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The dislocation behaviour and GND development in a nickel based superalloy during creep

Soran Birosca Orcid Logo, Gang Liu, Rengen Ding, Thomas Simm Orcid Logo, Jun Jiang, Chris Deen, Mark Whittaker Orcid Logo

International Journal of Plasticity, Volume: 118, Pages: 252 - 268

Swansea University Authors: Soran Birosca Orcid Logo, Thomas Simm Orcid Logo, Mark Whittaker Orcid Logo

Abstract

In the current study, dislocation activity and storage during creep deformation in a nickel based superalloy (Waspaloy) were investigated, focussing on the storage of geometrically necessary (GND) and statistically stored (SSD) dislocations. Two methods of GND density calculation were used, namely,...

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Published in: International Journal of Plasticity
ISSN: 0749-6419
Published: 2019
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URI: https://cronfa.swan.ac.uk/Record/cronfa48800
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Two methods of GND density calculation were used, namely, EBSD Hough Transformation and HR-EBSD Cross Correlation based methods. The storage of dislocations, including SSDs, was investigated by means of TEM imaging. Here, the concept of GND accumulation in soft and hard grains and the effect of neighbouring grain orientation on total dislocation density was examined. Furthermore, the influence of applied stress (below and above the yield stress of Waspaloy) during creep on deformation micro-mechanism and dislocation density was studied. It was demonstrated that soft grains provided pure shear conditions on at least two octahedral (111) slip systems for easy dislocation movement. This allowed dislocations to reach the grain boundary without significant geometrically necessary dislocation accumulation in the centre of the grain. Hence, the majority of the soft grains appeared to have minimum GND density in the centre of the grain with high GND accumulation in the vicinity of the grain boundaries. However, the values and width of accumulated GND depended on the surrounding grain orientations. Furthermore, it was shown that the hard grains were not favourably oriented for octahedral slip system activation leading to a grain rotation in order to activate any of the available slip systems. Eventually, (i) the hard grain resistance to deformation and (ii) neighbouring grain resistance for the hard grain reorientation caused high GND density on a number of octahedral (111) slip systems. The results also showed that during creep below the yield stress of Waspaloy (500 MPa/700&#x202F;&#xB0;C), the GND accumulation was relatively low due to the insufficient macroscopic stress level. However, the regions near grain boundaries showed high GND density. At 800 MPa/700&#x202F;&#xB0;C (above yield at this temperature), in addition to the movement of pre-existing dislocations (SSD and GND) at a higher mobility rate, large numbers of dislocations were generated and moved toward the grain boundaries. This resulted in a much higher GND density but narrower width of high intensity GNDs near the grain boundaries. 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spelling 2021-01-15T10:36:01.0590924 v2 48800 2019-02-12 The dislocation behaviour and GND development in a nickel based superalloy during creep 3445603fcc2ff9d27b476a73b223a507 0000-0002-8380-771X Soran Birosca Soran Birosca true false 10fa7732a6aee5613ff1364dc8460972 0000-0001-6305-9809 Thomas Simm Thomas Simm true false a146c6d442cb2c466d096179f9ac97ca 0000-0002-5854-0726 Mark Whittaker Mark Whittaker true false 2019-02-12 EEN In the current study, dislocation activity and storage during creep deformation in a nickel based superalloy (Waspaloy) were investigated, focussing on the storage of geometrically necessary (GND) and statistically stored (SSD) dislocations. Two methods of GND density calculation were used, namely, EBSD Hough Transformation and HR-EBSD Cross Correlation based methods. The storage of dislocations, including SSDs, was investigated by means of TEM imaging. Here, the concept of GND accumulation in soft and hard grains and the effect of neighbouring grain orientation on total dislocation density was examined. Furthermore, the influence of applied stress (below and above the yield stress of Waspaloy) during creep on deformation micro-mechanism and dislocation density was studied. It was demonstrated that soft grains provided pure shear conditions on at least two octahedral (111) slip systems for easy dislocation movement. This allowed dislocations to reach the grain boundary without significant geometrically necessary dislocation accumulation in the centre of the grain. Hence, the majority of the soft grains appeared to have minimum GND density in the centre of the grain with high GND accumulation in the vicinity of the grain boundaries. However, the values and width of accumulated GND depended on the surrounding grain orientations. Furthermore, it was shown that the hard grains were not favourably oriented for octahedral slip system activation leading to a grain rotation in order to activate any of the available slip systems. Eventually, (i) the hard grain resistance to deformation and (ii) neighbouring grain resistance for the hard grain reorientation caused high GND density on a number of octahedral (111) slip systems. The results also showed that during creep below the yield stress of Waspaloy (500 MPa/700 °C), the GND accumulation was relatively low due to the insufficient macroscopic stress level. However, the regions near grain boundaries showed high GND density. At 800 MPa/700 °C (above yield at this temperature), in addition to the movement of pre-existing dislocations (SSD and GND) at a higher mobility rate, large numbers of dislocations were generated and moved toward the grain boundaries. This resulted in a much higher GND density but narrower width of high intensity GNDs near the grain boundaries. It is concluded that although GND measurement by means of EBSD can provide great insight into dislocation accumulation and its behaviour, it is critical to consider SSD type which also contributes to the strain hardening of the material. Journal Article International Journal of Plasticity 118 252 268 0749-6419 EBSD, Dislocation, GND, Nickel, Superalloy, Creep, TKD 1 7 2019 2019-07-01 10.1016/j.ijplas.2019.02.015 http://dx.doi.org/10.1016/j.ijplas.2019.02.015 COLLEGE NANME Engineering COLLEGE CODE EEN Swansea University 2021-01-15T10:36:01.0590924 2019-02-12T08:54:12.0205536 College of Engineering Engineering Soran Birosca 0000-0002-8380-771X 1 Gang Liu 2 Rengen Ding 3 Thomas Simm 0000-0001-6305-9809 4 Jun Jiang 5 Chris Deen 6 Mark Whittaker 0000-0002-5854-0726 7 0048800-12022019085531.pdf birosca2019.pdf 2019-02-12T08:55:31.4100000 Output 7277672 application/pdf Accepted Manuscript true 2020-02-21T00:00:00.0000000 true eng
title The dislocation behaviour and GND development in a nickel based superalloy during creep
spellingShingle The dislocation behaviour and GND development in a nickel based superalloy during creep
Soran Birosca
Thomas Simm
Mark Whittaker
title_short The dislocation behaviour and GND development in a nickel based superalloy during creep
title_full The dislocation behaviour and GND development in a nickel based superalloy during creep
title_fullStr The dislocation behaviour and GND development in a nickel based superalloy during creep
title_full_unstemmed The dislocation behaviour and GND development in a nickel based superalloy during creep
title_sort The dislocation behaviour and GND development in a nickel based superalloy during creep
author_id_str_mv 3445603fcc2ff9d27b476a73b223a507
10fa7732a6aee5613ff1364dc8460972
a146c6d442cb2c466d096179f9ac97ca
author_id_fullname_str_mv 3445603fcc2ff9d27b476a73b223a507_***_Soran Birosca
10fa7732a6aee5613ff1364dc8460972_***_Thomas Simm
a146c6d442cb2c466d096179f9ac97ca_***_Mark Whittaker
author Soran Birosca
Thomas Simm
Mark Whittaker
author2 Soran Birosca
Gang Liu
Rengen Ding
Thomas Simm
Jun Jiang
Chris Deen
Mark Whittaker
format Journal article
container_title International Journal of Plasticity
container_volume 118
container_start_page 252
publishDate 2019
institution Swansea University
issn 0749-6419
doi_str_mv 10.1016/j.ijplas.2019.02.015
college_str College of Engineering
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hierarchy_top_title College of Engineering
hierarchy_parent_id collegeofengineering
hierarchy_parent_title College of Engineering
department_str Engineering{{{_:::_}}}College of Engineering{{{_:::_}}}Engineering
url http://dx.doi.org/10.1016/j.ijplas.2019.02.015
document_store_str 1
active_str 0
description In the current study, dislocation activity and storage during creep deformation in a nickel based superalloy (Waspaloy) were investigated, focussing on the storage of geometrically necessary (GND) and statistically stored (SSD) dislocations. Two methods of GND density calculation were used, namely, EBSD Hough Transformation and HR-EBSD Cross Correlation based methods. The storage of dislocations, including SSDs, was investigated by means of TEM imaging. Here, the concept of GND accumulation in soft and hard grains and the effect of neighbouring grain orientation on total dislocation density was examined. Furthermore, the influence of applied stress (below and above the yield stress of Waspaloy) during creep on deformation micro-mechanism and dislocation density was studied. It was demonstrated that soft grains provided pure shear conditions on at least two octahedral (111) slip systems for easy dislocation movement. This allowed dislocations to reach the grain boundary without significant geometrically necessary dislocation accumulation in the centre of the grain. Hence, the majority of the soft grains appeared to have minimum GND density in the centre of the grain with high GND accumulation in the vicinity of the grain boundaries. However, the values and width of accumulated GND depended on the surrounding grain orientations. Furthermore, it was shown that the hard grains were not favourably oriented for octahedral slip system activation leading to a grain rotation in order to activate any of the available slip systems. Eventually, (i) the hard grain resistance to deformation and (ii) neighbouring grain resistance for the hard grain reorientation caused high GND density on a number of octahedral (111) slip systems. The results also showed that during creep below the yield stress of Waspaloy (500 MPa/700 °C), the GND accumulation was relatively low due to the insufficient macroscopic stress level. However, the regions near grain boundaries showed high GND density. At 800 MPa/700 °C (above yield at this temperature), in addition to the movement of pre-existing dislocations (SSD and GND) at a higher mobility rate, large numbers of dislocations were generated and moved toward the grain boundaries. This resulted in a much higher GND density but narrower width of high intensity GNDs near the grain boundaries. It is concluded that although GND measurement by means of EBSD can provide great insight into dislocation accumulation and its behaviour, it is critical to consider SSD type which also contributes to the strain hardening of the material.
published_date 2019-07-01T04:01:42Z
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