Microstructure control by heat treatment for better ductility and toughness of Ti-6Al-4V produced by laser powder bed fusion

ABSTRACT

In this work, the effects of post-LPBF (laser powder bed fusion) heat treatments on microstructure evolution, tensile and Charpy properties of Ti-6Al-4V have been investigated. The results show that the original martensitic microstructure in the LPBF sample has converted to a lamellae mixture of α and β phases when post heat-treatment temperatures are below the β-transus (800°C, 850°C and 900°C) with air cooling. On this basis, a good balance of tensile strength and ductility was obtained from sample post heated at 800°C for 6 h followed by air-cooling, with an increase of ~42% in ductility and a significant toughness enhancement (almost 100% increase) compared to the as-built sample. The relationship betweenα lamellaethickness, β volume fraction and post-LPBF heat treatment has been established. Both α lamellae thickness and β volume fraction increase with the heat-treatment temperature.

KEYWORDS:

• Ti-6al-4v
• laser powder bed fusion
• heat treatment
• ductility
• charpy properties

Acknowledgements

This study was funded by CNIC Corporation Ltd. through a collaboration between Monash University and Commercial Aircraft Corporation of China Ltd. The authors would also like to acknowledge the use of facilities within the Monash Centre for Additive Manufacturing (MCAM), as well as the Monash Centre for Electron Microscopy (MCEM), a Node of Microscopy Australia.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available from the corresponding author, KZ, upon reasonable request.

Additional information

Funding

This work was supported by the CNIC Guotong Additive Manufacturing Co. Ltd.

Notes on contributors

Kun Zhang

Kun Zhang, PhD, is a research fellow at the Faculty of Engineering in Monash University, Australia. Her main research interests focus on developing the processes of additive manufacturing and powder metallurgy (e.g. hot isostatic pressing) of Ti-6Al-4V alloy and high strength beta titanium alloy. She received her master’s degree in Institute of Metal Research, Chinese Academy of Sciences, China in 2004 and her doctorate degree from University of Birmingham, UK in 2009.

Wen Hao Kan

Wen Hao Kan, PhD, is a research fellow at Faculty of Engineering in Monash University, Australia. He received his doctorate degree from the University of Sydney, Australia in 2018. His research focuses on additively manufactured titanium, aluminium and stainless steel alloys and studying the tribological behaviour of various engineering materials, and the recycling of industrial waste for the manufacturing of wear-resistant alloys.

Yang Liu

Yang Liu,a PhD candidate in Monash Centre for Additive Manufacturing of Monash University, Australia. He received his Bachelor Degree in Materials Engineering from Huazhong University of Science and Technology, China in 2012 and Master Degree from Institute of Metal Research, Chinese Academy of Sciences, China in 2015. His research mainly focuses on the relationship between thermomechanical process, microstructure and mechanical properties of titanium alloys.

Xiang Gao

Xiang Gao, is a research fellow in the Department of Materials Science and Engineering at Monash University. His research interests include the in-depth characterisation of microstructure of light metal and alloys using advanced electron microscopy.

Yuman Zhu

Yuman Zhu, PhD, academic manager of the Monash Centre for Additive Manufacturing. He has many-year research experience on metallic materials covering aluminium, titanium, nickel and magnesium alloys. His research interest involves an in-depth understanding of microstructure and mechanical properties in conventional and additive manufactured metals and alloys using state-of-the-art microscopy techniques.

Samuel Chao Voon Lim

Samuel Chao Voon Lim, PhD, is the team lead of Ti alloy research at the Monash Centre for Additive Manufacturing. He has many years of experience in thermomechanical processing of Ti alloys and other Light metals while working in research institutes in Australia and Singapore. He received his master’s degree in Mechanical Engineering from National University of Singapore in 2001 and his doctorate degree from Carnegie Mellon University, USA in 2008. His research interests are mainly in the process-microstructure-properties relationship of light-weight metals along with the processing of metallic composite materials.

Huizhi Peng

Huizhi Peng, is a PhD candidate in Monash Centre for Additive Manufacturing of Monash University, Australia. His main research interests cover statistic description on microstructure features and the application of additive manufacturing on Ti alloys (e.g. Ti-6Al-2Sn-4Zr-6Mo). He received his Bachelor degree from Material Science and Engineering in Central South University, China andHonours Degree in Material Science &Engineering in Monash University, Australia in 2020.

Aijun Huang

Aijun Huang, PhD, A  full time professor in the Department of Materials Science and Engineering, Monash University. Prof Huang is also the Head of Monash Centre for Additive Manufacturing which hosts the state-of-art metal 3D printing facilities. His research covers the entire spectrum of metal additive manufacturing (AM). Research efforts have covered; AM specific alloy design; metal powder manufacturing technology; component design for AM; AM process optimisation; post-AM process development including inspection, qualification and certification of final AM parts.