workshop on atomic-scale challenges in advanced materials: defects in materials turku, finland
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Composition dependent properties of Ni 2 MnGa based ferromagnetic shape memory alloys Qing-Miao Hu Institute of Metal Research, Chinese Academy of Sciences Wenhua Road 72, Shenyang 110016, China. Workshop on Atomic-Scale Challenges in Advanced Materials: Defects in Materials Turku, Finland - PowerPoint PPT PresentationTRANSCRIPT
Composition dependent properties of Ni2MnGa based ferromagnetic shape memory
alloys
Qing-Miao Hu
Institute of Metal Research, Chinese Academy of Sciences
Wenhua Road 72, Shenyang 110016, China
Workshop on Atomic-Scale Challenges in Advanced Materials:
Defects in MaterialsTurku, Finland
August 22-23, 2013
Co-workers
Dr. Hu-Bin LuoInstitute of Metal Research, Chinese Academy of Sciences
Dr. Chun-Mei LiInstitute of Metal Research, Chinese Academy of Sciences
Royal Institute of Technology/Uppsala University , Sweden
Prof. Rui YangInstitute of Metal Research, Chinese Academy of Sciences
Prof. Börje JohanssonRoyal Institute of Technology/Uppsala University , Sweden
Prof. Levente VitosRoyal Institute of Technology/Uppsala University , Sweden
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Background and MotivationGeneral
Mn: 3.86, Ni: <0.3, Ga: 0.00
Magnetic Transition:
Ferromagnetic Paramagnetic
Ni2MnGa: Heusler Alloys
c/a = 1
Structure Transition:
Cubic L21 Austinite
Orthorhombic Martensite
Reversible: Shape Memory Effect
c/a >1
c/a <1
202 K 376 K
Coupling between the structure and magnetic transitions leads to some unique properties:
•Giant magnetocaloric effect; •Magnetostriction; •Magnetoresistance.
Potential applications: •Magnetic refrigeration;•Magnetostrictive
transducers;•etc.
Background and MotivationGeneral
Perfect Ni2MnGa
How to control composition to achieve desirable TM? Can we find some easy predictors to connect composition and TM?
Khovaylo, et al., Phys. Rev. B 72, 224408 (2005)
Background and MotivationGeneral
Tsuchiya, et al., ISIJ International 46, 1283 (2006)
Fe doped Ni2MnGa
1. Number of valence electrons per atom (e/a) and TM
Chernenko, et al., Acat Mater. 50, 53 (2002)
Background and MotivationPredictors for the composition dependence of TM
2. c/a ratio of martensite and TM
Lanska, et al., J. Appl. Phys 95, 8074 (2004)
Background and MotivationPredictors for the composition dependence of TM
3. Energy difference between austinite and martensite (E) and TM
Chen, et al., Appl. Phys. Lett. 89, 231921 (2006)
Background and MotivationPredictors for the composition dependence of TM
Bungaro and Rabe, Phys. Rev. B, 2003
cdcdT
10
dTdc
T1
Ren and Otsuka, Mater Sci Forum (2000)
NiTi SMA： Larger C of the austenite corresponding to lower TM.4. Elastic modulus Cand TM?
Background and MotivationPredictors for the composition dependence of TM
Background and MotivationPhase stability: Structure of modulated martensite
The modulated structure is very complex: shear: changing c/a; shuffle: wave-like movement of atoms on [110]
Alloying effect on the modulated structure?
a
a
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
MethodEMTO-CPA
First-principles method based on density functional theory
Basis Sets: Exact muffin-tin orbitials (EMTO), spdf
Exchange-correlation functional: GGA-PBE
Coherent potential approximation for the random distribution of alloying atoms.
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Geometry of Ni2MnGa projected to (001) plane
Ga
Mn
Ni
Ni2MnGa
Ni2-xMnGa1+x
Indirect site-occupancy
MnNi
GaMn
GaNi
Direct site-occupancy
Results and DiscussionSite-occupancy in Ni2MnGa based alloys
Off-stoichiometric: Indrect: Ga-rich Ni-deficient alloys, forming
GaMn and MnNi.
Phys. Rev. B 79, 144112 (2009); 84, 024206 (2011)
Results and DiscussionSite-occupancy in Ni2MnGa based alloysFree energy of different site-occupancy configurations
Fe/Co/Cu doped:Indirect: Fe-doped Ga-deficient alloys
Co-doped Mn- or Ga-deficient alloysCu always take direct site-occupancy
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Results and DiscussionElastic modulus and TM
7.0 7.2 7.4 7.6 7.8141
144
147
150
153
156
7.0 7.2 7.4 7.6 7.810
15
20
90
95
100
105
Bulk
Mod
ulus (
GPa)
e/ a
Shea
r Mod
ulus
(GPa
)
C44 C
e/ a
9 12 15 180
100
200
300
400
500
600
T M (K
)
C7.35 7.50 7.65 7.80
0
100
200
300
400
500
600
T M (K
)
e/ a
Off-stoichiometric Ni2MnGa
Phys. Rev. B 79, 144112 (2009)
Fe/Co/Cu doped Ni2MnGa
7.4 7.5 7.6 7.7 7.8 7.9
2
4
6
8
10
Ni2+xMnGaCux
Ni2Mn1-xGaCux
Ni2MnGa1-xCux
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox
Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
C' (G
Pa)
e/ a
2 4 6 8 1050
100150200250300350400450
7.44 7.52 7.60 7.68 7.7650100150200250300350400450
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
T M (K
)
C' (GPa)
Ni2+xMnGaCux
Ni2Mn1-xGaCux
T M (K
)
e/ a
Phys. Rev. B 84, 024206 (2011)
Results and DiscussionElastic modulus and TM
0.0 0.2 0.4 0.6 0.8 1.0
6
8
10
12
14
16
C' (G
Pa)
Atomic fraction of Al, c
C'
100
120
140
160
180
200
TM
T M (K
)
Ni2Mn(Ga1-xAlx)
Acta Mater. 59, 5938(2011)
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)
)sinsin(sin 56
254
152 jAjAjj
Acta Mater. 59, 5938(2011)
Martynov et al.. J. Phys. III 2, 739(1992)
a
a
Two degrees of freedom optimization:
Shear: c/a; Shuffle:
5L modulated martensite:
Results and DiscussionPhase stability of Ni2Mn(Ga1-xAlx)
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (a) Ni2MnGa
non-modulated modulated
E (m
Ry)
c/a
0.90 0.92 0.94 0.96-0.12-0.10-0.08-0.06-0.04
E
(mR
y)
c/a
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (b) Ni2Mn(Ga0.9Al0.1)
non-modulated modulated
E (m
Ry)c/a
0.90 0.92 0.94 0.96-0.08-0.06-0.04-0.020.00
E (m
Ry)
c/a
0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5
-1
0
1
2
3 (c) Ni2Mn(Ga0.8Al0.2)
non-modulated modulated
E (m
Ry)
c/a
0.90 0.92 0.94 0.96-0.030.000.030.060.09
E (m
Ry)
c/a
0.00 0.05 0.10 0.15 0.20 0.25 0.30
0.00
0.03
0.06
0.09
0.12
E
AM
(m
Ry)
c
Critical point
0.0 0.1 0.2 0.3 0.9 1.00
50100150200
T M (K
)
c
No MT
Exp.
EAM=EA-EM
Martensite more stable
Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga
2 4 6 8 1050
100150200250300350400450
7.44 7.52 7.60 7.68 7.7650100150200250300350400450
Ni2+xMnGaCox
Ni2Mn1-xGaCox
Ni2MnGa1-xCox Ni2+xMnGaFex
Ni2Mn1-xGaFex
Ni2MnGa1-xFex
T M (K
)
C' (GPa)
Ni2+xMnGaCux
Ni2Mn1-xGaCux
T M (K
)
e/ a
Results and DiscussionPhase stability of Ni2(Mn1-xFex)Ga
L21 austinite becomes elastically softer with increasing Fe: Lattice vibration contribute more to the free nergy accordingly, stabilizing L21
EAM=EA-EM
Outline
Background and Motivation Method Results and Discussiono Site-occupancyo Elastic moduluso Phase stability
Summary
Summary
• We predict that indrect site-occupation occurs in some of the off-stoichiometric and Fe/Co/Cu doped Ni2MnGa alloys.
• The general TM~C′ correlation works for some of the alloys for which the TM~e/a correlation fails. However, there are several cases where both the general TM~C′ and TM~e/a correlations break down.
• We present a feasible approach to study the 5-layer modulated (5M) martensitic structure of Ni2MnGa-based alloy using first-principles methods. By using this approach, the 5M martensitic structure of Ni2MnGa is reasonably reproduced and the Al/Fe-doping effects are predicted.
Thank you for your attention!