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Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys
Thesis (PhD)--Stellenbosch University, 2026.
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| Format: | Thesis |
| Language: | English |
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Stellenbosch : Stellenbosch University
2026
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| _version_ | 1867613988240490496 |
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| access_status_str | Open Access |
| author | Cupido, Llewellyn Heinrich |
| author2 | Mahomed, Nawaz |
| author_browse | Cupido, Llewellyn Heinrich Mahomed, Nawaz |
| author_facet | Mahomed, Nawaz Cupido, Llewellyn Heinrich |
| author_sort | Cupido, Llewellyn Heinrich |
| collection | Thesis |
| dc_rights_str_mv | Stellenbosch University |
| description | Thesis (PhD)--Stellenbosch University, 2026. |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/135708 |
| institution | Stellenbosch University (South Africa) |
| language | English |
| last_indexed | 2026-06-10T12:44:52.743Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from SUNScholar — Stellenbosch University Repository |
| publishDate | 2026 |
| publishDateRange | 2026 |
| publishDateSort | 2026 |
| publisher | Stellenbosch : Stellenbosch University |
| publisherStr | Stellenbosch : Stellenbosch University |
| record_format | dspace |
| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/135708 Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys Cupido, Llewellyn Heinrich Mahomed, Nawaz Stellenbosch University. Faculty of Engineering. Dept. of Mechanical & Mechatronic Engineering. Thesis (PhD)--Stellenbosch University, 2026. Cupido, L. H. 2026. Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys. Unpublished doctoral dissertation. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/a5813faa-72ba-45a5-b4b8-272db8eeac27 Duplex stainless steel 2205 (DSS2205) exhibits complex non-monotonic strength evolution during thermal ageing at elevated temperatures, limiting predictive capability for long-term component life assessment. This dissertation develops and validates the METALS (Microstructure Evolution and Thermal Ageing-Linked Strength) model. An empirical multiphase framework coupling phase-field microstructural predictions with mechanical property evolution through phenomenological energy-strength relationships. A comprehensive six-month isothermal ageing study at 500 °C established the experimental foundation, revealing characteristic strength evolution: 47.9% hardening (695 to 1028 MPa, 0-504 hours), 13.6% softening to 873 MPa (1680 hours), and a recovery to 1020 MPa (4368 hours). TEM/EELS analysis at six timepoints identified competitive Cr₂N/MoN precipitation as the governing mechanism, with late-stage Ti/V-containing phases contributing to recovery behaviour. The phase-field model incorporates a critical enhancement distinguishing compositional (deviatoric) and volumetric (dilatational) misfit strain components. Volumetric contributions, while representing a small fraction of total elastic energy during peak precipitation (~5% at 1680h), generating compressive hydrostatic stresses that significantly influence precipitate dissolution kinetics. The elastic energy grows substantially at late stages (reaching ~23% at 3700h), correlating with increased dissolution activity. GPU-accelerated spectral methods enable 4368-hour predictions in ~72 hours, demonstrating practical computational efficiency. Validation demonstrates stage-dependent accuracy: good early-stage agreement (RMSE = 6.18 MPa, 0.5% error for 0-672 hours), moderate intermediate performance (RMSE = 79.48 MPa, 7.79% error for 672-2520 hours), and reasonable late-stage predictions (RMSE = 71.59 MPa, 6.06% beyond 2520h). Parametric sensitivity analysis reveals MoN activation energy critically governs intermediate-stage behaviour, which provides a clear pathway for model refinement. The systematic late-stage underprediction identifies the need for explicit TiN/VN phase incorporation. The validated framework enables quantitative strength predictions for DSS2205 components during service exposure, supports alloy composition optimisation through computational screening, and establishes a transferable methodology applicable to other high-chromium steel systems. The research demonstrates that empirically-calibrated phenomenological coupling within thermodynamically-consistent microstructural frameworks provides actionable predictive capability even when complete mechanistic understanding remains incomplete. Doctoral 2026-04-08T09:57:19Z 2026-04-08T09:57:19Z 2026-03 Thesis https://scholar.sun.ac.za/handle/10019.1/135708 en Stellenbosch University 221 pages : ill. application/pdf Stellenbosch : Stellenbosch University |
| spellingShingle | Cupido, Llewellyn Heinrich Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title | Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title_full | Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title_fullStr | Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title_full_unstemmed | Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title_short | Empirical Multiphase Model for Strength Evolution of High-Chromium Steel Alloys |
| title_sort | empirical multiphase model for strength evolution of high chromium steel alloys |
| url | https://scholar.sun.ac.za/handle/10019.1/135708 |
| work_keys_str_mv | AT cupidollewellynheinrich empiricalmultiphasemodelforstrengthevolutionofhighchromiumsteelalloys |