Session: 02-01-02: 7th Annual Conference-Wide Symposium on Additive Manufacturing: Metals II

Paper Number: 100169

100169 - Nuclear Irradiation Effects on Inconel 625 and 718 Specimens Fabricated via Laser Powder Bed Fusion 

Nickel-based superalloys, such as Inconel 625 and Inconel 718, possess high-temperature strength, creep resistance, and corrosion resistance, making them strong candidates for nuclear reactor applications. The appeal of using additive manufacturing (AM) for processing Inconel 625/718, and other nickel-based superalloys, is that conventional methods often face difficulties in their manufacturing due to their high hardness, inadequate machinability, high tool wear, and low thermal conductivity. Although nickel-based superalloy components fabricated via AM can potentially benefit future reactor designs, the effects of nuclear irradiation on additively manufactured, metallic components are still not well understood or documented in general. This is hindering their certified use in unique energy applications, especially for use in next-generation modular nuclear reactors. There are unique features within additively manufactured specimens that can influence their degradation due to nuclear irradiation, including gas-filled porosity, complex residual stress fields, nano-sized precipitates, and lack-of-fusion porosity.

This presentation summarizes the methods and findings related to a series of nuclear irradiation studies performed using the facilities at the University of Missouri Research Reactor (MURR). Experiments were performed to determine how additively manufactured (via laser powder bed fusion, i.e., L-PBF) Inconel 625 and 718 alloys respond to nuclear irradiation relative to their heat-treated and traditionally wrought counterparts. Two unique nuclear dosing methods were employed to evaluate their feasibility for more quickly determining nuclear irradiation effects on Inconel specimens. This was done to circumvent the long waiting time (before safe handling) associated with the radioactive decay of cobalt within each Inconel alloy which is much longer than any of the other alloy constituents and this complicates their efficient nuclear testing. The methods investigated included (1) use of an accelerator driven fast neutron flux of 3.0 x 10^9 neutrons/cm²/s and (2) use of full-spectrum nuclear irradiation on ultra-small specimens with a neutron flux of 6.3 x 10^13 neutrons/cm²/s in the MURR reactor. The logic here is that the use of fast neutrons and/or ultra-small specimens helps in reducing activation of specimens thus allowing for quicker wait times before their safe handling and characterization.

The micro-hardness, as well as microstructure, before and after irradiations for the investigated samples will be provided and discussed. Effects of specimen heat treatment and L-PBF build angle on hardness trends will be presented. The feasibility of using the two dosing methods for future nuclear accelerated testing will be discussed. Results indicate that all L-PBF specimens possess lower sensitivity to irradiation relative to wrought, and independent of radiation source/type. Heat treatments at various lengths and temperatures were found to produce precipitates in the Inconel alloys that affected hardness and radiation damage. 

Presenting Author: Scott M. Thompson Kansas State University

Presenting Author Biography: Scott M. Thompson is a Steve Hsu Keystone Associate Professor in the Alan Levin Department of Mechanical & Nuclear Engineering in the Carl R. Ice College of Engineering at Kansas State University (KSU). He received both his B.S. and Ph.D. in Mechanical Engineering from the University of Missouri (MU) in 2008 and 2012, respectively. Dr. Thompson’s research focuses on modeling the metals additive manufacturing (AM) process and in characterizing such parts (microstructure, properties, residual stress) before/after nuclear environmental exposure. He also performs research on heat exchanger design, heat pipes, heat transfer, and energy harvesting. His research efforts have led to 50+ published/peer-reviewed journal articles, 3 book chapters, and 80+ conference proceedings and presentations. He has helped secure and lead several externally-funded research projects from agencies such as the DoD, DoE, DARPA, NSF, and NASA. Thompson is a senior member of the AIAA and ASME.

Authors:

Scott M. Thompson Kansas State University
Bart Prorok Auburn University
John Gahl University of Missouri
Valentina O'Donnell University of Missouri
Mohanish Andurkar Kansas State University
Tahmina Keya Auburn University