strength and deformation of precious high entropy alloys · • heat treatment in liquid/ solid...
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Strength and deformation of precious high-entropy alloys
Leibniz Institute for Solid State and Materials Research Dresden (IFW Dresden)
Institute for Metallic Materials
Metal Physics
1. Project Meeting SPP 2006 CCA-HEA, Hannover, 14.02.-15.02.2018
Felix Thiel, Jens Freudenberger, Kornelius Nielsch
01.03.2018 2
http://www.periodictable.com/Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
• 5 principal elements
• homogeneous solid solution
• single phase
• simple crystal structure
• 5 principal elements
• multi-phase microstructure
benchmarking alloy for all HEAscleanly separation from conventional single phase alloys
High entropy alloysCompositional complex alloys
Binary phase diagrams in the Au-Cu-Ni-Pd-Pt system
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Okamoto H., and Massalski T.B.: Binary Alloy Phase Diagrams, II Ed. (1990)
• all show a homogeneous solid solution at high T
• all elements are fcc and do not show allotrope modifications
• no intermetallic phases form out of the melt
• homogeneity covers hole concentration range at high T
However: miscibility gabs and phase decompositions at low T
Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
Research issues
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Au-Cu-Ni-Pd-Pt
phase stability• quaternary/
quinary alloy
deformation mechanisms• at RT/ 77K• dislocation glide/ twinning
Hall-Petch type hardening• SPD for UFG microstructure
solid solution strengthening• effect of solutes to
quaternary alloys
strengthening by segregations
Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
Alloy processing
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Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
• alloying
• arc melting
• cold working• homogenization
• recrystallization
Vegard’s rule of mixture
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Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
• linear dependency of calculated and experimental lattice parameter
homogeneous solid solution coversthe whole concentration range
• solution treatment 1000°C/ 24h
• fcc structure
• single phase
Freudenberger, J et al.: Metals 135 (2017), p. 7
𝑎 =
𝑖=1
5
𝑥𝑖𝑎𝑖
AuCuNiPt
Segregations in AuCuNiPt
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• second heat treatment in liquid/ solid state 1100°C/ 17h
• Au & Cu at grain boundaries
low elemental melting point
pair mixing enthalpy
rmetpm
Tm°C
AuCuNiPdPt
144128125137139
10641085145515551768
Freudenberger, J et al.: Metals 135 (2017), p. 7Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
Pair mixing enthalpy
Cu Ni Pt
AuCuNi
-5.2 7.62.3
0.5-11.4-9.3
Solution treatment
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• single phase at T>950°C
• decomposition at T<900°C into two fcc phases
Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
1000
2000
3000
counts
18 19
-300
0
300
950°C/ 16h
DI
2q
500
1000
1500850°C/ 16h
counts
17 18 19
-300
0
300
DI
2q
500
1000
750°C/ 16h
counts
17 18 19
-300
0
300
DI
2q
0
1000
2000
3000
4000
1050°C/ 16h
co
un
ts
20 30 40
-500
50
DI
2q
Homogeneity of AuCuNiPdPt
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• atom probe tomography of a solution treated AuCuNiPdPt sample
• decomposition of Au-Cu-Pd and Ni-Ptphase separations of binary systems Cu-Ni, Pd-Pt & Au-Ni at low T
improved solution treatment (possible?)
Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018 in collaboration with KIT-IAM
Conclusions
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Felix Thiel | 1. Project Meeting | Hannover | 14.02.2018
• single phase at high T, phase decomposition at T < 900°C
• heat treatment in liquid/ solid area leads to segregations at grain boundaries
• APT shows elemental variations on atomic scale in homogenized state
Thank you for your attention!
Sven Donath, Lars Giebeler, David Geissler, Martin Heilmaier, Alexander Kauffmann, Christiane Mix, David Rafaja, Juliane Scheiter, Dirk Seifert, Sascha Seils, Christiane Ullrich
FR 1714/7-1