An effective approach for bonding of TZM and Nb-Zr system: Microstructure evolution, mechanical properties, and bonding mechanism

doi:10.1016/j.jmst.2020.09.054

Abstract

Abstract:

A novel method of liquid metallic film (LMF) bonding was developed to join titanium zirconium molybdenum alloy (TZM) and Nb-Zr alloy with a Ni interlayer. Using this method, a Ni-Zr liquid phase was formed by the eutectic reaction and then squeezed out from the gap due to a transient pressure, leaving an LMF. It not only achieved a reliable metallurgical bonding but also served as a transition layer between TZM and Nb-Zr alloy to reduce the mismatch between them thus further improving its performance. The bonding mechanism of the TZM and Nb-Zr system was discussed based on theoretical calculation and high-resolution microscopy analysis. The advantages of this method were established by comparing the microstructure and mechanical properties of LMF bonded joints with that of traditional contact-reaction brazing and direct diffusion bonding. Additionally, the feasibility of the LMF bonding method was also demonstrated by the reliable joining of other high-temperature and immiscible systems.

Key words: Bonding, Titanium zirconium molybdenum alloy (TZM), Diffusion, Microstructure, Mechanical properties

Z.W. Yang, J.M. Lin, J.F. Zhang, Q.W. Qiu, Y. Wang, D.P. Wang, J. Song. An effective approach for bonding of TZM and Nb-Zr system: Microstructure evolution, mechanical properties, and bonding mechanism[J]. J. Mater. Sci. Technol., 2021, 84: 16-26.

Figures/Tables 12

Fig. 1. (a) Schematic of LMF bonding equipment; (b, c) microstructure and content of parent materials; (d) XRD results of parent materials; (e) bonding parameter; (f) TEM image and SAED patterns of TZM.

Fig. 2. Comparison of the microstructure of TZM/Nb-Zr joints obtained by different bonding methods with 120 μm Ni foil at 1200 ℃ for 30 min: (a, b) LMF bonding; (c, d) contact-reaction brazing; (e) bright field image of Ni10Zr7 compound and its SAED pattern; (f) bright field image of NiZr compound and its SAED pattern.

Table 1 Chemical compositions of each phase (at.%) in Fig. 2.

Point	Ni	Nb	Zr	Possible phase
A	–	100.00	–	Nb
B	40.18	22.61	37.21	Ni₄₀Nb₂₃Zr₃₇
C	60.17	13.79	26.04	Ni₆₀Nb₁₃Zr₂₇
D	–	–	100.00	Zr
E	–	84.39	15.61	(Nb, Zr)

Fig. 3. Mechanical properties of TZM/Nb-Zr joints: (a) hardness and Young's modulus of reaction phases formed in contact-reaction brazing joint; (b) typical load-displacement curves; (c) joint shear strength tested at different temperatures; (d, e) fracture path and morphology analysis of contact-reaction brazed joint after shear test at 600 ℃; (f, g) fracture path and morphology analysis of LMF bonded joint after shear tests at 600 ℃.

Fig. 4. Interfacial microstructure and elemental line profiles across TZM/Nb-Zr joint obtained by diffusion bonding and LMF bonding: (a, c) LMF bonding; (b, d) direct diffusion bonding.

Fig. 5. Effect of surface roughness of TZM parent alloy on the interfacial microstructure and shear strength of direct diffusion bonded TZM and Nb-Zr joints.

Fig. 6. Schematic diagram of microstructure evolution mechanism of TZM/Ni/Nb-Zr joints: (a) atomic diffusion behavior and liquid phase appearing; (b, c) formation of contact-reaction brazed joint; (d, e) formation of LMF bonded joint.

Fig. 7. Typical microstructure images of TZM/Ni/Nb-Zr contact-reaction brazed joint and calculation of interface energy transition: (a) joint microstructure; (b, c) model for interface transformation in diffusion zone; (d) calculation of interface energy transition.

Fig. 8. Analysis of (Mo, Nb) diffusion layer: (a) TEM dark field image of the interface between TZM and (Mo, Nb) diffusion layer; (b) HRTEM observation of the area nearby point B; (c, d) HAADF and BF analysis of Mo atomic columns selected from (b); (e) elemental distribution of Mo, Nb, Zr, Ti and Ni along the yellow line in (a); (f, g) elements mapping of Nb and Mo.

Table 2 Chemical compositions of the marked points in Fig. 8 (at.%).

Point	Mo	Nb	Zr	Ni	Ti
A	52.41	47.32	0.24	0.00	0.03
B	67.91	31.27	0.78	0.03	0.01
C	85.41	11.91	2.66	0.00	0.02
D	99.53	0.10	0.15	0.00	0.22

Fig. 9. The minimum energy path for the exchange process between (a) Nb and a vacancy in pure Mo and vacancy in Mo with Ni nearby; (b) Mo and a vacancy in pure Nb and vacancy in Nb with Ni nearby; (c) the value of D/D0 in different diffusion processes at 1000-1500 K.

Fig. 10. Microstructure and corresponding elements line profiles across the interface of Mo/Nb and Mo/Cu joints obtained by LMF bonding: (a) Mo/Nb joint; (b) Mo /Cu joint.

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