(SiC-Si₃N₄)/2024Al Co-Continuous Composites With Controlled Microstructure And Optimized Property

In this paper,the porous SiC/Si₃N₄ ceramics prepared by freeze casting were used to study the effects of different solid loading and different Si₃N₄ contents on the microstructure,pore morphology and mechanical properties of porous ceramics.?SiC-Si₃N₄?/2024 Al co-continuous composites were prepared by pressure infiltration method.The solid loading and Si₃N₄ content on the microstructure and mechanical properties of the composites were investigated.The interfacial bonding was analyzed.The aging heat treatment process of the composites was determined,and the strength and fracture toughness of the composites were studied before and after aging.The thermal expansion coefficient and thermal conductivity of the composites were tested and the theoretical model was calculated.The results show that the ?-Si₃N₄ in the porous SiC/Si₃N₄ ceramics is completely transformed into ?-Si₃N₄.As the solid loading increases,the density increases,the porosity decreases and the wall thickness increases.The porous SiC/Si₃N₄ ceramic pore size distribution,found in the slurry solid content of 20%,30% bimodal distribution.Porous ceramic has high porosity and good porosity,and the lowest compressive strength is higher than that of squeeze casting pressure,and it is suitable as a preform for preparing co-continuous composite.?SiC-Si₃N₄?/2024 Al co-continuous composites prepared by pressure infiltration method.SiC/ Si₃N₄ and Al are synthesized by porous Si C/Si₃N₄ ceramics.The ceramic phase and the Al alloy are alternately arranged in a layered structure.Si₃N₄ and Al have a slight interface reaction,the formation of AlN,the reaction layer thickness of about 20nm-30 nm.SiC and Al interface clean,close together,did not produce brittle phase Al4C3,SiC and Si₃N₄ interface clear,with a close,no reaction layer.The hardness and elastic modulus of the composites increase with the increase of the content of the reinforcement.The fracture toughness decreases with the increase of the content of the reinforcement.The flexural strength decreases with the increase of the content of the enhanced phase,the maximum bending strength is 573 MPa,the compressive strength is 500 MPa,the yield platform is about 10%,and the compressive strength is 1136.82 MPa.The optimum aging process was determined at 175 ? for 7 h,which was earlier than 2024 Al alloy.Aging after the bending strength of up to 781 MPa,the maximum increase of 36.3%.The maximum fracture toughness is 15.1 MPa·m1/2,and the maximum increase is about 31.3%.The precipitated phase was precipitated at the grain boundary before aging,and the precipitated phase was dispersed in the precipitated phase.The precipitated phases were ? phase?Al2Cu?and S phase?Al2CuMg?.The co-continuous composite has a low coefficient of thermal expansion relative to the particle reinforced composite and decreases with increasing phase.The reason is that the co-continuous composite is continuously crossed and the Al alloy is restrained and limited to its expansion.The thermal conductivity of the composite decreases with the increase of the volume fraction of the reinforcement.