| 1. |
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| 2. |
- Adegoke, Olutayo, 1979-, et al.
(author)
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Influence of laser powder bed fusion process parameters on the microstructure and cracking susceptibility of nickel-based superalloy Alloy 247LC
- 2022
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In: Results in Materials. - : Elsevier. - 2590-048X. ; 13
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Journal article (peer-reviewed)abstract
- Microstructures of material conditions of nickel-based superalloy Alloy 247LC fabricated using laser powder bed fusion (L-PBF) were investigated. Experiments designed in a prior study revealed the L-PBF process parameters for which the material conditions displayed a reduced susceptibility to cracking. Certain process parameters produced material conditions with an increased susceptibility to cracking. In this study, the material conditions were investigated in detail to reveal their microstructure and to determine the cause of cracking. The reason for the transition between a reduced to an increased susceptibility to cracking was examined. The results revealed solidification cracking occurred at high-angle grain boundaries. Solidification cracking may have been promoted at high-angle grain boundaries because of the undercooling contribution of the grain boundary energy. Furthermore, Si segregation was observed in the cracks. Thus, the presence of Si most likely promoted solidification cracking. It was observed that a high crack density, which occurred in the high energy density material condition, was associated with a large average grain size. The fact that certain combination of process parameters produced microstructures with a low susceptibility to cracking, indicates that reliable Alloy 247LC material may be printed using L-PBF by employing improved process parameters. © 2022
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| 3. |
- Adegoke, Olutayo, 1979-, et al.
(author)
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Influence of laser powder bed fusion process parameters on the microstructure of solution heat-treated nickel-based superalloy Alloy 247LC
- 2022
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In: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 183
-
Journal article (peer-reviewed)abstract
- In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
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| 4. |
- Adegoke, Olutayo, et al.
(author)
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Influence of laser powder bed fusion process parameters on voids, cracks, and microhardness of nickel-based superalloy alloy 247LC
- 2020
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In: Materials. - 1996-1944. ; 13:17
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Journal article (peer-reviewed)abstract
- The manufacturing of parts from nickel-based superalloy Alloy 247LC by laser powder bed fusion (L-PBF) is challenging, primarily owing to the alloy’s susceptibility to cracks. Apart from the cracks, voids created during the L-PBF process should also be minimized to produce dense parts. In this study, samples of Alloy 247LC were manufactured by L-PBF, several of which could be produced with voids and crack density close to zero. A statistical design of experiments was used to evaluate the influence of the process parameters, namely laser power, scanning speed, and hatch distance (inherent to the volumetric energy density) on void formation, crack density, and microhardness of the samples. The window of process parameters, in which minimum voids and/or cracks were present, was predicted. It was shown that the void content increased steeply at a volumetric energy density threshold below 81 J/mm3. The crack density, on the other hand, increased steeply at a volumetric energy density threshold above 163 J/mm3. The microhardness displayed a relatively low value in three samples which displayed the lowest volumetric energy density and highest void content. It was also observed that two samples, which displayed the highest volumetric energy density and crack density, demonstrated a relatively high microhardness; which could be a vital evidence in future investigations to determine the fundamental mechanism of cracking. The laser power was concluded to be the strongest and statistically most significant process parameter that influenced void formation and microhardness. The interaction of laser power and hatch distance was the strongest and most significant factor that influenced the crack density. © 2020 by the authors.
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| 5. |
- Adegoke, Olutayo, et al.
(author)
-
Laser beam powder bed fusion and post processing of alloy 247LC
- 2019
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In: MS and T 2019 - Materials Science and Technology. - : Materials Science and Technology. - 9780873397704 ; , s. 27-34
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Conference paper (peer-reviewed)abstract
- Alloy 247LC is sensitive to cracking during laser beam powder bed fusion (PBF-LB) manufacturing. Post processing is thus required to close cracks and achieve desired properties. In this study, samples of Alloy 247LC were manufactured by PBF-LB and subsequently post processed by hot isostatic pressing (HIP), HIP + solution and ageing heat treatments. The microstructure was characterized. Results showed cracks in the as-built condition. Cracks were not detected after HIP. Bright microconstituents were observed in the region between the cells, mainly, because of the partitioning of Hf and Ta into the intercellular region, where they presumably form carbides. What is assumed to be oxides were prominent in the microstructure. Thermodynamic calculations showed rapid formation of ?’ precipitates in the alloy, due to the high total concentration of Al and Ta and this was linked to the high hardness values in the as-built condition. © 2019 MS&T19®
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| 6. |
- Adegoke, Olutayo
(author)
-
Processability of Laser Powder Bed Fusion of Alloy 247LC : Influence of process parameters on microstructure and defects
- 2020
-
Licentiate thesis (other academic/artistic)abstract
- This thesis is about laser powder bed fusion (L-PBF) of the nickel-based superalloy: Alloy 247LC. Alloy 247LC is used mainly in gas turbine blades and processing the blades with L-PBF confers performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBF is more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential in order to eventually solve the problem of cracking which is a major problem when manufacturing the alloy. In addition, dense parts with low void content should be manufactured and the parts should meet the required performance. Thus, the thesis answered some of the important questions related to process parameter-microstructure-defect relationships.The thesis presented an introduction in chapter 1. A literature review was made in chapter 2 to 4. In chapter 2, the topic of additive manufacturing was introduced followed by an overview of laser powder bed fusion. Chapter 3 focused on superalloys. Here, a review was made from the broader perspective of superalloys but was eventually narrowed down to the characteristics of nickelbased superalloys and finally Alloy 247LC. Chapter 4 reviewed the main research on L-PBF of Alloy 247LC. The methodology applied in the thesis was discussed in chapter 5. The thesis applied statistical design of experiments to show the influence of process parameters on the defects and microstructure, so a detail description of the method was warranted. This was given at the beginning of chapter 5 and followed by the description of the L-PBF manufacturing and the characterization methods. The main results and discussions, in chapter 6, included a preliminary investigation on how the process parameters influenced the amount of discontinuity in single track samples. This was followed by the results and discussions on the investigation of voids, cracks and microhardness in cube samples (detail presentation was given in the attached paper B). Finally, the thesis presented results of the microstructure obtainable in L-PBF manufactured Alloy 247LC. The initial results of the microstructure investigation were presented in paper A.
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| 7. |
- Adegoke, Olutayo, 1979-
(author)
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Processability of Laser Powder Bed Fusion of Alloy 247LC-Influence of process parameters on microstructure and defects
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- This thesis is about laser powder bed fusion (L-PBF) of the nickel-basedsuperalloy Alloy 247LC. Alloy 247LC is mainly used in gas turbine blades and processing the blades with L-PBF may confer performance advantage over the blades manufactured with conventional methods. This is mainly because L-PBFis more suitable, than conventional methods, for manufacturing the complex cooling holes in the blades. The research was motivated by the need for academia and industry to gain knowledge about the processability of the alloy using L-PBF. The knowledge is essential to eventually solve the problem of cracking encountered when processing the alloy. In addition, dense parts with low void content should be processed and the microstructure and properties should meett he required performance. Heat-treatment is usually performed to acquire final properties, so it is also of interest to study this aspect. Thus, the thesis answered some of the important questions related to process parameter-microstructure- property relationships.
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| 8. |
- Adegoke, Olutayo, et al.
(author)
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Review of laser powder bed fusion of gamma-prime-strengthened nickel-based superalloys
- 2020
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In: Metals. - : MDPI AG. - 2075-4701. ; 10:8
-
Journal article (peer-reviewed)abstract
- This paper reviews state of the art laser powder bed fusion (L-PBF) manufacturing of γ′ nickel-based superalloys. L-PBF resembles welding; therefore, weld-cracking mechanisms, such as solidification, liquation, strain age, and ductility-dip cracking, may occur during L-PBF manufacturing. Spherical pores and lack-of-fusion voids are other defects that may occur in γ′-strengthened nickel-based superalloys manufactured with L-PBF. There is a correlation between defect formation and the process parameters used in the L-PBF process. Prerequisites for solidification cracking include nonequilibrium solidification due to segregating elements, the presence of liquid film between cells, a wide critical temperature range, and the presence of thermal or residual stress. These prerequisites are present in L-PBF processes. The phases found in L-PBF-manufactured γ′-strengthened superalloys closely resemble those of the equivalent cast materials, where γ, γ′, and γ/γ′ eutectic and carbides are typically present in the microstructure. Additionally, the sizes of the γ′ particles are small in as-built L-PBF materials because of the high cooling rate. Furthermore, the creep performance of L-PBF-manufactured materials is inferior to that of cast material because of the presence of defects and the small grain size in the L-PBF materials; however, some vertically built L-PBF materials have demonstrated creep properties that are close to those of cast materials.© 2020 by the authors. Licensee MDPI, Basel, Switzerland.
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| 9. |
- Adegoke, Olutayo, et al.
(author)
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Scanning electron microscopy and atom probe tomography characterization of laser powder bed fusion precipitation strengthening nickel-based superalloy
- 2023
-
In: Micron. - 0968-4328 .- 1878-4291. ; 171
-
Journal article (peer-reviewed)abstract
- Atom probe tomography (APT) was utilized to supplement scanning electron microscopy (SEM) characterizationof a precipitation strengthening nickel-based superalloy, Alloy 247LC, processed by laser powder bed fusion (LPBF). It was observed that the material in the as-built condition had a relatively high strength. Using both SEMand APT, it was concluded that the high strength was not attributed to the typical precipitation strengtheningeffect of γ’. In the absence of γ’ it could be reasonably inferred that the numerous black dots observed in thecells/grains with SEM were dislocations and as such should be contributing significantly to the strengthening.Thus, the current investigation demonstrated that relatively high strengthening can be attained in L-PBF even inthe absence of precipitated γ’. Even though γ’ was not precipitated, the APT analysis displayed a nanometer scalepartitioning of Cr that could be contributing to the strengthening. After heat-treatment, γ’ was precipitated and itdemonstrated the expected high strengthening behavior. Al, Ta and Ti partitioned to γ’. The strong partitioningof Ta in γ’ is indicative that the element, together with Al and Ti, was contributing to the strain-age crackingoccurring during heat-treatment. Cr, Mo and Co partitioned to the matrix γ phase. Hf, Ta, Ti and W were found inthe carbides corroborating previous reports that they are MC.
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| 10. |
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| 11. |
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| 12. |
- Andersson, Joel, 1981-, et al.
(author)
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Effect of Different Solution Heat Treatments on the Hot Ductility of Superalloys : Part 3 - Waspaloy
- 2013
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In: Materials Science and Technology. - 0267-0836 .- 1743-2847. ; 29:1, s. 43-53
-
Journal article (peer-reviewed)abstract
- The susceptibility to heat affected zone cracking of Waspaloy has been investigated in terms of its hot ductility, measured as the reduction of area (RA). Gleeble testing with on-heating as well as on-cooling test cycles was carried out to illuminate the influence of different 4 h solution heat treatments between 996 and 1080°C. A ductility maximum of between 80 and 90%RA was found at 1050–1100°C for all conditions in the on-heating tests. Although the different heat treatment conditions showed similar macrohardness, the particle size and distribution of the γ′ and M23C6 phases differed, which significantly affected the on-heating ductility in the lower temperature test region. The ductile to brittle transition was initiated at 1100°C in the on-heating testing with indications of grain boundary liquation at the higher test temperatures. Ductility recovery, as measured in the on-cooling tests from 1240°C, was very limited with <30%RA for all conditions and test temperatures except for the 1080°C/4 h treatment, which exhibited 60%RA at 980°C.
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| 13. |
- Andersson, Joel, 1981-, et al.
(author)
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Effect of solution heat treatments on superalloys : Part 1 – alloy 718
- 2012
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In: Materials Science and Technology. - : Taylor & Francis Group. - 0267-0836 .- 1743-2847. ; 28:5, s. 609-619
-
Journal article (peer-reviewed)abstract
- The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954°C/15 h, 954°C/1 h, 982°C/1 h and 1050°C/3 h+954°C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by δ phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of δ phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.
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| 14. |
- Andersson, Joel, 1981-
(author)
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Fabrication and Weldability Aspects of Ni- and Ni–Fe Based Superalloys : A Review
- 2023
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In: Proceedings of the 10th International Symposium on Superalloy 718 and Derivatives. - : Springer Cham. - 9783031274473 - 9783031274497 ; , s. 659-696
-
Conference paper (peer-reviewed)abstract
- Superalloys are commonly used in structural components of aero-engines. Superalloys in general, Ni- and Ni–Fe-based superalloys, belong to an important group of materials used in aerospace applications. Fabrication and associated weldability aspects of structural components for the hot section of aero-engine gas turbines continue to be of high importance to the manufacturing industry within this discipline. Cracking and specifically hot cracking as well as strain age cracking is a serious concern during the welding and additive manufacturing (AM) of these structural components. The cracking phenomena can occur during welding, AM or subsequent heat treatment of precipitation-hardening superalloys. The cracking behaviour can be influenced by several factors, i.e., chemical composition in terms of hardening elements and impurities, the microstructure of base material, and weld zone, together with corresponding welding, AM and post-treatment process parameters. This paper provides a review of Ni- and Ni–Fe-based superalloys concerning fabrication and weldability aspects within the context of structural components of aero-engines. Also, the paper offers insight and analyses to research publication data of welding and AM of superalloys in the context of annual publication developed over the years as well as specific contributions from countries, affiliations, and specific researchers.
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| 15. |
- Andersson, Joel Håkan, 1981, et al.
(author)
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Effect of different solution heat treatments on hot ductility of superalloys Part 2-Allvac 718Plus
- 2012
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In: Materials Science and Technology. - : Taylor & Francis Group. - 1743-2847 .- 0267-0836. ; 28:6, s. 733-741
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Journal article (peer-reviewed)abstract
- The hot ductility of Allvac 718Plus for different solution heat treatments (954 degrees C-15 h, 954 degrees C-1 h, 982 degrees C-1 h and 1050 degrees C-3 h+954 degrees C-1 h) has been investigated using Gleeble testing. Substantial variations in the microstructure among the heat treatments affected the Gleeble test hot ductility only to a very limited extent. Constitutional liquation of the NbC phase was found to be the main cause for the poor ductility at high testing temperatures in the on-heating cycle as well as at the lower temperatures on-cooling. Grain boundary delta phase was seen to assist the constitutional liquation of the NbC phase. Based on established evaluation criteria for Gleeble ductility testing, a ranked indicator for weldability is suggested.
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| 16. |
- Andersson, Joel Håkan, 1981, et al.
(author)
-
Effect of solution heat treatments on superalloys Part 1 - alloy 718
- 2012
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In: Materials Science and Technology. - : Informa UK Limited. - 1743-2847 .- 0267-0836. ; 28:5, s. 609-619
-
Journal article (peer-reviewed)abstract
- The hot ductility as measured by Gleeble testing of Alloy 718 at four different solution heat treatments (954 degrees C/15 h, 954 degrees C/1 h, 982 degrees C/1 h and 1050 degrees C/3 h+954 degrees C/1 h) has been investigated. It is concluded that constitutional liquation of NbC assisted by delta phase takes place and deteriorates the ductility. Parameters established by analysing the ductility dependence on temperature indicate a reduced weldability of the material in the coarse grain size state (ASTM 3) while indicating an increased weldability when containing a large amount of delta phase due to a grain boundary pinning effect. The accumulation of trace elements during grain growth at the highest temperature is believed to be the cause for the observed reduced on-cooling ductility.
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| 17. |
- Andersson, Joel Håkan, 1981, et al.
(author)
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Hip-densification of alloy 718 and ati 718Plus®
- 2014
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In: 8th International Symposium on Superalloy 718 and Derivatives 2014; Pittsburgh; United States; 28 September 2014 through 1 October 2014. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781634396424 ; , s. 425-435
-
Conference paper (peer-reviewed)abstract
- Cast Alloy 718 and ATI 718Plus® have been investigated to disclose their ability to develop Hot Isostatic Pressing (HIP) porosity which may form as a consequence of the casting process. Artificial defects were manufactured in cast Alloy 718 and ATI 718Plus® block and sealed by electron beam welding prior to the HIP treatment which was carried out at three different temperatures, namely; 1120 °C, 1165 °C, and 1190 °C at a pressure of 100 MPa. It was seen that there are no significant difference in the ability to heal pores in between cast Alloy 718 and ATI 718Plus®. No major difference in between the three different temperatures were disclosed whereas the size of the pore seem to have the biggest impact on the ability to heal, which was supported by careful SEM characterization and by simplified calculations considering two different sizes of pores.
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| 18. |
- Andersson, Joel Håkan, 1981
(author)
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Hot Cracking and Grain Boundary Weaknesses of Nickel - Based Superalloys
- 2008
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Licentiate thesis (other academic/artistic)abstract
- Abstract Grain boundary weaknesses of nickel-based superalloys not only materialize during service in the hot turbine engine sections but also during the weld manufacturing. The performance, in this respect, of the most commonly used alloys at Volvo Aero Corporation (VAC), 718 and the higher temperature capacity Waspaloy, are therefore the main subjects for this thesis. The emerging Allvac 718® PLUSTM (718 Plus) is also included due to the prospect of replacing the expensive Waspaloy. The overall emphasis is on weldability through Varestraint testing but limited work was initially carried out on notch rupture sensitivity of 718 Plus.The notch rupture testing of 718Plus emphasized the importance of the secondary phases like delta-phase in the grain boundaries.Hot cracks were observed in all alloys with re-solidified products on the liquated and re-solidified grain boundaries. Grain boundary liquation and segregation of alloying elements was considered to be the primary reason for liquation of HAZ grain boundaries which caused cracking.Evidence of constitutional liquation of Nb rich MC type carbides in alloy 718 and 718 Plus were found in the region adjacent to the fusion zone and also on the cracked grain boundaries. The resolidified products along the hot cracks consisted of γ + MC type carbide and γ + Laves eutectics.
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| 19. |
- Andersson, Joel Håkan, 1981, et al.
(author)
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Investigation of Homogenization and its Influence on the Repair Welding of Cast Allvac 718Plus
- 2010
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In: Proceedings of The 7th International Symposium on Superalloy 718 and Derivatives, TMS (The Minerals, Metals and Materials Society). - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781617827709 ; 1, s. 439-454, s. 439-454
-
Conference paper (peer-reviewed)abstract
- Heat treatment experiments have been carried out to bring understanding to the efficacy of different temperatures and dwell times on the degree of homogenization of the cast Allvac 718Plus alloy which is prone to segregation mainly due to its high content of niobium. The effect of homogenization on weld repair was also examined. The homogenization heat treatment temperatures ranged from 1050°C to 1200°C with 1hr, 5 hrs and 10 hrs dwell times. The degree of homogenization was measured as the reduction of the amount of Laves phase by manual point counting in an optical microscope at high magnification. Longer range, interdendritic, patterns were established through line scan EDS analysis in SEM. It was found that short time (1hr) does not significantly reduce the amount of Laves phase whereas 5 hrs and 10hrs are much more efficient. Interdendritic homogenization does not occur to any measurable extent even at the highest temperature and longest dwell time (1200°C-10hrs) which was also reflected in bulk macro Vickers hardness tests.In the weld repair tests, one of the most homogenized material conditions (1125°C-5hrs +1200°C-10hrs) turned out to be the most prone to cracking while the number of weld cracks after a moderate homogenization heat treatment (1125°C-5hrs) was much smaller .
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| 20. |
- Andersson, Joel Håkan, 1981, et al.
(author)
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Repair welding of wrought superalloys: Alloy 718, Allvac 718Plus and Waspaloy
- 2012
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In: Science and Technology of Welding and Joining. - 1743-2936 .- 1362-1718. ; 17:1, s. 49-59
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Journal article (peer-reviewed)abstract
- The ability to weld repair three precipitation hardening superalloys, Alloy 718, Allvac 718Plus and Waspaloy, with GasTungsten Arc Welding is compared in this study. Four different solution heat treatment conditions for each material were examined; Alloy 718 and Allvac 718Plus heat treated at 954 °C-1 h, 982 °C-1 h, 954 °C-15 h and 1020 °C-1 h and Waspaloy for 4 h at 996 °C, 1010 °C, 1040 °C and at 1080 . By metallography, the total number of cracks was evaluated both in the HAZ and in the FZ which made it possible to consistently rate the repair weldability of these three materials. Alloy 718 was significantly the best one with Allvac 718Plus slightly better than Waspaloy. As expected, the solution heat treatment conditions only affected the HAZ cracking behavior.
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| 21. |
- Andersson, Joel Håkan, 1981
(author)
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Solidification Cracking of Alloy Allvac 718Plus and Alloy 718 at Transvarestraint Testing
- 2008
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In: EPD Congress 2008, TMS, ed. S. M. Howard, 2008.. ; , s. 157-169
-
Conference paper (other academic/artistic)abstract
- Allvac 718Plus is a newly developed superalloy with a good potential for use in fabricatedaircraft engine structures when service temperatures exceed 650°C; the limit for standard alloy718. Fabrication involves welding, where cracking usually is a prohibitive factor. Comparison ofthe solidification cracking behavior between these two alloys was made by Transvarestrainttesting. It was shown that the total amount of cracking was significantly lower for 718Plus alloy,which was associated with a lower amount of γ/Laves or γ/NbC eutectic-type constituents. Thisin turn is believed to be due to the lower iron content of the Allvac 718Plus material. Theanalysis of alloying element segregation both within primary dendrite and interdendriticconstituents clearly indicates that the segregation of Nb is the controlling factor in determiningthe final solidification microstructure in these alloys. The Nb concentrations of these constituentsare significantly higher compared to the bulk alloy concentration. This was confirmed by theSEM-EDS analysis and calculations assessed with JMatPro, the latter also indicated that alloy718 is more prone to form Laves and NbC eutectic-type constituents compared to Allvac 718Plusmaterial.
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| 22. |
- Andersson, Joel Håkan, 1981, et al.
(author)
-
Solidification of alloy 718, ati 718Plus® and waspaloy
- 2014
-
In: 8th International Symposium on Superalloy 718 and Derivatives 2014. - Hoboken, NJ, USA : John Wiley & Sons, Inc.. - 9781634396424 ; , s. 181-192
-
Conference paper (peer-reviewed)abstract
- Alloy 718, ATI 718Plus® and Waspaloy have been investigated in terms of what their respective solidification process reveals. Differential thermal analysis was used to approach the task together with secondary electron and back scattered electron detectors equipped with an energy dispersive X-ray spectroscopy detector. These experimental methods were used to construct pseudo binary phase diagrams that could aid in explaining solidification as well as liquation mechanisms in processes such as welding and casting. Furthermore, it was seen that Waspaloy has the smallest solidification range, followed by Alloy 718, and finally ATI 718Plus® possessing the largest solidification interval in comparison.
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| 23. |
- Andersson, Joel Håkan, 1981
(author)
-
Weldability of Ni-based superalloys
- 2014
-
In: 8th International Symposium on Superalloy 718 and Derivatives 2014; Pittsburgh; United States; 28 September 2014 through 1 October 2014. - : John Wiley & Sons, Inc.. - 9781634396424 ; , s. 249-262
-
Conference paper (peer-reviewed)abstract
- This paper reviews the inherent weldability of precipitation hardening Ni-based superalloys commonly used in structural components of aircraft engines. Weldability often refers to alloys resistant to cracking during welding which for superalloys is difficult to comprehend since specific liquation and cracking mechanism may differ in this class of materials. A new procedure of evaluating the weldability as well as susceptibility towards strain age cracking of these alloys is proposed in which standard metallographic examinations are used to understand the cracking mechanisms in parallel with systematic ductility measurements such as Varestraint or Gleeble testing.
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| 24. |
- Andersson, Joel Håkan, 1981
(author)
-
Weldability of Precipitation Hardening Superalloys – Influence of Microstructure
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Superalloys and in particular the precipitation hardened Ni-based superalloys havealways been used extensively in the hot sections of jet engines. Large hot structuralengine components with complex geometry have preferably been cast as single piececomponents since the large scale vacuum investment casting process becameavailable about fifty years ago. However, a recent trend is to cast smaller pieces whichcan be joined with sheet or forged parts to fabricate structural components. Therationale for this fabrication strategy is the possibility to save weight by the use of higherstrength wrought material, where geometry allows, and join these wrought parts withcast material where complex geometry is needed and where the demand for strength ismoderate. One of the major challenges using this strategy is the obvious fact thatnumerous welds must be made which requires the fundamental understanding, notleast metallurgical, of how different materials may be joined by specific weldingprocesses.The main objective of this research has, for this reason, been to examine and interpretthe weldability of precipitation hardened superalloys from a metallurgical standpoint.Two newly developed superalloys Allvac® 718PlusTM and Haynes® 282® are comparedwith the two well established Alloy 718 and Waspaloy. The understanding of theinfluence of secondary phases such as carbides and δ phase in the microstructure wasaddressed by systematic hot ductility testing (Gleeble) and by weldability testing(Varestraint). The effect of secondary phases were also analysed through practicalwelding as by electron beam welding (EBW), and by gas tungsten arc welding (GTAW).The research showed that all the techniques used (Varestraint testing, Gleeble testing,DSC thermal analysis and welding (GTAW repair and EBW)) in studying the weldabilityindependently provided important knowledge and most importantly that a combination ofthe results from these different techniques were necessary for the understanding of theweldability of these four alloys. From a microstructural point of view it has been possibleto show that δ phase contrary to what has generally been assumed improves theweldability due to its ability to inhibit grain growth and to assist in the healing of cracks.For future research, a new modified weldability testing method was developed where itis possible to perform Varestraint, Transvarestraint and spot-varestraint testing at ramspeeds from 15 to 300 mm/s using GTAW, plasma arc welding and laser welding.
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| 25. |
- Andersson, Joel, 1981-, et al.
(author)
-
HIP-Densification of Alloy 718 and ATI 718Plus
- 2014
-
In: 8th International Symposium on Superalloy 718 and Derivatives. - Hoboken, NJ, USA : John Wiley & Sons. - 9781119016809 - 9781119016854 ; , s. 425-436
-
Conference paper (peer-reviewed)
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