Study On Numerical Simulation Of Gas Pressure Infiltration SiC/Al Ceramic Matrix Composites

SiC/Al composites have the advantages of high strength, high stiffness, high thermalconductivity, low thermal expansion coefficient and low density. It is the ideal electronicpackaging material for high power electronic devices used in aerospace field. Gaspressure infiltration is an important technology for preparing SiC/Al composites. But thecomposites easily appeared partial pore and crack. In this paper, the process of gaspressure infiltration was simulated by the simulation software ProCAST. In order toanalysis the mechanism of generated defects, and optimize the process parameters of gaspressure infiltration so that qualified SiC/Al composites can be prepared. The mainresults are as follows.The filling and solidification process of melt in the complex three-dimensionalconnectivity are simulated. The interface heat transfer coefficients are optimized by theinverse module of ProCAST to improve the accuracy of simulation. The technologymakes a breakthrough for building porous ceramics feature modeling based on real pore.The characteristics of melt filling are reproduced accurately. By the simplified modelingwith micro pore, the loss of pressure, the distribution of shrinkage and residual stress canbe obtained. It can accurately predict the distribution of shrinkage and residual stress incomposites. And scientific explains the formation mechanism of shrinkage and crack.Through the simulation of gas pressure infiltration, the pressure loss of melt reaches2.95MPa/mm in the complex3D interconnected micron pore. It causes the low pressuremelt fills larger size pore firstly. Then the flow pauses and the velocity of melt decreases,the pressure increases so that the transverse fine pore can be filled. The center ofcomposites was the last cooling part and proned to form the shrinkage. It really existspore in the real composites. The thickness direction of composites existed the stressconcentration with tensile state, above100MPa (process conditions are preheatingtemperature650℃, infiltration temperature780℃and pressure8MPa). It caused the realcomposites cracked in the thickness. The residual stress was more lager with closer to therunner.Through the orthogonal experimental method, the process of gas pressure infiltration isoptimized and qualified SiC/Al composites are prepared. In order to reduce the interfacialreaction of SiC/Al (melt infiltration time), decreases shrinkage of composites and avoidcracking, the key parameters of preheating temperature, infiltration temperature and pressure were optimized by orthogonal experiment. It found that infiltration pressure wasthe main factor to the infiltration time and the residual stress. The infiltration timeincreased gradually with decreasing pressure. Preheating temperature was the mostimportant influence to shrinkage, the condition of shrinkage was improved withdecreasing preheating temperature. The residual stress increased firstly and then reducedwith the infiltration pressure and temperature decreasing. The residual stress decreasedwith preheating temperature decreasing. The optimum process parameters are preheatingtemperature550℃, infiltration temperature620℃and infiltration pressure8MPa. SiC/Alcomposites prepared by the optimum process were compact, and the porosity was only1%.SiC/Al composites with the volume fraction of SiC78%were prepared by optimumparameters. The thermal conductivity of composites is204.11W/m·K, the coefficient ofthermal expansion is8.95×10-6/K and density is3.07g/cm3. The composites conform tothe requirements of high power electronic devices used in aerospace.