Study On Thermodynamics And Interfacial Microstructure Of SiC_f/Ti Composites

As a new material for next generation aero engines, silicon carbide reinforced titanium composites(SiC_f/Ti composites)highly attract people's attention. However, due to the high reactivity of titanium, chemical interfacial reactions will take place in the interface between SiC and Ti-matrix. So far, there has been few research about the thermodynamic study on the interfacial reaction on SiC_f/Ti composites. In particular, The effect of different alloying elements in the Ti-matrix on the interfacial reactions in SiC_f/Ti composites has never been studied before.On the basis of thermodynamic activity in multi-components alloy system, by combining Miedema model and Kohler equation, prediction models of activity coefficients for binary and ternary solid state alloy have been established and testified by experimental data. Using only the physical parameters of pure metals, the activity coefficients of components in alloy systems can be theoretically calculated.Applying this model, the activity of Ti in SiC_f/Ti composites was evaluated, and the influence of different alloying elements on the interfacial chemical reactions in SiC_f/Ti composites at high temperature was investigated from a thermodynamic viewpoint. The calculation results showed that most alloying elements such as Al, Sn, Ni, Fe, Cu, Mn, Cr, Mo and V can reduce the activity of Ti, and hinder the interfacial chemical reactions in SiC_f/Ti composites, but alloying element such as Nb in most cases can decrease the stability of the interfacial chemical reactions in SiC_f/Ti composites.In addition, by means of Scanning electron microscope(SEM), Transmission electron microscope(TEM) and X-ray diffraction(XRD), the microstructure and especially the interfacial reactions between two different fiber(American SCS-6 SiC and Chinese SiC) reinforced Ti-matrix composites was investigated. First by SEM, the consolidating fault such as hole and crack in SiC_f/Ti composites was analyzed. Then the distributing of some elements such as C, Si, Ti, Al and V was analyzed by EDS and the feature has been explored. The interfacial reaction products were investigated by TEM and XRD, and it showed that the main phases are TiC and Ti5Si3. Finally, the thickness of reaction zone of SCS-6 SiC_f/Ti composites and Chinese SiC_f/Ti composites were measured by SEM. The growth rates of reaction zone at different temperature (800℃, 925℃)were calculated, and according to the dynamics of interfacial reaction, the Q and k0 of the reaction zone were calculated, respectively.