InfluenceoftheporosityofC/ConthecharacterizationofC/C-SiCcompositepreparedbyreactivemeltinfiltrationmethod资源-CSDN文库

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-1-

Influence of the porosity of C/C on the

characterization of C/C-SiC composite

prepared by reactive melt infiltration

method

Jiping Wang

State Key Laboratory for Mechanical Behavior of Materials

Xi'an Jiaotong University

Xi'an 710049, China, 710049

jipingwang@gmail.com

Zhihao Jin, Min Lin, Yonghui Zhang

State Key Laboratory for Mechanical Behavior of Materials

Xi'an Jiaotong University

Xi'an 710049, China, 710049

Abstract

C/C performs with four different open porosities in the range of 12.4%~45.7% were

reactive-melt-infiltrated (RMI) with silicon to rapidly fabricate C/C-SiC composites.

The influence of the C/C porosity on the Si infiltration during the processing and on

the microstructure and mechanical properties of the resulting C/C-SiC composites

were investigated by means of density measurement, XRD, SEM, and three-point

bending test, respectively. The results show that the higher porosity of C/C brought

more silicon infiltration during RMI processing. The porosity also played a key role to

dominate the content of β-SiC, residual Si and C phases, as well as the porosity of the

resulting C/C-SiC composites. The flexural strength and the fracture behavior of the

composites were strong influenced by the matrix content and the interface between

different phases. C/C-SiC derived from C/C with 24.8% porosity has the highest

flexural strength (325.1MPa) and shows a brittle fracture behavior.

Keywords: C/C-SiC; open porosity; reactive melt infiltration; mechanical property;

microstructure

1 Introduction

Carbon fiber reinforced pyrocarbon and silicon carbide composites (C/C-SiC) have many outstanding

properties, such as high strength at elevated temperature, low density, superior toughness and abrasive

properties

[1]

. They are widely used as high temperature structural components in aerospace area and

also as promising candidates for advanced brake and clutch systems

[2-5]

The methods for fabricating C/C-SiC composites from porous carbon/carbon composites (C/C)

include chemical vapor infiltration (CVI) technique

[6-8]

, liquid precursor infiltration and pyrolysis (PIP)

processing

[9-10]

, and reactive melt infiltration (RMI) method (or called as liquid silicon infiltration)

[11-12]

. For CVI processing, methyltrichlorosilane (CH

SiCl

) in gas phase was infiltrated and

Support by Research Fund for the Doctoral Program of Chinese Higher Education (No. 20070698104)

http://www.paper.edu.cn

-2-

decomposed at high temperature (1000~1200

C) to form SiC phase in the pores of C/C. However, CVI

processing need a long period to obtain densified C/C-SiC composites. PIP route uses liquid precursors

as SiC sources to fabricate C/C-SiC composites. Common precursors are such high molecular weight

polymers as polycarbosilane (PCS), polymethlsilane (PMS) and hexamethyldisilazane (HMDS).

However, most of them have high price because they are not commercial production. Moreover, in

order to achieve high densified composites more than 5 cycles were required. RMI process is the most

attractive method among the three feasible processes considering the processing time and the cost. This

method impregnates porous C/C by molten silicon; C and Si reacts to form SiC at high temperature

(above 1410

C). It is a near-net-shape process and only need one infiltration cycle to achieve full

densified production.

Therefore RMI has been extensively investigated since it was firstly developed near 30 years ago

[13]

. The basic investigations were focused on the kinetics of liquid Si infiltration into porous carbon,

and the mechanism of the reaction between solid carbon and liquid silicon

[14-17]

. However, the physical,

mechanical properties and frictional behavior of the resulting C/C-SiC are not only influenced by the Si

infiltration and Si/C reaction, but also dominated by the fiber-matrix interface and the contents and

distribution of different phase in the composites

[18-19]

. Various microstructures and phase compositions

of C/C-SiC composites can be achieved by modifying the fiber preform architecture and the content of

the pyrocarbon in C/C. When fiber preform was chosen and certain pyrocarbon was formed, the

porosity and the pore size distribution in C/C were fixed. Nevertheless, how the porosity of C/C

preform influences the microstructures and mechanical propertied of as-prepared C/C-SiC composites

is not yet clearly investigated.

In the present work, C/C composites were firstly made by CVI method, which derived from same

fiber architecture and has different porosity, then C/C-SiC composites were prepared by RMI

processing from the C/C The influence of the porosity of C/C on the microstructures and mechanical

properties of the C/C-SiC composite was investigated. Based on the present work, RMI processing will

be further understood and we can obtain an optimized porosity of C/C for preparing C/C-SiC with

excellent properties.

2 Experimental procedures

2.1 Material preparation

A quasi three-dimension (3D) carbon fiber was chosen as preforms; the fiber type is T300 (density 1.76

g/cm

) and its architecture was shown in Fig. 1. The bulk density of the preform is 0.51g/cm

and the

fiber volume ratio is 28.5%. C/C composites with four different porosities were prepared by chemical

vapor infiltration (CVI) method using ethene as precursor. Then the C/C was cut in size of 60 × 8 × 6

and consequently RMI with Si under vacuum atmosphere to form C/C-SiC composites. Averaged

Fig. 1. Schematics of the carbon fiber preform used as reinforcement.

size of commercial silicon particles (size 1~3 mm) were used. The reaction temperature and reaction

time of RMI processing were ~1600

C and 30 minutes, respectively.

Third level headings are lower case (except for first word and proper nouns), flush left, bold and in

point size 10. One line space before the third level heading and ½ line space after the third level

heading.

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