Title: Interplay of strain and phase evolution of laser powder bed fusion Ti–6Al–4V

Abstract

While additive manufacturing (AM) provides a method of producing geometrically complex and highly detailed structures, the generation of residual strain in AM processes like laser powder bed fusion (L-PBF) can negatively impact performance-enabling properties. In applications such as orthopedic implants, specific performance windows require optimized microstructures in order to obtain desirable properties from multi-phase alloys like Ti–6Al–4V. This research aims to quantify the microscale origins of strain in L-PBF manufactured Ti–6Al–4V by understanding how strain is distributed at the grain and sub-grain scale, the interplay between phase evolution and strain, and examining post-processing strain relief strategies to control these features. Model spinal cage implants were manufactured from Ti–6Al–4V powder via L-PBF and then subjected to strain relieving heat treatment cycles above and below the Ti–6Al–4V β transus as a function of time and cooling rate. Residual strain was then studied via high resolution electron backscatter diffraction (HR-EBSD), and 2D strain maps with sub-micron resolution were generated for each post-processing state. It was found that macroscale thermal strains decreased with heat treatment time, but additional contributions from phase stabilizing residual strains retained primarily in the α' grains as lattice distortive strain remained. Additionally, the retention of β phase significantly changed themore » strain and dislocation distribution while reducing overall residual strain. In conclusion, these results were validated and reinforced with 3D mesoscopic micromechanical modeling of strain behavior across simulated microstructures, confirming that the local lattice dilation of α’ martensite is a primary contributor of microscale strain generation and retention in L-PBF Ti–6Al–4V.« less

Authors:

Andrews, Caleb  ^[1];

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Heo, T. W. ^[2]; Shi, R. ^[2]; Başgül, C. ^[3]; Kurtz, S. ^[4]; Matthews, M. J. ^[2]; Taheri, M. L. ^[1]

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+ Show Author Affiliations

1. Johns Hopkins Univ., Baltimore, MD (United States)
2. Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
3. Drexel Univ., Philadelphia, PA (United States)
4. Exponent Engineering and Science Consulting, Philadelphia, PA (United States)

Publication Date:

Sat Aug 27 00:00:00 EDT 2022

Research Org.:

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

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); US Department of the Navy, Office of Naval Research (ONR); USDOE Laboratory Directed Research and Development (LDRD) Program

OSTI Identifier:

2007598

Alternate Identifier(s):

OSTI ID: 1890541

Report Number(s):

LLNL-JRNL-823443
Journal ID: ISSN 0921-5093; 1036177

Grant/Contract Number:  

AC52-07NA27344; B646330; N00014-20-1-2788; 18-SI-003

Resource Type:

Accepted Manuscript

Journal Name:

Materials Science and Engineering. A, Structural Materials: Properties, Microstructure and Processing

Additional Journal Information:

Journal Volume: 855; Journal ID: ISSN 0921-5093

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; titanium alloy; residual strains; lattice strains; additive manufacturing; electron backscatter diffraction (EBSD)