A study of arc weldability of γ′-strengthened cobalt-based superalloy
| dc.contributor.author | Abedi, Hamid | |
| dc.contributor.examiningcommittee | Khoshdarregi, Matt (Mechanical Engineering) | |
| dc.contributor.examiningcommittee | França, Rodrigo (Restorative Dentistry) | |
| dc.contributor.examiningcommittee | Bichler, Lukas (School of Engineering, University of British Columbia) | |
| dc.contributor.supervisor | Ojo, Olanrewaju | |
| dc.date.accessioned | 2023-08-24T18:07:38Z | |
| dc.date.available | 2023-08-24T18:07:38Z | |
| dc.date.issued | 2023-08-24 | |
| dc.date.submitted | 2023-08-24T15:33:30Z | en_US |
| dc.degree.discipline | Mechanical Engineering | en_US |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | |
| dc.description.abstract | CoWAlloy1 is a new gamma prime (γ′) precipitation-strengthened cobalt (Co)-based superalloy that is developed to replace conventional nickel (Ni)-based superalloys for high-temperature applications in land-based and aero turbine engines. Welding superalloys is an essential part of the manufacture and repair of complex-shaped components of turbine engines. Unfortunately, joining precipitation-hardened superalloys such as CoWAlloy1 is severely limited due to their high susceptibility to cracking during welding. Therefore, this research conducts a comprehensive study on the cracking susceptibility and corresponding properties of CoWAlloy1 that is subjected to gas tungsten arc welding (GTAW) and develops an effective approach to eliminate/minimize cracking during welding. The numerical model developed to simulate GTAW shows an adequate level of accuracy for predicting the solidification behavior of the fusion zone (FZ) and selecting the window of welding parameters that prevent FZ cracking during the welding of CoWAlloy1. Although optimum GTAW parameters prevent cracking in the FZ, welding produces heat-affected zone (HAZ) cracking in the alloy. A careful examination of the microstructure shows that a primary cause of HAZ cracking in this alloy is intergranular liquation due to the subsolidus liquation reaction of the MC-type carbides and γ′ precipitates, which are identified by electron microscopy and spectroscopy to be present in the material before welding. Detailed weldability studies reveal that the grain boundary elemental segregation of boron (B) controls the cracking susceptibility of the HAZ during welding. In addition, it is observed that a reduction in grain size contributes to the resistance of CoWAlloy1 to HAZ cracking. Accordingly, a new pre-weld heat treatment that couples reduction in grain boundary segregation of B with a small grain size is found to effectively inhibit HAZ cracking not only during welding but also after the post-weld heat treatment (PWHT). Furthermore, the new pre-weld heat treatment produces tensile properties and hot corrosion resistance after PWHT that are comparable to those of the alloy that has not been subjected to welding, which demonstrates that the new pre-weld heat treatment prevents the deleterious effects of welding on tensile properties and does not produce a substantial reduction in the hot corrosion resistance of this new superalloy. | |
| dc.description.note | October 2023 | |
| dc.identifier.uri | http://hdl.handle.net/1993/37488 | |
| dc.language.iso | eng | |
| dc.rights | open access | en_US |
| dc.subject | Co-based superalloy | |
| dc.subject | Microstructure | |
| dc.subject | Welding | |
| dc.subject | Liquation cracking | |
| dc.subject | Grain boundary segregation | |
| dc.title | A study of arc weldability of γ′-strengthened cobalt-based superalloy | |
| dc.type | doctoral thesis | en_US |
| local.subject.manitoba | no | |
| project.funder.identifier | https://doi.org/10.13039/501100000038 | |
| project.funder.name | Natural Sciences and Engineering Research Council of Canada |