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Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties
Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2024.
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University of Pretoria
2024
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| _version_ | 1867613584431775744 |
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| access_status_str | Open Access |
| author2 | Siyasiya, Charles Witness |
| author_browse | Siyasiya, Charles Witness |
| author_facet | Siyasiya, Charles Witness |
| collection | Thesis |
| dc_rights_str_mv | © 2023 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. |
| description | Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2024. |
| format | Thesis |
| id | oai:repository.up.ac.za:2263/99986 |
| institution | University of Pretoria (South Africa) |
| last_indexed | 2026-06-10T12:38:28.311Z |
| license_str | Other — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UPSpace — University of Pretoria Institutional Repository |
| publishDate | 2024 |
| publishDateRange | 2024 |
| publishDateSort | 2024 |
| publisher | University of Pretoria |
| publisherStr | University of Pretoria |
| record_format | dspace |
| source_str | UPSpace — University of Pretoria Institutional Repository |
| spelling | oai:repository.up.ac.za:2263/99986 Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties Siyasiya, Charles Witness ellardjholy@gmail.com/u20809515@tuks.co.za Mathabathe, Maria Ntsoaki Ellard, John Jimmy Masache UCTD Sustainable Development Goals (SDGs) Gamma-TiAl-based Alloys Mechanical properties Process optimisation Vacuum arc remelting Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2024. In the current research, the influence of powder characteristics blending, ingot melting parameters and the effects of Si, Mn, and Sn additions on the microstructures of Ti-48Al-2Nb-0.7Cr-0.3Si, Ti-48Al-2Nb-0.7Cr-0.3Mn and Ti-48Al-2Nb-0.7Cr-0.3Si-1Sn (at.%) alloys were investigated. The aim was to improve the microstructures and hence improve the mechanical properties for efficient hot deformation simulation and optimum hot-pack rolling without the use of the intermediate thermo-mechanical processes. The alloys were successfully fabricated from blended and uniaxial cold-pressed precursor powders and subsequently arc re-melted under vacuum and heat treated prior to the hardness and tensile tests at room temperature. The alloy with the best mechanical properties was further tensile tested at 750 °C and fatigue tested at room temperature. Its hot workability was tested in a Gleeble 1500DTM thermo-mechanical simulator by hot compression tests in the temperature and strain rate ranges of 1050-1200 °C and 0.001-0.1 s^(-1) respectively. Finally, the alloy was hot-pack rolled in a conventional two-high rolling mill by employing optimum parameters for hot-working of the alloy to produce a 4 mm -TiAl-based sheet. After the final rolling pass, the specimen was rapidly cooled in the air to room temperature and then heat treated in the α+ phase field. From the obtained results, irregular, spherical and angular-shaped powder particles of a mean size range of 8.12 to 101.24 m improved the density of the compacts. The melting of dense compacts using optimised arc voltage, current and vacuum level in the vacuum arc re-melting (VAR) process, improved the densities and homogeneity of the ingots. Unlike 0.3 at.%Si and 0.3 at.%Mn additions, 1 at.%Sn improved the castability of the alloy. The Si significantly improved the mechanical properties whereas Sn deteriorated the properties after heat treatment by hindering the nucleation of α_2 and Ti_5 Si_3 phases. 1050 to 1080 °C and 0.0087 to 0.071 s^(-1) were identified as optimum parameters for the hot-working of the Ti-48Al-2Nb-0.7Cr-0.3Si alloy. When hot-rolling was carried out within the optimum window with subsequent rapid cooling and heat treatment, a sheet with fine and equiaxed grains and with weak cube textured microstructure and improved mechanical properties was produced. Materials Science and Metallurgical Engineering PhD (Metallurgical Engineering) Restricted Faculty of Engineering, Built Environment and Information Technology SDG-09: Industry, innovation and infrastructure SDG-13: Climate action 2024-12-12T12:11:26Z 2024-12-12T12:11:26Z 2025-04 2024-11-24 Thesis * A2025 http://hdl.handle.net/2263/99986 https://doi.org/10.25403/UPresearchdata.27928908 © 2023 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. application/pdf University of Pretoria |
| spellingShingle | UCTD Sustainable Development Goals (SDGs) Gamma-TiAl-based Alloys Mechanical properties Process optimisation Vacuum arc remelting Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title | Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title_full | Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title_fullStr | Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title_full_unstemmed | Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title_short | Alloy design and process optimisation of gamma-TiAl-based alloys for improved mechanical properties |
| title_sort | alloy design and process optimisation of gamma tial based alloys for improved mechanical properties |
| topic | UCTD Sustainable Development Goals (SDGs) Gamma-TiAl-based Alloys Mechanical properties Process optimisation Vacuum arc remelting |
| url | http://hdl.handle.net/2263/99986 https://doi.org/10.25403/UPresearchdata.27928908 |