Session: 02-02 Design and Application of CMC Materials and Components

Paper Number: 126212

126212 - Influence of SiC Fiber Dispersion on the Mechanical Strength of SiCf/SiC Composites 

Among ceramic matrix composites (CMCs), silicon carbide (SiC) fiber-reinforced silicon carbide matrix (SiC_f/SiC) composites, has a high heat resistance temperature of over 1300℃ and has excellent oxidation resistance and high temperature stability. In addition, since its density is one-third that of metal, the utilization of SiC_f/SiC composites in high-temperature components such as gas turbine nozzles and rotor blades is on the rise.

The weaving and pretreatment of fibers in the process of fabricating continuous fiber-reinforced composites are crucial factors that significantly influence the material's properties. In the case of carbon fiber-reinforced plastics, various methods are used to create fabrics or prepregs using spread carbon fiber tows, leading to improved mechanical properties, including fatigue life.

However, research on the use of spread fibers in CMC manufacturing is limited, with most cases focusing on C/SiC using carbon fibers. In particular, studies on the effect of spreading or dispersion of SiC fibers on the mechanical properties of SiC_f/SiC It is still difficult to find similar cases.

In this study, we proposed a method for quantifying fiber dispersion within SiC composites based on whether the SiC continuous fibers were spread during manufacturing. We utilized spreading equipment, developed by the Korea Institute of Energy Research (KIER), to spread UBE Industries' Tyranno SA fibers. We subsequently coated the fibers with BN and SiC at the fiber-matrix interface, impregnated them with a polymer resin slurry containing ceramic nano fillers, and cured them to produce FRP composites.

Analysis of SEM images of non-spread and spread fiber-reinforced composites revealed that while fiber volume fractions decreased by nearly 9% with the application of the spreading process, while the pores in the matrix of the composite specimen were clearly reduced. This indicated that the spreading of fibers facilitated a more uniform slurry impregnation between the fibers during the curing process.

To quantify the fiber dispersion resulting from spreading, we measured the average distance between the closest six fibers for each of the 16 selected fibers at regular intervals in SEM images. The results showed that the distance between the surfaces of fibers in the spread specimens increased by an average of 2.23μm, representing a 42.6% increase compared to that in the non-spread specimens.

We manufactured SiC_f/SiC composite specimens using an LSI-based process, and conducted three-point bending tests to compare their mechanical strength. The flexural strength of the spread specimen was 673.7 MPa, which was 49.3% higher than the 451.2 MPa of the non-spread specimen, and the deviation of the strength results also decreased.

Given the lower fiber volume fraction in the spread specimens, it can be concluded that the improved fiber dispersion within the composite matrix, owing to the spreading of SiC fibers, significantly enhances the uniform matrix densification and mechanical strength of SiCf/SiC composites.

 

Presenting Author: Soo-Hyun Kim Korea Institute of Energy Research

Presenting Author Biography: Dr. Soo-Hyun Kim is currently a principal researcher at the Korea Institute of Energy Research in Daejeon, Rep. of Korea, and he has been involved in various government R&D project for the development of ceramic matrix composites (CMC) for high temperature application.
He studied structural analysis and optimal design of composite structures at the Department of Aerospace Engineering at the Korea Advanced Institute of Science and Technology, and was granted a Ph. D. degree in 2008.
His research is focused on the CMC manufacturing process optimization, evaluation of high temp. static and long-term strength and fatigue properties, and thermal-structural analysis and design for CMC hot section part.

Authors:

Soo-Hyun Kim Korea Institute of Energy Research
Seyoung Kim Korea Institute of Energy Research
In-Sub Han Korea Institute of Energy Research
Hyung-Joon Bang Korea Institute of Energy Research
Young-Hoon Seong Korea Institute of Energy Research
Seulhee Lee Korea Institute of Energy Research