Review Articles

Wide Gap Braze Repair of Gas Turbine Blades and Vanes—A Review

[+] Author and Article Information
Xiao Huang

Department of Mechanical and Aerospace Engineering,  Carleton University, 1125 Colonel By Drive, Ottawa, ON, K1S 5B6, Canadaxhuang@mae.carleton.ca

Warren Miglietti

Power System Mfg.—an Alstom Company, 1440 West Indiantown Road, Jupiter, FL 33458warren.miglietti@psm.com

J. Eng. Gas Turbines Power 134(1), 010801 (Oct 28, 2011) (17 pages) doi:10.1115/1.4003962 History: Received August 05, 2010; Revised March 31, 2011; Published October 28, 2011; Online October 28, 2011

Gas turbine blades and vanes in modern gas turbines are subjected to an extremely hostile environment. As such, sophisticated airfoil designs and advanced materials have been developed to meet stringent demands and at the same time, ensure increased performance. Despite the evolution of long-life airfoils, damage still occurs during service thus limiting the useful life of these components. Effective repair of after-service components provides life-cycle cost reduction of engines, and as well, contributes to the preservation of rare elements heavily used in modern superalloys. Among these methods developed in the last four decades for the refurbishment and joining of superalloy components, wide gap brazing (WGB) technology has been increasingly used in the field owing to its ability to repair difficult to weld alloys, to build up substantially damaged areas in one operation, and to provide unlimited compositional choices to enhance the properties of the repaired region. In this paper, the historical development of wide gap repair technology currently used in industry is reviewed. The microstructures and mechanical properties of different WGB joints are compared and discussed. Subsequently, different WGB processes employed at major OEMs are summarized. To conclude this review, future developments in WGB repair of newer generations of superalloys are explored.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Example of a serviced row one turbine blade from SGT6-5000F where tip and platform cracks were found [1]

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Figure 2

Two typical formulations of WGB filler alloy ((a) composite and (b) layered)

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Figure 3

Typical WGB thermal cycle (a) and (b) [(35),36]

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Figure 4

Illustration of isothermal solidification process in WGB

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Figure 5

Microstructures of braze joints with AMS 4777 + 30% additive alloy; (a) brazing temperature 1150 °C, (b) at 1250 °C [68]

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Figure 6

Microstructure WGB joint with X-40 + BNi-9

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Figure 7

(a) Boride formation within high melting additive alloy during brazing at 1145 °C (the microstructure was retained by quenching the samples from the braze temperature [72]). (b) Microstructure of a brazed joint consisting of 40/60 ratio of NB 150/IN 738 powder (Cr-rich blocky boride and eutectic Ni-rich boride) [79]. (c) Void formation between γ-Ni solid solution (intergranularly) in 30/70 of BNi 9 and IN 738 [80].

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Figure 8

Microstructure (BSE) and EDS maps of WGB joint with 40%BNi-9 brazed at 1200 °C for 20 min [86]

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Figure 9

Microstructure of WGB joint with 1/1 ratio between IN 738 and BNi 9 and 4 wt. % W (brazed at 1200 °C for 20 min) [30]

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Figure 10

Crack initiation and propagation associated with network borides surrounding the γ -Ni phase (tensile tested at 950 °C) [98]

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Figure 11

LCF crack initiation from porosity in WGB joint with X-40/BNi-9 [103]

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Figure 12

Wide gap braze BM/FM configuration, adapted from Ref. [28]

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Figure 13

Filler alloy placement in Refs. [113,114]

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Figure 14

Microstructure of the WGB region with SRB process [116]

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Figure 15

Schematic illustration of M-FillTM process (adapted from Refs. [107,118])

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Figure 16

Microstructure of WGB braze joint with LPDB process [97]

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Figure 17

Microstructure (C = base metal powder, D = low melting braze alloy, F = homogeneous layer) formed after brazing and diffusion treatment [126]

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Figure 18

Schematic illustrations of two types of process with sintered preforms. (Note that in (b) the low melting braze alloy does not flow during the preform sintering.) (a) Sintered preforms. (b) Sintered composite preform.

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Figure 19

Microstructure of MarM247 superalloy powder mixed with the Ni-Cr-Hf braze alloy after brazing cycle at 1238 °C for 12 h + 1232 °C for 4 h [138]

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Figure 20

Microstructure of the interface between a single crystal extension and CMSX-4 base metal joined with boron free braze alloy [139]



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