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Shape Memory Ceramics
SMC
Viscoelastic
Martensitic
Ferroelectric
Ferromagnetic
SMC Viscoelastic
• Mica based glass-ceramics
• Shape recovery up to 0.5% of deformation
• Process similar to shape memory polymers:
•
•
•
plastic deformation at high temperature
•
•
40-60% volumetric of mica
cooling down to room temperature to “freeze” the shape
heating up to high temperature to recover the original shape
• Heterostructure composed by:
glass matrix for the rest
Deformation recovery: mica glass-ceramic
n
es
ur
ng
ms
d
be
he
ll
r,
d
Figure Deformed
1 Torsional strain
recovery
of a mica at
glass-ceramic
in axial
compression
773K as
Mica based glass-ceramic
• Plastic deformation by slip of the basal plane of mica over
573 K
• The glass matrix follow the deformation elastically ->
residual stress generation
• At room-/low temperature the deformation is retained
• Increasing the T up to the point the mica basal plane can
slip under the residual stress from the glass matrix
• Recovery depends on several factors: max deformation,
temperature, deformation rate, heating time
Others viscoelastic SMC
• Not only mica glass-ceramics show shape memory effects
but also:
•
•
β-spomudene or 2ZnO-B2O3 glass-ceramics
ceramics containing small percentage of glass like: mica, silicon
nitride, carbon nitride, zirconia and allumina
• The deformation recovery in ceramics is a lot smaller
(around 0.1%)
• On observe a relaxation of residual stresses in the
process
• The recovery energy is much lower than in mica based
glass-ceramics
SMC martensitic
• The process is quite similar to the SMA
• Martensitic transformation:
•
Ceramics based on zirconia or partially stabilized zirconia
• Martensitic transformation and re-alignement of ferroelastic domains:
•
Typical of some ionic materials like Pb3(PO4)2 & LnNbO4
(Ln=La, Nd)
•
Superconductors like V-Si, Zr-Hf-V,Y-Ba-Cu-O, Bi-(Pb)-Sr-CaCu-O & Ti-Ba-Ca-Cu-O
• All show both shape memory effects and pseudo-elastic
deformation
Zirconia-stabilizer phase diagram
•
Stabilizers:
•
•
•
•
•
•
Y 2O 3
CeO2
MgO
CaO
......
TZP, CZP, Ce-TZP......
enomena. Because
d thermally stimue and shape-recove on the prestrain,
-deformation rate,
time [121, 123].
mory ceramics
unds undergo marons which can be
, often resulting in
ormation toughenion toughening via
one of the most
iability and strucmics, and has led to
logical importance
[125]. If the transthermoelastic or
pe recovery, that is,
Stabilized zirconia
Zirconia: shape memory mechanism
Ce stabilized zirconia
control, impact or creep resistance and ener
conversion.
From a thermodynamic point of view, pressure, l
temperature, is an independent variable that c
NiTinol
change the free energy and thus phase state of a mat
ial. It is well known that the Gibbs’ chemical f
energy, G, is defined as
G"H!¹S
where ¹ is temperature, H and S are the enthalpy a
entropy of the system, respectively. Based on the fi
and second laws of thermodynamics, it can be eas
derived that
dG"»dP!Sd¹
where P is pressure and » is volume. It is evident th
the free energy can be altered by varying either pr
sure or temperature. At a given temperature, the
crease in pressure will increase the free energy of
system. As a consequence, the system will tend
transform into other phases that have a lower f
energy under the pressure, or, to decrease its volu
through contraction, which will change the electro
structures and in turn the physical properties, a
thermodynamic state of the material. Pressureduced phase transitions have been observed in a v
wide range of materials. Of particular interest are
reversible pressure-induced transitions, which m
implicate shape-memory effect. More recently, a me
Ferroelectrics
• PLZT-(Pb, La)(Zr, Ti)O , PZST-Pb(Zr,Sn,Sn,Ti)O , PLSnZT-
8 Schematic illustration of the deformation processes
materials. (a) Stre
3 in the ferroelastic, ferromagnetic, and ferroelectric
3
sitic transformation by twinning and reorientation of martensite domains by detwinning, (b) magnetic field-induced trans
3
3 polarization of FE.
orientation of magnetic domains, (c) electric field-induced
AFE—FE transformation and
(Pb, La)(Zr, Sn, Ti)O , (Pb, Nb)(Zr, Sn, Ti)O
• (Sr,Ba)Nb O
manganites
RMnO
Y) domains will cause me
the(R=Ho,
ferroelectric
bohedral•orHexagonal
tetragonal structure
[175, 212].
As
strains, as illustrated in Fig. 8c. Suppose the
oned above, the compositions of the ferroelectric
2
6
-memory ceramics are usually so selected that
eramics have an antiferroelectric structure but
3
tude of the sublattice polarization remains es
unchanged during the transformation, then, ac
PZTs phase transformations
proper st
parent—m
it has be
compress
formation
sense of e
[179—181
tensitic t
guided
equation
where !
transform
Ferroelectrics & anti-ferroelectrics
Ferroelectric
Ferroelectric-antiferroelectric
metastable
2.2.4. Ferromagnetic shape-memo
ceramics
Some transition metal oxides undergo
netic—ferromagnetic, paramagnetic—antiferr
transformation, or orbital order—disorder
and the reversible transformations are al
panied by recoverable lattice distortions. In
gonal manganite spinels Mn (Zn, Cd)
!
[153, 154] and in the non-stoichiometric
ganites RMnO (R"Nd, Sm, Eu, Gd, Tb,
!"!
the orbital ordered and disordered pha
in a wide temperature interval, and s
ferromagnetic (or antiferromagnetic) or
Jahn—Teller
phase
transitions may ta
In the case of antiferroelectric metastability
on 3observe
a ferroelectric
or antiferroelectric
Figure
Comparison
of the longitudinal
strains for ferroelectric
resulting
in
a Spontaneous
shape-memory
effect.
Bec
phase at zero field depending on the history.
A deformation
is associated.
With
the
and antiferroelectric
materials.
(a)
strain
due
to polarof the
thedeformation
manganites
aretransformation
antiferromagnets
ization in a and
ferroelectric,
(b) field-induced
strain
temperature the stable phase is recovered
released.
from AFE to FE
Ne´state
el [148].
temperatures are very low, sp
magnetization of the compounds is only
Pb0.99Nb0.02((Zr0.6Sn0.4)0.94Ti0.06)0.98O3
•
Elastic deformation induced
by the electric field at
different temperatures
Ferromagnetic SMC
• Tetragonal manganites (spinels: Mn (Zn,Cd) Mn O )
• Ortomanganites non stoichiometric: (RMnO , R=Nd, Sm,
x
Eu, Gd, Tb, Dy)
1-x
3+x
2
4
Comparison SMA-Piezo-Magnetici
TA BLE I I Comparison of characteristics of shape-memory alloys, piezoelectric ceramics and magnetostrictive materials as actuation
materials
Properties
Shape-memory alloy
(Ti—Ni)
Piezoelectric
(PZT)
Magnetostrictive
(Terfenol-D)
Compressive stress (MPa)
Tensile strength (MPa)
Young’s modulus (GPa)
!800
800—1000
50—90 (P)
10—35 (M)
!0.1
0—100
!
3—5
300—600
60
30—55
60—90 (Y!)!
!110 (Y#)#
!0.001
1—20 000
0.75
50
!1.0
700
28—35
25—35 (Y")"
50—55 (Y$)$
!0.01
1—10 000
0.75
80
14—25
Maximum strain
Frequency (Hz)
Coupling coefficient
Efficiency (%)
Energy density (kJ m%&)
! modulus for constant electric field
# modulus for constant electric displacement
" modulus for constant magnetizing field
$ modulus for constant induction field
conventional piezoelectric or electrostrictive ceramics
have a superior dynamic response but their displacements are quite small and most of them are very
brittle. Combining SMAs with piezoelectric or magnetostrictive materials, field-activated smart composites can be designed, which may generate a larger
displacement than conventional piezoelectric ceramics
way as the stress-induced deformation of the martensites in ferroelastic SMAs. The next challenging
objective, therefore, is to explore new potentially commercial materials wherein the martensitic-like transformations and the reorientation of the domains can
be induced by magnetic fields or electric fields at
ambient temperatures. The design concepts and strat-
Confronto
tipi types
di attuatori
Comparison
different
of actuators
Table 1
Comparison of active materials
Max strain (! 10–6)
Max stress (MPa)
Density (kg/m3)
Modulus (GPa)
Efficiency (%)
Bandwidth (Hz)
Energy density (KJ/m3)
PZT5H
PMN
PLZT
PVDF
Terfinol-D
300
19
7500
62
56
1000
2.9
600
72
7500
120
75
1000
22
3000
180
~7500
~60
?
?
?
200
~1
1780
3
2
1000
~1
1800
90
9250
40
40
100
19
been discovered but are still in the developmental
stage.18
Piezoresistive polymers and polymer composites.
Another promising class of materials for force trans-
SMA Conducting Polymer
(NiTi)
Polymer
Hydro-gel
70000
190
6450
78
>3
3
>10
20000
180
~1500
5
>30
>1
>1
400000
0.3
~1300
<0.1
30
.1
0.4
Human
Muscle
400000
0.3
1037
.06
>35
4
0.8
ing some type of conducting particulates, such as
graphite. Such compounds are macroscopically
piezoresistive but also exhibit noise and hysteresis
due to the percolative nature of the conduction mechanism. Although some mildly piezoresistive polymers