Microstructure design of C/C composites through electrochemical corrosion for brazing to Nb

doi:10.1016/j.jmst.2021.06.074

Abstract

Abstract:

Surface structure of C/C composites has been regulated through electrochemical corrosion at room temperature to modify the residual stress and improve the joining strength when brazed to Nb. The unique crevice corrosion in C/C composites is investigated to reveal the change of corrosion depth and fiber size. The interlacing zone of carbon fiber reinforced brazing alloy replaces the reaction layer in the original joint. Joining area is increased dramatically and the continuous crack will be hindered. The interlacing zone eliminates the stress concentration and relieves the residual stress through reducing the property mismatch. All advantages contribute to the joining quality of C/C-Nb. Shear strength of C/C-Nb joint with 80 μm depth reached 37.7 MPa, which was 1.2 times higher than that of original joint. Surface structure design of C/C composites not only expands the application in structure component, but also exhibits the promising application in energy field.

Key words: Thermal corrosion, Electrochemical corrosion, C/SiC composites, Braze

Jin Ba, Xu Ji, Bin Wang, Peixin Li, Jinghuang Lin, Jian Cao, Junlei Qi. Microstructure design of C/C composites through electrochemical corrosion for brazing to Nb[J]. J. Mater. Sci. Technol., 2022, 104: 33-40.

Figures/Tables 12

Fig. 1. Schematic diagram of (a) electrochemical corrosion process, (b) the brazing assembly and (c) the shear test.

Fig. 2. Morphologies of (a, f) the original C/C composites and C/C composites corroded at (b) 2 V, (c) 3 V, (d) 4 V, (e) 5 V for 30 min and corroded at 3 V for (g) 5 min, (h) 15 min, (i) 30 min, (j) 60 min.

Fig. 3. Microstructures of brazing joints with C/C composites corroded at (a) 2 V/30 min, (b) 3 V/30 min, (c) 4 V/30 min, (d) 5 V/30 min, (e) 3 V/5 min, (f) 3 V/15 min, (g) 3 V/30 min and (h) 3 V/ 60 min.

Fig. 4. (a) Bright field image of carbon fiber/AgCuTi/carbon; (b) Element dispersion of Ag, Cu, Ti and C; (c) SAED analysis of TiC reaction layer; (d-f) Magnified HRTEM image of carbon fiber, carbon matrix and the interface between carbon fiber and matrix.

Fig. 5. Schematic diagram of C/C composites corrosion process: (a) the origin, (b) under 2 V and (c) 4 V.

Fig. 6. Microstructures of (a) C/C-Nb joint and interfaces of (b) C/C-AgCuTi and (c) AgCuTi-Nb. (d-f) XRD patterns of zone I-III marked in Fig. 6(a).

Fig. 7. Binary phase diagrams of (a) Cu-Nb[26] and (b)Ti-Nb[27].

Fig. 8. Typical microstructures of brazing joints adopted (a) the original C/C composites and (b) C/C composites with Cf/AgCuTi thickness of 80 μm.

Fig. 9. (a) Microstructure of brazing joint with the interlacing zone of 80 μm; the EPMA analysis of (b) C, (c) Ti, (d) Ag and (d) Cu.

Fig. 10. (a) Schematic diagram of the original joint model and the joint possessing Cf/AgCuTi zone model; Dispersion of residual stress in (b) the original joint and the joint with Cf/AgCuTi zone of (c) 25 μm, (d) 50 μm, (e) 75 μm and (f) 100 μm thickness.

Fig. 11. (a) Effect and estimation of Cf/AgCuTi thickness on shear strength of brazing joints; Fracture morphologies of (b) the original joint and (c) the joint with Cf/AgCuTi thickness of 80 μm.

Table 1 EDS compositional analysis result of markers in Fig. 11.

Position	Composition (at.%)				Possible Phase
	Ag	Cu	Ti	C
A	-	-	-	100.00	C
B	-	-	54.12	45.88	TiC
C	-	-	43.27	56.73	TiC
D	3.59	9.47	52.23	34.71	C_f/AgCuTi

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