Study On The Preparation And Properties Of SiC_p/Al Multi-layered Functionally Gradient Composites

The SiCp/Al composites have excellent thermal physical and mechanical propertieswhich make them have great development potential for electronic packaging.However, poor welding performance deeply impedes their application in electronicpackaging. The purpose of this thesis is to prepare SiCp/Al layered functionally gradientcomposites to improve their welding performance, and the experimental processcomprises two steps: Firstly, NaCl was used as the pore forming agent to preparelaminated gradient porous SiC preforms; and secondly, SiCp/Al layered gradientcomposites were prepared by pressureless infiltration.Porous SiC preforms were prepared with different sized SiC powders (W7and W14)combined with different volume fractions of NaCl powder. The effects of NaCl volumefraction and particle size of SiC on the performance of porous SiC preforms werestudied. The results shows that with the valume fraction of NaCl increasing from0to82%, the porosity of porous SiC preforms made from W7increases from47%to86%.The distribution and connectivity of porous are improved significantly, andthe distribution of porous gradually becomes more uniform and denser from straggling,accompanied with the gradual forming of a three dimensional thin walled network structureof SiC particles. When SiC and NaCl powders were mixed with the volume ratio of2:9,high porosity SiC preform with a porosity of86%was obtained. The effects of SiCparticle size on the porosity of the preforms are very small.SiCp/Al composites were prepared from SiC porous preforms with different porosities.The microstructure and properties of SiCp/Al composites with different SiC contentswere studied. SiCp/Al composites are composed of large aluminum alloy areas and highSiC volume fraction SiCp/Al compound area. With the increasing volume fraction ofaluminum alloy, the distribution of large aluminum alloy areas become uniformand denser, and SiCp/Al compound area gradually forms a three dimensional thin wallednetwork structure. With the increasing volume fraction of SiC from14%to53%, theaverage coefficient of thermal expansion (from25℃to300℃) of SiCp/Al compositesdecreases from16.1×10-6K-1to9.3×10-6K-1, the change trend consistents well with theTerner model.Three layer high gradient SiCp/Al composites were prepared by filling powders layerby layer，accompanied with regulating the NaCl volume fraction and particle size of SiC powder for each layer. Each layer of SiCp/Al gradient composites is uniform, and thecombination between layers is good. The SiC volume fraction of the top layer is14%,the middle layer40%and the lower layer62%. And the average coefficient of thermalexpansion (from25℃to300℃) of those three layers are19.1×10-6K-1,13.3×10-6K-1and9.2×10-6K-1respectively.