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Research Papers: Gas Turbines: Manufacturing, Materials, and Metallurgy

Brazing and Wide Gap Repair of X-40 Using Ni-Base Alloys

[+] Author and Article Information
Stephen Schoonbaert

1125 Colonel By Drive, Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Canada, K1S 5B6

Xiao Huang

1125 Colonel By Drive, Department of Mechanical and Aerospace Engineering, Carleton University, Ottawa, Canada, K1S 5B6xhuang@mae.carleton.ca

Scott Yandt, Peter Au

 Institute for Aerospace Research, Structures and Materials Performance Laboratory, National Research Council, 1200 Montreal Road, Ottawa, Canada K1A 0R6

J. Eng. Gas Turbines Power 130(3), 032101 (Apr 02, 2008) (10 pages) doi:10.1115/1.2836743 History: Received June 20, 2007; Revised June 22, 2007; Published April 02, 2008

Co-base superalloys are commonly used for vanes and parts of the combustion chamber in gas turbine engines. The Co-base superalloys are primarily solid solution strengthened and have good resistance to hot corrosion, creep, and thermal fatigue. In particular, Co-base alloy X-40 was used to fabricate the first stage NGV airfoils of T56 series engines; inspections after service have revealed that X-40 airfoils suffered from severe thermal fatigue damages. In this study, a new braze repair scheme is proposed; in which Ni-base alloys are used to repair the X-40 substrate in both narrow and wide gap configurations. Metallographic examination, X-ray mapping, and energy dispersive spectroscopy semiquantitative compositional analyses were carried out to study the microstructures in the braze joint in the as-brazed condition and after thermal exposure at 950°C. The results obtained so far suggest the formation of Cr-rich borides, eutectic phases, and various carbides in the joint. No TCP phases were found in the brazed joint and base metals adjacent to the joint. The high carbon content in the alloy X-40 may have played an important role in preventing the formation of TCP phases during brazing and subsequent thermal exposure.

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Copyright © 2008 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Narrow gap joint with controlled gap using tack weld

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Figure 2

Specimen cutaway showing the 7:4 ratio of filler metal powder (IN 738 or X-40) to braze powder (BNi-9)

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Figure 4

Example of elemental mapping of all selected elements (wide gap braze with X-40 and BNi-9)

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Figure 5

Optical image of narrow gap repair area

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Figure 6

(a) Narrow gap braze region between IN 738 and X-40. (b) Microstructure in braze gap region. Phases observed: refractory RP, CB, and APs in the IN 738 matrix. (c) RP phase observed along the IN 738/braze and X-40/braze interface. (d) Hexagonal CB in the IN 738 matrix. (e) Acicular carbon-rich phase found near the IN 738/braze interface.

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Figure 7

Elemental maps of selected elements for the narrow gap joint in the as-brazed condition

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Figure 8

(a) Narrow gap braze between IN 738 and X-40 after 840h thermal exposure at 950°C. (b) Phases observed in the braze and interface regions: (c) refractory RP, (d) CB, (e) acicular carbon-rich phase (AP), and Zr-rich phase (ZP).

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Figure 9

Elemental maps of the narrow gap joint after thermal exposure

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Figure 10

Optical image of repair of a wide gap repaired X-40 sample

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Figure 11

(a) Wide gap braze and interface regions. (b) Microstructure constituents in the region: (c) dark blocky phases (BPs), (d) angular CB, and (e) eutectic phases (EPs)

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Figure 12

(a) Microstructure of the interface in the wide gap braze with X-40+BNi-9. (b) Dark blocky carbide phase (BP). (c) Cr-rich carbon boride phase (CB).

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Figure 13

Microstructure of wide gap brazed joint after 840hours thermal exposure at 950°C

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