Special Issue "Welding Metallurgy and Weldability of Superalloys"

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Metal Casting, Forming and Heat Treatment".

Deadline for manuscript submissions: closed (31 July 2019).

Special Issue Editor

Prof. Dr. Joel Andersson
Website
Guest Editor
Department of Engineering Science, University West, Trollhättan, Sweden
Interests: additive manufacturing; welding and weldability testing; materials engineering and materials physics
Special Issues and Collections in MDPI journals

Special Issue Information

Dear Colleagues,

Fabrication and welding of structural superalloy components for aero-engines, land-based gas turbines, as well as for the energy sector (i.e., steam boilers) continues to be of high importance to the manufacturing industry. The components, which utilize superalloys, are usually referred to as the most demanding and where welding of these most often plays an essential role, not only in manufacturing, but also in repair and re-manufacturing. It is therefore of utmost importance that the welds used in the design are of suitable quality to account for the demanding environment. Numerous challenges exist to welding these alloys and caution needs to be exercised in order to avoid problems such as hot cracking or strain age cracking. In addition, there is a wide range of weldability testing methods available to predict, for example, susceptibility towards hot cracking, where each method has its unique characteristics. Nevertheless, the available weldability testing methods play a vital role in the fundamental study of the root cause for, for example, weld cracking, which can be further enhanced by characterization as well as simulation. This Special Issue intends to offer a dedicated platform for sharing new findings, communicating views about the accomplishments and future directions in superalloy welding and weldability testing research. We welcome reviews and original research articles in the areas of welding metallurgy, weldability, and associated topics of superalloys, achieved through either experimental techniques or theoretical calculations.

Assoc. Prof. Joel Andersson
Guest Editor

Manuscript Submission Information

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Keywords

  • welding metallurgy
  • weldability
  • varestraint
  • gleeble
  • hot cracking
  • strain age cracking
  • HAZ liquation cracking
  • solidification cracking
  • superalloys

Published Papers (7 papers)

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Editorial

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Open AccessEditorial
Welding Metallurgy and Weldability of Superalloys
Metals 2020, 10(1), 143; https://doi.org/10.3390/met10010143 - 17 Jan 2020
Abstract
Fabrication and welding of structural superalloy components for aero-engines, land-based gas turbines as well as for the energy sector (i [...] Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)

Research

Jump to: Editorial

Open AccessArticle
Heat-Affected-Zone Liquation Cracking in Welded Cast Haynes® 282®
Metals 2020, 10(1), 29; https://doi.org/10.3390/met10010029 - 23 Dec 2019
Cited by 3
Abstract
Varestraint weldability testing and Gleeble thermomechanical simulation of the newly developed cast form of Haynes® 282® were performed to understand how heat-affected-zone (HAZ) liquation cracking is influenced by different preweld heat treatments. In contrast to common understanding, cracking susceptibility did not [...] Read more.
Varestraint weldability testing and Gleeble thermomechanical simulation of the newly developed cast form of Haynes® 282® were performed to understand how heat-affected-zone (HAZ) liquation cracking is influenced by different preweld heat treatments. In contrast to common understanding, cracking susceptibility did not improve with a higher degree of homogenization achieved at a higher heat-treatment temperature. Heat treatments with a 4 h dwell time at 1120 °C and 1160 °C exhibited low cracking sensitivity, whereas by increasing the temperature to 1190 °C, the cracking was exacerbated. Nanosecond ion mass spectrometry analysis was done to characterize B segregation at grain boundaries that the 1190 °C heat treatment indicated to be liberated from the dissolution of C–B rich precipitates. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessArticle
Investigation of the Effect of Short Exposure in the Temperature Range of 750–950 °C on the Ductility of Haynes® 282® by Advanced Microstructural Characterization
Metals 2019, 9(12), 1357; https://doi.org/10.3390/met9121357 - 17 Dec 2019
Cited by 3
Abstract
A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes® 282® during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 °C has been used to investigate the [...] Read more.
A Gleeble-based test method has been developed to study the change in the ductility signature of Haynes® 282® during isothermal exposure from 5 s to 1800 s. A temperature range of 750 to 950 °C has been used to investigate the effect of age-hardening reactions. Microstructural constituents have been analyzed and quantified using scanning and transmission electron microscopy. Carbides present in the material are identified as primary MC-type TiC carbides, Mo-rich M6C secondary carbides, and Cr-rich M23C6 secondary carbides. Gamma prime (γ′) precipitates are present in all the material conditions with particle sizes ranging from 2.5 nm to 58 nm. Isothermal exposure causes the growth of γ′ and development of a grain boundary carbide network. A ductility minimum is observed at 800–850 °C. The fracture mode is found to be dependent on the stroke rate, where a transition toward intergranular fracture is observed for stroke rates below 0.055 mm/s. Intergranular fracture is characterized by microvoids present on grain facets, while ductility did not change during ongoing age-hardening reactions for intergranularly fractured Haynes® 282®. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessArticle
Varestraint Testing of Selective Laser Additive Manufactured Alloy 718—Influence of Grain Orientation
Metals 2019, 9(10), 1113; https://doi.org/10.3390/met9101113 - 18 Oct 2019
Cited by 3
Abstract
The effect of grain orientation on hot cracking susceptibility of selective laser additive manufactured Alloy 718 was investigated by Varestraint testing. Electron backscattered diffraction showed that cracks in heat affected zone (HAZ) of the welded samples occurred in high angle grain boundaries. The [...] Read more.
The effect of grain orientation on hot cracking susceptibility of selective laser additive manufactured Alloy 718 was investigated by Varestraint testing. Electron backscattered diffraction showed that cracks in heat affected zone (HAZ) of the welded samples occurred in high angle grain boundaries. The extent of HAZ cracking was smaller in samples tested parallel to the elongated grain orientation and larger in samples transverse to the elongated grain orientation. However, for solidification cracking in the weld metal, no significant difference with respect to grain orientation in the base metal was found. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessArticle
Comparison of Hot Cracking Susceptibility of TIG and Laser Beam Welded Alloy 718 by Varestraint Testing
Metals 2019, 9(9), 985; https://doi.org/10.3390/met9090985 - 05 Sep 2019
Cited by 6
Abstract
Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 [...] Read more.
Reduced hot cracking susceptibility is essential to ensure the flawless manufacturing of nickel superalloys typically employed in welded aircraft engine structures. The hot cracking of precipitation strengthened alloy 718 mainly depends on chemical composition and microstructure resulting from the thermal story. Alloy 718 is usually welded in a solution annealed state. However, even with this thermal treatment, cracks can be induced during standard industrial manufacturing conditions, leading to costly and time-consuming reworking. In this work, the cracking susceptibility of wrought and investment casting alloy 718 is studied by the Varestraint test. The test is performed while applying different welding conditions, i.e., continuous tungsten inert gas (TIG), low frequency pulsed TIG, continuous laser beam welding (LBW) and pulsed LBW. Welding parameters are selected for each welding technology in order to meet the welding quality criteria requested for targeted aeronautical applications, that is, full penetration, minimum cross-sectional welding width and reduced overhang and underfill. Results show that the hot cracking susceptibility of LBW samples determined by the Varestraint test is enhanced due to extended center line hot cracking, resulting in a fish-bone like cracking pattern. On the contrary, the minor effect of material source (wrought or casting), grain size and pulsation is observed. In fact, casting samples with a 30 times coarser grain size have shown better performance than wrought material. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessArticle
Influence of Heat Treatments on Heat Affected Zone Cracking of Gas Tungsten Arc Welded Additive Manufactured Alloy 718
Metals 2019, 9(8), 881; https://doi.org/10.3390/met9080881 - 10 Aug 2019
Cited by 7
Abstract
The weldability of additive manufactured Alloy 718 was investigated in various heat-treated conditions. The microstructure of the base metal was examined in detail in order to understand the effect of different pre-weld heat treatments; i.e., solution, solution and aging, and hot isostatic pressing. [...] Read more.
The weldability of additive manufactured Alloy 718 was investigated in various heat-treated conditions. The microstructure of the base metal was examined in detail in order to understand the effect of different pre-weld heat treatments; i.e., solution, solution and aging, and hot isostatic pressing. After welding, the variation in total crack lengths, maximum crack length and the total number of cracks in the heat affected zone (HAZ) were used as criteria for the cracking susceptibility of each material condition where wrought Alloy 718 was used as the reference material. Selective laser melting (SLM) manufactured Alloy 718 was susceptible to HAZ cracking in all material conditions. Total crack lengths in HAZ were highest in the SLM as-built condition and lowest in the SLM hot isostatic pressed condition. The cracks that were found in the HAZ of the welded materials consisted of liquation cracks, with eutectic product surrounding the cracks, as well as cracks from which liquation products were absent. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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Open AccessArticle
The Comparison of Cracking Susceptibility of IN52M and IN52MSS Overlay Welds
Metals 2019, 9(6), 651; https://doi.org/10.3390/met9060651 - 04 Jun 2019
Cited by 1
Abstract
Overlay-welding of IN52M and IN52MSS onto CF8A stainless steel (SS) was conducted by a gas tungsten arc welding process in multiple passes. An electron probe micro-analyzer (EPMA) was applied to determine the distributions and chemical compositions of the grain boundary microconstituents, and the [...] Read more.
Overlay-welding of IN52M and IN52MSS onto CF8A stainless steel (SS) was conducted by a gas tungsten arc welding process in multiple passes. An electron probe micro-analyzer (EPMA) was applied to determine the distributions and chemical compositions of the grain boundary microconstituents, and the structures were identified by electron backscatter diffraction (EBSD). The hot cracking of the overlay welds was related to the microconstituents at the interdendritic boundaries. The formation of γ-intermetallic (Ni3(Nb,Mo)) eutectics was responsible predominantly for the hot cracking of the 52M and 52MSS overlays. The greater Nb and Mo contents in the 52MSS overlay enhanced the formation of coarser microconstituents in greater amounts at the interdendritic boundaries. Thus, the hot cracking sensitivity of the 52MSS overlay was higher than that of the 52M overlay. Moreover, migrated grain boundaries were observed in the 52M and 52MSS overlays but did not induce ductility dip cracking (DDC) in this study. Full article
(This article belongs to the Special Issue Welding Metallurgy and Weldability of Superalloys)
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