Microstructural Development in Inconel 718 Nickel-Based Superalloy Additively Manufactured by Laser Powder Bed Fusion

Authors

Thinh Huynh, University of Central Florida
Abhishek Mehta, University of Central Florida
Kevin Graydon, University of Central Florida
Jeongmin Woo, University of Central Florida
Sharon Park, Johns Hopkins University
Holden Hyer, University of Central Florida
Le Zhou, Marquette UniversityFollow
D. Devin Imholte, Idaho National Laboratory
Nicolas E. Woolstenhulme, Idaho National Laboratory
Daniel M. Wachs, Idaho National Laboratory
Yongho Sohn, University of Central Florida

Document Type

Article

Publication Date

2022

Publisher

Springer

Source Publication

Metallography, Microstructure, and Analysis

Source ISSN

2192-9262

Original Item ID

DOI: 10.1007/s13632-021-00811-0

Abstract

Excellent weldability and high temperature stability make Inconel 718 (IN718) one of the most popular alloys to be produced by additive manufacturing. In this study, we investigated the effects of laser powder bed fusion (LPBF) parameters on the microstructure and relative density of IN718. The samples were fabricated with independently varied laser power (125–350 W), laser scan speed (200–2200 mm/s), and laser scan rotation (0°–90°). Archimedes’ method, optical microscopy, and scanning electron microscopy were employed to assess the influence of LPBF parameters on the relative density and microstructure. Optimal processing windows were identified for a wide range of processing parameters, and relative density greater than 99.5% was achieved using volumetric energy density between 50 and 100 J/mm³. Microstructural features including melt pool geometry, lack of fusion defect, keyhole porosity, and sub-grain cellular microstructure were examined and quantified to correlate to LPBF parameters. A simple empirical model was postulated to relate relative sample density and LPBF volumetric energy density. Melt pool dimensions were quantitatively measured and compared to estimations based on Rosenthal solution, which yielded a good agreement with the width, but underestimated the depth, particularly at high energy input, due to lack of consideration for keyhole mode. In addition, the sub-grain cellular-dendritic microstructure in the as-built samples was observed to decrease with increasing laser scan speed. Quantification of the sub-micron cellular-dendritic microstructure yielded estimated cooling rate in the order of 10⁵–10⁷ K/s.

Comments

Accepted version. Metallography, Microstructure, and Analysis, Vol. 11 (2022): 11-107. DOI. © 2022 Springer. Used with permission.

Recommended Citation

Huynh, Thinh; Mehta, Abhishek; Graydon, Kevin; Woo, Jeongmin; Park, Sharon; Hyer, Holden; Zhou, Le; Imholte, D. Devin; Woolstenhulme, Nicolas E.; Wachs, Daniel M.; and Sohn, Yongho, "Microstructural Development in Inconel 718 Nickel-Based Superalloy Additively Manufactured by Laser Powder Bed Fusion" (2022). Mechanical Engineering Faculty Research and Publications. 311.
https://epublications.marquette.edu/mechengin_fac/311