Investigation Of Mechanical, Oxidation And Ablation Properties Of Cu₃Si Modified C/C-SiC Composites

Carbon fiber reinforced carbon/silicon carbide binary matrix (C/C-SiC) composites, also named as C/SiC composites, possess excellent mechanical properties, low density, low thermal expansion coefficient, heat conductivity, oxidation resistance, ablation resistance and low-wear performance. Therefore, C/SiC composites are widely used in the field of aviation, aerospace and energy.To improve the comprehensive performance and reduce costs of C/C-SiC composite, Cu3Si modified C/C-SiC composites were fabricated by infiltrating Cu and Si into C/C felt performs. The microstructure and morphology were investigated by scanning electron microscopy (SEM), energy spectrum analysis (EDAX), X-ray diffraction (XRD) and metallographic microscope (OM). The mechanical, oxidation and ablation properties of Cu3Si modified C/C-SiC composites were studied. The results show that:(1) The Cu3Si modified C/C-SiC composite consists C, Si, β-SiC and Cu3Si. With the Cu content in infiltration agent Si-Cu increasing, the content of Cu3Si in the composite increased gradually. Meanwhile, the content of residual Si reduced gradually. The density of the material increased with increasing Cu, while the porosity decreased. The sample without Cu has higher density with the opening pore rate of6.37%. Good bonding between fiber and matrix has been obtained. With the increasing of Cu content in the melt penetration Si-Cu, the density of the material increased from2.21g·cm-3to2.80g·cm-3, while the opening pore rate increased from7.53%to9.40%.(2) On the mechanical properties of the melt penetration Si-Cu with0wt%,25wt%,50wt%and75wt%of Cu content, the flexural strength of Cu3Si modified C/C-SiC composites was47.33MPa,41.32MPa,39.57MPa and33.48MPa, respectively. And the compressive strength was306.21MPa,268.76MPa,254.28MPa and224.23MPa, respectively. Those suggest that the mechanical properties decreased with the increasing of Cu content in Si-Cu. The load-displacement curves of the material indicate good pseudo-plastic in bending test and typical brittle fracture characteristics in compression test.(3) In the non-isothermal oxidation process, while the oxidation temperature is in the range of700～1000℃,the weight loss ratio of the composites increases due to the oxidation of C. Only a little SiO2was formed with the oxidation of Cu3Si, Si, and SiC. As the oxidation temperature increases to1000～1300℃, lots of SiO2was formed with the oxidation Cu3Si, Si, and SiC which can cover the weight loss of the C oxidation. Therefore, the weight loss rate of the composites was nearly stable in this oxidation temperature range. However, for the isothermal oxidation process, the weight loss ratio of the composites increase as the regular of linearity and then slower. With oxidation time of4h, the weight loss ratio of the material reached a constant value. SiO2and CuO were formed with the reaction between Cu3Si and O2. The pores in material were filled by the generation of SiO2and CuO, which can not only block the O2into entering the matrix, but also reduce the reactive activity. The oxidation mechanism can protect the matrix and fiber to a certain extent and lead to a lower oxidation weight loss.(4) Mass ablation rate and ablation rate of Cu3Si modified C/C-SiC composite With Cu50%of ablation40s were0.0021g/s and0.0169mm/s, respectively. Those increased to0.0032/s and0.0228mm/s of the ablation60s, respectively. The ablation mechanism of the composites was mainly controlled by sublimation, erosion and oxidation. The sublimation of SiC and Cu3Si can reduce the surface temperature. On the other hand, the oxidation products, SiO2, CuO which cover the surface of the materials play a important role in inhibiting oxidation and to remedy defects.