Artificial porosity introduced during L-PBF of IN718, and its effect on fatigue performance before and after HIP

ABSTRACT

During laser powder bed fusion (L-PBF), the protective atmosphere, normally argon, can become trapped in cavities formed during the process. We have demonstrated this by introducing ø0.5 mm pores in the CAD file (totalling 0.5% by volume) and measuring a threefold increase in argon content, versus an identical IN718 build-job without pores. For critical applications where the material is subjected to cyclic loading, any defects can act as stress raisers and initiate cracks. The pores that were introduced drastically reduced the fatigue performance of said material. However, after Hot Isostatic Pressing (HIP), the material regained its properties as if the pores were never introduced. Still, the argon remains after HIP according to measurements as it lacks solubility and thus cannot leave the material. Worth noting is that a small quantity of argon originates from gas-atomisation of the powder and thus does not leave entirely during the remelting in L-PBF.

KEYWORDS:

• IN718
• argon
• fatigue
• hot isostatic pressing
• additive manufacturing
• pores

Acknowledgements

Linde AG and Quintus Technologies AB are acknowledged for funding of the study. Additional financial support was provided by the Swedish Governmental Agency for Innovation Systems (Vinnova), project number 2020-04408, and the Swedish Government via strategic competence (SC) funds. The authors are grateful towards all above mentioned organizations for the opportunity to carry out this research.

Disclosure statement

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

Additional information

Funding

The project members Quintus Technology and Linde are acknowledged for financial support of the research work through Swerim’s Membership Program ‘Powder Metallurgy’; Swerim Membership Research Consortia; Strategic Competence (SC) Funds from the Swedish Government.

Notes on contributors

Emil Strandh

Emil Strandh is employed as a Researcher and focuses on powder characterization and additive manufacturing of metals.

Johannes Gårdstam

Johannes Gårdstam is employed at Quintus Technologies as a Global Application Manager AMD.

Sophie Dubiez-Le Goff

Sophie Dubiez-Le Goff is employed at Linde as an Expert Powder Metallurgy for AM. She holds an PhD in Materials Science from MINES ParisTech.

Pelle Mellin

Pelle Mellin is employed as a Senior Researcher at Swerim and focuses on powder characterization and hot isostatic pressing, which in many projects is related to Additive Manufacturing. He holds a PhD in Materials Science from KTH Royal Institute of Technology.