Preparation and anisotropic properties of textured structural ceramics: A review

Journal of Advanced Ceramics 2019, 8(3): 289–332 https://doi.org/10.1007/s40145-019-0325-5 ISSN 2226-4108 CN 10-1154/TQ Review Preparation and anisotropic properties of textured structural ceramics: A review Zhuo ZHANGa,b, Xiaoming DUANa,b,c,*, Baofu QIUa,b, Zhihua YANGa,b,c, Delong CAIa,b, Peigang HEa,b, Dechang JIAa,b,c,*, Yu ZHOUa,b a Key Laboratory of Advanced Structural-Functional Integration Materials & Green Manufacturing Technology, Harbin Institute of Technology, Harbin 150001, China b Institute for Advanced Ceramics, School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China c State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin Institute of Technology, Harbin 150001, China Received: November 23, 2018; Revised: March 16, 2019; Accepted: March 22, 2019 © The Author(s) 2019. Abstract: Ceramics are usually composed of randomly oriented grains and intergranular phases, so their properties are the statistical average along each direction and show isotropy corresponding to the uniform microstructures. Some methods have been developed to achieve directional grain arrangement and preferred orientation growth during ceramic preparation, and then textured ceramics with anisotropic properties are obtained. Texture microstructures give particular properties to ceramics along specific directions, which can effectively expand their application fields. In this review, typical texturing techniques suitable for ceramic materials, such as hot working, magnetic alignment, and templated grain growth (TGG), are discussed. Several typical textured structural ceramics including α-Al2O3 and related nacre bioinspired ceramics, Si3N4 and SiAlON, h-BN, MB2 matrix ultra-high temperature ceramics, MAX phases and their anisotropic properties are presented. Keywords: texture; structural ceramics; anisotropic properties; strengthening and toughening mechanisms 1 Introduction Since the periodicity and density of the atoms in single crystals are not identical along different directions, the physical and chemical properties of single crystals along different directions are various. But most materials, either metals or ceramics, are polycrystalline materials composed of unoriented grains, resulting in their isotropic *Corresponding authors. E-mail: X. Duan, , ; D. Jia, properties. When some external conditions, such as stress fields, electromagnetic fields, and temperature fields, are applied during the process of material preparation, grains can be preferentially aligned along specific crystallographic directions, forming texture microstructures [1–3]. Performances of materials along preferred crystal lattice orientation can be enhanced by texturing so that they can be applied to more harsh service environments [4–6]. For many metallic materials, their slip systems can be activated at suitable temperature, and then grains can be easily oriented by deformation, such as rolling www.springer.com/journal/40145 J Adv Ceram 2019, 8(3): 289–332 290 and extrusion [7–12]. Subsequent heat treatment of deformed metal can result in oriented nucleation of recrystallization and preferred orientation growth [13– 17]. By appropriate deformation and heat treatment, texture degree and grain size of metals can be adjusted, and the required anisotropic properties can be obtained [18–21]. Unlike metals, atoms in ceramics are mainly interconnected by covalent and ionic bonds, which are strong enough to prevent plastic deformation. So deformation techniques are not suitable for texture formation of ceramics. Specific techniques, such as hot working, magnetic alignment, and templated grain growth (TGG), have been invented, which can effectively promote the preferred orientation of ceramic grains [2,22,23]. Textured ceramics have many superior properties compared with ceramics composed of randomly oriented grains. As for functional ceramics, texture microstructures can increase the critical current density of superconductors [24–26], increase the electrical conductivity of ionic conductors [27,28], heighten the magnetic anisotropy of hexaferrite ceramics [29–31], and improve the electromechanical coupling coefficient of piezoelectric ceramics [32–35]. As for structural ceramics, fracture toughness along specific directions increases with the incorporation of oriented grains, which favor the mechanisms of crack deflection, crack bridging, and grain pull-out [36–39]. Figure 1 shows the schematic diagram of the microstructure of a lamellar textured porous α-alumina (α-Al2O3) specimen prepared by hotpressing (HP) and its anisotropic mechanical properties and thermal conductivities [40]. Due to the texture microstructure, it possesses higher thermal conductivity along the lamella and better mechanical properties perpendicular to the lamella. There are many examples of textured materials with excellent performances in natural creatures. Natural materials, such as nacre, bone, and bamboo, usually combine stiff and soft components and possess hierarchical structures [41]. For example, many skeletal tissues consist of organic fibrils and mineral particles [42,43]. In the exoskeleton of Homarus americanus, the organic matrix consists of α-chitin fibrils and some noncrystalline proteins. Most of the α-chitin lattice cells are oriented with the long crystallographic axis towards the surface of the exoskeleton to provide mechanical support for the body [44]. Another typical example is that many mollusks protect themselves from predators by their hard external shells consisting of a brittle external calcite layer and a tough internal nacre layer. The nacre layer is composed of aragonite, chitin, and proteins, and possesses the brick-and-mortar structure employing a variety of toughening mechanisms such as crack deflection and microbuckling to induce a gradual “graceful failure” [45]. Inspired by specific structures of natural creatures, much research has been put into textured materials possessing hierarchical structures [46–58]. There have already been some reviews about textured metals and functional ceramics [32,59–63]. But there are few summaries about textured structural ceramics. In this review, an overview of preparation methods of textured structural ceramics is given. In addition, the state of the art of several typical textured structural ceramics and their anisotropic properties are discussed. The aim of this review is to give a brief introduction of textured structural ceramics for new researchers in this field and to provide some useful references for them. 2 Fig. 1 Schematic diagram of the microstructure and anisotropic mechanical properties and thermal conductivities of a lamellar textured porous α-Al2O3 specimen prepared by HP. Reproduced with permission from Ref. [40], © Elsevier Ltd and Techna Group S.r.l. 2015. Characterization of texture Texture can be divided into morphological texture where anisometric grains ar (...truncated)