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Airfoils
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in Evaluation of Gas Turbine Hot Section Blade Cracking under Oxidation, TMF, and Creep Conditions
> ASM Failure Analysis Case Histories: Power Generating Equipment
Published: 01 June 2019
Fig. 3 Predicted temperature using oxide depth measurements at 60% airfoil height
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in Evaluation of Gas Turbine Hot Section Blade Cracking under Oxidation, TMF, and Creep Conditions
> ASM Failure Analysis Case Histories: Power Generating Equipment
Published: 01 June 2019
Fig. 4 Predicted temperature using oxide depth measurements at 90% airfoil height
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Published: 01 June 2019
Fig. 1 Airfoil segment from a cast Stellite 31 turbine vane that failed by thermal fatigue. (a) and (b) Thermal fatigue cracks emanating from a leading edge and progressing along grain boundaries. The microstructure shows evidence of age hardening by intragranular precipitation of carbide
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in Metallurgical Investigation of a Turbine Blade and a Vane Failure from Two Marine Engines
> ASM Failure Analysis Case Histories: Offshore, Shipbuilding, and Marine Equipment
Published: 01 June 2019
Fig. 13 Axial deformation, i.e., bowing, in the turbine airfoil section.
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in Metallurgical Investigation of a Turbine Blade and a Vane Failure from Two Marine Engines
> ASM Failure Analysis Case Histories: Offshore, Shipbuilding, and Marine Equipment
Published: 01 June 2019
Fig. 16 Coating features of the vane along the airfoil section. (a) Convex side showing intact coating and shrinkage porosity; (b) Coating-matrix interface along convex side; (c) Vane coating and coating-matrix interface along concave side.
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Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001366
EISBN: 978-1-62708-215-0
... Claseup view of vane, showing transverse crack in vicinity of trailing edge. 1.14× Abstract An AMS 4126 (7075-T6) aluminum alloy impeller from a radial inflow turbine fractured during commissioning. Initial examination showed that two adjacent vanes had fractured through airfoils in the vicinity...
Abstract
An AMS 4126 (7075-T6) aluminum alloy impeller from a radial inflow turbine fractured during commissioning. Initial examination showed that two adjacent vanes had fractured through airfoils in the vicinity of the vane leading edges, and one vane fractured through an airfoil near the hub in the vicinity of the vane trailing edge. Some remaining vanes exhibited radial and transverse cracks in similar locations. Binocular and scanning electron microscope examinations showed that the cracks had been caused by high-cycle fatigue and had progressed from multiple origins on the vane surface. Structural analysis indicated that the fatigue loading probably had been caused by forced excitation, resulting in the impeller vibrating at its resonant frequency. It was recommended that the impeller design, control systems, and material of construction be changed.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0046966
EISBN: 978-1-62708-229-7
... Abstract A turbine vane made of cast cobalt-base alloy AMS 5382 (Stellite 31; composition: Co-25.5Cr-10.5Ni-7.5W) was returned from service after an undetermined number of service hours because of crack indications on the airfoil sections. This alloy is cast by the precision investment method...
Abstract
A turbine vane made of cast cobalt-base alloy AMS 5382 (Stellite 31; composition: Co-25.5Cr-10.5Ni-7.5W) was returned from service after an undetermined number of service hours because of crack indications on the airfoil sections. This alloy is cast by the precision investment method. Analysis (visual inspection, 100x/500x metallographic examination of sections etched with a mixture of ferric chloride, hydrochloric acid, and methanol, and bend tests) supported the conclusions that cracking of the airfoil sections was caused by thermal fatigue and was contributed to by low ductility due to age hardening, subsurface oxidation related to intragranular carbides, and high residual tensile macrostresses. No further conclusions could be drawn because of the lack of detailed service history, and no recommendations were made.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0090114
EISBN: 978-1-62708-229-7
... holes' surface was not coated. Investigation supported the conclusions that the cracking at the cooling holes was due to grain-boundary oxidation and nitridation at the cooling hole surface, embrittlement and loss of local ductility of the base alloy, temperature gradient from the airfoil surface...
Abstract
The first-stage blades in a model 501D5 gas turbine had 16 cooling holes. After 32,000 h of service, the blades exhibited cracking at the cooling holes. The blade material was wrought Udimet 520 alloy, with nominal composition of 57Ni-19Cr-12Co-6Mo-1W-2Al-3Ti-0.05C-0.005B. The cooling holes' surface was not coated. Investigation supported the conclusions that the cracking at the cooling holes was due to grain-boundary oxidation and nitridation at the cooling hole surface, embrittlement and loss of local ductility of the base alloy, temperature gradient from the airfoil surface to the cooling holes, which led to relatively high thermal stresses at the holes located at the thicker sections of the airfoil, and stress concentration of 2.5 at the cooling hole and the presence of relatively high total strain (an inelastic strain of 1.2%) at the cooling hole surface. Recommendations include applying the specially designed methods given in this case study to estimate the metal temperature and stresses in order to predict the life of turbine blades under similar operating conditions.
Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001758
EISBN: 978-1-62708-241-9
...) and extensive damage (“corn-cobbed”) to the HP rotor (right). Damage on the right normally results in engine shutdown Fig. 6 Trailing edge yielding and aluminide coating wrinkling associated with stress-rupture cracking on turbine airfoils Fig. 7 Entirely interdendritic stress-rupture...
Abstract
This article describes the visual, fractographic, and metallographic evidence typically encountered when analyzing stress rupture of turbine airfoils. Stress-rupture fractures are generally heavily oxidized, tend to be rough in texture, and are primarily intergranular and/or interdendritic in appearance compared to smoother, transgranular fatigue type fractures. Often, gross plastic yielding is visible on a macroscopic scale. Commonly observed microstructural characteristics include creep voiding along grain boundaries and/or interdendritic regions. Internal voids can also nucleate at carbides and other microconstituents, especially in single crystal castings that do not possess grain boundaries.
Series: ASM Handbook
Volume: 11A
Publisher: ASM International
Published: 30 August 2021
DOI: 10.31399/asm.hb.v11A.a0006824
EISBN: 978-1-62708-329-4
.... In cases where material is released in the turbine flow path, such as a broken airfoil, downstream components typically suffer secondary damage, and so the first component to fail is typically at the upstream end of the damaged zone ( Fig. 1 ). Fig. 1 Failed gas turbine rotor. From left to right...
Abstract
This article focuses on common failures of the components associated with the flow path of industrial gas turbines. Examples of steam turbine blade failures are also discussed, because these components share some similarities with gas turbine blading. Some of the analytical methods used in the laboratory portion of the failure investigation are mentioned in the failure examples. The topics covered are creep, localized overheating, thermal-mechanical fatigue, high-cycle fatigue, fretting wear, erosive wear, high-temperature oxidation, hot corrosion, liquid metal embrittlement, and manufacturing and repair deficiencies.
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in Metallurgical Investigation of a Turbine Blade and a Vane Failure from Two Marine Engines
> ASM Failure Analysis Case Histories: Offshore, Shipbuilding, and Marine Equipment
Published: 01 June 2019
Fig. 2 Cracked first steps MAR-M302 Turbine engine vane in the as-received condition. (a) Concave airfoil surface; (b) Convex airfoil surface. Metallographic sampling location indicated by arrow M.
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in Evaluation of Gas Turbine Hot Section Blade Cracking under Oxidation, TMF, and Creep Conditions
> ASM Failure Analysis Case Histories: Power Generating Equipment
Published: 01 June 2019
Fig. 1 Schematic of first-stage gas turbine blade that experienced cracking after 32,000 h in service. (a) Sectioning planes at three locations on the blade airfoil. (b) Cross-sectional view of the blade airfoil showing the cooling holes and numbering sequence
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Series: ASM Failure Analysis Case Histories
Volume: 1
Publisher: ASM International
Published: 01 December 1992
DOI: 10.31399/asm.fach.v01.c9001024
EISBN: 978-1-62708-214-3
... failure of a blade integrity monitor (BIM) system was also considered. The rotor blade comprised a long, hollow 6061-T651 aluminum alloy extrusion and 26 fiberglass “pockets” that provided the trailing-edge airfoil shape. Visual examination of the fracture surface of the aluminum extrusion indicated...
Abstract
A Marine Corps helicopter crash was investigated. Efforts were directed to the failure of one of the main rotor blades that had apparently separated in the air. The apparent failure of a blade integrity monitor (BIM) system was also considered. The rotor blade comprised a long, hollow 6061-T651 aluminum alloy extrusion and 26 fiberglass “pockets” that provided the trailing-edge airfoil shape. Visual examination of the fracture surface of the aluminum extrusion indicated fatigue crack growth followed by ductile overload separation. Examination of the fatigue fracture region revealed several pits that appeared to have acted as fracture origin sites. Time to failure was determined using fracture mechanics. It was concluded that failure was caused by a fatigue crack that grew to critical length without detection. The crack originated at pits that resulted from the use of an improperly designed heating element used to cure fiberglass repairs.
Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c0091761
EISBN: 978-1-62708-229-7
... to 6400 h of operation. Investigation (visual inspection, metallographic examination, and stress analysis) supported the conclusion that the differing microstructure of the airfoil resulted in changes in mechanical properties. Because normal operation includes cycling of loads and temperatures, the shroud...
Abstract
Turbine buckets in a 37.5-MW gas turbine made of Udimet 500 superalloy failed in service. The power plant was located 1 km (0.6 miles) from the Pacific Ocean and operated on No. 2 diesel fuel, which was supplied by tanker ship. Turbine bucket failures occurred on three units after 2500 to 6400 h of operation. Investigation (visual inspection, metallographic examination, and stress analysis) supported the conclusion that the differing microstructure of the airfoil resulted in changes in mechanical properties. Because normal operation includes cycling of loads and temperatures, the shroud tip fractured due to thermomechanical fatigue in its degraded state. Recommendations included special chromium or silicon-rich coating to minimize corrosion in gas turbines operating in a marine environment with operating temperatures in the range of type 2 corrosion (650 to 750 deg C, or 1200 to 1380 deg F). Additionally, it was suggested that fuel delivery, handling, and treatment be high quality, to maintain fuel contamination within design limits, and inlet air filtration must be designed for the coastal site. Also, changing the bucket tip by increasing its thickness and changing the casting technique would reduce the stress and make the design more tolerant of corrosion.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.aero.c0047720
EISBN: 978-1-62708-217-4
... Abstract Airfoil-shape impingement cooling tubes were fabricated of 0.25 mm (0.010 in.) thick Hastelloy X sheet stock, then pulse-laser-beam butt welded to cast Hastelloy X base plugs. Each weldment was then inserted through the base of a hollow cast turbine blade for a jet engine...
Abstract
Airfoil-shape impingement cooling tubes were fabricated of 0.25 mm (0.010 in.) thick Hastelloy X sheet stock, then pulse-laser-beam butt welded to cast Hastelloy X base plugs. Each weldment was then inserted through the base of a hollow cast turbine blade for a jet engine. The weldments were finally secured to the bases of the turbine blades by a brazing operation. One of the laser beam attachment welds broke after a 28-h engine test run. Exposure of the fracture surface for study under the electron microscope revealed the joint had broken in stress rupture. Failure was caused by tensile overload from stress concentration at the root of the laser beam weld, which was caused by the sharp notch created by the lack of full weld penetration. Radiographic inspection of all cooling-tube weldments was made mandatory, with rejection stipulated for joints containing subsurface weld-root notches. In addition, all turbine blades containing cooling-tube weldments were reprocessed by back-brazing. Back brazed turbine blades were reinstalled in the engine and withstood the full 150-h model test run without incident.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.marine.c9001657
EISBN: 978-1-62708-227-3
... a turbine blade disintegration and another one concerning a vane failure. Examination of the second stage turbine rotor blades of the first engine (no. 1), revealed that the majority of the blade tips were ripped off. One exception to this was a blade with most of its airfoil section removed...
Abstract
The circumstances surrounding the in-service failure of a cast Ni-base superalloy (Alloy 713LC) second stage turbine blade and a cast and coated Co-base superalloy (MAR-M302) first stage air-cooled vane in two turbine engines used for marine application are described. An overview of a systematic approach, analyzing the nature of degeneration and failure of the failed components, utilizing conventional metallurgical techniques, is presented. The topographical features of the turbine blade fracture surface revealed a fatigue-induced crack growth pattern, where crack initiation had taken place in the blade trailing edge. An estimate of the crack-growth rate for the stage II fatigue fracture region coupled with the metallographic results helped to identify the final mode of the turbine blade failure. A detailed metallographic and fractographic examination of the air-cooled vane revealed that coating erosion in conjunction with severe hot-corrosion was responsible for crack initiation in the leading edge area.
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.power.c9001602
EISBN: 978-1-62708-229-7
... transported by tanker ship. Turbine bucket failures occurred in three different units of the power plant after 2500 to 6400 h of operation. The buckets suffered tip shroud fracture, illustrated in Fig. 1 . Details of the fracture zone from the concave side of the airfoil are shown in Fig. 2 . Fig. 1...
Abstract
This article presents a failure analysis of 37.5 mW gas turbine third stage buckets made of Udimet 500 superalloy. The buckets experienced repetitive integral tip shroud fractures assisted by a low temperature (type II) hot corrosion. A detailed analysis was carried out on elements thought to have influenced the failure process: a) the stress increase from the loss of a load bearing cross-sectional area of the bucket tip shroud by the conversion of metal to the corrosion product (scale), b) influence of the tip shroud microstructure (e.g., a presence of equiaxed and columnar grains, their distribution and orientation), c) evidence of the transgranular initiation, and d) intergranular creep mechanism propagation. The most probable cause of the bucket damage was the combination of increased stresses due to corrosion-induced thinning of the tip shroud and unfavorable microstructures in the tip shroud region.
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in Stress-Rupture Characterization in Nickel-Based Superalloy Gas Turbine Engine Components
> Handbook of Case Histories in Failure Analysis
Published: 01 December 2019
Fig. 6 Trailing edge yielding and aluminide coating wrinkling associated with stress-rupture cracking on turbine airfoils
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Book Chapter
Series: ASM Failure Analysis Case Histories
Publisher: ASM International
Published: 01 June 2019
DOI: 10.31399/asm.fach.marine.c0046969
EISBN: 978-1-62708-227-3
... was considered to be premature. Investigation The airfoils of the uncoated blades exhibited splitting along the leading edges and swelling on the surfaces, indicating severe hot corrosion ( Fig. 1a ). Metallographic examination of an uncoated blade confirmed hot-corrosion damage by revealing...
Abstract
Aluminide-coated and uncoated IN-713 turbine blades were returned for evaluation after service in a marine environment because of severe corrosion. Based on service time, failure of these blades by corrosive deterioration was considered to be premature. Analysis (visual inspection, 2.7x micrographic examination on sections etched with ferric chloride and hydrochloric acid in methanol) supported the conclusions that the blades failed by hot-corrosion attack. Variation in rate of attack on coated blades was attributed to variation in integrity of the aluminide coating, which had been applied in 1966, when these coatings were relatively new. It is evident that maintaining the integrity of a protective coating could significantly increase the life of a nickel-base alloy blade operating in a hot and corrosive environment.
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in Metallurgical Investigation of a Turbine Blade and a Vane Failure from Two Marine Engines
> ASM Failure Analysis Case Histories: Offshore, Shipbuilding, and Marine Equipment
Published: 01 June 2019
Fig. 10 (Left) Hardness profile of another turbine blade from the same row in the same engine varying as a function of sampling location along the blade airfoil.
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