TY - JOUR
T1 - Multiscale defects enable synergetic improvement in yield strength of CrCoNi-based medium-entropy alloy fabricated via laser-powder bed fusion
AU - Jung, Heechan
AU - Lee, Jungwan
AU - Gu, Gang Hee
AU - Lee, Hyungsoo
AU - Seo, Seong Moon
AU - Zargaran, Alireza
AU - Kim, Hyoung Seop
AU - Sohn, Seok Su
N1 - Funding Information:
This study was supported by the Korea TechnoComplex Foundation Grant [ R2214141 ]; the National Research Foundation of Korea (NRF) grant funded by the Korea government ( MSIT ) [ NRF-2022R1A5A1030054 ]; the Korea Institute for Advancement of Technology (KIAT) grant funded by the Korean Government ( MOTIE ) [ P0002019 , The Competency Development Program for Industry Specialist]; and the Fundamental Research Program of the Korean Institute of Materials Science [ PNK8730 ].
Publisher Copyright:
© 2022 Elsevier B.V.
PY - 2023/1/5
Y1 - 2023/1/5
N2 - Recently, laser-powder bed fusion (L-PBF) has overcome a shortcoming concerning the relatively modest yield strength in the face-centered cubic structure of CrCoNi medium-entropy alloy (MEA); nevertheless, further enhancement remains challenging because the as-built defects are limited to dislocation cell structures and nano-inclusions. In this study, several the types of hierarchical defect structures are explored (including stacking faults, nano-twins, σ phase, and nano-precipitates) with the addition of Si to reduce the stacking fault energy and promote segregation at dislocation cells with Cr. The CrCoNiSi0.3 alloy is fabricated by the L-PBF process, and the effects of the Si addition and L-PBF processing on the hierarchical multiscale defects and corresponding mechanical responses are unraveled. The highest apparent density above 99.5 % is achieved under optimized conditions, exhibiting a high yield strength of 929 MPa owing to a synergetic effect from the generated defects comprising σ phase, nano-twins, and planar defects with moderate ductility of 14 %. In addition, the reduced stacking fault energy promotes deformation twinning, resulting in steady strain hardening. The alloy ultimately exhibits a tensile strength of 1264 MPa, with a moderate ductility of 14 %. A post-heat treatment induces a morphological change in the σ phase from a film-type at the cell walls to particulates at the cell junctions, leading to a significant increase in ductility without a loss of tensile strength, despite a loss of yield strength. This work provides insights to overcome the pre-existing limitations by imposing and adjusting multiscale defects.
AB - Recently, laser-powder bed fusion (L-PBF) has overcome a shortcoming concerning the relatively modest yield strength in the face-centered cubic structure of CrCoNi medium-entropy alloy (MEA); nevertheless, further enhancement remains challenging because the as-built defects are limited to dislocation cell structures and nano-inclusions. In this study, several the types of hierarchical defect structures are explored (including stacking faults, nano-twins, σ phase, and nano-precipitates) with the addition of Si to reduce the stacking fault energy and promote segregation at dislocation cells with Cr. The CrCoNiSi0.3 alloy is fabricated by the L-PBF process, and the effects of the Si addition and L-PBF processing on the hierarchical multiscale defects and corresponding mechanical responses are unraveled. The highest apparent density above 99.5 % is achieved under optimized conditions, exhibiting a high yield strength of 929 MPa owing to a synergetic effect from the generated defects comprising σ phase, nano-twins, and planar defects with moderate ductility of 14 %. In addition, the reduced stacking fault energy promotes deformation twinning, resulting in steady strain hardening. The alloy ultimately exhibits a tensile strength of 1264 MPa, with a moderate ductility of 14 %. A post-heat treatment induces a morphological change in the σ phase from a film-type at the cell walls to particulates at the cell junctions, leading to a significant increase in ductility without a loss of tensile strength, despite a loss of yield strength. This work provides insights to overcome the pre-existing limitations by imposing and adjusting multiscale defects.
KW - Additive manufacturing
KW - Laser-powder bed fusion
KW - Mechanical property
KW - Multiscale defects
KW - Segregation
UR - http://www.scopus.com/inward/record.url?scp=85144042094&partnerID=8YFLogxK
U2 - 10.1016/j.addma.2022.103360
DO - 10.1016/j.addma.2022.103360
M3 - Article
AN - SCOPUS:85144042094
SN - 2214-8604
VL - 61
JO - Additive Manufacturing
JF - Additive Manufacturing
M1 - 103360
ER -