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Title: Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing

Abstract

Gaussian laser intensity profiles are standard in laser-based metal additive manufacturing, although recent work in single-layer melt tracks showed that beam shaping could offer a feasible route towards microstructural control. Since thermal cycling and grain orientation templating in multilayer builds can alter microstructures, we compare three-dimensional 316L stainless steel cubes built using Gaussian and elliptical laser intensity profiles. Microstructural characterization confirms that elliptical beams result in a modified and improved microstructure compared to Gaussian beams. This assessment favoring the elliptical beam is based on: (1) the observed refinement of the columnar and equiaxed grains; (2) more importantly, the volume fraction occupied by equiaxed grains increases dramatically such that the average grain area is reduced by nearly 50%; (3) reduced texture in cubes built using an elliptical beam. The random orientation of small equiaxed grains in samples built using an elliptical beam also suggests a higher nucleation frequency. High-fidelity finite element simulations that deliver accurate thermal profiles by incorporating laser ray tracing and fluid dynamics were performed. Using a time-dependent solidification map based on local thermal gradients (G) and growth rates (R), our simulation results confirm the experimentally observed trend that an elliptical beam results in a favorable thermal profile.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1648176
Alternate Identifier(s):
OSTI ID: 1657687
Report Number(s):
LLNL-JRNL-805378
Journal ID: ISSN 0264-1275; S0264127520306067; 109071; PII: S0264127520306067
Grant/Contract Number:  
AC52-07NA27344; LDRD 18-SI-003
Resource Type:
Published Article
Journal Name:
Materials & Design
Additional Journal Information:
Journal Name: Materials & Design Journal Volume: 195 Journal Issue: C; Journal ID: ISSN 0264-1275
Publisher:
Elsevier
Country of Publication:
United Kingdom
Language:
English
Subject:
36 MATERIALS SCIENCE; laser powder bed fusion; beam shape; microstructure control; solidification; stainless steel

Citation Formats

Roehling, Tien T., Shi, Rongpei, Khairallah, Saad A., Roehling, John D., Guss, Gabe M., McKeown, Joseph T., and Matthews, Manyalibo J. Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing. United Kingdom: N. p., 2020. Web. https://doi.org/10.1016/j.matdes.2020.109071.
Roehling, Tien T., Shi, Rongpei, Khairallah, Saad A., Roehling, John D., Guss, Gabe M., McKeown, Joseph T., & Matthews, Manyalibo J. Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing. United Kingdom. https://doi.org/10.1016/j.matdes.2020.109071
Roehling, Tien T., Shi, Rongpei, Khairallah, Saad A., Roehling, John D., Guss, Gabe M., McKeown, Joseph T., and Matthews, Manyalibo J. Thu . "Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing". United Kingdom. https://doi.org/10.1016/j.matdes.2020.109071.
@article{osti_1648176,
title = {Controlling grain nucleation and morphology by laser beam shaping in metal additive manufacturing},
author = {Roehling, Tien T. and Shi, Rongpei and Khairallah, Saad A. and Roehling, John D. and Guss, Gabe M. and McKeown, Joseph T. and Matthews, Manyalibo J.},
abstractNote = {Gaussian laser intensity profiles are standard in laser-based metal additive manufacturing, although recent work in single-layer melt tracks showed that beam shaping could offer a feasible route towards microstructural control. Since thermal cycling and grain orientation templating in multilayer builds can alter microstructures, we compare three-dimensional 316L stainless steel cubes built using Gaussian and elliptical laser intensity profiles. Microstructural characterization confirms that elliptical beams result in a modified and improved microstructure compared to Gaussian beams. This assessment favoring the elliptical beam is based on: (1) the observed refinement of the columnar and equiaxed grains; (2) more importantly, the volume fraction occupied by equiaxed grains increases dramatically such that the average grain area is reduced by nearly 50%; (3) reduced texture in cubes built using an elliptical beam. The random orientation of small equiaxed grains in samples built using an elliptical beam also suggests a higher nucleation frequency. High-fidelity finite element simulations that deliver accurate thermal profiles by incorporating laser ray tracing and fluid dynamics were performed. Using a time-dependent solidification map based on local thermal gradients (G) and growth rates (R), our simulation results confirm the experimentally observed trend that an elliptical beam results in a favorable thermal profile.},
doi = {10.1016/j.matdes.2020.109071},
journal = {Materials & Design},
number = C,
volume = 195,
place = {United Kingdom},
year = {2020},
month = {10}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1016/j.matdes.2020.109071

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