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Comparison and Characterization of
NiTi and NiTiCu
Shape Memory Alloys
S. Dilibal, H.Adanir
Marmara University, Istanbul/TurkeyMay 23, 2013
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OUTLINE
Overview of Shape Memory Alloys
Applications of Shape Memory Alloys
Experimental study for NiTi and NiTiCu SMA’s
Characterization
Conclusion
Future works
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to obtain shape memory effect, martensitik transformation (MT)
is required.
diffusionless and reversible solid state transformation
high-temperature austenite (A) phase
low temperature martensite (M) phase
Cooling: forward MT to (A→M)
Heating: reverse MT (A←M)
when deformed in the martensitic state, material “remembers”
original shape upon back transformation to austenite.
MT is thermal or stress induced
Heating to recover deformation - shape memory effect (SME)
Unloading to recover deformation – pseudoelastic (PE)
Overview of Shape Memory Alloys
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Cooling
Heating
T oC
Shape Memory Effect (SME)
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Cooling
Heating
Shape Memory Effect (SME)
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Shape Memory Effect (SME)
Austenite
Martensite
sf
sr
A A A A
Mixed Phase
M M
s
e
T>Af
Superelastic behavior at austenite phase via stress induced martensite.
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1951 Au- 47.5% at.Cd
CuAlNi (14 %Al, 3.5%Ni wt.), CuZn (38.5/41.5% Zn wt.)
NiAl (% 36-38 Al wt.)
NiTi (equiatomic) SMA’s;
discovered in 1962 W.J. Buehler at the US Naval Ordnance Laboratory
Commercially known as NiTiNOL – (NiTi Naval Ordnance Laboratory)
Background of SMA’s
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The Advantages of SMA’s in the Engineering Application;
Simple training mechanism,
High power/weight ratio,
High corrosion resistance,
Low maintenance,
Can be controlled by electrical current.
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Applications of NiTi Based Shape Memory Alloys
Aeronautics Orthodontic Endodontic Angiography (stent)
Robotic Eyeglass frame and antenna Thin film and MEMS Art
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Lady and Baby monument developed by Sculpture Oliver Deschcamp.
Applications of NiTi Based Shape Memory Alloys
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NiTi -conjunction pins used in human bones.
NiTi-stends used in human body.
Applications of NiTi Based Shape Memory Alloys
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The first industrial application area is warplanes, coupling instead
of welding at the closest area of fuel storage units in 1969.
Applications of NiTi Based Shape Memory Alloys
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Ref.ASM Vol. 3
NiTi Shape Memory Alloys
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Ref. ASM Vol.3
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The Role of Precipitates in NiTi SMA’s
precipitate phases do not transform to martensite.
reduce the maximum transformation strain
since they are untransformable.
Aging create 10 to 700 nm TiNi precipitates with volume
fraction up to 16% in Ni-rich compositions.
• increase austenite yield strength,
• enhance fatigue properties, two way SME.
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To overcome some of disadvantages of the NiTi SMA’s.
NiTiX (X=Zr or Hf)
NiTiY(Y=Pd or Pt)
utilized to obtain potential high temperature SMA’s.
The addition of Cu shows a significant effect on transformation
temperature hysteresis loop.
The Ternary Element Addition
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(*) denotes experimental values,
(**) nickel-rich near equiatomic (composition dependent),
(#) depends on the composition and heat treatment,
(C) compression, (T) tension,
(A) Austenite.
Summary of SMA for the temperature hysterisis, critical stress
(austenite) and maximum transformation strain
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Experimental Study
Manufacturing of NiTi/NiTiCu → VAR Method
Characterization → Conventional MetallographyOptical MicroscopeSEM,EDS, DSC, Vickers Hardness Testing
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Produceed of NiTi SMA in VAR and VIR Method
a. Manufactured NiTi ingot using vacuum arc remelting (VAR) technique
b. 32.1g NiTi ingot (poured into the mold after three back to back melting in
zirkonia crucible)
c. Production of 2x2x65mm NiTi bars (after cutting by wire erosion technique)
a. b.
c.
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Alloy Ni %wt. Ti % wt. Cu% wt.
NiTi-1 54.97 45.03 -
NiTi-2 53.72 46.28 -
NiTiCu-1 59.66 37.75 2.59
NiTiCu-2 51.70 43.64 4.66
Chemical Composition of Produced SMA’s
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EDS Analysis Results for NiTi SMA’s
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EDS Analysis Results for NiTiCu SMA’s
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Optical Metallography and SEM Results for NiTi SMA’s
Light Optical Microscope was
used for metallographic
observations and to obtain the
micrographs of the surfaces.
SEM result clarify that there are
martensite plates with different
orientations and spherical shaped
Ti2Ni precipitation.
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Micrographs of NiTi-1 (a, b), and NiTi-2 (c, d) after heat treatment.
Optical Metallography Results for NiTi SMA’s
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Optical Metallography Results for NiTiCu SMA’s
Micrographs of NiTiCu-1 (a, b), and NiTiCu-2 (c, d) after heat treatment.
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DSC Result for NiTi SMA’s
Determination of Austenitic and Martensitic phase transformation temperature
using with DSC analysis.
• after 4 cycles at the heating/cooling rate of 10°C/min between 0 and 200˚C.
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DSC Result for NiTiCu SMA’s
Determination of Austenitic and Martensitic phase transformation temperature
using with DSC analysis.
• after 4 cycles at the heating/cooling rate of 10°C/min between 0 and 200˚C.
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Temp
(oC)NiTİ-1 NiTi-2 NiTiCu-1 NiTiCu-2
Ms 72 48 24 29
Mp 67 64 38 41
Mf 54 72 48 47
As 91 95 51 49
Ap 105 101 62 58
Af 114 110 67 71
DSC Analysis Results for NiTi and NiTiCu SMA’s
Ms: Martensite Start, Mp: Martensite Peak Mf: Martensite Finish,
As: Austenite Start , Ap: Austenite Peak, Af: Austenite Finish.
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Hardness Test Results
Alloy HV (0.1kg/mm2)
NiTi-1 204
NiTi-2 235
NiTiCu-1 319
NiTiCu-2 298
Vickers Hardness Test Results
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addition of Cu into NiTi SMA as a ternary alloy dramatically
decreased Ms, As and Af temperatures after 4 thermal cycles
under the stress-free condition between 0-200ºC.
a slight increase was observed on Mf temperature.
hardness is increased by the addition of Cu into the NiTi SMA
samples.
hardness is not increased by the increasing of Cu amount after
2.59%wt.
Conclusion:
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Future Works:
work is required to investigate the thermo-mechanical response
and transformation characteristics under stress-loaded condition
for NiTiCu SMA’s.
a candidate material to reduce the damage of debris impact in
space application.
as-cast production technique can be easily improved to produce
low cost SMA materials for any future applications.
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THANK YOU