eutectic high entropy alloys...
TRANSCRIPT
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Eutectic High‐Entropy Alloys (EHEAs)
Adrianna Lozinko & Sheng Guo
Industrial and Materials Science (IMS) DepartmentChalmers University of Technology, Gothenburg, Sweden
E‐mail: [email protected]
DTU, Aug 28, 2017
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outline
A brief introduction to HEAs Some issues with cast HEAs Eutectic HEAs Conclusions
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HEAs: new strategy for alloy design
Traditional alloys have only 1 (steels, Al alloys, Cu alloys, etc.) or 2 principal elements (NiAl, FeAl, etc.)
High‐entropy alloys have at least 5 (4?) principalmetallic elements, and have equal or close‐to‐equal compositions
Example, Al‐Co‐Cr‐Cu‐Fe‐Ni systemEquimole: AlCoCrCuFeNi Non‐equimole: AlCo0.5CrCuFe1.5Ni1.2Minor element addition: AlCo0.5CrCuFe1.5Ni1.2B0.1C0.15
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why are they called high‐entropy alloys?
1ln
N
i ii
R c c
they have high configuration entropy
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It is more convenient to define HEAs by the magnitude of configuration entropy in the hightemperature (ideal or regular solution) state: ∆Smix > 1.5R
(Miracle et al., Entropy, 2014)
what we talk about when we talk about high‐entropy alloys
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why high entropy?high‐entropy stabilizes the formation of solid solution phases
△Gmix =△Hmix ‐T△Smix
single phase solid solutionco‐existence of two solid solution phases
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(Murty, Yeh and Ranganathon, High
Entropy Alloys, Elsevier, 2014)
in the middle
why bother?high‐entropy alloys open up vast unexplored compositional space
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era of high‐entropy alloys?
(Adv.Eng.Mater, 2004)
(Yeh, et al., Mater Chem Phys, 2007)
N=1
N=2
N=3
N=4
N=5
N=6
N=7
Highly concentrated solid solutions
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potential of HEAs as structural materials
Very high hardness can be achieved
(after 1000 oc/12h)
(Yeh, et al., Adv Eng Mater, 2004)
AlCoCrFeNiTi0.5
y=2.26GPa
f=3.14GPa
p=23.3%
(Zhou et al., APL, 2007)
Disordered bcc solid solution was reserved after annealing at 1400 oc for 19h
(Senkov, et al., Intermetallics, 2011)
460 MPa@1600 oCbetter than superalloys
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(Gludovatz et al., Science, 2014)
CoCrFeMnNi
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some “hot areas” in HEAs (my personal perception)
phase selection and phase stability in concentrated multi‐component alloys
strength‐ductility trade offradiation resistancerefractory HEAsnew functionality(superconductivity,thermoelectricity, etc.)
(Li et al., Nature, 2016)
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ductile and oxidation resistant refractory high entropy alloys: single bcc solid solution
interested block
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some issue with cast HEAs Porosity, particular for large ingots Inhomogeneity/Segregation Conflict between strength/ductility
(Tong et al., Metall Mater Trans A, 2005)
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why eutectic alloys? highly stable microstructures that do not revert, or coarsen, easily at elevated temperatures;
high thermodynamic stability and kinetic resistance to thermaldegradation;
development of low‐energy lamellar and rod‐form boundary structures;
high strengths and creep resistance because their microstructures act as natural ‘in situ’ composite materials;
better castability (less porosity) better compositional homogeneity(less segregation)
Inspirations: Eutectics with high‐melting points have formed the basis for a number of interesting candidate high‐temperature alloys for application to the high temperature components of gas turbine engines.
(Glicksman, Principle of Solidification, 2011)
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eutectic high‐entropy alloysan example: AlCoCrFeNi2.1
~ 2.5 kg of homogenous and almost casting defects free large ingots
(Lu et al., Sci Rep, 2014)
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eutectic high‐entropy alloys
soft fcc/ hard NiAl‐like B2 eutetic microstructuremelting temperature ~ 1350 oC (NiAl: 1674 oC) density of ~ 7.4 g/cm3 (NiAl: 6 g/cm3)
(Lu et al., Sci Rep, 2014)
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RT ‐70 oC ‐196 oC
(Lu et al., Acta Mater, 2016)
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AlCoCrFeNi2.1 after tensile testing to fracture
no phase transformation till fracture
a large number of dislocations seen in the L12phase, but not in the B2 phase
(Lu et al., Acta Mater, 2016)
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In‐situ synchrotron x‐ray diffraction
no phase transformation during tensile deformation deformation behavior resembles that of fcc alloys (limited role of B2 ) {200} and {311} planes show lowest elastic modulus and sustain larger lattice
strain
(Lu et al., Acta Mater, 2016)
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eutectic high‐entropy alloys: dual‐phase (soft/hard) solid solutions
(Wani et al., Mater Res Lett, 2016)
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(Wani et al., Mater Sci Eng A, 2016)
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Summary High‐entropy alloys are highly concentrated, multi‐component
alloys (the name is a bit controversial, but a name is just a name) New materials new properties (high‐temperature/cryogenic temperature, etc.) & new applications Structural or functional properties? Eutectic high‐entropy alloys could become interesting
engineering materials, if they can be further optimized
understanding deformation mechanism helps alloy design
Every material
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Thanks for your attention!Sheng Guo
Industrial and Materials Science DepartmentChalmers University of Technology
Gothenburg, SwedenE‐mail: [email protected]