Title: Schmid factor crack propagation and tracking crystallographic texture markers of microstructural condition in direct energy deposition additive manufacturing of Ti-6Al-4V

Abstract

Metallic additive manufacturing (AM) provides a customizable and tailorable manufacturing process for new engineering designs and technologies. The greatest challenge currently facing metallic AM is maintaining control of microstructural evolution during solidification and any solid state phase transformations during the build process. Ti-6Al-4V has been extensively surveyed in this regard, with the potential solid state and solidification microstructures explored at length. In this study, we evaluate the applicability of previously determined crystallo- graphic markers of microstructural condition observed in electron beam melting powder bed fusion (PBF-EB) builds of Ti-6Al-4V in a directed energy deposition (DED) build process. The aim of this effort is to elucidate whether or not these specific crystallographic textures are useful tools for indicating microstructural conditions in AM variants beyond PBF-EB. Parent β-Ti grain size was determined to be directly related to α-Ti textures in the DED build process, and the solid state microstructural condition could be inferred from the intensity of specific α-Ti orientations. Qualitative trends on the as-solidified β-Ti grain size were also determined to be related to the presence of a fiber texture, and proposed as a marker for as-solidified grain size in any cubic metal melted by AM. Analysis of the DED Ti-6Al-4Vmore » build also demonstrated a near complete fracture of the build volume, suspected to originate from accumulated thermal stresses in the solid state. Crack propagation was found to only appreciably occur in regions of slow cooling with large α +β colonies. Schmid factors for the basal and prismatic α-Ti systems explained the observed crack pathway, including slower bifurcation in colonies with lower Schmid factors of both slip systems. Colony morphologies and localized equiaxed β-Ti solidification were also found to originate from build pauses during production and uneven heating of the build edges during deposition. Tailoring of DED Ti-6Al-4V microstructures with the insight gained here is proposed, along with cautionary insight on preventing unplanned build pauses to maintain an informed and controlled thermal environment for microstructural control.« less

Authors:

Saville, Alec I. ^[1]; Benzing, Jake T. ^[2]; Vogel, Sven C. ^[3]; Buckner, Jessica ^[4]; Donohoue, Collin ^[5]; Kustas, Andrew B. ^[4]; Creuziger, Adam ^[6]; Clarke, Kester D. ^[1]; Clarke, Amy J. ^[1]

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+ Show Author Affiliations

1. Colorado School of Mines, Golden, CO (United States)
2. National Inst. of Standards and Technology (NIST), Boulder, CO (United States)
3. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
4. Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
5. Lockheed Martin Corporation, Lakewood, CO (United States)
6. National Inst. of Standards and Technology (NIST), Gaithersburg, MD (United States)

Publication Date:

Wed Jul 06 00:00:00 EDT 2022

Research Org.:

Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)

OSTI Identifier:

1882623

Report Number(s):

SAND2022-10467J
Journal ID: ISSN 2214-8604; 708768

Grant/Contract Number:  

NA0003525; 2019260337; 1624836; DMR-1828454; 89233218CNA000001

Resource Type:

Accepted Manuscript

Journal Name:

Additive Manufacturing

Additional Journal Information:

Journal Volume: 58; Journal ID: ISSN 2214-8604

Publisher:

Elsevier

Country of Publication:

United States

Language:

English

Subject:

36 MATERIALS SCIENCE; Ti-6Al-4V; Directed energy deposition; Crystallographic texture; Solidification; Cracking