X‐ray Tomography Study on Green State Joining of Silicon Carbide Using Polymer Precursors

Abstract

X-ray tomography has been used to investigate the density variations in SiC joints formed using polymer pastes. It has been demonstrated that X-ray tomography provides accurate bulk density measurements and volumetric density gradients. The results suggest that the magnitude of the applied pressure after green state joining and the amount of polymer (polycarbosilane, PCS) in the joining pastes influence the green density of the joints. All joints are prepared and applied in air atmosphere and at room temperature. The green densities of the joints increase from 54% to 66% of theoretical with the increase of the applied pressure from ambient to 138 MPa. Highest joint density without applied pressure is achieved using paste containing 50 vol% PCS. Furthermore, allylhydridopopolycarbosilane-(AHPCS-) containing pastes resulted in higher densities at the joint-matrix interface, indicating infiltration of polymer into the matrix.

Recent advances in joining of SiC-based materials (monolithic SiC and SiCf/SiC composites): Joining processes, joint strength, and interfacial behavior

“…Joining of SiC-based materials to themselves can be also achieved using preceramic polymers as as-received interlayer by dissolving, coating, crosslinking, and pyrolysis and/or sintering procedures and even further reinfiltration, which process has been rapidly developed in recent two decades since the first fabrication of inorganic ceramic by the organic precursor conversion method [120]. Recently, the preceramic polymers used for joining of SiC-based materials were mainly involved in methyl-hydroxyl-siloxane [121], polysiloxane [19,122,123], polymethylsiloxane [113,124,125], polysilazane [126,127], polymethylsilane [128][129][130], and allylhydridopolycarbosilane [131,132], as shown in Table 9. Generally, the resulting SiC/SiC joint bending strength values were less than 200 MPa in spite of the formation of interlayer with identical or similar CTE to the SiC-based materials, which were much lower than those obtained by reaction forming/ bonding [115][116][117][118].…”

Monitoring the process of densification of 3D and 4D (tridirectional and tetradirectional) carbon/carbon composites

“…In this way, a correlation between CT units (HUs) as a function of the linear attenuation coefficient can be obtained, where the only one variable is porosity. 15,16 The value of the mass attenuation coefficient of graphite for the effective energy of the beam 75 keV used in this work is 0.1632 cm 2 /g and this value was obtained from the table of the NIST available at www.nist.gov. 16 Thus, the linear attenuation coefficient was calculated as the product of density and the mass attenuation…”