shape memory alloys

1. T.Y. B.TECH
SCHOOL OF MECHANICAL ENGINEERING
ADVANCED MATERIALS
SHAPE MEMORY ALLOY
PRESENTATION BY:-
ADITYA BULBULE (PA-05)
KAIWALYA GONDCHAR (PA-06)
JAYESH KASAR (PA-08)
PIYUSH KANCHAN(PA-16)
KAUSHIK SINGH(PA-53)
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2. INTRODUCTION:-
● Shape memory alloys exhibit what is called the shape memory effect.
If such alloys are plastically deformed at one temperature, they will
completely recover their original shape on being raised to a higher
temperature.
● In recovering their shape the alloys can produce a displacement or a
force as a function of temperature.
● We can make metals change shape, change position, pull, compress,
expand, bend or turn, with heat as the only activator.
● The most effective and widely used alloys include Ni Ti (Nickel
Titanium -NiTiNOL), Cu Zn Al and Cu Al Ni.
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3. WHAT ARE SHAPE MEMORY
ALLOYS?
● Shape memory alloys are a unique class of
metal alloys that can recover apparent
permanent strains when they are heated
above a certain temperature.
● The shape memory alloys have two stable
phases :-
Austenite
Twinned
Martensite
Detwinned
Martensite3

4. SHAPE MEMORY EFFECT
● The shape memory effect (SME) occurs because a temperature-induced phase
transformation reverses deformation, as shown in the previous hysteresis curve.
Typically the martensitic phase is monoclinic or orthorhombic (B19' or B19).
● Martensite is thermodynamically favored at lower temperatures, while austenite (B2
cubic) is thermodynamically favored at higher temperatures.
● Since these structures have different lattice sizes and symmetry, cooling austenite into
martensite introduces internal strain energy in the martensitic phase.
● To reduce this energy, the martensitic phase forms many twins this is called
"self-accommodating twinning" and is the twinning version of geometrically necessary
dislocations. Since the shape memory alloy will be manufactured from a higher
temperature and is usually engineered so that the martensitic phase is dominant at
operating temperature to take advantage of the shape memory effect, SMAs "start"
highly twinned.

5. PHASE TRANSFORMATION

6. SHAPE MEMORY EFFECT OF
NITINOL: -
● At high temperatures, nitinol assumes an interpenetrating simple cubic structure
referred to as austenite (also known as the parent phase).
● At low temperatures, nitinol spontaneously transforms to a more complicated
monoclinic crystal structure known as martensite (daughter phase). There are four
transition temperatures associated to the austenite-to-martensite and
martensite-to-austenite transformations.
● Starting from full austenite, martensite begins to form as the alloy is cooled to the
so-called martensite start temperature, or Ms
, and the temperature at which the
transformation is complete is called the martensite finish temperature, or Mf
.
● When the alloy is fully martensite and is subjected to heating, austenite starts to form
at the austenite start temperature, As
, and finishes at the austenite finish temperature,
Af
.

7. ...
● The cooling/heating cycle shows thermal hysteresis. The hysteresis width
depends on the precise nitinol composition and processing. Its typical value
is a temperature range spanning about 20-50 K (20-50 °C; 36-90 °F) but it can
be reduced or amplified by alloying and processing
● Crucial to nitinol properties are two key aspects of this phase transformation.
First is that the transformation is "reversible", meaning that heating above the
transformation temperature will revert the crystal structure to the simpler
austenite phase. The second key point is that the transformation in both
directions is instantaneous.
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8. ...
● Martensite's crystal structure (known as a monoclinic, or
B19' structure) has the unique ability to undergo limited
deformation in some ways without breaking atomic bonds.
● This type of deformation is known as twinning, which
consists of the rearrangement of atomic planes without
causing slip, or permanent deformation.
● It is able to undergo about 6–8% strain in this manner.
When martensite is reverted to austenite by heating, the
original austenitic structure is restored, regardless of
whether the martensite phase was deformed.
● Thus the name "shape memory" refers to the fact that the
shape of the high temperature austenite phase is
"remembered," even though the alloy is severely deformed
at a lower temperature.

9. TYPES OF SHAPE MEMORY
EFFECTS:-
1.ONE WAY MEMORY EFFECT
● Alloy in martensite state is
mechanically deformed and when
reheated to a temperature above the
austenite finish temperature, it
recovers original macroscopic shape.
● This is possible because no matter
what the post deformation
distribution of martensite variants,
there is only one reversion pathway to
parent phase for each variant when
reheated.
Starting from martensite (a), adding
a reversible deformation for the
one-way effect (b), heating the
sample (c) and cooling it again (d).
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10. ...
2. TWO WAY MEMORY EFFECT
● Shape memory alloys can be processed to
remember both hot and cold shapes. They can
be cycled between two different shapes without
the need of external stress.
● Self–accommodation of the martensite
microstructure is lost in the two-way effect due
to the presence of these internal stresses.
● Internal stress is usually a result of irreversible
defects which can be introduced through cyclic
deformation above austenite finish temperature.
Starting from martensite (a),
adding severe deformation
with an irreversible amount
for the two-way (b), heating
the sample (c) and cooling it
again (d).
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11. DIFFERENT TYPES OF SMA
● Copper-Zinc-Aluminum (CuZnAl):CuZnAl was the first copper
based SMA to be commercially exploited and the alloys typically
contain 15-30 wt% Zn and 3-7 wt% Al.
● The useful transformation temperature for this system ranges
from -100C to +100C.
● The major advantage of the CuZnAl alloys is that they are made
from relatively inexpensive metals by conventional metallurgical
processes which makes them the cheapest of the commercial
SMAs.
● The major disadvantages of this alloy system are that the
martensitic phase is stabilized by long term aging even at room
temperature causing an increase of the transformation
temperature, and the alloy structure decomposes when exposed
to temperatures above 100C. 11

12. ...
● Copper-Aluminum: Copper-aluminum-nickel (CuAlNi) alloys have undergone
extensive development and are now preferred to the CuZnAl alloys.
● The alloys typically contain 11-14.5% Al and 3-5% Ni and have transformation
temperatures in the range 80-200C dependant on their composition, the
transformation temperature is particularly sensitive to the aluminum content.he
major advantages of the CuAlNi system are its wide range of useful
transformation temperatures, its stability at elevated temperature making it the
only system that can be used for applications above 100C, its small hysteresis
and its relatively low cost.
● Some improvement of the mechanical properties can be obtained by reducing
the aluminum content below 12%, adding 2% manganese to reduce the
transformation temperature and 1% titanium as a grain refiner but these
additions can affect the stability of the alloy structure.
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13. PSEUDOELASTICITY OR
SUPERELASTIC EFFECT:-
● Pseudo-elasticity occurs in shape memory alloys when the alloy
is completely composed of Austenite (temperature is greater
than Austenite finish temperature).
● The martensitic phase is generated by stressing the metal in the
austenitic state and this martensite phase is capable of large
strains.
● With the removal of the load, the martensite transforms back into
the austenite phase and resumes its original shape.
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14. ADVANTAGES
The prime advantages of shape memory alloy are :
1. High Strength 7. High Power to Weight Ratio
2. Good Elasticity 8. Light Weight
3. Fatigue Resistance 9. Biocompatibility
4. Wear Resistance 10.Diverse field of application
5. Easy Fabrication
6. Easy to Sterilize
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15. DISADVANTAGES:
The prime disadvantages of shape memory alloy are :
1. Initially Expensive
2. Sensitive of material properties in fabrication
3. Residual stress develop in thin film
4. Non linearity of actuation force
5. Lower maximum frequency compared to other microactuator device 6.
Poor fatigue property
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16. APPLICATIONS
AIRCRAFT MANEUVERABILITY
The wire on the bottom of the wing is
shortened through the shape memory
effect, while the top wire is stretched
bending the edge downwards, the
opposite occurs when the wing must be
bent upwards. The shape memory effect
is induced in the wires simply by heating
them with an electric current
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17. THERMAL AND ELECTRICAL ACTUATORS: -
● Nitinol can be used to replace conventional actuators
(solenoids, servo motors, etc.), such as in the
Stiquito, a simple hexapod robot.
● Nitinol springs are used in thermal valves for fluidics,
where the material both acts as a temperature
sensor and an actuator.
● It is used as autofocus actuator in action cameras
and as an Optical Image Stabilizer in mobile phones
● It is used in pneumatic valves for comfort seating
and has become an industry standard.
● The 2014 Chevrolet Corvette incorporates nitinol
actuators, which replaced heavier motorized
actuators to open and close the hatch vent that
releases air from the trunk, making it easier to close

18. DAMPING SYSTEMS IN STRUCTURAL
ENGINEERING: -
● Super elastic Nitinol finds a variety of
applications in civil structures such as bridges
and buildings. One such application is
Intelligent Reinforced Concrete (IRC), which
incorporates Ni-Ti wires embedded within the
concrete. These wires can sense cracks and
contract to heal macro-sized cracks
● ·Another application is active tuning of
structural natural frequency using Nitinol wires
to dampen vibrations.

19. BIOCOMPATIBLE AND BIOMEDICAL APPLICATIONS: -
● Nitinol is highly biocompatible and has properties suitable for use in
orthopedic implants. Due to Nitinol’s unique properties it has seen a large
demand for use in less invasive medical devices. Nitinol tubing is commonly
used in catheters, stents, and super elastic needles.
● In colorectal surgery [1], the material is used in devices for reconnecting the
intestine after removing the pathology.
● Nitinol is used for devices developed by Franz Freudenthal to treat Patent
ductus arteriosus, blocking a blood vessel that bypasses the lungs and has
failed to close after birth in an infant.
● A more recent application of nitinol wire is in female contraception,
specifically in intrauterine devices.

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MINIATURIZED WALKING ROBOT
The implementation of SMA wires
coupled with a simple DC control system
can be used to drive small objects
without the addition of relatively heavy
motors, gears, or drive mechanisms.
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21. ...
ROBOTIC MUSCLE
Shape memory alloys mimic human
muscles and tendons very well. SMA's are
strong and compact so that large groups
of them can be used for creating a life-like
movement unavailable in other systems.
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22. CONCLUSION:-
Future applications include engines in cars and airplanes and electrical
generators utilizing the mechanical energy resulting from the shape
transformations.
NiTiNOL with its shape memory property is also envisioned for use as car
frames.
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23. REFERENCES:-
❏ “Materials Science and engineering” by William D.Callister, Jr.
❏ http://smart.tamu.edu
❏ Shape Memory Applications Inc._Shape Memory Alloys.
❏ http://www.sma-inc.com/SMAPaper.html
❏ http://scholar.google.co.in/scholar?q=Shape+Memory+effect+of+Nitinol&hl=en&as_sdt=0&as
_vis=1&oi=scholart
❏ https://www.nitinol.com/wp-content/uploads/2012/01/038.pdf
❏ https://www.hindawi.com/journals/amse/2016/4173138/·
https://www.medicaldesignbriefs.com/component/content/article/mdb/features/articles/23077
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