Characterization of microstructure and high strain rate deformation response of C250 maraging steel fabricated by directed energy deposition process
| dc.contributor.author | Guo, Lulu | |
| dc.contributor.examiningcommittee | Wu, Nan (Mechanical Engineering) | |
| dc.contributor.examiningcommittee | Khoshdarregi, Matt (Mechanical Engineering) | |
| dc.contributor.examiningcommittee | Medraj, Mamoun (Concordia University) | |
| dc.contributor.supervisor | Ojo, Olanrewaju | |
| dc.contributor.supervisor | Andersson, Joel | |
| dc.date.accessioned | 2024-12-11T16:22:16Z | |
| dc.date.available | 2024-12-11T16:22:16Z | |
| dc.date.issued | 2024-11-22 | |
| dc.date.submitted | 2024-12-03T19:29:43Z | en_US |
| dc.date.submitted | 2024-12-10T22:32:04Z | en_US |
| dc.degree.discipline | Mechanical Engineering | |
| dc.degree.level | Doctor of Philosophy (Ph.D.) | |
| dc.description.abstract | C250 maraging steel, known for its high strength and good toughness, is ideal for applications requiring exceptional high strain rate properties. Its carbon-free composition is suitable for the directed energy deposition-arc (DED-Arc) method, an additive manufacturing (AM) process with a low cost and high deposition rate. However, the thermal cycles in DED-Arc significantly impact the microstructure of C250 alloy. This could lead to undesirable high strain rate properties, necessitating post-fabrication heat treatment. Research gaps remain in understanding the microstructure and dynamic deformation response of DED-Arc fabricated C250 steel. Besides, AM enables fabricating complex geometries, but accurate constitutive models governing the stress-strain relationship of materials are essential for reliable finite element analysis (FEA) predictions of dynamic deformation. Yet, no reliable models have been proposed to predict the dynamic deformation behaviors of DED-Arc built C250 alloy. Therefore, this study aims to investigate the microstructure and dynamic deformation responses of DED-Arc built C250 steel at different strain rates and temperatures and to develop appropriate constitutive models based on the observed flow behavior. Microstructure analyses indicate the absence of strengthening precipitates and the presence of retained austenite phase in as-built DED-Arc C250 steel, leading to inferior dynamic mechanical performance compared to heat-treated wrought C250 alloy. However, commercial heat treatment significantly improves the dynamic mechanical performance of heat-treated DED-Arc C250 steel, making it comparable to that of the heat-treated wrought C250 alloy. This substantial improvement is mainly attributed to the formation of nano-sized, needle-shaped, and coherent Ni3Mo strengthening precipitates during the heat treatment. Modifications are made to the Johnson-Cook constitutive models to predict the dynamic deformation behaviors of as-deposited and heat-treated DED-Arc C250 alloy, respectively. These modifications consider the variable thermal softening effects and coupled effects of strain rate and strain in the flow behavior of the as-deposited specimen. In the heat-treated condition, the modified model accounts for the combined effects of strain rate and strain, as well as joint influences of strain rate and temperature on the flow behavior at elevated temperatures. The enhanced predictive capability of the modified Johnson-Cook models is further validated through verification tests under new dynamic compression conditions. | |
| dc.description.note | February 2025 | |
| dc.identifier.uri | http://hdl.handle.net/1993/38705 | |
| dc.language.iso | eng | |
| dc.rights | open access | en_US |
| dc.subject | High strain rate deformation behavior | |
| dc.subject | Additive manufacturing | |
| dc.subject | C250 maraging steel | |
| dc.title | Characterization of microstructure and high strain rate deformation response of C250 maraging steel fabricated by directed energy deposition process | |
| dc.type | doctoral thesis | en_US |
| local.subject.manitoba | no | |
| project.funder.name | Natural Sciences and Engineering Research Council (NSERC) of Canada |