Papers by Keyword: C/SiC Composite

Abstract: This paper study on the influence of ultrasonic vibration assisted grinding (UAG) process on surface topography and properties of C/SiC composites. Through the surface quality experiments of common grinding (CG) and UAG, the height distribution parameters and function parameters are obtained and used to analyze the characteristics of the material surface topography. The relationship between grinding process and the composites surface quality is pointed out by experimental research. The orthogonal design is employed to optimize ultrasonic parameters and grinding parameters. The optimized condition is carried out to modify the surface quality. The results show that ultrasonic vibration has a great influence on height and surface bearing properties; the surface roughness is improved by the small vibration amplitude and low frequency. The grinding depth is the key factor on surface topography modification and the feed rate is the second. According to the research, an important technical support is carried out to improve the surface performance of C/SiC composites.

Abstract: The compression properties of C/SiC composite and Inconel X-750 helical springs were investigated from room temperature (RT) to 1000°C in air. The density of C/SiC spring is 1.74 g/cm³, only ~1/5 of X-750 value (8.17 g/cm³) and the spring constants of C/SiC and X-750 springs at RT are 3.47 and 5.61 N/mm, respectively. The spring constants of X-750 spring decreased with increase of temperature. X-750 spring could keep excellent property below 600°C, but its spring constant was only 36.7% of RT value at 800°C and permanent deformation appeared. At 1000°C, it could not restore and was destroyed. The spring constants of C/SiC spring at 400°C and 600°C were appreciably higher than the RT value, and then decreased with temperature elevating. Above 800°C, the spring constant decreased with test progressing because of the oxidation of carbon fibers and SiC matrix. But it has a spring constant of 2.40 N/mm (69.2% of the RT value) at 1000°C and can revert to its original dimensions.

Abstract: C/SiC composite and TC4 alloy were successfully brazed using 70Ag28Cu2Ti (wt. %) as filler metal at 820 °C~920 °C for 5 min ~30 min. The effects of brazing parameters on the microstructures, phase composition, shear strength of the brazed joints were investigated by SEM, XRD. The mechanical performances of the brazed joints were measured by a universal mechanical testing machine. The results show that successful joining of C/SiC composite and TC4 alloy owes to interfacial reactions between the brazing alloy and the parent materials, and resultantly produce TiC, Ti5Si3 and Ti-Cu serial compounds at the interfaces; the interfacial structure of the brazed joint is C/SiC composite / TiC / Ti5Si3 /Ag (s.s) +Cu (s.s) / TiCu2 / Ti3Cu4 / TiCu / Ti2Cu / TC4 from C/SiC composite side to TC4 alloy side; the maximum shear strength of the brazed joint is 53.3 MPa at 860°C for 10min.

Abstract: C⁄SiC composites were plasma sprayed with Yb₂SiO₅⁄LaMgAl₁₁O₁₉ (LMA) coatings with varying Yb₂SiO₅ layer thickness. The effect of Yb₂SiO₅ layer thickness on the thermal cycling life of the Yb₂SiO₅LMA coatings was investigated. The results showed that the thermal cycling life is significantly dependent on the Yb₂SiO₅ layer thickness. It decreased from 130 cycles to 35 cycles as Yb₂SiO₅ layer thickness increased from 50 µm to 100 µm. Further increasing Yb₂SiO₅ layer thickness to 200 µm made it decrease to 2 cycles. The influencing mechanism of Yb₂SiO₅ layer thickness for the thermal cycling life was clarified based on the thermal expansion behavior, the chemical stability at high temperature and the microstructure analysis.

Abstract: A numerical investigation was conducted to determine the mechanical behavior of C/SiC composites bolt under room temperature and elevated temperature. The influence of the contact friction coefficient on the stress and displacement was considered in the finite element analysis. The FEA results provided some valuable data for the engineering application of C/SiC composites bolt.

Abstract: C/SiC substrates and M3 bolts were prepared by precursor infiltration and pyrolysis (PIP) process firstly, then the joints with four joining methods (2 φ3mm soft pins, S-A; 2 M3 bolts, S-B; 2 φ3mm soft pins plus 8 φ1mm soft pins, S-C; 2 M3 bolts plus 8 φ1mm soft pins, S-D) were assembled, finally several PIP cycles were continued to finish densification. The influences of different joining methods and PIP cycles (3 or 6) on the stripping properties of C/SiC joints were investigated, and the fracture modes were analyzed. The stripping loads of the joints adopting 6 PIP cycles are almost two to six times the values adopting 3 PIP cycles, and the corresponding fracture modes are pins or bolts rupture and pull-out, respectively. When adopting 3 PIP cycles, the bearing ability of the joints with bolts (S-B and S-D) is about 51% higher than that of joints with pins (S-A and S-C), but when adopting 6 PIP cycles, the values with pins (S-A and S-C) is about 67% higher than that with bolts (S-B and S-D). Besides, the introduction of φ1mm pins enhances the bearing ability of the joints with 3 and 6 PIP cycles about 45% and 14%, respectively.

Abstract: An experimental study of low velocity impact (LVI) was carried out on 2D carbon fabric reinforced silicon carbide (C/SiC) ceramic matrix composites. The C/SiC composite specimens were impacted by using a free-drop impact machine at different energy levels ranging from 1J to 9J and acoustic emission (AE) technique was used to detect the damage process. The results indicated that AE signals could evaluate the LVI damage behaviors of C/SiC composites from the different aspects. By comparing impact load process with AE hits and AE amplitude, the damage process could be determined. In the loading stage, matrix cracking mainly occurred in the composites; when impact load reached peak load, delamination and fiber fracture started to produce; in the unloading stage, the damage modes were mainly delamination and matrix cracking. AE event count fractions could quantify the main damage modes at different impact energy levels. At lower impact energy, matrix cracking was the main damage mode; when impact energy were between 3J and 6J, delamination and matrix cracking became the main damage modes; at higher impact energy, fiber fracture was the main damage mode.

Abstract: Carbon fiber reinforced silicon carbide (C/SiC) composites are considered as one of the most potential thermal structure materials. However, the non-machinability of the three dimension woven fabric restrict the wide application of the c/sic composites. In this paper, we discuss the effect of machinability on the properties of 3D-c/sic composites, such as the modulus, mechanical properties, and so on. The results show that c/sic composites exhibit excellent mechanical properties after machinability, an extensive microstructure study is also carried out to understand the properties of the composites.

Abstract: ZrC-Zr2Si coating was prepared on carbon fiber reinforced silicon carbide matrix composites (C/SiC) by pack cementation method to prevent these composites from oxidation. SEM, EDS and XRD were applied to analyze the surface and cross-section morphologies, element distribution and phase composition of the coating, respectively. The results show that the coating made by the technique exhibits excellent oxidation resistance. The optimizing infiltration composition and process was: 60wt.%Zr-Si, 30wt.%PCS-DVB, 10wt.%Al2O3, holding 8 hours at 1400°C in Ar protecting atmosphere, ZrC-Zr2Si coating is obtained, homogeneous and density. The weight loss percentage of the coated C/SiC is only 1.52％after oxidation in air at 1500°Cfor 30min.

Abstract: An anisotropic damage constitutive model is developed to describe the damage behavior of C/SiC composites. Different kinematic and isotropic hardening functions were employed in damage yield function to describe accurately the damage nonlinear hardening. The damage variable is defined by the principle of energy equivalence. The degradation of stiffness and the unrecoverable deformation induced by micro-crack propagation were considered in this model. The constants of constitutive model are identified and the damage evolution processes under tensile and shear loading. Uniaxial tension and shear tests have been used to valid the constitutive model to C/SiC composites.