Abstract
Components made by laser powder bed fusion (L-PBF) additive processes require extensive trial and error optimization to minimize defects and arrive at targeted microstructure and properties. In this work, in situ infrared thermography and ex situ surface roughness measurements were explored as methodologies to ensure Inconel® 718-part quality. For a given laser energy of 200 Watts, prismatic samples were produced with different exposure times (80 to 110 µs) and point spacings (80 to 110 µm). The infrared intensities from laser–material interaction zones were measured spatially and temporally. The conditions leading to higher IR intensity and lowest surface roughness values correlated well with less porosity and coarse solidification grain structure. The transition from highly columnar to misoriented growth is attributed to changes in thermal gradients and liquid–solid interface velocities. Hardness measurements and electron microscopy of the as-processed and post-processed heat-treated samples show complex transitions in microstructural states including the heavily dislocated FCC matrix, reduction of dislocation density, and copious precipitation, respectively. These results show that the geometry-process-structure-property correlations are dynamic, and they cascade depending on the transitions of phase states from powder to liquid to solid, as well as phase decompositions and deformations within the solid FCC phase. Validity of using analytical weld process models to describe the above phenomena is also highlighted.
Original language | English |
---|---|
Pages (from-to) | 5775-5798 |
Number of pages | 24 |
Journal | Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science |
Volume | 49 |
Issue number | 11 |
DOIs | |
State | Published - Nov 1 2018 |
Funding
The authors of this work would like to acknowledge and thank the funding contributor Applied Optimization, Inc. under the NASA STTR Phase II program (Contract Number: NNX15CA24C). Part of the research is based upon work supported by the US Department of Energy, Office of Energy, Efficiency, and Renewable Energy, Advanced Manufacturing Office under Contract Number DE-AC05-00OR22725. The microscopy was supported by using instrumentation (FEI Talos F200X S/TEM) provided by the Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. D.W. Coffey assisted with the experimental work. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. (http://energy.gov/downloads/doe-public-access-plan). Manuscript submitted May 6, 2018. The authors of this work would like to acknowledge and thank the funding contributor Applied Optimization, Inc. under the NASA STTR Phase II program (Contract Number: NNX15CA24C). Part of the research is based upon work supported by the US Department of Energy, Office of Energy, Efficiency, and Renewable Energy, Advanced Manufacturing Office under Contract Number DE-AC05-00OR22725. The microscopy was supported by using instrumentation (FEI Talos F200X S/TEM) provided by the Department of Energy, Office of Nuclear Energy, Fuel Cycle R&D Program and the Nuclear Science User Facilities. D.W. Coffey assisted with the experimental work. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. (http://energy.gov/download s/doe-public-access-plan).