română FLORENTINA MARILENA CLICINSCHI, CRISTINA ANTONELA BANCIU, DORINEL TĂLPEANU, MAGDALENA VALENTINA LUNGU, CRISTINA CORNELIA COSTEA, GABRIELA BEATRICE SBÂRCEA, DELIA PĂTROI, VIRGIL EMANUEL MARINESCU
Abstract
The aim of this research was to obtain composite ceramic materials based on a silicon carbide (SiC) matrix modified with sintering additives (Al2O3 and Y2O3) and reinforced with 1 wt.% or 5 wt.% milled carbon fibers (Cf) using the spark plasma sintering (SPS) technique. SPS processing was carried out under vacuum at an applied axial pressure of 50 MPa and a sintering temperature of 1850°C, with a holding time of 10 minutes. The structural and morphological characteristics of the silicon carbide-based composites were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Physical and mechanical properties, including bulk density, apparent porosity, Vickers hardness, elastic modulus, friction coefficient, and specific wear rate, were evaluated for all sintered specimens. XRD analysis indicated the predominance of the β-SiC phase in the composite materials. The results showed that all samples sintered at 1850°C achieved bulk densities above 3 g/cm3 and apparent porosities below 1.72%, corresponding to a densification degree of at least 98.28%. Furthermore, all analysed specimens exhibited Vickers hardness values exceeding 1568 HV, modulus of elasticity in the range of 240-299 GPa, and an average friction coefficient between 0.41 and 0.93 in dry sliding conditions.
Keywords
Spark Plasma Sintering, β-SiC, carbon fibers, ceramic composites, mechanical and tribological properties
LONGHAI YE
Abstract
Tensile behavior of Two-dimensional carbon fiber reinforced silicon carbide composite （2D-C/SiC） composites was also studied systematically under quasi-static and high strain rate conditions at temperatures of 20, -70, -150 ℃ to the liquid nitrogen temperature ( -196 ℃). Mechanical loading was performed on a universal testing system with low strain rates and a split Hopkinson tensile bar system with dynamic regimes, with strain rates between 10−3 and 300 s−1. In all test conditions, the material showed a clear nonlinear stress-strain behavior before failure, which is indicative of its pseudo-plastic deformation behavior. Cooling and loading rate were both found to enhance strength. Tensile resistance was observed to rise significantly as the environment changed to cryogenic temperatures. An analogous strengthening behavior was noted as strain rate increased, which is rate-dependent mechanical behavior. Fractographic analysis also helped to understand the mechanisms of damage. In the quasi-static loading, strong fiber pull-out characteristics were observed, indicating progressive interfacial debonding before ultimate failure. Conversely, specimens with dynamic loading exhibited significantly shorter pull-out lengths, suggesting a higher interfacial constraint and more sudden fracture mechanisms. At low temperatures, fracture surfaces appeared irregular and rugged. Instead of massive bundle extraction, localized fiber cluster pull-out with comparatively smooth fracture traces on the extracted clusters dominated failure.
Keywords
2D-C/SiC, composite material, low temperature, dynamic tensile