Deformation of NiTiCu Shape Memory Single Crystals · 2008. 4. 18. · transformation (B19 and...
Transcript of Deformation of NiTiCu Shape Memory Single Crystals · 2008. 4. 18. · transformation (B19 and...
Deformation of NiTiCu Shape MemorySingle Crystals
H. Sehitoglu, X. Zhang,T.Kotil,1 H. J. Maier, 2Y. Chumlyakov
University of Illinois, Department of Mechanical and Industrial Engineering,Urbana, IL
1University of Paderborn, Lehrstuhl f. Werkstoffkunde, Paderborn,2Siberian Physical-Technical Institute,Tomsk, Russia
Presentation at the ASME ESDA Conference, July 8-11, 2002
Supported by the National Science Foundation, Mechanics and Materials Program,Engineering Directorate, Air Force Office of Scientific Research, Aerospace and Materials
Sciences
Introduction
• What is Shape Memory?• Shape memory is the ability of the material to recover large strains through a phase
transformation from martensitic to austenitic crystal states upon heating
• Why ‘Single Crystals’?• Clear understanding of SME and pseudoelasticity without GB effects.• Permits study of the influence of plasticity in the B2 phase.• Many of the polycrystalline NiTiCu alloys exhibit significant texture.
• Why’ Seek Alternatives to NiTi’?• To alter strength, the transformation temperature range, and eliminate aging treatments
for pseudoelasticity.
• Why’ Measure electrical Resistance?• To separate transformation from detwinning effects
What are shape memory alloys?
Shape Memory T<As
Strain
Stre
ss
PseudoleasticityT>Af
Austenite>Martensiteor Martensite Reorientation
Austenite < Martensite
Heat above Af
Austenite>Martensite
Austenite<Martensite
What makes them work?
A thermal or stress induced martensitic transformation.
Self accomodation
Schematic Illustration of The Mechanism ofThe Shape-Memory Effect
Parent Phase
Twinned Martensite
Detwinned Martensite
Applied Stress or
Stress free
Adapted from Figure 1 in [1]
[1] Otsuka, K. and Kakeshita, T., MRS Bulletin, Feb. 2002, 91
10
8
6
4
2
0
100500-50-100Temperature [
oC]
Cooling
Heating
NiTi10Cu
As= 0oC
Af= 31oC
Ms= 21oC
Mf= -11oC
M → Α
M ← Α
NiTiCu Shape Memory Alloys
Major Features:Stable Martensite Start TemperaturesTwo Stage Transformation ( B2 to B19 to B19’) for near 10%CuLower Transformation strains compared to NiTiNarrower Transformation Temperature Range compared to NiTi
Missing Information:Transformation Strains ( Calculations and Experiments)Single Crystal Information- Tension Compression Asymmetry,Crystal Orientation DependenceClear Understanding of Two Stages of Transformation ( B2 B19 B19’)The Role of Detwinning of B19’
800
600
400
200
0450400350300250200
Temperature (K)
<100> <011> <111> <012> <123>
NiTiCuCompression
Ms
Austenite Slip
Md
Critical Stress versus Temperature ( NiTi10Cu)
H. Sehitoglu et al. Met. Mats. Trans.,2001, 32A, 477-489
M>MM>A
700
600
500
400
300
200
100
0
543210Strain [%]
NiTi10Cu [012]
Temperatue = 100oC
Temperatue = 20oC
Temperatue = -60oC
100oC
20oC
-60oC
0.6
0.5
0.4
0.3
0.2
0.1
0.0
543210Strain [%]
NiTi10Cu [012]
Temperatue = 100oC
Temperatue = 20oC
Temperatue = -60oC
100oC
20oC
-60oC
Two Stage Transformation in NiTiCu- Schematic
a
n
Twinned Martensite, B19’
Habit Plane
1-f
b
b
B19 Martensite
m
m
b
1
1
B19 Martensite
B2
B2
f
CUBIC
MONOCLINIC
0.2898nm
0.4265nm
0.302nm
ORTHOROMBIC
0.288nm
0.456nm
96°
1 =1
2(FOrth
T ⋅FOrth − I) =1
2[b ⊗ m + m ⊗ b + (b ⋅ b)m ⊗ m]
Cubic to Ortohorombic Transformation
2 =1
2[(FMonoFOrth
−1 )T ⋅(FMonoFOrth− 1 ) − I] =
1
2[b ⊗ ′ m + ′ m ⊗ b + (b ⋅ b ) ′ m ⊗ ′ m ]
Ortohorombic to Monoclinic Transformation
Tension
Compression
NiTiCu ( 10%Cu)
Sehitoglu et al. (2001), Acta Mater., 49, 3621-3634 (image visible upon printing)
Single Step Transformation (B2 to B19’)
Tension Compression
Schematic of Variants, Habit Planes, Twins,CVPs
Twinned Martensite
bm
na
CVP
1-f
f
1-f
Detwinned Martensite
Two Step Transformation Single StepTransformation
B19' Detwinning
B2→B19
cubic→orthorhombic
B19→B19'
orthorhombic→monoclinic
B2→B19'
cubic→monoclinic
SingleStep
TwoSteps
[111] 2.55 3.49 7.05 8.67 8.33
[001] 2.78 0.70 2.98 2.98 3.49
[122] 4.64 2.60 7.83 9.39 8.71
[012] 5.01 0.41 5.32 6.19 6.32
[011] 5.57 0.44 5.87 7.00 7.14
Table 1 Transformation Strains Under Tension( in percent)
Monoclinic/Orthorombic Structure inMartensite in NiTiCu
Internally Twinned Martensite
200
150
100
50
0
543210Strain [%]
0.8
0.6
0.4
0.2
0.0
NiTi10Cu [012]
Tension at -60 oC
Stress-strain Electrical Resistance- Strain
Heating at Zero Stress
B'
D'
OAB : Martensite (-60 oC)
D' : Austenite ( 60 oC)
O,O' : Martensite (-60 oC)
BC
C'O, O'
A
A'
6
5
4
3
2
1
0
-1
-60 -40 -20 0 20 40 60Temperature [
oC]
0.6
0.5
0.4
0.3
0.2
0.1
0.0
-0.1
NiTi10Cu [012]Heating At Zero Stress
ReverseDetwinning∆ε ≅ 1.5%
M → Α∆ε ≅ 3.7%
Reverse Detwinning∆R/R ≅ 0.44
M → Α∆R/R ≅ 0.13
A'
D'
C
C'
Electrical Resistance
Strain
B'
A B
Temperature
Stra
in
Ms1
Transformation Strain
Af1M
f2 As
2
InelasticStrain
Step 1
As1
CUBICORTHORHOMBICMONOCLINIC
Step 2 B19->B19’
B2->B19
B19’Detwinning
8
6
4
2
0
-100 -50 0 50 100Temperature [
oC]
0.8
0.6
0.4
0.2
0.0
Strain Electrical Resistance
NiTi10Cu [012]
Martensite Detwinning∆R/R ≅ 0.44
M → Α∆ε ≅ 3.8%
Martensite Detwinning∆ε ≅ 1%
M → Α∆R/R ≅ 0.12
C
C'
D'
NiTiCu [111]
-8
-6
-4
-2
0
2
4
6
8
-140 -120 -100 -80 -60 -40 -20 0 20 40 60 80 100 120 140
Temperature (°C)
NiTiCu[111] OrientationStrain vs. Temperature
150
50
Cycle 1Cycle 4
50,75,100,150 MPa Tension Hold
100 MPa Compression Hold
2.55
3.49
-1.38
-1.18
Experimental strain - temperature hysteresis curves for a solutionizedTi-50.37at%Ni [123] single crystal
14
12
10
8
6
4
2
0
-2
-4
-6
-200 -160 -120 -80 -40 0 40 80Temperature (oC)
10.51% Detwinning Strain
-5.45% Detwinning Strain-5.53% CVP Strain
max strain
NiTi- Solutionized [123]
175 MPa
125 MPa
100 MPa
75 MPa25 MPa
0 MPa
-125 MPa
-170 MPa
-245 MPa
6.49% CVPStrain
Experimental strain - temperature hysteresis curves for an aged (1.5hrs @ 823K) Ti-50.37%Ni [123] single crystal
14
12
10
8
6
4
2
0
-2
-4
-6
-200 -160 -120 -80 -40 0 40 80Temperature (oC)
10.51% Detwinning + CVP Strain
-5.45% CVP Strain
-5.53% Detwinning + CVP Strain
NiTi- 823K 1.5Hrs [123]
210 MPa
100 MPa75 MPa
50 MPa
25 MPa
0 MPa
-175 MPa
-250 MPa
6.49% CVP Strain
170 MPa
Maximum Strain (%) vs Stress (MPa) Data for Solutionized (SL) &Over-aged (OA) NiTi
12
11
10
9
8
7
6
5
4
3
2
1
0
-600 -400 -200 0 200 400 600Stress (MPa)
10.51%10.27%
8.75%
7.55%
6.49%5.98%
5.21%4.82%
2.72%
5.53%5.45%5.06%
4.38%
3.58%
2.98%
CVP StrainDetwinning + CVP Strain
[012]-OA[012]-SL
[111]-OA[111]-SL
[011]-OA[011]-SL
[001]-OA[001]-SL
[123]-OA[123]-SL
Stage IElasticBehavior
Stage III
A>M
A>M;MartensiteElasticity
Slip ofMartensite
Elastic StrainPseudoelastic Strain
SME Strain
Inelastic Strain
Strain
Stre
ss
Em
EA
Recovarable Strain
Heat above Af
(B2 → B19 → B19' → B19' Detwinning
Stage II
1000
900
800
700
600
500
400
300
200
100
08.07.06.05.04.03.02.01.00.0
Strain (%)
8
6
4
2
0
86420Strain(%)
NiTi-Cu<001>Compression
Stress-Strain Response- Incremental Compression ,NiTi10Cu<100>
500
400
300
200
100
0
6543210Strain [%]
0.5
0.4
0.3
0.2
0.1
0.0
NiTi10Cu[012]
Stress-strain Electrical Resistance
Martensite Reverse Detwinning∆R/R ≅ 0.17
M → Α∆R/R ≅ 0.13
A → Μ∆R/R ≅ 0.13
Martensite Detwinning∆R/R ≅ 0.19
B'
B
P
P'
O O'
A'
A
Heating at Zero Stress
(1) In NiTiCu alloys with 10%Cu detwinning of the martensite phaseplays a significant role in deformation in addition to the two stagetransformation (B19 and B19’phases). (2) In the tensile experiments at 20 oC, the electrical resistancemeasurements confirmed that the end of the stress plateau region is the conclusion of the transformation and the onset of detwinning.(3) In the tensile experiments below martensite finish temperatures (-60°C) the detwinning of the martensite variants produces a largechange in resistance.(3) The relationship between strain and electrical resistance is notlinear when the electrical resistance change occurs due to bothdetwinning of the martensite variants and austenite to martensitetransformation.
Conclusions