Effect of Pore Structure of Organic Resin-based Porous Carbon on Joining Properties of Cf/SiC Composites

doi:10.15541/jim20220294

Abstract

Abstract:

Joining technology has become an important part of the preparation and engineering application of large or complex-shaped C_f/SiC composites. In this study, the stable joining of C_f/SiC composites was achieved via the Si-C reaction joining method by using the phenolic resin as the carbon precursor. Effects of the bulk density and pore size of porous carbon blanks on the joining properties and microstructure of the joints were investigated. Effect of the content of inert fillers on the joining properties and microstructure of joint were discussed. Bulk density and pore size of the resin-based porous carbon blank are suitable to be set in the range of 0.71-0.90 g·cm^-3 and 200-600 nm, respectively. The size of free silicon increases gradually with the increase of the pore size. The flexural strength of the joined specimens can reach (125±12) MPa at pore size of 190 nm. Addition of SiC inert filler is obviously beneficial to reduce the volume shrinkage of the porous carbon blank. Flexural strength of the joined specimens reached the highest value, i.e., (216±44) MPa at the inert filler content of 50%. Overall, this study provides theoretical guidance for the stable joining of C_f/SiC composites, which has significance for realizing the preparation and engineering application of complex-shaped or large C_f/SiC composites.

Key words: porous carbon, reaction bonded joining, C_f/SiC composites, microstructure property, mechanical

CLC Number:

TQ174/TB332

WU Xishi, ZHU Yunzhou, HUANG Qing, HUANG Zhengren. Effect of Pore Structure of Organic Resin-based Porous Carbon on Joining Properties of C_f/SiC Composites[J]. Journal of Inorganic Materials, 2022, 37(12): 1275-1280.

Figures/Tables 11

Fig. 1 Microstructures of joints with different volumn densities ((a) 0.51, (b) 0.70, (b) 0.90) and (d) flexural strengths of the joined specimens

Table 1 Composition of resin solution and properties of porous carbons after pyrolysis

Sample	PF/%	EG/%	Pore former^*	Residual carbon^**/%	Average pore size/nm	Bulk density/(g·cm^-3)
1	50	50	FeCl₂ (1%)	23+1.1	190±15	0.73±0.01
2	50	50	H₃BO₃(1.5%)	24.3±0.9	642±15	0.74±0.01
3	50	50	FeCl₂ (1%) + H₃BO₃(1.5%)	24.1±1.7	1226±48	0.74±0.03
4	50	50	H₃BO₃(2.5%)	25.8±2.1	1552±38	0.79±0.03
5	50	50	H₃BO₃(3.5%)	26.7±1.5	2363±54	0.79±0.03

Fig. 2 Morphologies of the polished surfaces before and after HF-HNO3 corrosion of RBSC fabricated from preforms with different pore sizes (a, f) 190 nm; (b, g) 642 nm; (c, h) 1226 nm; (d, i) 1552 nm; (e, j) 2363 nm

Fig. 3 XRD patterns of the RBSC fabricated from preforms with different pore sizes

Table 2 Properties of the RBSC fabricated from preforms with different pore sizes

Pore size/nm	Open porosity/%	Density/ (g·cm^-3)	Flexural strength/MPa	Residual Si/(%, in volume)
190	0.97	2.93	296±28	16
642	1.26	2.91	268±46	14
1226	1.87	2.88	248±22	16
1552	3.51	2.81	238±44	12
2363	18.76	2.10	115±32	13

Fig. 4 Surface microstructures after HF-HNO3 corrosion of joining samples with different pore sizes (a) 14 nm; (b) 190 nm; (c) 316 nm; (d) 642 nm; (e) 1226 nm

Table 3 Properties of joining samples with different pore sizes

Pore size/nm	Flexural strength/MPa	Strength retention/%
14	90±28	61
190	125±12	85
316	77±10	52
642	107±15	73
1226	65±22	44

Table 4 Composition of resin-based slurry

Sample	PF/ %	EG/ %	Dispersant^*/%	Pore former^** (FeCl₂)/%	α-SiC powder/%
1	40	40	4	1	20
2	35	35	4	1	30
3	30	30	4	1	40
4	25	25	4	1	50
5	22.5	22.5	4	1	55

Fig. 5 (a) Schematic of the action of inert filler and (b) volume shrinkage and porosity change curves of porous carbon blanks

Fig. 6 Microstructures of the joint with different contents of inert filler ((a) 30%; (b) 40%; (c) 50%; (d) 55%, in mass) and (e) partial enlargement of (d)

Fig. 7 Flexural strength of the joined samples with different contents of inert filler

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