Classification of Materials: Smart Materials

1. SMART MATERIALS:
SYNTHESIS, PROPERTIES AND
APPLICATIONS
By
Dr. Ashutosh Singh Raghubanshi

2. SMART MATERIALS
 Group of materials with unique properties
 Possess capabilities to respond to stimuli and
environmental changes
 Mostly responding to changes in shape upon
application of externally applied driving forces
 Magnitude of change is significant

3. CLASSIFICATION OF SMART MATERIALS
 Shape memory alloys
 Piezoelectric materials
 Electrostrictive materials
 Magnetostrictive materials
 Rheological materials / fluids
 Electrochromic materials
 Smart gels
 Optical fibres
 pH-sensitive materials
 Light-sensitive materials

4. BASIS OF CLASSIFICATION
 Based on INPUT and OUTPUT
 Example :
INPUT
 Change in TEMPERATURE
 Change in MAGNETIC FIELD
OUTPUT
 Change in LENGTH
 Change in VISCOSITY
 Change in ELECTRICAL CONDUCTIVITY

5.  Respond to a change in shape and / or length upon
application of a stimulus
 Input always transformed into strain
 Strain used to introduce motion or dynamics into a
system
 Most widely used in SMART STRUCTURES
 Used as ACTUATORS
 Sometimes used as sensors depending on input and
output directions
GROUP I

6. Respond to stimuli with a change in key MATERIAL PROPERTY
( Electrical conductivity, viscosity)
More in SENSORS and less in mechanical structures
Mostly used to design complex modules : Clutches
Fasteners
Valves
Various Switches
Sometimes used in ACTUATOR SYSTEMS
(Electrorheological fluids, Magnetorheological fluids)
GROUP II

7. CLASSIFICATION OF SMART MATERIALS
 Expand and contract with the application of
voltage.
 Piezoceramics are the most widely used
smart material.
 Applications
 Ink Jet Printers.
 Sonar.
 Medical Diagnostics.
 High frequency stereo-speakers.
 Computer Keyboards.
 Microphones.
1. PIEZOELECTRIC MATERIALS

8. 2. Shape Memory Alloys
 Are metals that can be deformed and returned to
their original shape by heating or stress changes.
(Large deformation due to martensitic phase change)
 Applications
Aeronautical applications.
Surgical tools.
Muscle wires.

9. 3. Magnetostrictive Materials
Expand and contract with the application of
magnetic fields.
Applications
– High-power sonar transducers.
– Motors.
– Hydraulic actuators.

10. 4. Active Fluids
Respond to an electric (electrorhelogical) or a
magnetic (magnetorheological) field with a change
in viscosity.
Fluid can change from a thick fluid to nearly a solid
substance in millisecond when exposed to
magnetic/electric field
Applications
– Tunable dampers.
– Vibration-isolation systems.
– Clutches.
– Brakes.
– Resistance Controls.

11. Halochromic Materials:
Changes their color due to changing acidity
Application :Paints changing color to indicate
corrosion in the metal underneath them
Chromogenic systems change color in response
to electrical ,optical or thermal changes
Application: Light sensitive sun glasses darkens
when exposed to bright sunlight

12. WHAT IS A SHAPE MEMORY ALLOY
Memory metals recover their original shape when
heated above a certain critical temperature after plastic
deformation.
This effect is known as Thermo-elasticity .
Ni-Ti , Cu-Zn-Al , Cu-Al-Ni , Fe-Mn-Si, Fe-Cr-Ni-Si-Co,
Fe-Ni-Mn .
One way Shape memory effect

13. SHAPE MEMORY MATERIALS
 Other names: Thermo-responsive materials, SMART
METALS,
Memory metals, Marmem alloys, etc.
 Exhibit two distinct properties :
 Shape Memory Effect ( SME )
 Superelasticity ( SE )
 Examples :
 Shape memory alloys ( SMAs )
 Shape memory ceramics (SMACs)
 Shape memory polymers ( SMPs) or smart gels

14. HISTORY OF SHAPE MEMORYALLOYS
Year Scientists System Phenomenon
1932 A.Olander Au-Cd Pseudoelastic behaviour
1938 Greninger and
Mooradian
Cu-Zn Formation and disappearance
of martensite plates with
decrease and increase in
temperature
1949 Kurdjumov and
Khandros
- Thermoelastic behaviour of
martensite
1951 Chang and Read Au-Cd Thermoelastic behaviour of
martensite
1961 Buehler and Wiley Ni-Ti Shape memory effect
1968 Johnson and
Alicandri
Ni-Ti Implant applications
1980s - - Orthodontic and orthopaedic
applications
1990s - - Stent applications
( SE, SME )

15. COMPOSITION OF SHAPE MEMORY ALLOYS
Alloy System Composition
( at. % )
Transformation
Temperature
( ◦C)
Transformation
Hysteresis
( ◦C )
Ag-Cd 44-49 Cd -190 to – 150 15
Au-Cd 46.5-50 Cd 30 to 100 15
Cu-Al-Ni 14-14.5 wt.% Al
3-4.5 wt.% Ni
-140 to 200 35
Cu-Sn 15 Sn -120 to 30 -
Cu-Zn 38.5-41.5 wt.%Zn -180 to -10 10
Cu-Zn-X
( X = Si, Sn, Al )
A few wt.% of X -180 to -10 10
In-Ti 18-23 Ti 60 to 100 4
Ni-Al 36-38 Al -180 to 100 10
Ni-Ti 49.5 Ni -50 to 110 30
Fe-Pt 25 Pt -130 4
Mn-Cu 5-35 Cu -250 to 180 25

16. Free recovery applications ( e.g. blood-clot filters )
Constrained recovery applications
( e.g. hydraulic couplings )
Force actuators ( e.g. fire safety valves and circuit-
board edge connectors )
Proportional control ( e.g. fluid flow control valve )
Superelastic applications
( e.g. eyeglass frames and guidewires for steering
catheters into vessels in the body )
Damping applications (e.g. automobile bumpers
and earthquake resistant structures).
CLASSIFICATION OF APPLICATIONS OF SHAPE
MEMORY ALLOYS

17. SMA Blood Clot Filter (Ni-Ti alloy)

18. MECHANISM OF SHAPE MEMORY EFFECT
It occurs due to the reversible solid state phase transformation
from martensite (Monoclinic) to parent phase (B.C.C.) .
As martensitic transformation is a diffusion less process, phase
change takes place only by the atomic rearrangements.
The formation of parent phase (austenite) on heating does not
require nucleation. Parent phase forms as a result of reverse
motion of martensite boundaries.

19. Transformation Temperatures
• As and Af are the austenite start and finish temperatures,
and Ms and Mf are the martensite start and finish
temperatures
• The hysteresis width of the shape memory alloys generally
varies between 15 and 50 degree

20. What is Super-elasticity?
 It refers to the ability of
the materials to
recover their
original shape and size
when heated above Af (
Martensite Finish
Temperature ) just by
unloading.
 Also known as
Mechanical Memory
Effect.

21. SUPERELASTICITY
It refers to the unique ability of certain materials to
undergo large elastic deformation
Though many alloys exhibit super elastic effect, only
those based on Ni-Ti found to be biologically and
chemically compatible with the human body
While stainless steel exhibits a recovery strain of
0.5%, Ni-Ti shows a recovery strain of 11%
Though over a range of binary, ternary and quaterary
alloys are used, it is those based on binary Ni-Ti
alloys with Ni=50.6-50.1 at.% found to be highly
suitable

22. APPLICATIONS OF SUPERELASTIC
SMA’S
Cellularphone antennae
Eyeglass frames
Orthodontic archwires
Medical guidewires

23. Why Cu-Al-Ni shape memory alloy?
• Cost effective as compared to Ni-Ti alloy.
• Higher recovery force as compared to Fe-
based alloys.
• Higher thermal stability as compared to Cu-Zn-
Al and Ni-Ti alloys.
• A promising high temperature shape memory
material.

24. Problems related with conventional Cu-Al-Ni
alloys
Extremely brittle due to high anisotropy ratio (≈14) and
large grain size (500-1000 µm) when prepared by
conventional casting technique.
Inferior mechanical properties, like poor fatigue
properties.
Intergranular fracture
How to deal with the problem of brittleness?
Reducing the grain size of the material to improve the
mechanical properties.

25. Processing Techniques for Producing
Fine-grained Shape Memory Alloys
Casting route with alloying addition, such as B, Ti, Zr, Co
and rare earths
There is a significant reduction in grain size compared to
conventional casting but the level of grain refinement is
limited.
Microstructure of a Cu-11.92Al-
3.78Ni (wt%) alloy prepared by
conventional casting route
Microstructure of a Cu-12Al-4Ni
(wt%) alloy prepared by casting
route with 0.1 wt% Boron

26.  Coarse grain-size
 Brittleness
 Low strength
 Low ductility
 Loss of alloying elements ( e.g., Zn in Cu-Zn-Al )
 Low recovery strain
General Problems In Ingot Metallurgy Route

27. POWDER METALLURGY ROUTE
Why Powder Metallurgical Processing?
Fine grain size material as compared to cast material
leading to improved mechanical properties.
Better compositional control
Challenge in powder metallurgical processing
Achievement of near full density in materials
How to achieve near full density materials?
Powder metallurgy route involving “compaction-
sintering-mechanical working”

28. Processing Methods used for producing Shape
Memory Alloys by Powder Metallurgy Route
1) Elemental powder mixture – Mechanical alloying –
Sintering
 Higher amount of residual porosity was present in the sintered
compacts resulting in poor shape memory properties
2) Elemental powder mixture - Mechanical alloying - Hot
pressing - Hot extrusion
 Achievement of near full density material with improved shape
memory properties
 Requirement of controlled atmosphere during mechanical
alloying and encapsulation of the hot pressed compacts in
copper before hot extrusion makes the consolidation process
complex

29. 3) Prealloyed Powder - Hot Isostatic Pressing
4) Prealloyed Powder – High Energy Milling - Hot
Isostatic Pressing
 The shape memory alloy obtained had required
transformation temperature. However, the production of
pre-alloyed powder makes the processing route
economically unattractive
5) Prealloyed powder - Hot Isostatic Pressing - Hot
Rolling

30. What Is Mechanical Alloying?
Mechanical alloying (MA) is a solid-state powder
processing technique involving repeated welding,
fracturing, and rewelding of powder particles in a
high-energy ball mill to form alloy at room
temperature

31. Planetary ball mill
Fritsch Pulverisette P-5 four station ball mill.

32.  Smaller grain-size
 No loss of alloying elements
 High ductility
 High shape recovery strain
Benefits of Mechanical Alloying

33. Mechanism of Mechanical Alloying
Ductile components get flattened to platelet shape by
micro forging process
Flattened particles get cold welded together and form a
composite lamellar structure
Work hardening takes place causing particle
defragmentation
Elemental lamellae become convoluted rather being
linear.
Alloying takes place because of the decreased lamellae
distances.

34. Powders morphology during mechanical alloying in Attritor Mill
SEM of milled powder a) 2 hr b) 4 hr c) 8 hr d) 16 hr e) 40 hr

35. XRD Patterns of Milled Powders

36. XRD profile of the 40 hour milled powder and sintered-
hot pressed - quenched compact of 40 hr milled powder

37. SEM micrograph of sintered-hot pressed-
quenched compact
(A) un-etched specimen showing
small residual porosity
(A) etched specimen showing
martensitic structure
pores

38. Elemental mapping showing the uniform distribution of
the alloying elements

39. DSC Studies on the sintered- hot pressed – quenched compacts
The Austenitic temperature of the alloy was 254 ºC which makes it
suitable in the higher temperature applications.

40. CONCLUSIONS
Copper-based shape memory alloys are beneficial in
high temperature applications like electric circuit
breakers.
The brittleness of the Cu-based SMA can be improved
by refining the grain size.
Mechanical alloying is beneficial in the refinement of
grain size and ensuring chemical homogeneity.
Ni-Ti SMAs are the best alternatives to biomaterials
based on Ti alloys