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Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments / JOSHUA AGBESEYI

Swansea University Author: JOSHUA AGBESEYI

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Abstract

This thesis has been produced as a result of academic (Swansea University) and Industrial (Langley Alloys Ltd.) collaboration, facilitated through Swansea University’s M2A organisation under the Masters by Research (MSc) scheme of study. The scope of this investigation was set in the hopes of contri...

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Published: Swansea, Wales, UK 2023
Institution: Swansea University
Degree level: Master of Research
Degree name: MSc by Research
Supervisor: Williams, Geraint. and Wint, Natalie.
URI: https://cronfa.swan.ac.uk/Record/cronfa63723
first_indexed 2023-06-27T13:03:31Z
last_indexed 2024-11-25T14:12:48Z
id cronfa63723
recordtype RisThesis
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The scope of this investigation was set in the hopes of contributing to the current collective understanding and literature surrounding the localised electrochemical breakdown activity in Super Duplex Stainless Steels (SDSS). With specific consideration being given to highlighting the influence of Copper and Tungsten alloying additions on SDSS&#x2019;s observed passivation and breakdown tendencies, when immersed and anodically polarised in a range of acidic &amp; alkaline chloride media. This would, ideally, give an idea into how said additions impact and dictate the consequential states of nobility in the dual-phasic microstructure and bulk-alloy. In pursuit of these aims, it was the scope of this study to electrochemically investigate 3 different high Cr-content (25wt%) SDSS alloys of identical composition (excluding Cu- and W wt%) in various chloride-containing aqueous media. Consequently this would help ascertain their strengths/weaknesses in given conditions, with specific consideration to their addition-differences which would then be attributed to observed differences corrosion features with specific element additions. The alloys investigated in this study were UNS-S3550 (Ferralium&#xAE; 255) UNS-S3750 (SAF 2507) and UNS-S3760 (Zeron&#xAE;100). Under external anodic-polarisation these alloys were tested in various deoxygenated electrolyte solutions of 0.6M NaCl(aq) at a maintained ambient temperature of 25&#xB0;C, in both alkaline and acidic conditions ranging from pH 3 to 11. Adjustment of pH was achieved via drop-wise addition of NaOH and HCl. PP and SVET analysis was employed to help quantify, map and explain the bulk &amp; localised ionic-transport behaviour (respectively), both under open-circuit and non-polarised conditions. Findings from bulk anodic current characterisation using potentiodynamic polarisation were in good agreeance with observations made in a previous iteration of this study. That is to say it was found that in these conditions, anodic current increases typically associated with the phenomena of passive layer (PL) breakdown were mainly a result of transpassive dissolution kinetics, spotted with instances of localised pitting. Post-corrosion microscopy showed the anodic dissolution to unfold as a surface-wide, selective etching of constituent phases, typically attacking the less noble ferrite phase. This was later further supplemented with localised in-situ SVET scanning, showing the corrosive damage to evolve as an anodic &#x201C;front&#x201D;, steadily progressing across the active region of the corroding surface until stoppage of polarisation. Hysteresis loop data from potentiodynamic polarisation (PP) sweeps demonstrated a clear benefit of Cu-additions in mitigation of pitting damage in both acidic and alkaline chloride media. 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spelling 2023-06-27T14:05:23.2638942 v2 63723 2023-06-27 Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments 4439e70d2f038772744785e908eab851 JOSHUA AGBESEYI JOSHUA AGBESEYI true false 2023-06-27 This thesis has been produced as a result of academic (Swansea University) and Industrial (Langley Alloys Ltd.) collaboration, facilitated through Swansea University’s M2A organisation under the Masters by Research (MSc) scheme of study. The scope of this investigation was set in the hopes of contributing to the current collective understanding and literature surrounding the localised electrochemical breakdown activity in Super Duplex Stainless Steels (SDSS). With specific consideration being given to highlighting the influence of Copper and Tungsten alloying additions on SDSS’s observed passivation and breakdown tendencies, when immersed and anodically polarised in a range of acidic & alkaline chloride media. This would, ideally, give an idea into how said additions impact and dictate the consequential states of nobility in the dual-phasic microstructure and bulk-alloy. In pursuit of these aims, it was the scope of this study to electrochemically investigate 3 different high Cr-content (25wt%) SDSS alloys of identical composition (excluding Cu- and W wt%) in various chloride-containing aqueous media. Consequently this would help ascertain their strengths/weaknesses in given conditions, with specific consideration to their addition-differences which would then be attributed to observed differences corrosion features with specific element additions. The alloys investigated in this study were UNS-S3550 (Ferralium® 255) UNS-S3750 (SAF 2507) and UNS-S3760 (Zeron®100). Under external anodic-polarisation these alloys were tested in various deoxygenated electrolyte solutions of 0.6M NaCl(aq) at a maintained ambient temperature of 25°C, in both alkaline and acidic conditions ranging from pH 3 to 11. Adjustment of pH was achieved via drop-wise addition of NaOH and HCl. PP and SVET analysis was employed to help quantify, map and explain the bulk & localised ionic-transport behaviour (respectively), both under open-circuit and non-polarised conditions. Findings from bulk anodic current characterisation using potentiodynamic polarisation were in good agreeance with observations made in a previous iteration of this study. That is to say it was found that in these conditions, anodic current increases typically associated with the phenomena of passive layer (PL) breakdown were mainly a result of transpassive dissolution kinetics, spotted with instances of localised pitting. Post-corrosion microscopy showed the anodic dissolution to unfold as a surface-wide, selective etching of constituent phases, typically attacking the less noble ferrite phase. This was later further supplemented with localised in-situ SVET scanning, showing the corrosive damage to evolve as an anodic “front”, steadily progressing across the active region of the corroding surface until stoppage of polarisation. Hysteresis loop data from potentiodynamic polarisation (PP) sweeps demonstrated a clear benefit of Cu-additions in mitigation of pitting damage in both acidic and alkaline chloride media. W-additions were also found to be beneficial for suppression of corrosion damage when compared to non-Cu/W containing grades (UNS-S3750). E-Thesis Swansea, Wales, UK Corrosion, Super Duplex Stainless Steel, Tungsten, Copper, Chloride, SVET, Potentiodynamic Polarisation 23 2 2023 2023-02-23 COLLEGE NANME COLLEGE CODE Swansea University Williams, Geraint. and Wint, Natalie. Master of Research MSc by Research M2A, Langley Alloys (UK) 2023-06-27T14:05:23.2638942 2023-06-27T13:58:49.1542568 Faculty of Science and Engineering School of Engineering and Applied Sciences - Materials Science and Engineering JOSHUA AGBESEYI 1 63723__27988__26348a4baf814123bae6ebdaf664a2b0.pdf 2023_Agbeseyi_J.final.63723.pdf 2023-06-27T14:03:50.3870645 Output 4132014 application/pdf E-Thesis – open access true Copyright: The Author, Joshua Agbeseyi, 2023. true eng
title Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
spellingShingle Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
JOSHUA AGBESEYI
title_short Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
title_full Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
title_fullStr Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
title_full_unstemmed Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
title_sort Influence of Copper (Cu) and Tungsten (W) additions on the passivity and breakdown of Super Duplex Stainless Steels in chloride-containing environments
author_id_str_mv 4439e70d2f038772744785e908eab851
author_id_fullname_str_mv 4439e70d2f038772744785e908eab851_***_JOSHUA AGBESEYI
author JOSHUA AGBESEYI
author2 JOSHUA AGBESEYI
format E-Thesis
publishDate 2023
institution Swansea University
college_str Faculty of Science and Engineering
hierarchytype
hierarchy_top_id facultyofscienceandengineering
hierarchy_top_title Faculty of Science and Engineering
hierarchy_parent_id facultyofscienceandengineering
hierarchy_parent_title Faculty of Science and Engineering
department_str School of Engineering and Applied Sciences - Materials Science and Engineering{{{_:::_}}}Faculty of Science and Engineering{{{_:::_}}}School of Engineering and Applied Sciences - Materials Science and Engineering
document_store_str 1
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description This thesis has been produced as a result of academic (Swansea University) and Industrial (Langley Alloys Ltd.) collaboration, facilitated through Swansea University’s M2A organisation under the Masters by Research (MSc) scheme of study. The scope of this investigation was set in the hopes of contributing to the current collective understanding and literature surrounding the localised electrochemical breakdown activity in Super Duplex Stainless Steels (SDSS). With specific consideration being given to highlighting the influence of Copper and Tungsten alloying additions on SDSS’s observed passivation and breakdown tendencies, when immersed and anodically polarised in a range of acidic & alkaline chloride media. This would, ideally, give an idea into how said additions impact and dictate the consequential states of nobility in the dual-phasic microstructure and bulk-alloy. In pursuit of these aims, it was the scope of this study to electrochemically investigate 3 different high Cr-content (25wt%) SDSS alloys of identical composition (excluding Cu- and W wt%) in various chloride-containing aqueous media. Consequently this would help ascertain their strengths/weaknesses in given conditions, with specific consideration to their addition-differences which would then be attributed to observed differences corrosion features with specific element additions. The alloys investigated in this study were UNS-S3550 (Ferralium® 255) UNS-S3750 (SAF 2507) and UNS-S3760 (Zeron®100). Under external anodic-polarisation these alloys were tested in various deoxygenated electrolyte solutions of 0.6M NaCl(aq) at a maintained ambient temperature of 25°C, in both alkaline and acidic conditions ranging from pH 3 to 11. Adjustment of pH was achieved via drop-wise addition of NaOH and HCl. PP and SVET analysis was employed to help quantify, map and explain the bulk & localised ionic-transport behaviour (respectively), both under open-circuit and non-polarised conditions. Findings from bulk anodic current characterisation using potentiodynamic polarisation were in good agreeance with observations made in a previous iteration of this study. That is to say it was found that in these conditions, anodic current increases typically associated with the phenomena of passive layer (PL) breakdown were mainly a result of transpassive dissolution kinetics, spotted with instances of localised pitting. Post-corrosion microscopy showed the anodic dissolution to unfold as a surface-wide, selective etching of constituent phases, typically attacking the less noble ferrite phase. This was later further supplemented with localised in-situ SVET scanning, showing the corrosive damage to evolve as an anodic “front”, steadily progressing across the active region of the corroding surface until stoppage of polarisation. Hysteresis loop data from potentiodynamic polarisation (PP) sweeps demonstrated a clear benefit of Cu-additions in mitigation of pitting damage in both acidic and alkaline chloride media. W-additions were also found to be beneficial for suppression of corrosion damage when compared to non-Cu/W containing grades (UNS-S3750).
published_date 2023-02-23T20:23:06Z
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