Comparison and Characterization of

NiTi and NiTiCu

Shape Memory Alloys

S. Dilibal, H.Adanir

Marmara University, Istanbul/TurkeyMay 23, 2013

OUTLINE

Overview of Shape Memory Alloys

Applications of Shape Memory Alloys

Experimental study for NiTi and NiTiCu SMA’s

Characterization

Conclusion

Future works

to obtain shape memory effect, martensitik transformation (MT)

is required.

diffusionless and reversible solid state transformation

high-temperature austenite (A) phase

low temperature martensite (M) phase

Cooling: forward MT to (A→M)

Heating: reverse MT (A←M)

when deformed in the martensitic state, material “remembers”

original shape upon back transformation to austenite.

MT is thermal or stress induced

Heating to recover deformation - shape memory effect (SME)

Unloading to recover deformation – pseudoelastic (PE)

Overview of Shape Memory Alloys

Cooling

Heating

T oC

Shape Memory Effect (SME)

Cooling

Heating

Shape Memory Effect (SME)

Shape Memory Effect (SME)

Austenite

Martensite

sf

sr

A A A A

Mixed Phase

M M

s

e

T>Af

Superelastic behavior at austenite phase via stress induced martensite.

1951 Au- 47.5% at.Cd

CuAlNi (14 %Al, 3.5%Ni wt.), CuZn (38.5/41.5% Zn wt.)

NiAl (% 36-38 Al wt.)

NiTi (equiatomic) SMA’s;

discovered in 1962 W.J. Buehler at the US Naval Ordnance Laboratory

Commercially known as NiTiNOL – (NiTi Naval Ordnance Laboratory)

Background of SMA’s

The Advantages of SMA’s in the Engineering Application;

Simple training mechanism,

High power/weight ratio,

High corrosion resistance,

Low maintenance,

Can be controlled by electrical current.

Applications of NiTi Based Shape Memory Alloys

Aeronautics Orthodontic Endodontic Angiography (stent)

Robotic Eyeglass frame and antenna Thin film and MEMS Art

Lady and Baby monument developed by Sculpture Oliver Deschcamp.

Applications of NiTi Based Shape Memory Alloys

NiTi -conjunction pins used in human bones.

NiTi-stends used in human body.

Applications of NiTi Based Shape Memory Alloys

The first industrial application area is warplanes, coupling instead

of welding at the closest area of fuel storage units in 1969.

Applications of NiTi Based Shape Memory Alloys

Ref.ASM Vol. 3

NiTi Shape Memory Alloys

Ref. ASM Vol.3

The Role of Precipitates in NiTi SMA’s

precipitate phases do not transform to martensite.

reduce the maximum transformation strain

since they are untransformable.

Aging create 10 to 700 nm TiNi precipitates with volume

fraction up to 16% in Ni-rich compositions.

• increase austenite yield strength,

• enhance fatigue properties, two way SME.

To overcome some of disadvantages of the NiTi SMA’s.

NiTiX (X=Zr or Hf)

NiTiY(Y=Pd or Pt)

utilized to obtain potential high temperature SMA’s.

The addition of Cu shows a significant effect on transformation

temperature hysteresis loop.

The Ternary Element Addition

(*) denotes experimental values,

(**) nickel-rich near equiatomic (composition dependent),

(#) depends on the composition and heat treatment,

(C) compression, (T) tension,

(A) Austenite.

Summary of SMA for the temperature hysterisis, critical stress

(austenite) and maximum transformation strain

Experimental Study

Manufacturing of NiTi/NiTiCu → VAR Method

Characterization → Conventional MetallographyOptical MicroscopeSEM,EDS, DSC, Vickers Hardness Testing

Produceed of NiTi SMA in VAR and VIR Method

a. Manufactured NiTi ingot using vacuum arc remelting (VAR) technique

b. 32.1g NiTi ingot (poured into the mold after three back to back melting in

zirkonia crucible)

c. Production of 2x2x65mm NiTi bars (after cutting by wire erosion technique)

a. b.

c.

Alloy Ni %wt. Ti % wt. Cu% wt.

NiTi-1 54.97 45.03 -

NiTi-2 53.72 46.28 -

NiTiCu-1 59.66 37.75 2.59

NiTiCu-2 51.70 43.64 4.66

Chemical Composition of Produced SMA’s

EDS Analysis Results for NiTi SMA’s

EDS Analysis Results for NiTiCu SMA’s

Optical Metallography and SEM Results for NiTi SMA’s

Light Optical Microscope was

used for metallographic

observations and to obtain the

micrographs of the surfaces.

SEM result clarify that there are

martensite plates with different

orientations and spherical shaped

Ti2Ni precipitation.

Micrographs of NiTi-1 (a, b), and NiTi-2 (c, d) after heat treatment.

Optical Metallography Results for NiTi SMA’s

Optical Metallography Results for NiTiCu SMA’s

Micrographs of NiTiCu-1 (a, b), and NiTiCu-2 (c, d) after heat treatment.

DSC Result for NiTi SMA’s

Determination of Austenitic and Martensitic phase transformation temperature

using with DSC analysis.

• after 4 cycles at the heating/cooling rate of 10°C/min between 0 and 200˚C.

DSC Result for NiTiCu SMA’s

Determination of Austenitic and Martensitic phase transformation temperature

using with DSC analysis.

• after 4 cycles at the heating/cooling rate of 10°C/min between 0 and 200˚C.

Temp

(oC)NiTİ-1 NiTi-2 NiTiCu-1 NiTiCu-2

Ms 72 48 24 29

Mp 67 64 38 41

Mf 54 72 48 47

As 91 95 51 49

Ap 105 101 62 58

Af 114 110 67 71

DSC Analysis Results for NiTi and NiTiCu SMA’s

Ms: Martensite Start, Mp: Martensite Peak Mf: Martensite Finish,

As: Austenite Start , Ap: Austenite Peak, Af: Austenite Finish.

Hardness Test Results

Alloy HV (0.1kg/mm2)

NiTi-1 204

NiTi-2 235

NiTiCu-1 319

NiTiCu-2 298

Vickers Hardness Test Results

addition of Cu into NiTi SMA as a ternary alloy dramatically

decreased Ms, As and Af temperatures after 4 thermal cycles

under the stress-free condition between 0-200ºC.

a slight increase was observed on Mf temperature.

hardness is increased by the addition of Cu into the NiTi SMA

samples.

hardness is not increased by the increasing of Cu amount after

2.59%wt.

Conclusion:

Future Works:

work is required to investigate the thermo-mechanical response

and transformation characteristics under stress-loaded condition

for NiTiCu SMA’s.

a candidate material to reduce the damage of debris impact in

space application.

as-cast production technique can be easily improved to produce

low cost SMA materials for any future applications.

THANK YOU