@article{ed44317823594283a6e4e9195e5035ed,
title = "Phase transformation pathways in Ti-6Al-4V manufactured via electron beam powder bed fusion",
abstract = "The design of additively manufactured metallic alloys with tailored mechanical properties requires a detailed understanding of the microstructural evolution throughout the printing process. In Ti-6Al-4V, this involves a complex combination of phase transformations, leading to microstructural and property variations within a single as-fabricated build. The origin of such property variations and the sequence of phase changes occurring during the cyclic heating and cooling process remain uncertain. We have studied the phase transformation pathway by following how, in particular, the β phase growth varies within the build. Samples manufactured by electron beam powder bed fusion were analysed using electron microscopy and atom probe tomography techniques. We demonstrate that a significant β phase fraction variation occurs within a given build plane. We reveal that the high-temperature β phase can be separated into two categories, depending on whether it was retained from cooling from above the β transus temperature, or nucleated below it. This is the first direct evidence of the coexistence of both types of β transformation products in Ti-6Al-4V. The abrupt cyclic nature of the additive manufacturing process is what has facilitated this unusual transformation sequence. The work provides a complete and general description of the phase transformation pathway, informed by these observations. The implication of the phase transformation pathway on hardness is discussed in relation to chemical variation and oxygen pickup.",
keywords = "Additive manufacturing, Electron beam melting, Phase transformations, Ti-6Al-4V",
author = "Davids, {William J.} and Hansheng Chen and Keita Nomoto and Hao Wang and Sudarsanam Babu and Sophie Primig and Xiaozhou Liao and Andrew Breen and Ringer, {Simon P.}",
note = "Funding Information: The authors acknowledge the facilities, scientific and technical assistance of Sydney Microscopy & Microanalysis (SMM), a University of Sydney core research facility and the University's node of Microscopy Australia. In doing so, we particularly acknowledge Drs. Vijay Bhatia and Takanori Sato. We also acknowledge gratefully the expertise and support from the Sydney Manufacturing Hub at the University of Sydney. We note that the research was sponsored by the Department of Industry, Innovation and Science under the auspices of the AUSMURI program. The authors also gratefully acknowledge financial support from the Department of the Navy, Office of Naval Research under ONR award number N00014–18–1 – 2794 . 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 research was also sponsored by the US Department of Energy , Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office under contract DE-AC05–00OR22725 with UT-Battelle, LLC. Access to the Oak Ridge National Laboratory's (ORNL) additive manufacturing equipment at ORNL's Manufacturing Demonstration Facility (MDF) was facilitated by US Department of Energy's Strategic Partnership Projects (SPP) mechanism. More information can be found at https://science.energy.gov/lp/strategic-partnership-projects . Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, under contract DE-AC05–00OR22725 with UT-Battelle, LLC. The authors also acknowledge Dr Peter Davies, Dr Brad Wynne and Professor W.Mark Rainforth for the use of their parent beta reconstruction code. The authors acknowledge Dr. Wei Xu at Deakin University in VIC, Australia, for providing the l -PBF Ti-6Al-4V sample. Funding Information: The authors acknowledge the facilities, scientific and technical assistance of Sydney Microscopy & Microanalysis (SMM), a University of Sydney core research facility and the University's node of Microscopy Australia. In doing so, we particularly acknowledge Drs. Vijay Bhatia and Takanori Sato. We also acknowledge gratefully the expertise and support from the Sydney Manufacturing Hub at the University of Sydney. We note that the research was sponsored by the Department of Industry, Innovation and Science under the auspices of the AUSMURI program. The authors also gratefully acknowledge financial support from the Department of the Navy, Office of Naval Research under ONR award number N00014–18–1–2794. 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 research was also sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Advanced Manufacturing Office under contract DE-AC05–00OR22725 with UT-Battelle, LLC. Access to the Oak Ridge National Laboratory's (ORNL) additive manufacturing equipment at ORNL's Manufacturing Demonstration Facility (MDF) was facilitated by US Department of Energy's Strategic Partnership Projects (SPP) mechanism. More information can be found at https://science.energy.gov/lp/strategic-partnership-projects. Research sponsored by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, under contract DE-AC05–00OR22725 with UT-Battelle, LLC. The authors also acknowledge Dr Peter Davies, Dr Brad Wynne and Professor W.Mark Rainforth for the use of their parent beta reconstruction code. The authors acknowledge Dr. Wei Xu at Deakin University in VIC, Australia, for providing the L-PBF Ti-6Al-4V sample. Publisher Copyright: {\textcopyright} 2021",
year = "2021",
month = aug,
day = "15",
doi = "10.1016/j.actamat.2021.117131",
language = "English",
volume = "215",
journal = "Acta Materialia",
issn = "1359-6454",
publisher = "Elsevier",
}