About this Abstract |
| Meeting |
MS&T25: Materials Science & Technology
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| Symposium
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Additive Manufacturing, Directed Energy Deposition of Metals: Processing – Microstructure – Mechanical Property Relationships
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| Presentation Title |
Investigation of Micro-Cracks with Mechanical and Electropolishing of Additively Manufactured TiAl |
| Author(s) |
Collin Pickersgill, Zhaoying Ding, Chenwei Shao, Yu Zou |
| On-Site Speaker (Planned) |
Collin Pickersgill |
| Abstract Scope |
Titanium Aluminide alloys are a material of interest for many lightweight, high temperature structural applications. The process of fabricating these alloys with additive manufacturing provides routes for design customization in complex shapes and with efficient source material use but requires ongoing characterization and testing to develop the maturity of the technology. Following thorough investigation of the intermetallic Ti-48Al-2Nb-2Cr alloy fabricated with DED, it has been found that favourability for micro and nanoscale cracking in the grain structures can be attributed to melt pool stresses during the printing process. We found that these stresses form strain concentrations within bulk grains that lead to intragranular cracking under the abrasive stresses of mechanical polishing as well as the moment of fracture under tensile stress. These microcracks form preferentially in certain regions of the heterostructure based on plastic mobility and are distinct from documented instances of cracking during fabrication with L-DED. These cracks occur in parallel within globular γm grains pervasively across the surface and reflect the crystalline favorability to propagate in slip directions. Cracking seems to occur only on the surface at a limited depth after mechanical polishing, and electropolishing was proven as a method to produce a crack-free surface. Reverse polishing was also used to determine the onset of cracking. Additionally, significant strengthening was observed in the sample, suggesting phenomena such as room temperature oxygen strengthening or work hardening in the microstructure. |