Preparation And Characterization Of Laminated Al/Al₂O₃ Composites With Nacreinspired Hierarchical Complexity

Nacre is a kind of natural composite layered materials,It is wide attention because it has an unique structure and excellent mechanical properties by the scientific community,and mimicking structural feature of pearl layer on shell has become upsurge.The traditional preparation process of composite materials is the simple combination of each material,which improved the mechanical properties of the material itself is limited,the laminated structure of nano nacre typical "brick and mortar",and a variety of micro level toughened structure,nacre structure makes the structure has the advantages of compared to synthetic material.Therefore,the preparation of a new type of composite structure with nacre like nacre has become a novel method for preparing high strength composite.In this paper,on the basis of nacre structure,preparation of Al₂O₃ porous ceramic skeleton by freeze drying method,as an imitation of nacre structure Calcium Carbonate Tablets layer structure,combined with the pressure infiltration process to penetrate into the porous ceramic skeleton by Aluminum Alloy,simulating the nacre layer structure of Al alloy /Al₂O₃ laminated composites.The aluminum alloy is the matrix of the composite material,and the alumina porous ceramic is the reinforcing phase of the composite.Through the control of the ceramic preparation process can prepare different porous ceramics with different laminated structure,structure and experiment found that nacre structure of porous alumina ceramics prepared by freeze drying the great similarity,finally the microstructure observation and mechanical properties test of Al alloy /Al₂O₃ laminated composite materials in this paper,the main results are as follows:?1?Prepared by freeze drying of porous alumina ceramics skeleton,observing internal porous ceramics is composed of laminated porous structure to a step change,the lower the temperature the pore structure is more dense,the body strength is more high,by adding glycerol can inhibit the excessive growth of ice crystals,make the pore the structure is more compact,by adjusting the proportion of alumina powder in the slurry,preparation of porous ceramics with different porosity,porous ceramic with internal cross laminated structure obviously,and between layer and layer and bridging structure between layers width can reach tens of micron,laminated stacking structure of nacre in comparison of several hundreds of nanometers the aragonite tablets,the structure is very similar.?2?The wettability of aluminum and alumina ceramics were studied in the experiment,founding that in normal experimental conditions,aluminum and alumina ceramic is difficult to wet,wetting can effectively improve the performance of aluminum by adding Mg and Si alloy,and in the anaerobic environment of high vacuum in Aluminum Alloy and alumina can occur wetting,experimental comparison that compared to the pressureless infiltration process,pressure infiltration process with short time efficient compact structure,and by mechanical pressure infiltration method Aluminum Alloy infiltration in the pores of porous alumina ceramics,successfully prepared ceramic reinforced aluminum matrix composite,compact structure and uniform composite materials.?3?Through the observation of microstructure of Al alloy /Al₂O₃ laminated composite materials found in the pressure infiltration process,retained the integrity of porous laminated structure of alumina ceramics,have a very good combination between layers of metal layer and the porous alumina ceramics,through the CT analysis of the porosity of the composite material and the content of each component the combined energy spectrum distribution of metal layer and ceramic layer in composite materials;the composite materials are the mechanical properties tests showed that porous alumina ceramics skeleton has good toughening effect on Aluminum Alloy matrix hardness,strength of composite materials were much higher than Aluminum Alloy matrix,and in the experiment.Composite materials in different direction of longitudinal and transverse strength values have significant difference,which is due to the laminated porous ceramic skeleton.The toughening mechanisms of composites are analyzed,including the interface between composite layers,the deflection of interlayer cracks and the bridging structures between composites.