Texture Development And Mechanical Properties Of Alumina Ceramics Fabricated By Templated Grain Growth

As a typical advanced structural material,alumina?Al₂O₃?ceramics are one of the most widely used industry materials in the modern society.Al₂O₃ has many advantages,such as high strength,high temperature resistance,abrasion resistance,corrosion resistance,and insulation etc.However,the same as other ceramics,Al₂O₃ ceramics also have fatal weakness,that is,they are brittle and sensitive to defects.Thus,they have bad reliability and poor resistance to damage,restricting its further development and large-scale engineering applications.Therefore,improving the toughness and reliability of Al₂O₃ ceramics and understanding the related toughening mechanism have been a hot topic.Texturing ceramics is one of the most effective method to improve the toughness of ceramics.However,there are very limited study on the fabrication and properties of textured alumina ceramics with fine grain sizes.In this work,we fabricated highly [0001] oriented alumina ceramics by templated grain growth via using nano-matrix.The texturing mechanism was explored,and the effects of microstructure and texture fraction on the mechanical properties of alumina ceramics were systematically investigated.First,alumina platelets were synthesized by molten salt method.The effects of raw materials,molten salts,their ratios,and additives on the morphology development of alumina platelets were studied.Al2?SO4?3 raw material produces agglomerations,while ?-Al₂O₃ yields well-dispersed particles.Chloride salts result in overlapping phenomena,but sulfates tend to produce single crystals.Increase molten salt amount is beneficial to fabricate well-dispersed platelets with large particle size.Adding SiO₂ promotes the growth of platelets along the radial direction and prevents the growth along the thickness direction,leading to the large aspect ratio²3.When SiO₂ and Ca O are used as sintering aids,a small amount of Si O₂ and Ca O sintering is favorable for radial growth,but higher concertation produced the platelets with reduced sizes.Then,highly [0001] oriented alumina ceramics were textured by templated grain growth via using 30 nm matrix,and 5 vol% platelet templates.The results show that with the increase of sintering temperature,the textured fraction of ceramics is increased from 9.62% to 93.6%.When sintered at 1500 °C for 4 h,a high texture degree ⁹3.6% was achieved.Highly textured ceramics are consisted of tabular grains with ¹7 ?m in diameter and ².3 ?m in thickness.With the increase of texture fraction,the fracture mode and path of the samples have changed greatly.The crack propagation mode has been changed from straight expansion tocrack bridging and deflection,and its propagation path is enhanced.Finally,the effects of texture fraction and orientation on the mechanical properties such as fracture mode,flexural strength,fracture toughness and Vickers hardness were studied and compared with randomly oriented ceramics.It was found that,flexural strength and fracture toughness of alumina ceramics increased with the increase of texture fraction from 9.62% to 93.6%.The hardness,flexural strength and fracture toughness of the ceramics with the texture degree of 93.6%were 15.4 GPa,589 MPa,4.6 MPa.m1/2,respectively.Besides,the mechanical properties of the textured ceramics are higher along the [0001] direction than that perpendicular to this direction,confirming that the c-direction is the dominant direction of the ceramics.This work proves that texturing is very effective to produce ceramics with significantly improved mechanical properties.We believe that this work can lay the foundation for preparing high quality textured structural ceramics,and can add new contributions to the improvement of toughness by nano-texturing,so it is important from both scientific and engineering view points.