Research On The Fundamental Technology Of SiC Reinforced Steel Matrix Surface Composite Prepared By Casting Infiltration Method

Ferrous matrix surface composites reinforced with SiC particle were prepared by V-EPC casting-infiltration method, and the microstructure of the composites layer has different characteristics. The microstructure characteristics of infiltrated zone were discussed and the forming mechanisms of microstructure under different technological conditions were analyzed. The result indicated that:1. The SiC particles could be decomposed in the high temperature molten ferrous metal during infiltration , which result in a substantial increase of the C,Si contents in the composites layer and prone to form the flake graphite in the microstructure. So inhibiting the graphitization in the composites layer is the key step in preparing process of casting-infiltration composite material.2. The SiC particles would decompose gradually in contacting with molten metal. During this process, the SiC particles decomposed into Si,C atoms and diffused into the matrix. The silicon atoms are in the form of substitutional solid solution in iron, its diffusion activation energy is higher than the carbon atoms which form the interstitial solid solution. So the silicon atoms have lower diffusion speed to form the high content gradient of silicon in the decomposed zone.3. When the matrix was cast steel with 4.2% Cr, a lot of net carbides formed in the infiltrated layer and the hardness was greatly increased. A lot of carbides (M₂₃C₆C,M₇C₃ and M₃C) result from increase of Cr content in matrix, and then avoided the formation of graphite in infiltrated zone.4. When the matrix was gray cast-iron, there were some residual particles in infiltrated zone, which result from the incomplete decomposition of SiC particles. The gray cast-iron matrix contents 1.6% Si and 3.2% C. From the view of chemical equilibrium, the higher contents of Si and C of gray cast-iron than that of steel would inhibit the decomposition of SiC.5. During the casting-infiltration process, the molten metal ignited the combustion synthesis reaction of Cr₂O3/Al or Ti/C in the casting-infiltration zone, the combustion synthesis reaction between Cr₂O₃ and Al formed Cr and Al₂O₃, then the chromium diffused into matrix and formed solid solution. Ti and C lead to a new reinforced phase TiC, and the dispersive distribution of TiC particles increased the hardness of the composite layer. Moreover, Ti avoids formation of graphite in infiltrated zone.