3D Printing Preparation And Mechanical Properties Of Multistage Gradient Bionic Al₂O₃ Ceramics

Alumina ceramic composites have stable physical and chemical properties,excellent mechanical properties,dielectric properties,wear resistance,moderate sintering temperature and low production cost,widely used in aerospace,deep-sea exploration,equipment manufacturing,vehicles,medical engineering,electronic components,defense industry and other engineering technology fields.However,the conflicting relationship between strength and toughness of alumina ceramic composites makes it increasingly difficult for them to meet the demanding mechanical properties required by extreme service environments.Natural biomaterials are able to exhibit excellent mechanical properties that far exceed those of man-made materials through their complex and delicate natural biomaterial structures even though the mechanical properties of their own constituents are not outstanding,providing a natural blueprint for the bionic toughness design of ceramic composites.However,the inherent physical and chemical properties of alumina ceramic composites make it difficult to produce ceramic composites with complex cross-scale multi-level composite bionic structures by conventional ceramic fabrication processes.Therefore,the use of bionic theory to design and develop alumina ceramic composites with synergistic optimization of strength and toughness and improve the related preparation process is of great theoretical value and scientific significance to promote its development and application in the field of high precision technology.Based on the bionics theory,cross-scale multi-level composite Bouligand structure with a hammer-like dactyl clubs of peacock mantis shrimp were used as the bionic model and the bionic Bouligand structure was established.Alumina ceramic composites with single/multi-stage bionic Bouligand structure were prepared using alumina ceramics as matrix,flake alumina and mullite short fibers as reinforcing phases by conventional direct writing 3D printing technique.Coupled stress field-assisted direct writing 3D printing technique was designed to improve the fineness of alumina ceramic composites.Based on the study of mechanical properties of submillimeter scale single-stage bionic Bouligand structured alumina ceramics,it was found that the higher the solid phase content of alumina ceramics was,the higher its density was and the higher its microhardness,flexural strength and fracture toughness were.The crack torsion ability of the bionic Bouligand structure with different deflection angles was different.15° deflection elevated the flexural strength and fracture toughness of the specimens to the highest among the three deflection angles.An excessively large deflection angle would reduce its ability to guide crack deflection and lower the ultimate load of the specimen.Based on the study of mechanical properties of multi-stage bionic Bouligand alumina ceramic composites with micron-scale reinforced phases,it was found that the addition of micron-scale reinforced phases was effective in compensating for the lack of crack deflection caused by the excessive spiral angle of bionic Bouligand structure on submillimeter scale.When flake alumina was used as reinforcing phase,the crack diffusion energy was consumed mainly by increasing transgranular fracture and grain pulling out,thus improving the toughness of multi-stage bionic alumina ceramic specimens.However,when the content of flake alumina was too high,it leaded to a smaller grain size of flake grain,thus the toughness of bionic ceramic composites would not increase but decrease.When mullite short fiber was used as the reinforcing phase,the reinforcing fiber could complement the matrix defects and consume the crack diffusion energy through the ways of fiber fracture and fiber pulling out,therefore improving the fracture toughness of multi-stage bionic alumina ceramic specimens.Based on the conventional direct writing 3D printing technology,a coupled stress field-assisted3 D printing device was designed and built to realize the preparation of multi-stage bionic Bouligand structured alumina ceramic specimens by coupled stress field-assisted 3D printing.Relevant mechanical test results showed that the flexural strength and toughness of the two kinds of multistage bionic alumina ceramic samples with flake alumina and mullite staple fiber as reinforcement phase were further improved by coupling stress field.In this study,the influence mechanism of solid phase content,structure scale and material parameters on mechanical properties of bionic alumina ceramic composites was systematically and comprehensively studied based on the above theoretical tests combined with direct writing ceramics3 D printing technology.The use of coupled stress field-assisted direct writing 3D printing technology improved the refinement of the traditional direct writing ceramics 3D printing preparation process and further enhanced the mechanical properties of multi-stage bionic alumina ceramic composites,providing a theoretical basis for the development of new bionic alumina ceramic composites and its preparation processes.