Effect of Heat Treatment on Composition, Microstructure and Mechanical Property of Domestic KD-SA SiC Fibers

doi:10.15541/jim20220548

Abstract

Abstract:

Polycrystalline near stoichiometric SA type SiC fibers have a prospective application in the fields of the new generation aero engine and hypersonic vehicles due to their excellent temperature resistance. In this work, microstructure evolution, tensile strength as well as fracture behavior of the second-generation domestic F-II SiC and the third-generation SA (F-III) SiC fibers before and after heat treatment were studied. The results showed that F-III fiber was mainly composed of β-SiC grains (~200 nm) and a small amount of free carbon, while F-II fiber was composed of β-SiC grains (~5 nm), free carbon and amorphous SiC_xO_y phase. Compared with the F-II fiber, the F-III fiber showed lower tensile strength at room temperature, owing to their larger grain size and pores. However, after heat treatment at 1800 ℃, the structure and strength of F-III fiber remained almost unchanged, while the strength of F-II fiber decreased sharply due to decomposition of SiC_xO_y phase and grain growth. The excellent high temperature resistance of SA type fiber could be attributed to high crystallinity, large grain size, low carbon and oxygen content in microstructure and composition.

Key words: SiC fibers, heat treatment, microstructure, tensile strength

CLC Number:

TQ174

WU Shuang, GOU Yanzi, WANG Yongshou, SONG Quzhi, ZHANG Qingyu, WANG Yingde. Effect of Heat Treatment on Composition, Microstructure and Mechanical Property of Domestic KD-SA SiC Fibers[J]. Journal of Inorganic Materials, 2023, 38(5): 569-576.

Figures/Tables 10

Table 1 Composition and general properties of SiC fibers before and after heat treatment

Parameter	F-II	F-II-1800 ℃	F-III	F-III-1800 ℃
C/Si	1.34	1.42	1.08	1.08
Al content/ (%, in mass)	/	/	<1.00	<1.00
O content/ (%, in mass)	0.98	0.53	0.07	0.05
Diameter/μm	12.0	11.9	9.9	9.9
Density/ (g·cm^-3)	2.72	2.66	3.08	3.09
Tensile strength/ GPa	2.7	0.9	1.8	1.8
Elastic modulus/GPa	260	207	372	366

Fig. 1 Si2p XPS spectra of (a) F-II, (b) F-II-1800 ℃, (c)F-III, and (d)F-III-1800 ℃ fibers

Fig. 2 (a) XRD patterns and (b) Raman spectra of SiC fibers

Table 2 Raman characteristics of free carbon phase of the fibers

Sample	D Band		G Band		I_D/I_G	L_a/nm
Sample	Position/cm^-1	FWHM	Position/cm^-1	FWHM	I_D/I_G	L_a/nm
F-II	1356.3	112.5	1599.8	122.7	1.39	13.8
F-II-1800 ℃	1351.3	59.9	1586.8	63.2	1.09	17.6
F-III	1352.9	79.9	1590.1	89.0	1.12	17.2
F-III-1800 ℃	1354.3	64.9	1593.0	72.8	1.18	16.3

Fig. 3 SEM morphologies of (a-c) F-II, (d-h) F-II-1800 ℃, (i-l) F-III, and (m-p) F-III-1800 ℃ fibers

Fig. 4 TEM and HRTEM images of (a-e) F-II fibers, (f-j)F-II-1800 ℃ fibers, and (k-o) F-III-1800 ℃ fibers

Fig. 5 (a-c) TEM images and (d-f) elemental distributions of the F-II-1800 ℃ fibers

Fig. 6 Schematic diagram of (a) formation process of skin-core structure of F-II-1800 ℃and (b) thermal stability of F-III fibers

Fig. 7 (a) Representative strain-stress curves and (b) Weibull plots of the fibers

Fig. 8 Fracture morphologies of (a, b) F-II, (c) F-II-1800℃, and (d) F-III fibers

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