Study On The Synthesis And Properties Of C_f/ZrB₂-ZrC-SiC Composites By In-situ Reaction

Fiber reinforced ultra-high temperature ceramic matrix composites (Cf/UHTCs) arewidely applied in the aerospace field, and is a research hotspots at present. The preparationmethod is introduction of high-temperature ceramic (UHTCs) phase into the matrix of Cf/SiCcomposites. The excellent anti-oxidant and anti-ablation performance ofultra-high-temperature ceramics can improve high-temperature performance of materials.Ultra-high temperature ceramic phase includes transition metal carbides and borides, amongwhich the most studied is ZrB2and ZrC. In this study, taking into account the ability of thesubject ZrB2and ZrC damage tolerance at high temperatures and their the anti-destructioncapabilities, a two-phase ZrB2and ZrC ultra-high temperature ceramic phase is introduced intothe matrix of the Cf/SiC composites. Cf/ZrB2-ZrC-SiC fiber-reinforced ultra-high temperatureceramic matrix composites are desired with high performance.Cf/ZrB2-ZrC-SiC composites are fabricated by in-situ reaction method with zirconiumpowder, silicon powder, boron carbide and phenolic resin as raw materials.To determine the preparation process of Cf/ZrB2-ZrC-SiC composites, the heat treatmentprocess of the matrix ZrB2-ZrC-SiC is firstly determined. At nine temperature points among900°C-1700°C, the raw material mixture is heated respectively. After analysis of phasecomposition of the resultant material for each temperature, it is determined that the minimumtemperature synthesis target powder product was1600°C. At this temperature, the raw materialmixture is heat-treated in an inert gas Ar environment and the vacuum environmentrespectively. With comparing the resultant microstructure and matrix composition, inert gasatmosphere is determined as the best environment for the substrate synthesis. And thefabrication mechanism of the matrix is analyzed. Thus, the optimum heat treatment process forthe synthesis of matrix is1600°C and inert gas environment.Fibers reinforcement with no interface, carbon interface and C/SiC interface are preparedby Chemical vapor deposition. And then the fibers are filled with matrix by infiltration andpyrolysis process. To increase the composite density, the process is repeated for several times. Finally Cf/ZrB2-ZrC-SiC composites of three types of interface are fabricated after hightemperature treatment.The density, open porosity and ultra high-temperature phase content of threeCf/ZrB2-ZrC-SiC composite are compared, and their mechanical properties are analyzed. Inaddition, after comparison of their flexural strength and fracture behavior, it is confirmed thatthe Cf/ZrB2-ZrC-SiC composites with C/SiC interface possess better performance. Theanti-oxidant and anti-ablation performance of this type of composite is tested. After that, themorphology and phase composition on the surface are tested. A molten glass layer is formed onthe surface of the composite. Its composition is ZrO2and SiO2, which is the product ofoxidation of the matrix on the surface. This layer can protect the interior materials from thecorrosion of oxidation atmosphere, with blocking the channel of oxygen diffusing into theinterior material. Thus, after oxidation and ablation, there is no obvious cracks and exposedfiber on the surface of composites, and no obvious falling off of material. This shows that theanti-destruction capability of the composite material is better, and is able to withstand bothhigh temperatures and shock tests.