Creep of IN738LC manufactured with laser powder bed fusion: effect of build orientation and twinning

ABSTRACT

The microstructural anisotropy caused by the highly oriented solidification of the metal Laser Powder Bed Fusion (PBF-LB/M) process affects mechanical short- and long-term properties. Component build orientation influences grain morphology and orientation, and thus, mechanical properties. While the creep behaviour of samples manufactured parallel and perpendicular to the build direction are studied intensively, the 45° build orientation remains uncharacterised. In this study, IN738LC creep samples are manufactured via PBF-LB/M in three build orientations (0°, 45° and 90°). While the results of 90° and 0° are as expected, where 90° achieves the longest time to rupture and largest rupture strain, the 45° specimen shows the least fracture time. Differences in microstructure and twinning behaviour are identified as one of the root causes for this unexpected behaviour. This study discusses the correlation between microstructure, twinning and build orientation and their effect on creep behaviour, with special focus on the 45° build orientation.

KEYWORDS:

• Laser powder bed fusion
• IN738LC
• build orientation
• creep
• microstructure
• twinning

Disclosure statement

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

Patents

There are no patents resulting from the work reported in this manuscript.

Notes

1. Hausner ratio, h = .$\frac{\mathrm{Tapped}\mathrm{Powder}\mathrm{Density}}{\mathrm{Bulk}\mathrm{Powder}\mathrm{Density}}$

2. Volume energy density,E_V = $\frac{\mathrm{Laser}\mathrm{Power}}{\mathrm{Scan}\mathrm{Speed}\times \mathrm{Hatch}\mathrm{Distance}\times \mathrm{Layer}\mathrm{Thickness}}$

Additional information

Funding

The research project (FVV project no.1401) was performed by the Institute of Materials Technology of the Technical University Darmstadt under the guidance of Prof. Dr.-Ing. Matthias Oechsner and by the Materials Testing Institute at the University of Stuttgart under the guidance of Prof. Dr.-Ing. Stefan Weihe. Based on a decision taken by the German Bundestag, it was supported by the Federal Ministry for Economic Affairs and Climate Action (BMWK) and the AIF (German Federation of Industrial Research Associations eV) within the framework of the industrial collective research (IGF) programme (IGF No. 21220 N/1) The authors gratefully acknowledge the support received from the funding organisations, from the FVV eV and from all those involved in the project.