Thermally activated dependence of fatigue behaviour of CrMnFeCoNi high entropy alloy fabricated by laser powder-bed fusion
File(s)
Accepted version
OA Location
Author(s)
Jin, Minsoo
Hosseini, Ehsan
Holdsworth, Stuart R
Pham, Minh-Son
Type
Journal Article
Abstract
The CrMnFeCoNi high-entropy alloy demonstrates a promising potential for applications over a range of temperature. The alloy also shows excellent printability to be fabricated by additive manufacturing for complex structures. Nevertheless, there are limited studies on the thermo-mechanical behaviour of the alloy, in particular when fabricated by laser powder-bed fusion. This study provides an in-depth understanding of the relationship between as-built cellular microstructures and fatigue behaviour at a range of temperatures (22–600 °C) in particular concerning the stability of dislocation cells and thermo-mechanical dependence of the fatigue behaviour of the alloy. At all tested temperatures, the alloy exhibits a very short duration cyclic hardening with a low hardening rate followed by a cyclic softening. The high density of dislocations already existing in as-built condition were able to accommodate most of the prescribed strain. Hence, only a small number of mobile dislocations needs to be generated, causing a short cyclic hardening phase. Upon further loading, the back stress associated with the long-range stress field was dominant factor governing the cyclic softening behaviour. The similitude relationship provided insights into the stability of as-built cells, in particular it explains why the size of as-built cells did not change during cyclic loading at 22 °C. The significant reduction in dislocation density due to the increased annihilation rate and untanglement of dislocation substructures thanks mainly to thermal assistance at elevated temperatures led to a decrease in cyclic strength and related properties (yield stress, friction and back stress, hysteresis loop shape parameter and energy per cycle). The LPBF HEA shows an insignificant strain rate dependence of the primary cyclic hardening and softening in the range of 10−3s−1 and 10−2s−1. However, the dynamic strain ageing results in a secondary cyclic hardening at 400 °C and the reversed strain sensitivity at temperatures from 200° to 400 °C. The fracture mode was transgranular at 22–400 °C but changed to more intergranular-like at 600 °C due to the decohesion of grain boundaries, resulting in a reduction in fatigue life.
Date Issued
2022-03-01
Date Acceptance
2022-01-04
Citation
Additive Manufacturing, 2022, 51, pp.1-13
ISSN
2214-8604
Publisher
Elsevier BV
Start Page
1
End Page
13
Journal / Book Title
Additive Manufacturing
Volume
51
Copyright Statement
© 2022 Elsevier B.V. All rights reserved. This manuscript is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International Licence http://creativecommons.org/licenses/by-nc-nd/4.0/
Identifier
https://www.sciencedirect.com/science/article/pii/S2214860422000082?via%3Dihub
Subjects
Science & Technology
Technology
Engineering, Manufacturing
Materials Science, Multidisciplinary
Engineering
Materials Science
High-entropy alloys
Additive manufacturing
Laser powder bed fusion
Themal fatigue
Cyclic plasticity
STRAIN-RATE SENSITIVITY
CRACK GROWTH-BEHAVIOR
AISI 316L
MICROSTRUCTURAL EVOLUTION
EXPANSION COEFFICIENT
MECHANICAL-PROPERTIES
DISLOCATION BEHAVIOR
TENSILE PROPERTIES
INTERNAL-STRESSES
DEGREES-C
0910 Manufacturing Engineering
Publication Status
Published
Article Number
ARTN 102600
Date Publish Online
2022-01-06