Study On Formation And Evolution Mechanism Of Interface Microstructure And Defects Of C_f/Al Composites

This paper in view of corrosion-area and uncorrosion-area of Cf/Al compositestructures which was store in atmosphere for8years, observe the microstructureand defects, through the analysis of preparative process and verification of testreproduce, analyse the formation of microstructure and defect, get the relationshipof microstructure and preparation, which has important scientific significance andengineering value on use of preparative process to improve composites with lowcost and high efficiency.Through the observation of morphology and microstructure on corrosion-areaand uncorrosion-area, the analysis of phase, it shows that the different content ofinternal defects and interface reaction products Al4C3make different damagecharacteristics of composite structures. the calculation of temperaturecharacteristics of different area of component in preparation process shows thatthe production of Al4C3and shrinkage defects have relation with castingtemperature and cooling speed.According to the calculation results, design the verification test to study theinfluence casting temperature and cooling speed made in the production of Al4C3.Casting temperature of670℃,700℃and740℃are selected, the result shows that,with casting temperature rises, interface reaction of Cf/Al composite materials isincreasing rapidly, the size of Al4C3phase increases, while the length-diameter ratiodecreases, the content and temperature rough meet exponential relation. Because ofthe cooling speed control is difficult, high temperature exposure test on the preparedof composite material is made to simulate cooling process, the influencetemperature and time in the process of cooling made on interface reaction isresearched. The results showed that: after heat preservation in550℃, interfacereaction was not significant, the reason may be that the graphitization degree ofM40J carbon fiber is higher, so the force of constraint to carbon atoms increases;and the orientation of microcrystalline along the fiber axial arrangement is greater,microcrystalline edge which make it easy to form the nuclear reduced, so a highertemperature is needed to make the interface reaction obvious. When dealed withheat preservation in600℃, along with time extended, interface reaction obviouslyincrease; while the ratio of the content of Al4C3and time lower, the reason may bethat the nucleation position on fiber surface decrease, and the size of Al4C3phasedecreases, which makes it difficult for carbon atoms to spread through, whichmakes it difficult for Al4C3to grow up infinitely; When treated in640℃, temperature provide enough energy for nucleation, which makes nucleation positionare no longer limited to microcrystalline edge and flaws, moreover the diffusionability of carbon atoms increases with the rise of temperature, So with the timeincreases, the content of Al4C3increase linearity.Integrate with the result of high temperature exposure test, thermodynamicstheory and dynamics theory are used to analyse the feasibility and reaction rate ofinterface reaction in different temperature. Thermodynamic calculation shows thatinterface reaction can happen during200K~1200K theoretically. Dynamicscalculation shows that, for M40J/6061Al composite materials, diffusion rateconstant is almost zero when temperature is below840K, which makes interfacereaction can not occur; diffusion rate constant increase quickly since860K, so theretention time should as far as possible to be reduced when temperature ablow860k,the diffusion activation energy of carbon in the aluminum is735.129kJ/mol, theinterface reaction activation energy is367.564kJ/mol.