Evaluation of pore re-opening after HIP in LPBF Ti–6Al–4V

ABSTRACT

Higher build rates in Laser Powder Bed Fusion (LPBF) process in combination with Hot Isostatic Pressing (HIP) have been proposed to reduce the cost-per-part of additive manufacturing. However, inert gas trapped in the pores could cause healed pores to re-grow after elevated temperature exposure. Therefore, understanding the possible effects of this pore re-opening phenomenon is crucial in maintaining quality of parts subjected to elevated temperatures during service. The aim of the present study was to investigate pore re-opening after HIP in Ti–6Al–4V parts by exposing samples to different elevated temperatures for varying times. The changes in the pore content were studied using microscopy and micro X-ray computed tomography in combination with gas content analysis. Based on the results, it was concluded that for typical service temperatures of Ti–6Al–4V, pore re-opening was minimal.

KEYWORDS:

• Additive manufacturing
• laser powder bed fusion
• Hot Isostatic Pressing
• HIP
• Ti–6Al–4V
• pore
• porosity
• µ-CT

Acknowledgements

Special thanks to our colleagues Abdul-Shaafi Shaikh, Janne Hongisto and Jenni Setola for their extra support in the preparation of this work. The authors are also grateful to the Quintus Technologies AB (Västerås, Sweden) for performing the optimised HIP test cycles.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the European Union’s Horizon 2020 Framework Programme research an innovation programme under grant number 820774.

Notes on contributors

Topi Kosonen

Topi Kosonen, R&D Engineer. Topi Kosonen (M.Sc. in Technology) graduated from Helsinki University of Technology with a major in Applied Materials Science. His Master's Thesis dealt with Hot Isostatic Pressing (HIP) and principles of metal powder densification during HIPping. He started his career at the Technical Research Centre of Finland (VTT) and worked extensively with new materials and advanced manufacturing technologies. He joined EOS Finland Oy in 2016 where he has focused on post-treatment (heat treatment, vacuum heat treatment and HIPping) of laser melted materials, especially Ti- and CoCr-alloys.

K. Kakko

Katri Kakko, Project Manager. Katri Kakko (M.Sc. in Technology) graduated from Aalto University with a major in Applied Materials Science. Her thesis and early career included research on powder metallurgy and additive manufacturing. In recent years, her work has mainly focused on the development of titanium powders and processes for additive manufacturing.

N. Raitanen

Niko Raitanen, R&D Engineer. Niko Raitanen (M.Sc. in Technology) graduated from Tampere University of Technology in early 2018 majoring in Metallic and Ceramic Materials. He completed his thesis for EOS Finland Oy regarding statistical analysis of process monitoring data in LPBF and has since worked for the company with a strong focus on data science.