Formation of carbon interphase on low electric conductive SiC fibers for SiC_f/SiC composites by electrophoretic deposition process and their mechanical properties

Abstract

Continuous silicon carbide fiber-reinforced silicon carbide (SiC f /SiC) composites have been expected as nextgeneration highly reliable heat resistant materials. It is well-known that the interface between fiber and matrix acts as an important role for toughening and strengthening SiC f /SiC composites, and it should be optimally controlled to achieve high performance SiC f /SiC composites with excellent fracture tolerance. In this study, polypyrrole (Ppy) as an electric conductive polymer was coated on amorphous SiC fibers to increase their surface electric conductivity so that electrophoretic deposition (EPD) method can be applied to form the interphase on the SiC fibers, and carbon interphase was formed on the SiC fibers by EPD method. In addition, unidirectional SiC f /SiC composites were fabricated by polymer impregnation and pyrolysis (PIP) process, and their mechanical properties were evaluated. Thin Ppy coating with the thickness of around 200 nm drastically increased the surface electric conductivity of the amorphous SiC fibers, and the surface of Ppy-coated SiC fibers was wholly and uniformly coated with flaky graphite particles by EPD. The average thickness of the carbon interphase formed on the Ppy-coated SiC fibers by EPD became thicker with an increase in EPD voltage, and it was revealed that the SiC f /SiC composites with carbon interphase formed by EPD showed pseudo-ductile fracture behavior and excellent mechanical properties, and the formation of the thick carbon interphase (average thickness; 0.7 « 0.4 ¯m, EPD voltage; 5 V) provided the higher bending strength and fracture energy under the experimental condition in present study. These results demonstrated that Ppy coating on the lowconductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high performance SiC f /SiC composites.

Mechanical properties of SiCf/SiC composites with h‐BN interphase formed by the electrophoretic deposition method

“…On the other hand, the electric conductivity of the SiC fibers with Ppy coating was 1.7 × 10 2 S/m, and the SiC fibers were wholly coated with flaked h‐BN particles by the EPD, and uniform flaked h‐BN coating on the SiC fibers was successfully achieved (Figure 4C). From these results, it is demonstrated that Ppy coating is very effective to form uniform h‐BN coating on the SiC fibers by the EPD as reported in our previous paper 25 …”

“…Before h-BN coating on the SiC fibers by EPD, thin conductive polymers, polypyrrole (Ppy), were coated on the SiC fibers to improve the electric conductivity of their surface according to our previous paper. 25 Ammonium peroxodisulfate ((NH 4 ) 2 S 2 O 8 , APS, FUJI-FILM Wako Pure Chemical Corporation, Japan) and 2,6naphthalenedisulfonic acid disodiumsalt (C 10 H 6 (SO 3 Na) 2 , NDA, Tokyo Chemical Industry Co., Ltd., Japan) were used as an oxidant and a doping agent, respectively. APS and NDA were dissolved in distilled water, and each concentration was adjusted to be 0.01 M. The SiC fiber preforms were soaked in the APS-NDA aqueous solution, and the solution was stirred with a magnetic stirrer.…”

“…From these results, it is demonstrated that Ppy coating is very effective to form uniform h-BN coating on the SiC fibers by the EPD as reported in our previous paper. 25 In order to clarify the effect of exfoliation of h-BN particles by wet-jet milling on the interphase formation on SiC fibers, coarse h-BN particles with the average size of 1. the h-BN particles were clearly observed (Figure 4D), and it was very difficult to form h-BN interphase on the SiC fibers densely by EPD using h-BN particles without exfoliation by wet-jet milling. On the other hand, flaked h-BN particles exfoliated by wet-jet milling were coated on the SiC fibers densely, and gaps among the h-BN particles were not observed.…”

“…[17][18][19][20][21][22][23][24] In addition, the application of the EPD process is considered to be difficult to form the interphase on SiC fibers with low electric conductivity, but our group demonstrated that polypyrrole (Ppy) coating on the low-conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving highperformance SiC f /SiC composites as well as conventional gas-phase-based process. 25 In this study, the present authors focused on the h-BN interphase, which shows better oxidation resistance than carbon, and tried to form dense and uniform h-BN coating on low-conductive SiC fibers by the EPD method using flaked h-BN suspension prepared by wetjet milling. In addition, unidirectional SiC f /SiC composites with the h-BN interphase formed by the EPD method were prepared by the polymer impregnation and pyroly- sis (PIP) method, and their mechanical properties were evaluated.…”

“…We have already demonstrated that the EPD method is effective to form the carbon interphase on SiC fibers and SiC f /SiC composites with the carbon interphase formed by EPD shows excellent mechanical properties 17–24 . In addition, the application of the EPD process is considered to be difficult to form the interphase on SiC fibers with low electric conductivity, but our group demonstrated that polypyrrole (Ppy) coating on the low‐conductive SiC fibers was very effective to improve their surface electric conductivity, and uniform and sufficient carbon coating was successfully formed on the SiC fibers by EPD for achieving high‐performance SiC f /SiC composites as well as conventional gas‐phase‐based process 25 …”