| 1. |
- Shen, Rickard, 1985-, et al.
(author)
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Comparison of EBSD-based plastic strain estimation of Alloy 690 strained at 500–650 °C and at room temperature
- 2017
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Reports (other academic/artistic)abstract
- The validity of plastic strain estimation using electron backscatter diffraction (EBSD) in a warm deformed material with cold deformed reference materials has been investigated. Nickel-base Alloy 690, recovery heat treated at 1050 °C, was used in this study and deformed at room temperature and at 500– 650 °C. Grain orientation spread (GOS) was used as misorientation metric.Both GOS and hardness of the warm deformed materials were lower than for cold deformed materials of comparable applied strain, and was attributed to dynamic recovery. The hardness of the warm deformed materials was nonetheless comparable to cold deformed materials with similar GOS, although being slightly lower on average. These results show that GOS does not give an accurate estimate of applied deformation for warm deformation. It still gives a rough estimate of the effective plastic strain, albeit results suggest it may be a slight overestimation.
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| 2. |
- Shen, Rickard, 1985-, et al.
(author)
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Effects of PWHT on the microstructure and mechanical properties of ERNiCrFe-7 all-weld metal
- 2015
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In: Welding in the World. - : Springer Berlin/Heidelberg. - 0043-2288 .- 1878-6669. ; 59:3, s. 317-323
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Journal article (peer-reviewed)abstract
- The effects on the microstructure and room temperature mechanical properties of the nickel-based filler metal ERNiCrFe-7 due to a post weld heat treatment (PWHT) at 610 °C have been studied. It was shown that PWHT caused an increase in yield strength and ultimate tensile strength, but at the cost of reduced ductility and impact toughness. Crack tip opening displacement (CTOD) fracture toughness tests revealed an initial increase in maximum CTOD when a short PWHT was given, but declined with prolonged PWHT. The PWHT also caused a transition in fracture mechanism from microvoid coalescence to quasi-cleavage in room temperature air. Chromium-rich M23C6 type grain boundary carbides were present already in the as-welded weld metal, and were observed to coarsen during the PWHT. Intragranular M23C6 carbides were not observed in the as-welded state, but were precipitated during the 610 °C PWHT. Precipitation of these intragranular carbides is believed to be the main reason for the changes in mechanical properties.
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| 3. |
- Shen, Rickard, 1985-, et al.
(author)
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Experimental and theoretical investigation of three Alloy 690 mockup components: Base metal and welding induced changes
- 2014
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In: International Journal of Nuclear Energy. - : Hindawi Publishing Corporation. - 2314-6060 .- 2356-7066. ; 2014
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Journal article (peer-reviewed)abstract
- The stress corrosion cracking (SCC) resistance of cold deformed thermally treated (TT) Alloy 690 has been questioned in recent years. As a step towards understanding its relevancy for weld deformed Alloy 690 in operating plants, Alloy 690 base metal and heat affected zone (HAZ) microstructures of three mockup components have been studied. All mockups were manufactured using commercial heats and welding procedures in order to attain results relevant to the materials in the field. Thermodynamic calculations were performed to add confidence in phase identification as well as understanding of the evolution of the microstructure with temperature. Ti(C,N) banding was found in all materials. Bands with few large Ti(C,N) precipitates had negligible effect on the microstructure, whereas bands consisting of numerous small precipitates were associated with locally finer grains and coarser M23C6 grain boundary carbides. The Ti(C,N) remained unaffected in the HAZ while the M23C6 carbides were fully dissolved close to the fusion line. Cold deformed solution annealed Alloy 690 is believed to be a better representation of this region than cold deformed TT Alloy 690.
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| 4. |
- Shen, Rickard, 1985-, et al.
(author)
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Microstructural study of Alloy 690 base metal and HAZ from mockup components – Influence of Ti(C,N) banding
- 2015
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In: Fontevraud 8 - Contribution of Materials Investigations and Operating Experience to LWRs’ Safety, Performance and Reliability. - : International Atomic Energy Agency.
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Conference paper (peer-reviewed)abstract
- The Alloy 690 base metal and heat affected zones (HAZs) of three component mockups have been studied using light optical microscopy and scanning electron microscopy. All mockups were manufactured as part of the production of replacement components using commercial heats. Welding and post weld heat treatments were performed in the same way as for components in field in order to obtain microstructures representative to the ones in operating plants.All three Alloy 690 base metals exhibited Ti(C,N) banding, but to a different extent. In all cases, the bands extended through the material’s longitudinal direction. In two of these materials the Ti(C,N) bands were correlated with M23C6 carbide coarsening, fine grain banding and reduced grain boundary tortuosity in the longitudinal direction.Full carbide dissolution was observed near the fusion line. The coarser carbides in the banded regions were overall less affected, but were also fully dissolved when close enough to the fusion line. The region affected by carbide dissolution spanned roughly 300‑1000 μm wide depending on mockup. The Ti(C,N) precipitates however appeared unaffected. The lack of carbides near the fusion line, where the weld induced strains typically are highest, suggest that inducing cold work after a solution anneal may produce a material more representative of the HAZ than cold working the material in the thermally treated state.
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| 5. |
- Shen, Rickard, 1985-
(author)
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On the low primary water stress corrosion cracking susceptibility of weld deformed Alloy 690
- 2017
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Doctoral thesis (other academic/artistic)abstract
- It has been shown in recent years that the nickel-base Alloy 690 can become susceptible to stress corrosion cracking (SCC) in the primary water of nuclear power plants with pressurized water reactors if it has been sufficiently deformed at room temperature. Although the material is not intentionally used in a deformed state, it can become deformed by various manufacturing processes. Welding is believed to be the process that is most likely to cause susceptibility, yet it does not seem quite that detrimental in experiments. The overall purpose of this work was to investigate why weld-induced deformation does not seem to cause the same degree of susceptibility as cold deformation.The work started with a microstructural investigation, presented in Paper A, to assess if any of the changes caused by welding can explain the difference in behavior. While a beneficial change in the microstructure was observed, it was not enough to explain the differences.The focus was then turned towards addressing knowledge gaps of the method used to assess weld-induced deformation. This method is based on measuring misorientations using electron backscatter diffraction (EBSD). It was shown in Paper B that kernel average misorientation (KAM) is closer related to the degree of hardening than the degree of deformation, and that it can be used to obtain a qualitative map of hardness at the micrometer scale. Improvements to the KAM-based method were presented in Paper C along with estimates near welds from component mockups.The validity of using a misorientation-based method on warm deformation was tested in Paper D. It was shown that the method gives a rough estimate of the degree of strain hardening, although the data suggests it is a small overestimation. The overestimation would mean that weld deformation may have a lower hardness than the strain estimate implies, which is beneficial for SCC resistance.
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| 6. |
- Shen, Rickard, 1985-, et al.
(author)
-
Plastic strain assessment of Alloy 690 heat affected zones from component mockups using KAM and GOS
- 2017
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Reports (other academic/artistic)abstract
- The plastic strain level in Alloy 690 heat affected zones (HAZs) of three component mockups have been assessed using misorientations quantified by electron backscatter diffraction (EBSD). Kernel average misorientation (KAM) and grain orientation spread (GOS) were used in this work, and both gave the same results. The plastic strain increased towards the weld interface in all mockups and reached around 0.05 logarithmic strain for two mockups, and 0.10 for the third.While GOS was straightforward to use, KAM was shown to be sensitive to measurement imprecision, and also dependent on EBSD step length, kernel design and average grain size. This work shows how these drawbacks of KAM can be overcome. The results suggest that KAM’s size dependencies can be interpreted as a dependency on the ratio between kernel length scale and the average grain size of the material.
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| 7. |
- Shen, Rickard Ruici, 1985-, et al.
(author)
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Overcoming the drawbacks of plastic strain estimation based on KAM
- 2018
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In: Ultramicroscopy. - : Elsevier B.V.. - 0304-3991 .- 1879-2723. ; 184, s. 156-163
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Journal article (peer-reviewed)abstract
- Plastic strain estimation using electron backscatter diffraction (EBSD) based on kernel average misorientation (KAM) is affected by random orientation measurement error, EBSD step length, choice of kernel and average grain size. These sensitivities complicate reproducibility of results between labs, but it is shown in this work how these drawbacks can be overcome. The modifications to KAM were verified against a similar misorientation metric based on grain orientation spread (GOS), which does not show sensitivity to these factors. Both metrics were used in parallel to estimate the plastic strain distribution in Alloy 690 heat affected zones from component mockups, and showed the same results where the grain size was correctly compensated for.
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| 8. |
- Shen, Rickard Ruici, 1985-
(author)
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Review of the Effect of Cold Work on Stress Corrosion Cracking
- 2012
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In: Materials Science and Technology - Nuclear Materials, Advanced Course. - Helsinki : Helsinki University Press. - 9789526049069 ; , s. 133-145
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Conference paper (other academic/artistic)abstract
- It is well known that Alloy 690 is highly resistant against primary water stress corrosion cracking (SCC), yet not completely immune. Cold work, which is known to accelerate SCC crack growth rates (CGRs), has been shown to occasionally enhance the CGR in Alloy 690 base metal to alarmingly high levels. While Alloy 690 is not typically used in a heavily cold worked condition, effective plastic strains of comparable level have been estimated in Alloy 690 heat affected zone (HAZ). Much recent work on Alloy 690 has been focused on build up data in order to clarify whether or not these high CGRs are of concern for operating power plants.How cold work affects SCC CGR is still unclear. Based on trends in experimental data, some factors are believed to increase CGRs. The clearest trend is that of crack orientation. Aligning the plane and direction of crack growth with those of cold deformation generally yields a much higher CGR than other orientations. Inhomogeneous microstructure due to banding, fractured second phase particles and grain boundary voids also seem to enhance crack growth. The presence of these factors does however not guarantee high CGRs, and the lack of them does not guarantee low CGRs.
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| 9. |
- Shen, Rickard, 1985-, et al.
(author)
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Spatial correlation between local misorientations and nanoindentation hardness in nickel-base alloy 690
- 2016
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In: Journal of Materials Science and Engineering. - : Elsevier. - 2161-6213 .- 0921-5093. ; 674, s. 171-177
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Journal article (peer-reviewed)abstract
- Misorientation increases with plastic strain in metals, and this observation has been used as an empirical assessment of plastic strain in recent years. The method has been validated for a sample area corresponding to a 100 µm×100 µm square, but on the micrometer scale misorientations no longer seem to correlate with plastic strain. Misorientations are however not dependent on plastic strain but rather on dislocation density, which means it should also be related to hardness. Therefore, we have in this work compared maps of predicted hardness calculated from misorientation determination with maps of actual hardness measured by nanoindentation. It was shown that the predicted and measured hardness maps do indeed correlate spatially in nickel-base Alloy 690, although the measured values have a significantly smaller hardness variation. This is explained by a presumably high and uniform density of statistically stored dislocations, which contribute to hardness but do not affect the misorientation determination from electron backscatter diffraction. Thus local misorientation can be used to qualitatively map the local effective plastic strain distribution, for example to identify regions of increased hardness.
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| 10. |
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- 2019
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Journal article (peer-reviewed)
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