Effect of Tungsten Addition on the Nucleation of Borides in Wide Gap Brazed Joint

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Daniel McGuire ◽  
Xiao Huang ◽  
Doug Nagy ◽  
Weijie Chen
Keyword(s):  
Fatigue Life ◽  
Gas Turbine ◽  
Thermal Fatigue ◽  
Braze Alloy ◽  
Microstructural Analysis ◽  
Cost Effective ◽  
Filler Alloy ◽  
Thermal Fatigue Life ◽  
Brazed Joint ◽  
Wide Gap

Wide gap brazing (WGB) is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. However, it has been shown that WGB joints of nickel-based superalloys suffer from reduced ductility and thermal fatigue life due to the presence of brittle intermetallics and porosities in the brazed joint. In order to disperse the brittle intermetallic compounds, potentially increase the ductility of the repaired region, and reduce the risk of the thermomechanical fatigue failure, elemental tungsten (W) was added to the braze additive filler alloy IN738 by mechanical alloying. The alloyed IN738 was then brazed with the addition of 30 wt %, 50 wt %, and 80 wt % of braze alloy (BNi-9). After brazing at 1200°C for 20 min, microstructural analysis of WGB joints showed a decreasing trend of discrete boride size and the amount of eutectic and script-shaped borides with the increases of W. The increase in the braze alloy to additive filler alloy ratio diminished the effect of W addition due the dissolution of W particulates.

Effect of Tungsten Addition on the Nucleation of Borides in Wide Gap Brazed Joint

2009 ◽  
Author(s):  
Daniel McGuire ◽  
Xiao Huang ◽  
Doug Nagy ◽  
Weijie Chen
Keyword(s):  
Fatigue Life ◽  
Gas Turbine ◽  
Braze Alloy ◽  
Microstructural Analysis ◽  
Cost Effective ◽  
Filler Alloy ◽  
Mechanical Fatigue ◽  
Thermal Fatigue Life ◽  
Brazed Joint ◽  
Wide Gap

Wide gap brazing (WGB) is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. However, it has been shown that WGB joints of nickel-based superalloys suffer from reduced ductility and thermal fatigue life due to the presence of brittle intermetallics and porosities in the brazed joint. In order to disperse the brittle intermetallic compounds, potentially increase the ductility of the repaired region, and reduce the risk of the thermo-mechanical fatigue failure, elemental tungsten (W) was added to the braze additive filler alloy IN738 by mechanical alloying. The alloyed IN738 was then brazed with the addition of 30, 50 and 80 wt% of braze alloy (BNi-9). After brazing at 1200°C for 20 minutes, microstructural analysis of WGB joints showed a decreasing trend of discrete boride size and the amount of eutectic and script-shaped borides with the increases of W. The increase in the braze alloy to additive filler alloy ratio diminished the effect of W addition due the dissolution of W particulates.

Effect of Ruthenium, Rhenium and Yttria Additions on the Microstructure of Wide Gap Brazing of IN738

2007 ◽  
Author(s):  
Xiao Huang ◽  
Scott Yandt ◽  
Doug Nagy ◽  
Matthew Yao
Keyword(s):  
Mechanical Properties ◽  
High Temperature ◽  
Life Cycle Cost ◽  
Filler Metal ◽  
Braze Alloy ◽  
Cost Effective ◽  
Brazed Joints ◽  
Brazed Joint ◽  
Wide Gap ◽  
Boride Phases

Modern gas and steam turbine components are subject to severe thermomechanical loads and extremely high temperature in order to provide increased performance and efficiency. Most high temperature turbine components are made of superalloys specifically developed for high temperature and high mechanical stress applications but at considerable cost. Defects may occur during manufacturing of superalloy castings as well as after service. Repair of these components, rather than replacement, helps to reduce the life cycle cost. Wide gap brazing is a cost effective and reliable means to repair gas turbine hot section components with defect sizes exceeding 0.3 mm. With proper control of the braze alloy and brazing cycle, the repaired region has been reported to posses mechanical properties approaching that of the parent materials. In order to further improve the mechanical properties of the repaired region and to explore the possibility of employing the wide gap brazing method to repair single crystal components in the future, three alloying additions, Ruthenium (Ru), Rhenium (Re) and yttria (Y2O3), were incorporated into the braze filler metal by mechanical alloying. The microstructures of the wide gap brazed joints with Ru, Re and yttria additions were studied and compared to a braze joint with standard wide gap braze alloys of IN738 and AWS BNi-9. It has been found that two types of borides formed in all braze alloys, namely eutectic γ-Ni-rich and boride phases and discrete boride containing primarily Cr and W (or Ru). The addition of Ru to the filler metal did not seem to modify the microstructural constituents after brazing. However, Ru partitioned strongly to the discrete borides. No isolated elemental Ru region was observed. On the other hand, Re addition was found to change the occurrence and distribution of both types of borides. The eutectic boride constituent was significantly reduced and finer discrete boride particles were observed. The addition of yttria did not change the boride formation but led to the generation of more voids in the brazed joint.

Improvement of Nozzle Life in Gas Turbines

1979 ◽  
Author(s):  
T. L. Flowers ◽  
A. W. Anderson ◽  
J. Brunso
Keyword(s):  
Fatigue Life ◽  
Gas Turbine ◽  
Thermal Fatigue ◽  
Gas Turbines ◽  
Development Program ◽  
Fatigue Cracking ◽  
Thermal Gradients ◽  
Thermal Fatigue Life ◽  
Industrial Gas Turbine

The time between major overhauls of an industrial gas turbine is often determined by the thermal fatigue life of the first stage turbine nozzle. The thermal fatigue cracking results from thermal strains induced by the temperature transients and the resulting thermal gradients within the nozzle assembly. This paper discusses a joint GE/ARAMCO development program undertaken in order to investigate the causes of these gradients and to develop means to reduce the magnitudes and the number of occurrences in a MS5002A industrial gas turbine.

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