| 1. |
- Andersson, Joel Håkan, 1981, et al.
(författare)
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Repair welding of wrought superalloys: Alloy 718, Allvac 718Plus and Waspaloy
- 2012
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Ingår i: Science and Technology of Welding and Joining. - 1743-2936 .- 1362-1718. ; 17:1, s. 49-59
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Tidskriftsartikel (refereegranskat)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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| 2. |
- Andersson, Joel, 1981-, et al.
(författare)
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Repair welding of wrought superalloys : Alloy 718, Allvac 718Plus and Waspaloy
- 2012
-
Ingår i: Science and Technology of Welding and Joining. - : Taylor & Francis Group. - 1362-1718 .- 1743-2936. ; 17:1, s. 49-59
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Tidskriftsartikel (refereegranskat)abstract
- The ability to weld repair three precipitation hardening superalloys, i.e. Alloy 718, Allvac 718Plus and Waspaloy, with gas tungsten 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 954uC–1 h, 982uC–1 h, 954uC–15 h and 1020uC–1 h and Waspaloy for 4 h at 996uC, 1010uC, 1040uC and at 1080uC. By metallography, the total number of cracks was evaluated in both the heat affected zone and the fusion zone, 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 heat affected zone cracking behaviour.
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| 3. |
- De Backer, Jeroen, 1987-, et al.
(författare)
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Thermoelectric method for temperature measurement in friction stir welding
- 2013
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 18:7, s. 541-550
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Tidskriftsartikel (refereegranskat)abstract
- Previous research within friction stir welding (FSW) has demonstrated that online control of welding parameters can improve the mechanical properties and is necessary for certain applications to guarantee a consistent weld quality. One approach to control the process is by adapting the heat input to maintain a stable welding temperature, within the specified operating boundaries. This requires accurate in-process temperature measurements. This paper presents a novel method to measure the temperature at the interface of the FSW tool and workpiece. The method is based on the thermoelectric effect between dissimilar materials. The measurements are compared to thermocouple measurements and to a physical model and show good correspondence to each other. Experiments demonstrate that the method can quickly detect temperature variations, due to geometrical variations of the workpiece or due to parameter changes. This allows use of the method for online control of robotic FSW.
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| 4. |
- Eriksson, Ingemar, et al.
(författare)
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Measurements of fluid flow on keyhole front during laser welding
- 2011
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 16:7, s. 636-641
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of a high speed video survey of melt flow on the front face of a keyhole created during fibre laser welding. Using fast Fourier transform techniques, quantitative values of fluid flow velocities down the keyhole front have been established. The results have led to a phenomenological understanding of some of the quality problems which arise at excess welding speeds. The downward flow velocity on the keyhole front is found to be generally independent of welding speed, and proportional to laser power
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| 5. |
- Karlsson, Leif, 1952-, et al.
(författare)
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Orientation relationships of intragranular austenite in duplex stainless steel weld metals
- 2014
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:4, s. 318-323
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Tidskriftsartikel (refereegranskat)abstract
- Formation and characteristics of fine intragranular austenite were studied for low energy input duplex stainless steel welds. Microstructures were largely ferritic with some allotriomorphic grain boundary austenite, Widmanstätten type austenite, fine intragranular austenite and nitrides. Electron backscattered diffraction analysis revealed that grain boundary austenite had a random orientation relationship (OR) with one of the adjacent ferrite grains and was close to Kurdjumov-Sachs (KS) with the other, whereas Widmanstätten austenite always showed an OR near KS. The finest intragranular austenite was mainly randomly oriented, whereas coarser austenite more often was close to KS. It is argued that the OR of intragranular austenite with the ferritic matrix is governed by a combination of composition, determining driving force for nucleation at temperature, cooling rate and the availability of nitrides acting as nucleation sites. A random OR is most likely for higher cooling rates and compositions promoting nucleation at lower temperatures. © 2014 Institute of Materials, Minerals and Mining.
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| 6. |
- Li, Peigang, 1978-, et al.
(författare)
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Influence of oxides on cold lap formation in tandem GMAW
- 2012
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 17:8, s. 643-648
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Tidskriftsartikel (refereegranskat)abstract
- The connection between the formation of cold laps and the presence of Mn‐Si oxides was studied. The underlying purpose is to understand the fundamental mechanisms of cold lap formation and to avoid it. Tandem gas metal arc welding (GMAW) was used to produce welded specimens in two different shielding gases (pure Ar and pure CO2) with base metal S355 MC (EN-10149-2) and wire G3Si1 (EN ISO 14341-A). Cross-sections of welds in the cold lap location were evaluated by light optical microscopy and scanning electron microscopy combined with energy dispersive spectroscopy. The results showed that the Mn‐Si oxides significantly enhanced cold laps formation, especially the overlap type cold lap formation. The Mn‐Si oxides originated from oxidation of the droplets. These oxides transfers to the surface of the weld pool at the weld toe, where they contributed to the formation of the cold laps.
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| 7. |
- Ramjaun, T., et al.
(författare)
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Effect of interpass temperature on residual stresses in multipass welds produced using low transformation temperature filler alloy
- 2014
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:1, s. 44-51
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Tidskriftsartikel (refereegranskat)abstract
- Weld filler alloys that exploit transformation plasticity through low austenite to martensite transformation temperatures offer an effective method of reducing residual stresses in strong steel welds. However, in multipass welds, the heat input from later weld passes may be insufficient to retransform prior welding passes, leading to the accumulation of thermally induced strains and elevated residual stresses. In this work, the residual stress distributions produced around arc welds fabricated with a martensitic weld filler alloy that transforms at a low temperature have been studied as a function of the number of passes deposited and the interpass temperature. It is found that when the interpass temperature is above the transformation temperature of the weld metal, the entire multipass weld transforms as a single entity, thus permitting the optimum exploitation of the transformation plasticity. In contrast, the deposition of new metal with a relatively low interpass temperature leads to increased residual stresses in the underlying layers, reducing or eliminating the beneficial stress states previously created.
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| 8. |
- Ramjaun, T., et al.
(författare)
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Effects of dilution and baseplate strength on stress distributions in multipass welds deposited using low transformation temperature filler alloys
- 2014
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:6, s. 461-467
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Tidskriftsartikel (refereegranskat)abstract
- Transformation plasticity can be utilised to control residual stresses in steel welds. This requires special filler alloys that transform at a sufficiently low temperature to compensate for accumulated thermal contraction strains. However, the welding parameters needed to optimise the effect in multipass joints have yet to be established. This topic has been investigated by characterising the residual stress distribution in multipass welds fabricated with different welding alloys and baseplates using neutron diffraction to assess the effects of dilution and baseplate strength. While the use of richly alloyed weld metal does enhance fatigue performance in single pass joints, the extent of stress relief that can be derived from transformation plasticity is reduced due to incomplete martensitic transformation when further layers are deposited. For all cases studied, compressive stresses were measured in the weld metal with balancing tensile stress in the heat affected zone of the plate. The magnitude of the tension was observed to be a function of the strength of the baseplate. Recommendations are also presented for the combination of welding and material parameters that lead to the optimum exploitation of transformation plasticity as a method for boosting the fatigue performance of multipass welded joints.
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| 9. |
- Ramjaun, T., et al.
(författare)
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Surface residual stresses in multipass welds produced using low transformation temperature filler alloys
- 2014
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 19:7, s. 623-630
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Tidskriftsartikel (refereegranskat)abstract
- Tensile residual stresses at the surface of welded components are known to compromise fatigue resistance through the accelerated initiation of microcracks, especially at the weld toe. Inducement of compression in these regions is a common technique employed to enhance fatigue performance. Transformation plasticity has been established as a viable method to generate such compressive residual stresses in steel welds and exploits the phase transformation in welding filler alloys that transform at low temperature to compensate for accumulated thermal contraction strains. Neutron and X-ray diffraction have been used to determine the stress profiles that exist across the surface of plates welded with low transformation temperature welding alloys, with a particular focus on the stress at the weld toe. For the first time, near surface neutron diffraction data have shown the extent of local stress variation at the critical, fusion boundary location. Compression was evident for the three measurement orientations at the fusion boundaries. Compressive longitudinal residual stresses and tensile transverse stresses were measured in the weld metal.
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| 10. |
- Tolf, E., et al.
(författare)
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Surface breaking cracks in resistance spot welds of dual phase steels with electrogalvanised and hot dip zinc coating
- 2012
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Ingår i: Science and technology of welding and joining. - 1362-1718 .- 1743-2936. ; 18:1, s. 25-31
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Tidskriftsartikel (refereegranskat)abstract
- In normal production of resistance spot welded galvanised structures, it is difficult to completely avoid surface breaking cracks. Known key factors to cause cracking are zinc coating, electrode wear during subsequent welding and insufficient electrode cooling. In this report, an embrittlement mechanism was investigated that could be coupled to the galvanisation method for dual phase steels. With identical bulk material and weld parameters, the first 50 spot welds were crack free with electrogalvanised coating, while only 10 out of 50 were crack free with hot dip galvanised coating. Energy dispersive X-ray spectroscopy analysis of the worn electrode surfaces used for welding of the hot dip galvanised coating revealed areas of aluminium oxide. Since aluminium oxide is a very strong isolator, the electrical resistance will increase, which in turn is suggested to increase the surface temperature of the spot weld and thereby increase the probability for liquid metal embrittlement and surface cracks.
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