Title: Energy Coupling Mechanisms and Scaling Behavior Associated with Laser Powder Bed Fusion Additive Manufacturing

Abstract

In situ optical absorptivity measurements are carried out to clarify the physics of the laser-material interactions involved and to validate both finite element and analytical models describing laser powder bed fusion processing. Absorption of laser energy is evaluated directly using precise calorimetry measurements and compared to melt pool depths for common structural metal alloys (Ti-6Al-4V, Inconel 625, and stainless steel 316L) as a function of incident laser power, scan velocity and laser beam diameter. Changes in both absorptivity and melt pool depths for all materials are found to vary strongly across the conduction-keyhole mode threshold. A hydrodynamic finite element model is coupled to a ray-tracing-based absorptivity model, yielding excellent agreement with the experimental results and elucidating additional physics. The experimental results are further analyzed using normalized enthalpy (β) and normalized thermal diffusion length (L*_th) relations and demonstrate that the normalized melt pool depth (d* = d/a, where d is melt pool depth and a is beam radius) is proportional to βL*_th, while absorptivity follows an asymptotic exponential function against βL*_th. Expressions for melt pool depth and laser absorptivity across different materials and laser scan systems are derived and thus provide useful tools to accelerate the optimization of laser processing parametersmore » for metal 3D printing processes.« less

Authors:

Ye, Jianchao ^[1]; Khairallah, Saad A. ^[1]; Rubenchik, Alexander M. ^[1]; Crumb, Michael F. ^[1]; Guss, Gabe ^[1]; Belak, Jim ^[1]; Matthews, Manyalibo J.  ^[1]

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• Search DOE PAGES for ORCID "0000-0003-3519-7221"

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+ Show Author Affiliations

1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Publication Date:

Thu May 16 00:00:00 EDT 2019

Research Org.:

Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1569671

Alternate Identifier(s):

OSTI ID: 1513062

Report Number(s):

LLNL-JRNL-763217
Journal ID: ISSN 1438-1656; 950524

Grant/Contract Number:  

AC52-07NA27344; 18‐SI‐003; 17‐SC‐20‐SC

Resource Type:

Accepted Manuscript

Journal Name:

Advanced Engineering Materials

Additional Journal Information:

Journal Volume: 21; Journal Issue: 7; Journal ID: ISSN 1438-1656

Publisher:

Wiley

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; additive manufacturing; laser welding; metals and alloys; simulations; thermal analysis