Microstructure and mechanical properties in the TLP joint of FeCoNiTiAl and Inconel 718 alloys using BNi2 filler

doi:10.1016/j.jmst.2020.05.050

Abstract

Abstract:

High entropy alloy (HEA) of FeCoNiTiAl and Inconel 718 superalloy were firstly transient liquid phase (TLP) bonded by BNi2 filler due to the diffusion of Si and B in the filler to the base metals. The effects of bonding time on microstructure evolution and mechanical properties of the TLP joints were investigated. Owing to the complete isothermal solidification of the joints bonded for 30 min ~ 120 min at 1100 °C, no athermally solidified zones (ASZs) formed by eutectic phases were observed in the welded zone. Thus the TLP joints were only composed by the isothermally solidified zone (ISZ) and two diffusion affected zone (DAZ) adjacent to the dissimilar base metals and the negative effect of the ASZ on joint properties can be avoided. In addition, the increase of the bonding time can also make the TiB₂ borides precipitated in the DAZ near HEA and the brittle borides or carbides in the DAZ near IN718 alloy decrease and reduce the possibility of the stress concentration happened in the joints under loading. Therefore, the highest shear strength (632.1 MPa) of the TLP joints was obtained at 1100 °C for 120 min, which was higher than that of the joint bonded for 30 min, 404.2 MPa. Furthermore, the extension of the bonding time made the fracture mechanism of the joint be transformed from the intergranular fracture to the transgranular fracture. However, as the brittle borides in the DAZ near IN718 can not be eliminated completely and refining of grains also happened in such region, all the TLP joints fractured inner the DAZ near IN718 alloy.

Key words: FeCoNiTiAl alloy, Inconel 718 alloy, Microstructure evolution, Mechanical properties, Fracture mechanism

Lin Yuan, Jiangtao Xiong, Yajie Du, Jin Ren, Junmiao Shi, Jinglong Li. Microstructure and mechanical properties in the TLP joint of FeCoNiTiAl and Inconel 718 alloys using BNi2 filler[J]. J. Mater. Sci. Technol., 2021, 61: 176-185.

Figures/Tables 14

Table 1 Chemical compositions (wt. %) of the base metals and the filler.

Alloy	Ni	Co	Fe	Cr	Nb	Mo	Ti	Al	C	B	Si
IN718	Balance	0.17	17.43	18.41	5.23	3.12	0.98	0.47	0.06	0.005	0.32
HEA	30.61	30.73	29.12	-	-	-	6.10	3.44	-	-	-
BNi2	Balance	-	3.12	7.00	-	-	0.05	0.05	0.06	2.98	4.52

Fig. 1. Assembly samples (a) to be bonded and (b) in the shear test of FeCoNiTiAl and IN718 alloys with BNi2 filler.

Fig. 2. (a) The microstructure, (b) its partial enlarged details, (c) the DAZ morphology adjacent to the HEA and (d) the DAZ morphology adjacent to the IN718 alloy in the TLP joint bonded at 1100 °C for 60 min.

Table 2 Chemical compositions (at. %) of reaction phases in Fig. 2.

Zone	Ni	Co	Fe	Cr	Nb	Mo	Ti	Al	C	B	Si
DAZ near IN718	4.22	1.17	2.43	20.98	18.15	14.25	1.2	0.47	0.06	36.65	0.42
DAZ near HEA	3.41	3.80	3.96	0.02	-	-	15.95	0.36	5.62	68.87	0.01
ISZ	44.12	3.86	8.12	4.45	2.44	3.56	2.11	2.09	16.52	8.18	4.55

Fig. 3. (a) The focused region in TEM analysis (i.e. yellow line represented the TEM thin foil), (b) its HADDF patterns and corresponding elemental mapping of Ni, Fe, Co, Cr, C, Si, Nb, Mo, Ti and Al.

Table 3 Chemical compositions (at. %) of reaction phases in Fig. 3(b).

Phase	Ni	Co	Fe	Cr	Nb	Mo	Ti	Al	C	B	Si
A	55.14	0.01	14.85	12.15	4.55	0.97	1.21	0.32	2.26	-	8.53
B	0.53	0.11	0.32	0.24	49.78	0.63	9.04	0.41	30.78	-	8.19
C	0.91	0.09	2.10	50.33	28.15	8.77	1.05	0.25	3.96	-	4.39
D	1.03	0.31	1.10	22.79	17.11	8.97	25.60	0.75	19.05	-	3.27

Fig. 4. Selected area electron diffraction (SAED) patterns of reaction phases in Fig. 3(a), including (a) Phase A, (b) Phase B, (c) ISZ and (d) DAZ adjacent to IN718 base metal.

Fig. 5. (a) HADDF pattern of the region on the interface between ISZ and DAZ, (b) the enlarged view of the Region 1, (c) SAED pattern and (d) HRTEM image of the Phase C.

Fig. 6. (a) Microstructure of the DAZ near HEA base metal, (b) its HADDF patterns and corresponding elemental mapping of Ni, Fe, Co, Cr, C, Si, Nb, Mo, Ti, Al, (c) SAED patterns of Phase E and (d) the HRTEM image including FFT pattern of HEA alloy.

Fig. 7. Microstructure and the corresponding DAZ adjacent to the IN718 alloy of the TLP joints bonded at 1100 °C for (a) 30 min, (b) 60 min, (c) 90 min and (d) 120 min.

Fig. 8. Evolution of the crystallography characteristics in the TLP joints bonded for (a) 30 min, (b) 60 min, (c) 90 min and (d) 120 min.

Fig. 9. (a) Hardness and (b) modulus distributions across the joints bonded at 1100 °C for 30 min and 120 min.

Fig. 10. Cross sections of the fracture in the joints bonded for (a) 30 min, (b) 60 min, (d) 90 min, (e) 120 min and (c) the shear strengths of the TLP joints.

Fig. 11. Fracture morphologies of the TLP joints bonded at 1100 °C for (a) 30 min, (b) 60 min, (c) 90 min and (d) 120 min.

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