabricated. All three were based on highly textured a-alumina interlayers, but each with a different oxide laminate matrix and a correspondingly different ther￾mal mismatch between the textured interlayers and the matrix. Alginate-based, aqueous gel casting was used to produce a flexible tape for all the compositions studied. The highly textured alumina (TA) interlayers were derived from gel-cast tapes containing aligned alumina seed platelets. It has been found that the strongest texture derived from 9.1 vol% of the seed platelets in the gelled precursor tape. Using the March–Dollase model for texture analysis, the oriented volume frac￾tion in the highly textured interlayers was estimated to vary from 60 to 80%. Introduction In a conventional ceramic the anisotropic single crystal properties are averaged in the isotropic, randomly oriented polycrystal. Texturing a polycrystalline material, by controlling the orientation distribution of crystallites with respect to the coordinate system of a component, could be used to tailor electronic and structural properties and obtain some of the single crystal anisotropy. Such texture could be used to reduce thermal expansion mismatch, and hence the risk of microcracking [1], while texture control offers a useful alternative to aligned second-phase reinforce￾ment [2]. Most recently, it has been reported that the formation of texture in a-alumina can effectively lower the residual stress and make the stress distribution narrower [3]. In general, processing to develop texture in ceramics differs significantly from the conventional powder processing of dense, fine-grained and equiaxed microstructures. Textured ceramics have been fabri￾cated by several techniques: sinter-forging [4], hot￾pressing [5], slip-casting [6], gel-casting in a magnetic field [1, 7, 8], and, most commonly, by ‘templating’, using seeded grain growth [2, 9–13]. Textured micro￾structures have been reported in a single-phase iron titanate ceramic laminate, containing a predetermined configuration of the textured and non-textured layers [8]. The design of ceramic composites with layered macrostructures is also receiving considerable research attention because they exhibit decreased sensitivity to surface defects and have demonstrated non-cata￾strophic failure in some laminate systems [14–16]. A key feature in multilayer ceramic systems is the ability to deflect propagating cracks and two different mechanisms of crack deflection have previously been employed. Propagating cracks can be deflected either along weak interfaces with adjacent layers [14, 15] or into layers exhibiting residual biaxial compressive stress [17–19]. Essentially, the first mechanism depends on matrix/interface strength ratio and has had varying degrees of success. However, controlling the strength M. Wei (&) Æ D. Zhi Department of Materials Science and Metallurgy, University of Cambridge, Cambridge CB2 3QZ, UK e-mail: dr.m.wei@gmail.com D. G. Brandon Department of Materials Engineering, Technion – Israel Institute of Technology, Haifa 32000, Israel J Mater Sci (2006) 41:7425–7436 DOI 10.1007/s10853-006-0808-y 123 Oxide ceramic laminates with highly textured a-alumina interlayers: I. Texture control and laminate formation Ming Wei Æ Dan Zhi Æ David G. Brandon Received: 18 August 2005 / Accepted: 29 November 2005 / Published online: 20 September 2006
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