Abstract
In electron beam melting (EBM) powder bed fusion (PBF), variations in electron beam scan strategies can be used to control thermal transients in the additive manufacturing process, both in the melt pool and in previously deposited layers. In this study, three different EBM beam scan strategies, i.e. the standard raster scan, ordered spot scan, and random spot scan patterns, were used to fabricate three identical Ti-6Al-4V blocks. Using scanning electron microscopy and electron backscatter diffraction, variations in microstructure and crystallographic texture, such as α lath thickness, prior beta β grain size and orientation, α/α lath boundary (LB) distributions, are investigated with respect to the applied scan strategy. Both spot scan strategies result in coarser α laths and smaller prior β grains with width and height < 1/3 of the value of the typical large columnar grains, observed in raster scan samples. The combined fraction of type 2 and type 4 α/α LBs measured in the three samples was found to be between 0.50 and 0.85, which is greater than the expected combined fraction of ~0.36 for a random distribution of α variants. This suggests the presence of a mild to weak variant selection in EBM Ti64.
| Original language | English |
|---|---|
| Article number | 109165 |
| Journal | Materials and Design |
| Volume | 196 |
| DOIs | |
| State | Published - Nov 2020 |
Funding
The authors acknowledge the scientific and technical input and support from ORNL's Manufacturing Demonstration Facility (MDF) , and especially acknowledge the contributions of Sabina Kumar (University of Tennessee Knoxville, UTK) and Dr. Suresh Babu (ORNL/UTK) for several fruitful discussions. Further, the authors wish to thank Dr. Adam Pilchak (AFRL) for providing the BOR code and Brian Welk (OSU) for his valuable inputs and discussions. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University. This project is supported by the Australia–US Multidisciplinary University Research Initiative (MURI) program, under ONR award number N00014-18-1-2794 and project “Rationalization of Liquid/Solid and Solid/Solid Interphase Instabilities During Thermal-Mechanical Transients of Metal Additive Manufacturing”. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Office of Naval Research. The authors acknowledge the scientific and technical input and support from ORNL's Manufacturing Demonstration Facility (MDF), and especially acknowledge the contributions of Sabina Kumar (University of Tennessee Knoxville, UTK) and Dr. Suresh Babu (ORNL/UTK) for several fruitful discussions. Further, the authors wish to thank Dr. Adam Pilchak (AFRL) for providing the BOR code and Brian Welk (OSU) for his valuable inputs and discussions. Electron microscopy was performed at the Center for Electron Microscopy and Analysis (CEMAS) at The Ohio State University. This project is supported by the Australia–US Multidisciplinary University Research Initiative (MURI) program, under ONR award number N00014-18-1-2794 and project “Rationalization of Liquid/Solid and Solid/Solid Interphase Instabilities During Thermal-Mechanical Transients of Metal Additive Manufacturing”. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the Office of Naval Research.
Keywords
- Beam scan strategy
- Electron backscatter diffraction (EBSD)
- Electron beam melting (EBM)
- Microstructural variation
- Scanning electron microscopy (SEM)
- Ti-6Al-4 V