| 1. |
- Draxler, Joar, et al.
(författare)
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A numerical model for simulating the effect of strain rate on eutectic band thickness
- 2020
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Ingår i: Welding in the World. - : Springer. - 0043-2288 .- 1878-6669. ; 64:10, s. 1635-1658
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Tidskriftsartikel (refereegranskat)abstract
- Large tensile strains acting on the solidifying weld metal can cause the formation of eutectic bands along grain boundaries. These eutectic bands can lead to severe liquation in the partially melted zone of a subsequent overlapping weld. This can increase the risk of heat-affected zone liquation cracking. In this paper, we present a solidification model for modeling eutectic bands. The model is based on solute convection in grain boundary liquid films induced by tensile strains. The proposed model was used to study the influence of strain rate on the thickness of eutectic bands in Alloy 718. It was found that when the magnitude of the strain rate is 10 times larger than that of the solidification rate, the calculated eutectic band thickness is about 200 to 500% larger (depending on the solidification rate) as compared to when the strain rate is zero. In the paper, we also discuss how eutectic bands may form from hot cracks.
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| 2. |
- Singh, Sukhdeep, 1988, et al.
(författare)
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Heat-Affected-Zone Liquation Cracking in Welded Cast Haynes® 282®
- 2020
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:1
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Tidskriftsartikel (refereegranskat)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 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.
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| 3. |
- Singh, Sukhdeep, 1988, et al.
(författare)
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Influence of Hot Isostatic Pressing on the Hot Ductility of Cast Alloy 718 : The Effect of Niobium and Minor Elements on the Liquation Mechanism
- 2020
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 51:12, s. 6248-6257
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Tidskriftsartikel (refereegranskat)abstract
- The influence of two hot isostatic pressing (HIP) treatments on liquation behavior was investigated and compared with regard to the extent of heat-affected zone liquation cracking in cast Alloy 718. The extent of liquation was seen to increase after HIP treatment at 1190 °C due to solute changes caused by the homogenization of Nb, which contributed to extensive grain boundary melting. The HIP treatment at 1120 °C exhibited lower liquation with contributions from particle liquation of the Laves phase and constitutional liquation of NbC carbides. This was also reflected in a lower ductility recovery temperature, with slower recovery for the former due to the extensive liquation. Interestingly, the nil ductility temperatures were both below the predicted equilibrium solidus of the alloy, which suggests that the ductility drop is related to liquation caused by solute segregation at the grain boundaries. © 2020, The Author(s).
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| 4. |
- Singh, Sukhdeep, 1988
(författare)
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Weldability of Cast Superalloys - Effect of homogenization heat treatments on hot cracking susceptibility of cast Alloy 718, ATI® 718Plus®, and Haynes® 282®
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Precipitation hardened Ni- and Ni–Fe-based superalloys are used in high-temperature sections of aero engines owing to their superior mechanical properties compared to those of the other alloys. However, their better mechanical performance is accompanied by its own challenges during the manufacturing process. For the fabrication of hot structural components, instead of the traditional single piece castings, welding is widely employed by joining wrought parts in sections, where high strength is required, and cast parts, where complex geometrical shapes are needed. This can be challenging, as superalloys are known for their lack of amenability to welding. A weld-cracking phenomenon known as “hot cracking”is of concern during their welding. Especially, the cast materials are known to be more prone to cracking owing to the higher extent of segregating phases that remain from the casting process.The present study investigates the weldability of Alloy 718 and two recently developed Ni-based superalloys ATI® 718Plus® and Haynes® 282® with respect to heat affected zone liquation (HAZ) cracking susceptibility. Pre-weld homogenization treatments were performed at 1120 °C and 1190 °C to study the effect of different microstructures on cracking extent. The testing approach consisted of using Varestraint weldability test to assess the HAZ liquation cracking susceptibility and Gleeble thermomechanical simulator for evaluation of hot ductility behaviour. The results revealed that a lower heat treatment temperature at 1120 °C for 4 h was beneficial in minimizing the influence of liquation, and that the grain growth also contributed to lowering the cracking susceptibility in the HAZ. JMatPro simulations and microstructural evaluation on elements such as Nb as solute and precipitate former in Alloy 718 and ATI® 718Plus®, and Mo in Haynes® 282® were found to be important in the liquation mechanism. Secondary ion mass spectroscopy (SIMS) analysis revealed B, which is a strong melting point depressant, to segregate along the grain boundaries in all the three alloys. In addition, in this thesis, different liquation mechanisms were discussed and an explanation for the overall HAZ liquation cracking mechanism for cast superalloys was proposed.
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