Abstract
This paper presents the results of microstructural analysis of novel preceramic paper-derived SiCf/SiC composites fabricated by spark plasma sintering. The sintering temperature and pressure were 2100/2200 °C and 60/100 MPa, respectively. The content of fibers in the composites was approx. 10 wt %. The SiCf/SiC composites were analyzed by positron annihilation methods, X-ray diffraction technology, scanning electron microscopy, and Raman spectroscopy. Longer sintering time causes the proportion of the 6H-SiC composition to increase to ~80%. The increase in sintering temperature from 2100 °C to 2200 °C leads to partial transition of 4H-SiC to 6H-SiC during the sintering process, and the long-life component of positrons indicates the formation of Si vacancies. The Raman characteristic peaks of turbostratic graphite appear in the Raman spectrum of SiC fibers, this is caused by the diffusion of carbon from the surface of the SiC fiber and the preceramic paper during the high-temperature sintering process.
Highlights
Silicon carbide (SiC) has excellent properties—such as low density, high specific strength, high specific modulus, resistance to thermal shock, low coefficient of thermal expansion, radiation tolerance, and chemical inertness [1,2]
The SiC fibers (SiCf)/SiC composites with more advantageous strength reliability and damage tolerance properties are being developed for nuclear energy and aerospace fields [5]
Another design based on the formation of a laminated structure layer-by-layer reinforced with SiC fibers was suggested in the previous study, in which the novel preceramic paper-derived SiCf/SiC composites were successfully fabricated using spark plasma sintering (SPS) [1], which has the advantage of being faster than other processes—such as reactive melt infiltration (RMI) [7], chemical vapor infiltration (CVI), polymer infiltration pyrolysis (PIP) [8], etc
Summary
Silicon carbide (SiC) has excellent properties—such as low density, high specific strength, high specific modulus, resistance to thermal shock, low coefficient of thermal expansion, radiation tolerance, and chemical inertness [1,2]. The implementation of so-called interface layer coating—such as pyrolytic carbon or boron nitride deposited on the surface of the SiC fibers (SiCf)—can improve the macroscopic mechanical properties of the SiCf/SiC composites by preventing the integration of fibers [3] Another design based on the formation of a laminated structure layer-by-layer reinforced with SiC fibers was suggested in the previous study, in which the novel preceramic paper-derived SiCf/SiC composites were successfully fabricated using spark plasma sintering (SPS) [1], which has the advantage of being faster than other processes—such as reactive melt infiltration (RMI) [7], chemical vapor infiltration (CVI), polymer infiltration pyrolysis (PIP) [8], etc. The main goal of this study was to analyze the microstructure of the paper-derived SiCf/SiC composites fabricated by SPS
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