The effect of thermomechanical processing parameters on the texture of Ti-6Al-4V forgings as a precursor to coarse grain growth.
| dc.contributor.author | Wiley, Richard | |
| dc.date.accessioned | 2024-05-19T23:50:57Z | |
| dc.date.available | 2024-05-19T23:50:57Z | |
| dc.date.issued | 2023 | |
| dc.description.abstract | This thesis explores the relationship between forging parameters - total strain, strain rate, and forging temperature - and the emergence of abnormal grains during subsequent heat treatment of Ti-6Al-4V. Abnormal grain growth can compromise material properties, making its understanding crucial for optimizing manufacturing processes. Through systematic experiments, varying the forging temperature between 875 and 975°C and the strain rate between 0.1s⁻¹ and 10s⁻¹ , the study reveals how different forging conditions influence the as-forged microstructure through the alteration of the kinetics of flow softening and how this affects abnormal grain formation. Microstructural analysis through optical and scanning electron microscopy methods demonstrate correlations between these forging parameters and the occurrence of non-uniform grain distributions. The insights gained offer strategies to mitigate abnormal grain growth during heat treatment, advancing materials science and manufacturing practices. The results show that forging temperature and strain rates impact prior beta grain size differently. Higher forging temperatures at 975°C lead to larger grain sizes due to increased boundary mobility favouring grain growth. Lower forging temperatures at 875°C produce more consistent grain sizes due to uniform boundary energies resulting from a weaker texture. For samples forged at 925°C, varying strain rates cause significant differences in grain size due to the shift from dynamic recovery to dynamic recrystallisation as the primary strain relief mechanism. This shift in mechanisms is also reflected in stress-strain responses, with dynamically recrystallised samples showing higher peak stress and more transience. The dynamic recrystallisation process leads to the nucleation of strain-free grains with distinct orientations, contributing to a weaker textured material. The study validates that abnormal grain growth is influenced by strain rate and forging temperature, with increased strain-strengthening precursor texture. Lower forging temperatures lead to weaker texture and more normal grain growth. From the findings, it is recommended to forge above critical rates for recrystallization, at the required forging temperature. The research suggests forging above 5s⁻¹ up to 925°C or 0.95 Tβ, although this is adjustable to 0.1s⁻¹ at 875°C/0.9 Tβ. Billet size indirectly affects abnormal grain occurrence by affecting the strain rate, with smaller billets displaying uniform grain size after annealing. Thus, changes in the thickness of Ti-6Al-4V parts could cause abnormal grain growth in thicker sections during annealing and should be considered prior to forging. | |
| dc.identifier.uri | https://hdl.handle.net/10092/107084 | |
| dc.identifier.uri | https://doi.org/10.26021/15354 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.rights | All Right Reserved | |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | |
| dc.title | The effect of thermomechanical processing parameters on the texture of Ti-6Al-4V forgings as a precursor to coarse grain growth. | |
| dc.type | Theses / Dissertations | |
| thesis.degree.discipline | Mechanical Engineering | |
| thesis.degree.grantor | University of Canterbury | |
| thesis.degree.level | Masters | |
| thesis.degree.name | Master of Engineering | |
| uc.college | Faculty of Engineering |