ti and shape memory alloys
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http://personal.cityu.edu.hk/~appchung
Ti and Shape Memory Alloys:
Ir. Dr. Jonathan C.Y. Chung
Associate Professor
Department of Physics and Materials Science
City ni!ersity of "ong #ong
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$hy %e choose Ti alloy&
'. Corrosion(resistant
). "igh strength from lo% temperature
up to *+,oC
-. o% density: /.+g cm(-0Al: ).*1 g cm(-2 Cu: 3.1*g cm(-2 4e: 5.33g cm(-6
/. Strength is relati!ely lo% %hen pure
+. A lot stronger %hen alloyed
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T%o Crystalline forms of pure Ti
'. Alpha α: 7room temperature to 33-oC8( "e9agonal close paced 7"CP8( sually strong and ;rittle( 33-oC8( =ody Centered Cu;ic 7=CC? the same as steel at roomtemperature8( ess strong ;ut not so ;rittle( Slightly easier to form into different shapes
However, the properties of commercially pure titanium (99-99.5%) arelargely determined by the oygen content.
Hence, improper hot wor!ing such as forging may affect theproperties.
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4our groups of Ti alloy
". #lpha titanium alloys:Commercially pure? Ti(Pd
$. ear-alpha titanium alloys:Ti(''Sn(+@r().)+Al('Mo(,.)Si?Ti(*Al(+@r(,.+Mo(,.)+Si?Ti(+.+Al(-.+Sn(-@r('
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Purposes of Alloying
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Steels
Mild SteelTensile strength: ),, MPa
"igh Strength Alloy SteelTensile strength: B+,,(',,, MPa
ltra("igh Strength SteelTensile strength: >',,, MPa
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Alpha titanium alloys
Strong
"igh strength at high temperatures 733-oC8
ood %elda;ility Difficult to %or
5,MPa m('E)
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Alpha(;eta titanium alloys
Apprecia;le amount of ;eta phase at
room temperature
Can ;e solution treated? Fuenched and
aged to gi!e higher strength
Tensile strength: 11,('--, MPa
4racture toughness: -,(*,MPa m('E)
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=eta titanium alloys
Gntirely ;eta phase at room temperature afterFuenching 7fast cooling8? or sometimes e!en uponair cooling
Heady for cold %oring 7forming8 Can ;e solution treated? Fuenched and aged to gi!e
higher strength In high strength condition the alloys ha!e lo%
ductility Poor fatigue performance Tensile strength: ')),('/+, MPa 4racture toughness: >+, MPa m('E)
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$elda;ility
Commercially pure titanium? α and near(α titaniumalloys ha!e good %elda;ility
Some α(β alloys are %elda;le: e.g. Ti*Al(/
β alloys are generally not %elda;le and < can cause a lot of pro;lem during %elding
at high temperatures TI %eld is the most %idely used process
Glectron(;eam? laser? plasma arc and friction%elding processes can also ;e used Hesistance spot and seam %elding is only used
%hen fatigue life is not important
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Shape
memory
Alloy7SMA8 Ti
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$hat is shape memory
materials&
olan Initiatiati!e Center? Israel
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$hat is shape memory effect
7SMG8&
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$hy there is shape memory
properties&
artensitic
transformation*
4ormation of non(
eFuili;rium phase
non(diffusion
transformation
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Shape Heco!ery 7shape
memory8
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Superelastic Properties
7Pseudoelastic8
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Typical oading and nloading
=eha!ior of Superelastic
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/uperelastic 0evices
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Thermo(controller
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Transformation temperature of
SMA: As? Af? Ms
"eating: As? Af
Cooling: Ms? Mf
Superelasticproperties is
the ;est around
Af ♦ Cooling
♦ "eating
As Af
HsHf
MsMf
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Manipulation of transformation
temperatures
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The Gnd
KLA