Strength and deformation of precious high entropy alloys · • heat treatment in liquid/ solid area leads to segregations at grain boundaries • APT shows elemental variations on

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

01.03.2018 3

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

01.03.2018 4

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


Alloy processing

01.03.2018 5


• alloying

• arc melting

• cold working• homogenization

• recrystallization

Vegard’s rule of mixture

01.03.2018 6


• 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

01.03.2018 7

• 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

01.03.2018 8

• single phase at T>950°C

• decomposition at T<900°C into two fcc phases


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

01.03.2018 9

• 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

01.03.2018 10


• 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

Documents

Strength and deformation of precious high entropy alloys · • heat treatment in liquid/ solid area leads to segregations at grain boundaries • APT shows elemental variations on