Preparation And Properties Of Nacre-like Structural Al₂O₃ Ceramic Composites

For ceramic materials,atoms are bound together by ionic bonds or covalent bonds.This combination has higher energy and directionality,making ceramics have excellent properties,such as corrosion resistance,high temperature resistance and high strength.These excellent properties have made remarkable use of ceramics in aerospace,engine preparation,biomedicine and other fields.However,due to its inherent brittleness,it also inevitably leads to catastrophic failure.Nacre,as a kind of natural structural material with high performance,scientists take this as a source of inspiration and provide a simple and efficient processing method for preparing high toughness and high strength ceramic materials by imitating its microstructure.Freezing casting is an efficient method for preparing nacre-like materials.This process is based on the nacre structure.By the anisotropic growth characteristics of alumina,the freezing casting method and hot-pressing sintering method are used to align alumina platelets together as "brick" structure,and the mixture of mineral phase and nano-particles is used as "mortar"structure to connect together to obtain nacre-like structural composite ceramic materials.In this paper,different samples are prepared by adjusting different interlaminar phases and introducing microstructure such as gradient structure,so as to explore the interaction force between interfaces and reveal the mechanism of high strength and high toughness of samples.The results show that the ceramic composites with nacre structure can be easily and efficiently prepared by freezing casting and hot-pressing sintering.This paper is divided into the following three parts:(1)The nacre-like alumina ceramics with silicon nitride as interlayer phase were successfully prepared by freezing casting method and hot-pressing sintering,and its effect on the mechanical properties of the nacre-like alumina ceramics was studied,and the mechanisms of improving its strength and toughness were revealed.It is found that there is a solid solution reaction between Al2O3 and Si3N4,which react to β-Sialon phase and Sialon-X phase,which help to enhance the combination of "brick" structure.The formation of Sialon phase and the enhancement of interlayer bonding lead to a significant increase in flexural strength.(2)From the view of interlaminar phase control,the paper further investigates the use of zirconia nanoparticles as the interlaminar phase to provide phase transformation toughening.The results show that the introduction of zirconia significantly improves the properties of the material,and explores the toughening mechanism of zirconia at the interface of alumina "brick"when the sample fails.The coupling effect of "brick" structure and stress-induced transformation toughening is the main reason for improving mechanical properties.(3)To explore the possibility of improving the mechanical properties of the nacre-like alumina composite ceramics to a greater extent,in addition to the change of the inorganic phase between the layers,we explore the influence of the change of microstructure on the mechanical properties of the materials by introducing the gradient and Bouligand structure from the perspective of structure.At the interface,the introduction of enhanced phase materials,such as carbon nanotubes and silicon carbide whiskers,improves the flexural strength at the interface.The results show that the introduction of enhanced phase materials at the interface greatly improves the mechanical properties of the material.On the basis of zirconia as interlayer inorganic phase,the performance of ceramic composites with carbon nanotubes has been significantly improved.