Fatigue Properties of Narrow and Wide Gap Braze Repaired Joints

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Thomas Henhoeffer ◽  
Xiao Huang ◽  
Scott Yandt ◽  
Peter Au
Keyword(s):  
Gas Turbine ◽  
Braze Alloy ◽  
Butt Joint ◽  
Parent Material ◽  
Fatigue Properties ◽  
Wave Form ◽  
Narrow Gap ◽  
Creep Tests ◽  
Wide Gap ◽  
Fatigue Failures

With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material, this is largely based on the results of tensile or accelerated creep tests for most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed that the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. An analysis of the fracture surfaces using a scanning electron microscope revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases.

Fatigue Properties of Narrow and Wide Gap Braze Repaired Joints

2010 ◽  
Author(s):  
Thomas Henhoeffer ◽  
Xiao Huang ◽  
Scott Yandt ◽  
Peter Au
Keyword(s):  
Gas Turbine ◽  
Braze Alloy ◽  
Butt Joint ◽  
Parent Material ◽  
Fatigue Properties ◽  
Wave Form ◽  
Narrow Gap ◽  
Creep Tests ◽  
Wide Gap ◽  
Fatigue Failures

With the increasing utilization of braze repair in the gas turbine industry, the properties of braze joints under simulated service conditions become vital in selecting braze repair over other processes. While braze repair has often been claimed to deliver mechanical properties equivalent to that of the parent material; this is largely based on the results of tensile or accelerated creep tests. For most gas turbine hot section components failure occurs as a result of thermal fatigue or thermomechanical fatigue. The damage that occurs under such conditions cannot be assessed from tensile or creep testing. This study was undertaken to characterize the fatigue properties of narrow and wide gap brazed X-40 cobalt-based superalloy and compare these properties to that of the X-40 parent material. Butt joint narrow gap and wide gap specimens were vacuum brazed using BNi-9 braze alloy. X-40 and IN-738 were used as additive materials in wide gap braze joints. To characterize the fatigue properties of the braze joints and parent material, isothermal fatigue tests were conducted at 950°C and under load control using a fully reversed sinusoidal wave form having stress amplitude of 75% of the yield strength of the parent material. The braze specimens were fatigue tested in the as-brazed condition. The fatigue test results showed the fatigue lives of the brazed specimens were lower than that of the parent material, particularly for the narrow gap samples and wide gap samples containing IN-738 additive alloy. All fatigue failures in the brazed samples occurred in the braze joints. Analysis of the fracture surfaces using SEM revealed that porosity was the major contributing factor to fatigue failures in the wide gap braze joints. The testing life debit observed in the narrow gap braze samples can be attributed to the presence of brittle boride phases in the braze joint. This study also included examination of techniques for reducing the aforementioned porosity and presence of brittle intermetallic phases.

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.

Microstructure and Oxidation Behavior of Narrow Gap Brazing and Wide Gap Brazing Joints With Boron/Silicon-Free Nickel Base Braze Alloys

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Xiao Huang
Keyword(s):  
Base Alloy ◽  
Braze Alloy ◽  
Applied Pressure ◽  
Sample Surface ◽  
Narrow Gap ◽  
Scale Spallation ◽  
Scanning Calorimetry ◽  
Oxidation Test ◽  
Heating And Cooling ◽  
Wide Gap

Abstract In this study, the microstructure and solidus and liquidus of several Ni-Co-Hf-Zr-Ti-Al braze alloys were first examined with the objective to develop a B- and Si-free low-melting braze alloy for narrow gap (NGB) and wide gap brazing (WGB) and turbine component repair applications. Among various alloys examined, differential scanning calorimetry (DSC) was used to measure the solidus and liquidus during heating and cooling cycles. Following the measurements of liquidus and solidus, the microstructure was evaluated using SEM. Equations for calculating solidus and liquidus based on alloy's compositions were established, and the functions of each elements on these two characteristic temperatures were discussed. One selected alloy with a liquidus of 1201 °C was further employed for NGB and WGB experiments. The results showed that it was able join Cannon Muskegon single crystal (CMSX)-4 at 1240 °C without interfacial voids, and with the use of externally applied pressure and extended homogenization treatment, the interfacial intermetallic compounds were substantially removed. Furthermore, the same braze alloy was used to fill a large artificial cavity in a WGB scheme at a reduced temperature of 1200 °C. The braze alloy was able to fully bond the filler powder alloy in addition to join the two alloys to an IN 738 substrate. Finally, oxidation test was conducted at 1050 °C (isothermal in static air) for 100 h after NGB of CMSX-4 and WGB of IN 738. The results showed that the oxide formed on the standalone braze alloy is very dense and there is no sign of spallation. It contained primarily NiO (+CoO) with no other elements measured. For the NGB joints, large amount of scale spallation was observed on base alloy CMSX-4 while the NGB joint remained spallation free. The oxide formed on the NGB was NiO with partitions of Co, Al, Ti, Cr, and W. The WGB joint region in IN 738 showed oxide scale spallation on the IN 738 substrate side, leaving behind steps and depression on the sample surface. In the WGB joint itself, there were three notable phases after oxidation test; however, no scale spallation could be found. For the majority part of the surface, a Ni-rich oxide covered the surface. There were areas of smaller oxide particles with higher Cr content. Overall, the new boron/silicon-free braze alloy was found to be able to join several superalloys in both WGB and NGB schemes without occurrence of defects and the oxidation resistance was superior to both substrate alloys examined in this study.

A Study of the Diffusion Brazing Process Applied to the Single Crystal Superalloy CMSX-4

2006 ◽  
Author(s):  
A. Schnell ◽  
A. Stankowski ◽  
E. de Marcos
Keyword(s):  
Single Crystal ◽  
Gas Turbine ◽  
Braze Alloy ◽  
Transient Liquid Phase ◽  
Surface Preparation ◽  
Parent Material ◽  
Main Concern ◽  
Test Procedures ◽  
Mechanical Integrity ◽  
Diffusion Brazing

The requirement for economic reconditioning of the latest ALSTOM gas turbine generation with Single Crystal (SX) superalloys has lead to the development of advanced repair processes such as Diffusion Brazing or Transient Liquid Phase bonding. Diffusion Brazing (DB) of conventionally cast polycrystalline turbine components has been carried out for many years but the requirement for this joining and repair technique to be applied to DS and SX superalloys has emerged only more recently. The main concern for the use of a braze-repair process for the more highly loaded SX components is the ability to guarantee sufficient thermal and mechanical integrity throughout the component lifetime. Such high strength braze joints in SX superalloys can be achieved by combining a brittle phase-free and high γ′ content microstructure, while maintaining the crystallographical orientation of the SX parent material within the repair zone. Prior to the brazing process, a suitable crack surface preparation is essential, and this is achieved by the employment of specifically optimized Fluoride Ion Cleaning (FIC) process. This guarantees the complete removal of oxide from the crack surfaces and promotes the flow of the braze alloy for complete filling down to the crack tip. This paper presents the development of the DB process which has been specifically tailored for the repair of SX superalloys. The principles of the diffusion brazing process as applied to the CMSX-4 superalloy are discussed and the parameters which control the brazing kinetics are outlined. The optimization of the brazing heat treatment cycle will be presented. This paper also demonstrates the retention of the single crystal micro-structure in the repair zone, and demonstrates the test procedures developed to achieve the required thermal and mechanical integrity of braze repairs for application in SX gas turbine components.

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.

Fatigue Testing Method of Test Coupon and Structurally Equivalent Samples of Carbon Fiber Reinforced Polymer for Gas Turbine Engine Parts and Assemblies

2018 ◽  
Vol 284 ◽  
pp. 43-47
Author(s):  
M.S. Nikhamkin ◽  
N.A. Sazhenkov ◽  
D. Samodurov
Keyword(s):  
Carbon Fiber ◽  
Gas Turbine ◽  
Polymer Composite ◽  
Fiber Reinforced Polymer ◽  
Carbon Fiber Reinforced Polymer ◽  
Fatigue Properties ◽  
Fiber Reinforced ◽  
Test Coupon ◽  
Reinforced Polymer ◽  
Carbon Fiber Reinforced

The carbon fiber reinforced polymer composite are widely used in industry as major structural materials. They represent the greatest interest for the production of gas turbine engines parts because of their high specific strength. But before adaptation these materials into the structure, it is necessary to conduct a number of tests, both on test coupon and on structurally equivalent samples for determining physical, in particular, fatigue properties of these materials. However, the high cost of manufacturing coupons for such tests has a negative impact on the adaptation of carbon fiber reinforced polymer composite into the composition of final products. In this paper it is presented a method for fatigue tests of test coupon and structurally equivalent samples of carbon fiber reinforced polymer, aimed at reducing the consumption of coupons which are necessary for obtaining fatigue properties. Based on the developed method, a series of carbon fiber coupons was tested and the fatigue limit was obtained. At the same time, the use of coupons was minimized.

Instability of the flow between rotating cylinders: the wide-gap problem

1964 ◽  
Vol 20 (1) ◽  
pp. 35-46 ◽  
Author(s):  
E. M. Sparrow ◽  
W. D. Munro ◽  
V. K. Jonsson
Keyword(s):  
Viscous Fluid ◽  
Closed Form ◽  
Solution Method ◽  
Analytical Investigation ◽  
Radius Ratio ◽  
Narrow Gap ◽  
Rotating Cylinders ◽  
Coaxial Cylinders ◽  
Wave Numbers ◽  
Wide Gap

An analytical investigation is carried out to determine the conditions for instability in a viscous fluid contained between rotating coaxial cylinders of arbitrary radius ratio. A solution method is outlined and then applied to cylinders having radius ratios ranging from 0·95 to 0·1. Consideration is given to both cases wherein the cylinders are rotating in the same direction and in opposite directions. Results are reported for the Taylor numbers and wave-numbers which mark the onset of instability. The present results are also employed to delineate the range of applicability of the closed-form instability predictions of Taylor and of Meksyn, which were derived for narrow-gap conditions.

Life-Refurbishment of Service-Degraded Gas Turbine Buckets

2004 ◽  
Author(s):  
Yomei Yoshioka ◽  
Daizo Saito ◽  
Kazutoshi Ishibashi ◽  
Junji Ishii ◽  
Atsuhiko Izumi ◽  
...  
Keyword(s):  
Gas Turbine ◽  
Low Cycle Fatigue ◽  
Hot Isostatic Pressing ◽  
Development Program ◽  
Charpy Impact ◽  
Turbine Rotor ◽  
Fatigue Properties ◽  
Maintenance Cost ◽  
Life Consumption ◽  
Non Destructive

Various methods have been developed, and used in practice, to reduce the maintenance cost of gas turbine hot parts by extending the replacement life. The life-refurbishment process by Hot Isostatic Pressing (HIP) is one of our accomplishments for the buckets retired due to the scheduled life and was confirmed to rejuvenate the microstructures and the tensile, Charpy impact, creep and low cycle fatigue properties to a condition equivalent to or even better than the new ones under the development program. According to above mentioned accomplishments, a number of HIP refurbished buckets were reinstalled in a Chubu Electric Power Co. Inc. (CEPCO) 1100°C-class gas turbine rotor on December 1999 and operated successfully for 2 years under the joint program. Those buckets also served for destructive and non-destructive evaluations after operation. From those tests, we reconfirmed the reliability of the HIP refurbished buckets and also validated that the life-consumption rate was the same as new ones.

Cross-Weld Creep Comparison of Power Plant Steels CrMoV, P91 and P92

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
David W. J. Tanner ◽  
Wei Sun ◽  
Thomas H. Hyde
Keyword(s):  
Heat Affected Zone ◽  
Failure Time ◽  
Parent Material ◽  
Strength Reduction ◽  
Weld Strength ◽  
Creep Tests ◽  
Type Iv ◽  
Different Temperatures ◽  
Using Data ◽  
Reduction Factors

Results obtained from high temperature creep tests of ferritic steel CrMoV, P91 and P92 cross-weld specimens are compared. Data are presented normalized with the results of the corresponding parent metals in order to compare the materials tested at different temperatures and stresses, and to identify characteristic cross-weld material trends. All cross-weld failures occurred in the heat-affected zone (HAZ) adjacent to the parent metal, known as type IV, at earlier test durations than for the parent material specimens. The relative performance of the cross-welds was found to decrease with decreasing stress. The CrMoV cross-weld specimens showed by far the lowest weld strength reduction factors and greatest notch strengthening, determined by testing uniaxially loaded bars with semicircular circumferential notches located in the heat-affected zone. The P91 and P92 cross-weld specimens were found to have similar (high) weld strength reduction factors and showed little or no notch strengthening. The failure time of a P92 cross-weld specimen relative to the P92 parent material could be estimated using data from P91 cross-weld and relative parent material tests.

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