Fatigue properties of narrow and wide gap braze repaired joints

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DOIResolve DOI: http://doi.org/10.1115/1.4002824
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Journal titleJournal of Engineering for Gas Turbines and Power
Article number92101
SubjectAccelerated creep tests; Additive materials; Braze alloys; Braze joints; Butt joints; Cobalt-based superalloy; Contributing factor; Fatigue failures; Fatigue life; Fatigue properties; Fatigue tests; Fracture surfaces; Fully reversed; Gas turbine industry; Intermetallic phasis; Isothermal fatigue; Load control; Narrow gap; Parent materials; Repaired joints; Scanning Electron Microscope; Service conditions; Sinusoidal wave; Stress amplitudes; Thermomechanical fatigue; Wide gap; Yield strength; Borides; Cobalt; Creep; Creep testing; Damage detection; Fatigue testing; Gas turbines; Materials; Mechanical properties; Repair; Scanning electron microscopy; Tensile strength; Tensile testing; Turbomachinery; Vacuum brazing; Fatigue of materials
AbstractWith 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. © 2011 American Society of Mechanical Engineers.
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AffiliationNational Research Council Canada (NRC-CNRC); Aerospace (AERO-AERO)
Peer reviewedYes
NPARC number21271146
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Record identifier8c37047a-5a76-45a4-9182-33f68f9526dc
Record created2014-03-24
Record modified2016-05-09
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