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Title: Strengthening mechanisms in directed energy deposited austenitic stainless steel

Abstract

Microstructures and mechanical properties are evaluated in austenitic stainless steel structures fabricated by directed energy deposition (DED) considering the effects of applied loading orientation, build geometry, and distance from the deposition baseplate. Locations within an as-deposited build with different thermomechanical history display different yield strength, while those locations with similar history have approximately the same yield strength, regardless of test specimen orientation. Thermal expansion of deposited material near the baseplate is inhibited by the mechanical constraint imposed by the baseplate, promoting plastic deformation and producing a high density of dislocations. Concurrently, high initial cooling rates decrease away from the baseplate as the build is heated, causing an increased spacing of cellular solidification features. An analysis of strengthening mechanisms quantitatively established for the first time the important strengthening contribution of high dislocation densities in the materials (166–191 MPa) to yield strength that ranged from 438 to 553 MPa in the present DED fabricated structures. A newly adopted mechanistic relationship for microsegregation strengthening from the literature indicated an additional important contribution to strengthening (123–135 MPa) due to the cellular solidification features. These findings are corroborated by the measured evolution of microstructure and hardness caused by annealing the DED material. Finally, these resultsmore » suggest that the mechanical properties of deposited austenitic stainless steels can be influenced by controlling thermomechanical history during the manufacturing process to alter the character of compositional microsegregation and the amount of induced plastic deformation.« less

Authors:
ORCiD logo [1];  [2];  [2];  [3]
  1. Univ. of California, Davis, CA (United States); Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  2. Sandia National Lab. (SNL-CA), Livermore, CA (United States)
  3. Univ. of California, Davis, CA (United States); Univ. of California, Irvine, CA (United States)
Publication Date:
Research Org.:
Sandia National Lab. (SNL-CA), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1492362
Report Number(s):
SAND-2018-13858J
Journal ID: ISSN 1359-6454; 670837
Grant/Contract Number:  
AC04-94AL85000
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 164; Journal Issue: C; Journal ID: ISSN 1359-6454
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 42 ENGINEERING; Additive Manufacturing (AM); Mechanical Properties; Microstructure; Strengthening Mechanism; Austenitic Stainless Steels

Citation Formats

Smith, Thale R., Sugar, Joshua D., San Marchi, Chris, and Schoenung, Julie M. Strengthening mechanisms in directed energy deposited austenitic stainless steel. United States: N. p., 2018. Web. doi:10.1016/j.actamat.2018.11.021.
Smith, Thale R., Sugar, Joshua D., San Marchi, Chris, & Schoenung, Julie M. Strengthening mechanisms in directed energy deposited austenitic stainless steel. United States. doi:10.1016/j.actamat.2018.11.021.
Smith, Thale R., Sugar, Joshua D., San Marchi, Chris, and Schoenung, Julie M. Tue . "Strengthening mechanisms in directed energy deposited austenitic stainless steel". United States. doi:10.1016/j.actamat.2018.11.021.
@article{osti_1492362,
title = {Strengthening mechanisms in directed energy deposited austenitic stainless steel},
author = {Smith, Thale R. and Sugar, Joshua D. and San Marchi, Chris and Schoenung, Julie M.},
abstractNote = {Microstructures and mechanical properties are evaluated in austenitic stainless steel structures fabricated by directed energy deposition (DED) considering the effects of applied loading orientation, build geometry, and distance from the deposition baseplate. Locations within an as-deposited build with different thermomechanical history display different yield strength, while those locations with similar history have approximately the same yield strength, regardless of test specimen orientation. Thermal expansion of deposited material near the baseplate is inhibited by the mechanical constraint imposed by the baseplate, promoting plastic deformation and producing a high density of dislocations. Concurrently, high initial cooling rates decrease away from the baseplate as the build is heated, causing an increased spacing of cellular solidification features. An analysis of strengthening mechanisms quantitatively established for the first time the important strengthening contribution of high dislocation densities in the materials (166–191 MPa) to yield strength that ranged from 438 to 553 MPa in the present DED fabricated structures. A newly adopted mechanistic relationship for microsegregation strengthening from the literature indicated an additional important contribution to strengthening (123–135 MPa) due to the cellular solidification features. These findings are corroborated by the measured evolution of microstructure and hardness caused by annealing the DED material. Finally, these results suggest that the mechanical properties of deposited austenitic stainless steels can be influenced by controlling thermomechanical history during the manufacturing process to alter the character of compositional microsegregation and the amount of induced plastic deformation.},
doi = {10.1016/j.actamat.2018.11.021},
journal = {Acta Materialia},
issn = {1359-6454},
number = C,
volume = 164,
place = {United States},
year = {2018},
month = {11}
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on November 13, 2019
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