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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