Title: Process-Defect-Structure-Property Correlations During Laser Powder Bed Fusion of Alloy 718: Role of In Situ and Ex Situ Characterizations

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 paper, 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. Finally, validity ofmore » using analytical weld process models to describe the above phenomena is also highlighted.« less

Authors:

Foster, S. J. ^[1]; Carver, K. ^[2]; Dinwiddie, R. B. ^[2]; List, F. ^[2]; Unocic, K. A. ^[3]; Chaudhary, A. ^[4]; Babu, S. S. ^[5]

---

+ Show Author Affiliations

1. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering; Oerlikon AM US, Charlotte, NC (United States)
2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division. Manufacturing Demonstration Facility
3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Materials Science and Technology Division
4. Applied Optimization Inc., Dayton, OH (United States)
5. Univ. of Tennessee, Knoxville, TN (United States). Dept. of Materials Science and Engineering. Dept. of Mechanical and Aerospace and Biomedical Engineering; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Manufacturing Demonstration Facility

Publication Date:

Tue Aug 14 00:00:00 EDT 2018

Research Org.:

Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States); Univ. of Tennessee, Knoxville, TN (United States); Applied Optimization Inc., Dayton, OH (United States)

Sponsoring Org.:

USDOE Office of Energy Efficiency and Renewable Energy (EERE), Energy Efficiency Office. Advanced Manufacturing Office; USDOE Office of Nuclear Energy (NE), Fuel Cycle Technologies (NE-5); National Aeronautics and Space Administration (NASA)

OSTI Identifier:

1468183

Grant/Contract Number:  

AC05-00OR22725; NNX15CA24C

Resource Type:

Accepted Manuscript

Journal Name:

Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science

Additional Journal Information:

Journal Volume: 49; Journal Issue: 11; Journal ID: ISSN 1073-5623

Publisher:

ASM International

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE