Effect of Heat Treatment on Microstructure and Mechanical Properties of Stoichiometric SiC/SiC Composites

Abstract

Polymer impregnation and pyrolysis (PIP) is one of the most attractive fabrication processes for silicon carbide (SiC) composites due to the shape flexibility, mass production and relatively low cost. In particular, advanced PIP SiC/SiC composite with high-crystallinity and nearstoichiometric composition is expected to have superior thermo-mechanical properties including good oxidation resistance, due to the reduction of impurities and well-organized crystal structure. Additionally, by applying a thin carbon interphase by chemical vapor infiltration (CVI), control of the crack propagation and oxidation resistance are also achieved. In this study, a CVI + PIP hybrid process based on the recently developed stoichiometric PIP process was performed. Specifically, matrix crystallization was enhanced by heat treatment in Ar, and its effect on microstructures and mechanical properties were evaluated. Stoichiometric SiC/SiC composites exhibit superior flexural strength up to 1573 K in Ar and 1273 K in air. This is because the stoichiometric composition in PIP-SiC matrix reduces inner oxidation by impurities. Also, the thin pyrolytic carbon interphase tailored by CVI process effectively controls crack propagation at fiber and matrix interphase. In a similar manner, the microstructure of the stoichiometric PIP-SiC matrix, constructed by the mixture of amorphous SiC and highly crystalline SiC, was stable against the high-temperature heat exposure up to 1773 K in Ar. In particular, stoichiometric SiC/SiC composites heated at 1773 K in Ar provides superior stability of mechanical properties up to 1573 K even in air atmosphere, although extensive crystallization, in the case of heat treatment at 1973 K in Ar, caused brittle composite fracture.

Erosive Wear Mechanism of New SiC/SiC Composites by Solid Particles

“…1). State of the art in SiC/SiC composites has solved most of the potential issues of near-net shaping and machining, joining technology and evaluation technology [68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86]. There are no doubts that SiC/SiC composites are at the forefront of advanced materials technology and prime candidates for structural material in severe environments.…”

Evaluation of Tensile Properties of SiC/SiC Composites with Miniaturized Specimens

“…A recent study revealed the width effect on tensile strength of various types of SiC/SiC composites. 24) In that report, a three directionally woven TyrannoÔ-SA fiber reinforced composite made by the modified PIP process 25) and a cross-plied TyrannoÔ-SA fiber reinforced laminate composite made by the nano-infiltration transient eutectic phase (NITE) process 26,27) were evaluated. Both composites featured a highly crystalline and near stoichiometric SiC matrix.…”

Cracking Resistance of Silicon Carbide Composites by Single‐ and Double‐Notched Specimen Techniques

“…However, small pores were distributed in the PIP–SiC matrix as shown in Table I, resulting in a comparably lower density of ∼2.1 g/cm 3 . Details of the PIP process are described in Nozawa et al 17 …”