Characterisation of ATI 718Plus produced by wire-arc additive manufacturing process: microstructure and properties
| dc.contributor.author | Asala, Gbenga | |
| dc.contributor.examiningcommittee | Deng, Chuang (Mechanical Engineering) Bassuoni, Mohamed (Civil Engineering) Jahazi, Mohammad (Mechanical Engineering, Ecole de technologie superieure) | en_US |
| dc.contributor.supervisor | Ojo, Olanrewaju (Mechanical Engineering) Andersson, Joel (Mechanical Engineering) | en_US |
| dc.date.accessioned | 2019-07-11T21:41:43Z | |
| dc.date.available | 2019-07-11T21:41:43Z | |
| dc.date.issued | 2019-07--05 | en_US |
| dc.date.submitted | 2019-07-05T21:13:39Z | en |
| dc.degree.discipline | Mechanical Engineering | en_US |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | en_US |
| dc.description.abstract | ATI 718Plus is a γ'-strengthened variant of the extensively used Alloy 718 which was developed in a bid to enhance the operating temperatures of Alloy 718, in aero-engines and power-plants. To facilitate the application of this alloy, several studies have been performed to investigate the microstructure and properties of ATI 718Plus produced by using the conventional processes that are used to manufacture Alloy 718. However, there is the lack of detailed information on the microstructure and associated properties of the ATI 718Plus produced by additive manufacturing (AM). This research work is therefore carried out to comprehensively characterise the microstructure and the corresponding properties of ATI 718Plus produced by wire-arc additive manufacturing (WAAM), which is a low-cost but high deposition AM technique. Extensive segregation of the alloying elements is observed in WAAM ATI 718Plus. Alloying elements like Nb, Ti, and Mo significantly partitioned into the interdendritic regions of the deposit promoting the formation of secondary phase particles, identified as the detrimental Laves phase and MC-type carbides. The segregation of Nb and Ti also prompted the inhomogeneous precipitation of strengthening phase (γ' and γ" precipitates) within the deposit. In the as-processed condition, WAAM ATI 718Plus display an inferior dynamic impact resistance compared to the wrought ATI 718Plus. This is attributed to the presence of solidification constituents and the inhomogeneous distribution of the strengthening phase precipitates. Similarly, WAAM ATI 718Plus, in the as-processed condition, exhibits a significantly lower hot corrosion resistance in comparison to the wrought alloy. The depletion of Nb and Mo in the dendrite core regions, decreases the local corrosion resistance of the alloy, leading to accelerated degradation of the as-processed alloy. Based on the understanding accrued from electron microscopy and spectroscopy techniques and in corroboration with thermodynamic calculations, post-deposition heat treatment is developed to improve the microstructure of the additive manufactured alloy. The post-deposition heat treatment comprises a homogenisation treatment prior to the application of the standard heat treatment and aging. A significant improvement is observed in the dynamic impact response and the hot corrosion resistance after subjecting the WAAM ATI 718Plus to the newly developed post deposition heat treatment procedure. | en_US |
| dc.description.note | October 2019 | en_US |
| dc.identifier.citation | 1. G. Asala, J. Andersson and O.A. Ojo, “Improved dynamic impact behavior of wire-arc additive manufactured ATI 718Plus superalloy” Material science and Engineering A. Vol.738 pp.111–124, 2018, 2. G. Asala, J. Andersson and O.A. Ojo, “A study of the dynamic impact behavior of IN 718 and ATI 718Plus” Philosophical Magazine. Vol. 99, No.4, 419-437, 2019, 3. G. Asala, J. Andersson and O.A. Ojo, “Microstructural analyses of ATI 718Plus produced by wire-arc additive manufacturing process” Metallurgical and Materials Transactions A: Volume 48, Issue 9, pp 4211–4228, 2017, 5. G. Asala, J. Andersson and O.A. Ojo, “Analysis and constitutive modelling of high strain rate deformation behaviour of wire–arc additive-manufactured ATI 718Plus superalloy” The International Journal of Advanced Manufacturing Technology, 1-19, 2019, 6. G. Asala, J. Andersson and O.A. Ojo, “Precipitation behaviour of γ’ precipitates in the fusion zone of TIG welded ATI 718Plus” The International Journal of Advanced Manufacturing Technology Vol. 87(9), pp 2721–2729, 2016 | en_US |
| dc.identifier.citation | 7. G. Asala and O.A. Ojo, “On post-weld heat treatment cracking in TIG welded superalloy ATI 718Plus” Results in Physics, Vol. 6, pp196–198, 2016, • G. Asala, J. Andersson and O.A. Ojo, “Microstructure dependence on the dynamic impact behavior of ATI 718Plus superalloy” 9th International Symposium on Superalloy 718 and Derivatives. TMS Pittsburgh, PA. June 2018. | en_US |
| dc.identifier.uri | http://hdl.handle.net/1993/34028 | |
| dc.language.iso | eng | en_US |
| dc.rights | open access | en_US |
| dc.subject | Additive manufacturing, WAAM, Microstructure, High strain rate, Hot corrosion, TIG welding, Heat treatment | en_US |
| dc.title | Characterisation of ATI 718Plus produced by wire-arc additive manufacturing process: microstructure and properties | en_US |
| dc.type | doctoral thesis | en_US |