Investigation Of C/C-ZrC-SiC-Cu_xSi_y Composites Fabricated By Melt Infiltration

Charactered with light mass and high strength,C/C composites are widely used in aerospace applications as materials for hot end components.The modification by Cu,Zr C and Si C can significantly enhance the ablation resistance of C/C composites.However,the surface oxide layer of modified composites easily occurs structural damage at high temperature,which limits the further improvement of composites’ablation resistance.Aiming to integrate the heat absorbing effect of Cu with the protective effect of Zr C and Si C,the pressure assisted reactive melt infiltration was employed to fabricate C/C-Zr C-Si C-Cu_xSi_ycomposites.The phase composition and microstructure of fabricated composites were analyzed,meanwhile the generation process of ceramic matrix and the evolution mechanism of oxide layer during ablation were investigated.Furthermore,the mechanical property and anti-ablation property of composites were analyzed in detail.The main conclusions are listed below:（1）By adopting pressure assisted reactive melt infiltration,C/C-Cu,C/C-Zr C-Cu and C/C-Zr C-Si C-Cu_xSi_y-Cu composites were fabricated using Cu as infiltrating material.Zr C improved the wettability between Cu and matrix,which caused the mechanical property and ablation property of C/C-Zr C-Cu composites higher than C/C-Cu composites.The generated Cu_xSi_y increased the combination between Cu and substrate,and the uniformity of ceramic matrix was improved then.During ablation,the proportion of Si C played a decisive role to the morphology of Si O₂and the ablation property of composites.Under the heat flux of 3.2MW/m²,the C/C-Zr C-Si C-Cu_xSi_y-Cu composites with 12.5 wt.%Si C owned better ablative performance compared with others,their linear and mass ablation rates were 3.5±0.1μm/s and 3.4±0.1 mg/s,respectively.（2）By infiltrating Zr₂Cu into C/C skeleton,C/C-Zr C-Zr_xCu_ycomposites were fabricated using Zr₂Cu as infiltrating material.The infiltrated matrix contained three different Zr C-Zr_xCu_y structures,and the dimensions of Zr C particles were decreased sequentially from matrix boundary to inside.At ablation test,the heat absorbing effect of Cu₂O slowed down the increasement of surface temperature,meanwhile the generated porous Zr O₂ segregated the substrate from oxygen atmosphere.As ablation period extends,the further melted Zr O₂ was transformed into a continuous structure.Thus,the linear and mass ablation rates of composites at 60 s ablation test reached-1.7±0.1μm/s and 1.7±0.1mg/s,respectively.（3）By infiltrating Zr₂Cu into C/C-Si C preform,C/C-Zr C-Si C-Cu_xSi_ycomposites with low porosity were fabricated.Micropores in substrate were mostly filled by Si C,meanwhile the large-scale infiltrator among fiber bundles was constituted by the shell of continuous Zr C with separated Si C,and the core of Zr C-Cu_xSi_y particles with embedded Cu_xSi_y-Si-Si C or Si-Si C aggregations.During short-term ablation,the dense Si O₂ cover on surface restrained the oxygen permeating into substrate.At 30 s ablation,the linear and mass ablation rates of composites reached 1.7±0.1μm/s and 1.3±0.1 mg/s,respectively.At 30s ablation,the linear and mass ablation rates of composites respectively changed to 3.8±0.2μm/s and 1.2±0.1 mg/s due to the structural damage and continuous generation of oxides.（4）At high temperature mechanical test,the C/C-Zr C-Si C-Cu_xSi_ycomposites occurred matrix transformation,including structural change of C/C skeleton,growth process of Zr C and Si C grains,meltage of Cu_xSi_y,and phase transition of Si,which caused the significant variation of composites’mechanical property.At room temperature,the continuous matrix and low porosity caused the bending and compressive strength of composites reaching 331 MPa and 282 MPa,respectively.At 800^°C test,the continuous Cu_xSi_y enhanced the strength and plasticity of substrate,causing the composites tested at 800^°C owned better mechanical property compared with other temperatures,the bending and compressive strength were 341 MPa and 308 MPa,respectively.With the experimental temperature rising to 1200^°C,the average size of Zr C grains was increased,meanwhile the great aggregation of melted Cu_xSi_y resulted in the generation of large-size cavities inside ceramic matrix,leading to the structural damage of substrate.Therefore,the bending and compressive stress of composites were respectively reduced to 227 MPa and 238 MPa,and the fracture mode was changed from pseudoplastic to brittle.