Abstract
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.
Original language | English |
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Article number | 103360 |
Journal | Additive Manufacturing |
Volume | 61 |
DOIs | |
Publication status | Published - 2023 Jan 5 |
Bibliographical note
Publisher Copyright:© 2022 Elsevier B.V.
Keywords
- Additive manufacturing
- Laser-powder bed fusion
- Mechanical property
- Multiscale defects
- Segregation
ASJC Scopus subject areas
- Biomedical Engineering
- General Materials Science
- Engineering (miscellaneous)
- Industrial and Manufacturing Engineering