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superalloys
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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
... at carbides and other microconstituents, especially in single crystal castings that do not possess grain boundaries. gas turbine engine components creep deformation overheating nickel-base superalloy interdendritic stress-rupture fracture stress-rupture testing stress-rupture life Cast nickel...
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 Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001829
EISBN: 978-1-62708-241-9
... Abstract An investigation was conducted to better understand the time-dependent degradation of thermal barrier coated superalloy components in gas turbines. First-stage vanes are normally subjected to the highest gas velocities and temperatures during operation, and were thus the focus...
Abstract
An investigation was conducted to better understand the time-dependent degradation of thermal barrier coated superalloy components in gas turbines. First-stage vanes are normally subjected to the highest gas velocities and temperatures during operation, and were thus the focus of the study. The samples that were analyzed had been operating at 1350 °C in a gas turbine at a combined-cycle generating plant. They were regenerated once, then used for different lengths of time. The investigation included chemical analysis, scanning electron microscopy, SEM/energy dispersive spectroscopy, and x-ray diffraction. It was shown that degradation is driven by chemical and mechanical differences, oxide growth, depletion, and recrystallization, the combined effect of which results in exfoliation, spallation, and mechanical thinning.
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
... 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...
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.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001311
EISBN: 978-1-62708-215-0
... Abstract Several nickel-base superalloy (UNS N06600) welded heat-exchanger tubes used in processing black liquor in a kraft paper mill failed prematurely. Leaking occurred through the tube walls at levels near the bottom tube sheet. The tubes had been installed as replacements for type 304...
Abstract
Several nickel-base superalloy (UNS N06600) welded heat-exchanger tubes used in processing black liquor in a kraft paper mill failed prematurely. Leaking occurred through the tube walls at levels near the bottom tube sheet. The tubes had been installed as replacements for type 304 stainless steel tubes. Visual and stereoscopic examination revealed three types of corrosion on the inside surfaces of the tubes: uniform attack, deeper localized corrosive attack, and accelerated uniform attack. Metallographic analysis indicated that pronounced dissimilar-metal corrosion had occurred in the base metal immediately adjacent to the weld seam. The corrosion was attributed to exposure to nitric acid cleaning solution and was accelerated by galvanic differences between the tubes and a stainless steel tube sheet and between the base metal of the tubes and their dendritic weld seams. A change to type 304 stainless steel tubing made without dendritic weld seams was recommended.
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Published: 01 January 2002
Fig. 7 Electron images of a superalloy shaft fracture. (a) Backscattered electron image. (b) Secondary electron image. Bright areas are lead contamination.
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Published: 15 January 2021
Fig. 22 (a) Incipient melting in A286 superalloy. (b) Incipient melting showing widened grain boundaries in A286 superalloy. Marble’s etch. (c) Aluminum 6061 heated close to the melting point. Keller’s etch
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Published: 15 January 2021
Fig. 24 (a) Etched Waspaloy superalloy. (b) Ti-6Al-4V with alpha case. 2% HF etch
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Published: 15 January 2021
Fig. 7 Electron images of a superalloy shaft fracture. (a) Backscattered electron image. (b) Secondary electron image. Bright areas are lead contamination.
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Published: 15 January 2021
Fig. 11 Fracture surfaces of a nickel-base superalloy turbine blade. (a) Secondary electron image of interdendritic stress-rupture fracture at the trailing edge (TE) of single-crystal turbine blade casting showing creep voids on the fracture surface. (b) Scanning electron microscopy
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in Thermomechanical Fatigue—Mechanisms and Practical Life Analysis
> Failure Analysis and Prevention
Published: 15 January 2021
Fig. 4 Cross section of a nickel-base superalloy after thermomechanical fatigue testing. Image shows surface oxidation at bottom and oxide spike forming in the center of the specimen. Chemical etchant used highlights aluminum in the microstructure. Microstructure shown as white in image
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in Thermomechanical Fatigue—Mechanisms and Practical Life Analysis
> Failure Analysis and Prevention
Published: 15 January 2021
Fig. 5 Single-crystal nickel-base superalloy specimens tested at a mechanical strain of 1.3%, a minimum temperature of 550 °C (1020 °F), a maximum temperature of 1050 °C (1920 °F), and 300 s cycles but having different thermomechanical fatigue (TMF) waveforms. (a) Out-of-phase TMF exhibiting
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Image
Published: 30 August 2021
Fig. 2 Deformation mechanism map for the cast nickel-base superalloy MAR-M200 with a grain size of 100 μm. Source: Ref 3
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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
... 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...
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
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001827
EISBN: 978-1-62708-241-9
... of high-temperature oxidation on the hot corrosion process. Preventative measures are also discussed. gas turbine thermal fatigue cracking hot corrosion superalloys corrosion cavities spark optical emission spectrometry operating temperature GTD 111 (cast nickel-base superalloy) FSX 414...
Abstract
Gas turbines and other types of combustion turbomachinery are susceptible to hot corrosion at elevated temperatures. Two such cases resulting in the failure of a gas turbine component were investigated to learn more about the hot corrosion process and the underlying failure mechanisms. Each component was analyzed using optical and scanning electron microscopy, energy dispersive spectroscopy, mechanical testing, and nondestructive techniques. The results of the investigation provide insights on the influence of temperature, composition, and microstructure and the contributing effects of high-temperature oxidation on the hot corrosion process. Preventative measures are also discussed.
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
... 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...
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 Handbook Archive
Volume: 11
Publisher: ASM International
Published: 01 January 2002
DOI: 10.31399/asm.hb.v11.a0003517
EISBN: 978-1-62708-180-1
.... The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural...
Abstract
This article focuses on the life assessment methods for elevated-temperature failure mechanisms and metallurgical instabilities that reduce life or cause loss of function or operating time of high-temperature components, namely, gas turbine blade, and power plant piping and tubing. The article discusses metallurgical instabilities of steel-based alloys and nickel-base superalloys. It provides information on several life assessment methods, namely, the life fraction rule, parameter-based assessments, the thermal-mechanical fatigue, coating evaluations, hardness testing, microstructural evaluations, the creep cavitation damage assessment, the oxide-scale-based life prediction, and high-temperature crack growth methods.
Series: ASM Failure Analysis Case Histories
Volume: 2
Publisher: ASM International
Published: 01 December 1993
DOI: 10.31399/asm.fach.v02.c9001357
EISBN: 978-1-62708-215-0
... Abstract Two 20 MW turbines suffered damage to second-stage blades prematurely. The alloy was determined to be a precipitation-hardening nickel-base superalloy comparable to Udimet 500, Udimet 710, or Rene 77. Typical protective coatings were not found. Test results further showed that the fuel...
Abstract
Two 20 MW turbines suffered damage to second-stage blades prematurely. The alloy was determined to be a precipitation-hardening nickel-base superalloy comparable to Udimet 500, Udimet 710, or Rene 77. Typical protective coatings were not found. Test results further showed that the fuel used was not adequate to guarantee the operating life of the blades due to excess sulfur trioxide, carbon, and sodium in the combustion gases, which caused pitting. A molten salt environmental cracking mechanism was also a factor and was enhanced by the working stresses and by the presence of silicon, vanadium, lead, and zinc. A change of fuel was recommended.
Image
Published: 15 January 2021
Fig. 10 (a) Creep damage in a tube. (b) Creep void in carbon steel showing oxide and decarburization. Nital etch. (c) Beginning creep in Manaurite superalloy. Marble’s etch. (d) Advanced creep in same Manaurite superalloy shown in (c). Marble’s etch. (e) Scanning electron microscope image
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Image
in Thermomechanical Fatigue—Mechanisms and Practical Life Analysis
> Failure Analysis and Prevention
Published: 15 January 2021
Fig. 6 (a) Cross section near the fracture surface of a single-crystal nickel-base superalloy tested in thermomechanical fatigue (TMF) conditions. Note the oxide spike emanating from the fracture surface and the oxidized slip planes. The oxide spike occurs along an active slip plane
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Series: ASM Failure Analysis Case Histories
Volume: 3
Publisher: ASM International
Published: 01 December 2019
DOI: 10.31399/asm.fach.v03.c9001840
EISBN: 978-1-62708-241-9
.... bimetal plate shear failure impact energy nickel-base superalloy carbon steel plastic deformation shear testing adhesion strength Inconel 625 (nickel-base superalloy) UNS N06625 ASTM A517 (low carbon steel) Introduction Despite the fact that Inconel 625 as a nickel-based superalloy...
Abstract
Explosive cladding is a viable method for cladding different materials together, but the complicated behavior of materials under ballistic impacts raises the probability of interfacial shear failure. To better understand the relationship between impact energy and interfacial shear, investigators conducted an extensive study on the shear strength of explosively cladded Inconel 625 and plain carbon steel samples. They found that by increasing impact energy, the adhesion strength of the resulting cladding can be improved. Beyond a certain point, however, additional impact energy reduces shear strength significantly, causing the cladding process to fail. The findings reveal the decisive role of plastic strain localization and the associated development of microcracks in cladding failures. An attempt is thus made to determine the optimum cladding parameters for the materials of interest.
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