Co-deformation of metallic and intermetallic phases in Mg-Al-Ca alloys
| العنوان: | Co-deformation of metallic and intermetallic phases in Mg-Al-Ca alloys |
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| المؤلفون: | Zubair, Muhammad |
| المساهمون: | Korte-Kerzel, Sandra, Tasan, Cemal Cem |
| المصدر: | Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme, Karten (2022). doi:10.18154/RWTH-2022-00793 = Dissertation, RWTH Aachen University, 2022, Kumulative Dissertation |
| بيانات النشر: | RWTH Aachen University, 2022. |
| سنة النشر: | 2022 |
| مصطلحات موضوعية: | DIC, co-deformation, mg alloys, electron microscopy, mechanical properties, slip transfer, ddc:620 |
| الوصف: | Dissertation, Rheinisch-Westf��lische Technische Hochschule Aachen, 2022; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme, Karten (2022). = Dissertation, Rheinisch-Westf��lische Technische Hochschule Aachen, 2022 Mg-Al-Ca alloys have a dual phase microstructure comprising a soft ��-Mg phase reinforced with a hard intermetallic interconnected Laves phase skeleton. The excellent creep properties of these alloys are attributed to the presence of Laves phases in the microstructure. However, it is not entirely clear how the amount, type, and morphology of the Laves phases can affect the elevated temperature tensile and creep properties of these alloys. Furthermore, the two mechanically and crystallographically different phases (��-Mg and Laves phases) provide an opportunity to study the co-deformation behaviour of such heterogeneous materials. This thesis, therefore, focuses on the two main aspects: i) effect of Laves phases on the mechanical properties of Mg-Al-Ca alloys and ii) co-deformation of metallic and intermetallic phases. The Ca/Al ratio can be used to manipulate the amount, type, and morphology of Laves phases. Therefore, three different Mg-Al-Ca alloys with varying Ca/Al ratio (Ca/Al: 0.32, 0.62 and 1.03) were produced. The alloys were microscopically and mechanically investigated using SEM, EDS, EBSD, micro-hardness, tensile and creep testing. The results show that an increase in Ca/Al ratio from 0.32 to 1.03 results in a higher volume fraction of Laves phase in the as-cast microstructure, higher yield strength, UTS and better creep properties at a temperature of 170 ��C. However, the alloy with the highest Ca/Al ratio exhibits lowest ductility. The co-deformation mechanisms of the same Mg-Al-Ca alloys were studied using DIC, quasi in-situ tensile deformation in SEM (at 170 ��C), EBSD, and TEM. The strain maps obtained from DIC experiments showed that the strain is highly heterogeneous at the microstructural level and tends to concentrate along slip lines and twins in the ��-Mg phase and along the ��-Mg/Laves phase interfaces. Moreover, it was found that cracks preferentially nucleate in the Laves phase at the intersections of slip in the ��-Mg and Mg-Laves phase interfaces as well as at the intersections of twins in the matrix and Mg-Laves phase interfaces. Consequently, cracks in the Laves phase were mainly observed in microstructural regions that underwent significant basal slip and tensile twinning. Euler number analysis also confirmed that the interconnectivity of the Laves phase decreases with deformation because of cracking. In addition to cracks in the Laves phase, slip transfer was also observed in the (Mg,Al)2Ca phase at strain concentration points. Atomistic simulations of the Mg/Mg2Ca system confirmed that dislocation slip in the Mg2Ca phase was triggered by the interaction of basal dislocation of the Mg matrix with the interface. However, the slip transfer mechanisms across the Mg/Mg2Ca interface were affected by temperature and orientation relationship between both phases. In line with atomistic simulations, basal slip lines in the (Mg,Al)2Ca phase were also observed at strain concentration points in deformed alloys investigated using SEM and TEM. The co-deformation mechanism based on experimental results is proposed within this thesis. Finally, nanoindentation with constant and variable strain rate was conducted to determine the mechanical properties and thermally activated deformation mechanisms of the individual phases in Mg-Al-Ca alloys. It was observed that the hardness of the ��-Mg phase decreases with temperature while that of the Laves phases stays constant until 200 ��C. The strain rate sensitivity, m, was nearly the same for ��-Mg and ��-Mg/Laves interfaces while the activation volume was lower for indents made across interfaces. Nanoindentation creep tests indicated that the creep resistance of the Mg2Ca phase is higher than that of the ��-Mg phase. The findings of this thesis provide valuable insights for the design of creep resistant Mg-Al-Ca alloys by manipulating the Ca/Al ratio. Additionally, the methods involved in this thesis are generally applicable to study the co-deformation of multiphase alloys with mechanically heterogeneous microstructural components. They may, therefore, be of interest to researchers working on other multi-phase alloys such as dual-phase steels or titanium alloys. Published by RWTH Aachen University, Aachen |
| اللغة: | English |
| DOI: | 10.18154/rwth-2022-00793 |
| URL الوصول: | https://explore.openaire.eu/search/publication?articleId=doi_dedup___::23776a4d9e92f57d6821e3e038ad29ab |
| حقوق: | OPEN |
| رقم الأكسشن: | edsair.doi.dedup.....23776a4d9e92f57d6821e3e038ad29ab |
| قاعدة البيانات: | OpenAIRE |
| DOI: | 10.18154/rwth-2022-00793 |
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