The effect of annealing on the microstructure of Cu-Al-Ni-Mn shape memory alloy microwires

38 Pages·2015·5.07 MB·English

The Effect of Annealing on the Microstructure of Cu-Al-Ni-Mn Shape Memory Alloy
Microwires
by
Keerti Shukla
Submitted to the
Department of Materials Science and Engineering
in Partial Fulfillment of the Requirements for the Degree of
Bachelor of Science in Materials Science and Engineering
ARCHNES
at the MASSACHUS-TTS INSTITUTE
OF ELCHNOLOLGY
Massachusetts Institute of Technology SEP 3 0 2015
June 2015
LIBRARIES
0 2015 Keerti Shukla. All rights reserved
The author hereby grants to MIT permission to reproduce and to distribute publicly paper and
electronic copies of this thesis document in whole or in part in any medium now known or
hereafter created.
Signature redacted
Signature of A uthor..................................................
Keerti Shukla
Department of Materials Science and Engineering
May 1, 2015
Signature redacted
C ertified by .......................................................................................................................................
Christopher A. Schuh
Head of Department of Materials Science and Engineering
Danae and Vasilios Salapatas Professor of Metallurgy
Thesis Supervisor
Signature redacted
Accepted by......................... ........................ Beah
Geoffrey Beach
Professor of Materials Science and Engineering
Chairman, Undergraduate Thesis Committee
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The Effect of Annealing on the Microstructure of Cu-Al-Ni-Mn Shape Memory Alloy
Microwires
by
Keerti Shukla
Submitted to the
Department of Materials Science and Engineering
in Partial Fulfillment of the Requirements for the Degree of
Bachelor of Science in Materials Science and Engineering
Abstract
Shape memory alloys exhibit superelasticity and the shape memory effect by undergoing a
diffusionless phase transformation between the austenite and martensite phases. Nickel-titanium
alloys are currently the most common material used. However, due to their expensive cost,
alternatives such as Cu-based alloys have been investigated. Cu-based alloys have exhibited the
shape memory effect and have achieved 6-8% strain recovery. This work investigates Cu-Al-Ni-
Mn shape memory alloys in the form of microwires with the potential application in smart
textiles. Wire microstructure and composition, transition temperatures, and strain recovery were
analyzed after the wires were subjected to varying annealing times and temperatures. These data
were used to determine the ideal conditions to achieve the most shape memory and
superelasticity.
Thesis Supervisor: Christopher A. Schuh
Title: Head of Department and Danae and Vasilios Salapatas Professor of Metallurgy
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Acknowledgements
First and foremost, I would like to thank Nihan Tuncer for advising me and guiding me
throughout the entire thesis project. She patiently answered all my questions and was always
willing to help out with experiments. This project would not have been possible without her help
and support.
I would like to thank Professor Chris Schuh, my thesis advisor, for giving me a change to do my
Senior Thesis project in his group. He has not only been a thesis advisor, but also a role model
and advisor in my time at in DMSE at MIT.
I would also like to thank Ike Feitler for his immense help with experimentation. Whether it was
advice on how to measure something, collecting materials, or machinery expertise, he was
always there to assist. Don Galler also helped me with SEM imaging and EDS data.
In addition to Nihan and Professor Schuh, the other members of the Schuh group have also been
kind in welcoming me into the group, keeping me company in lab, and answering any questions I
had.
Last but certainly not least, I would like to thank my parents, family, and friends for their
constant support, guidance, and genuine interest in my lab work and research. Their excitement
helped the sometimes long and stressful days go by quickly and this project would not have been
possible without their support and encouragement.
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Table of Contents
Abstract ...........................................................................................................................................3
Acknowledge ments ........................................................................................................................ 5
Table of Contents ........................................................................................................................... 7
List of Figures ................................................................................................................................. 9
List of Tables ................................................................................................................................ 10
List of Equations .......................................................................................................................... 10
1. Introduction .............................................................................................................................. 11
1 .1 Sh ap e M em o ry E ffect ................................................................................................................................................ 1 1
1 .2 S u p e re la sticity ............................................................................................................................................................. 1 2
1 .3 C ry sta llo g ra p h y ........................................................................................................................................................... 1 3
1.4 Transformation Temperatures ............................................................................................................................ 14
1 .5 M ate ria ls S ele ctio n ..................................................................................................................................................... 1 6
1 .6 O b je ctiv e s ...................................................................................................................................................................... 1 7
2. Experimentation ....................................................................................................................... 19
2 .1 W ire P ro d u ctio n .......................................................................................................................................................... 1 9
2 .2 M icro stru ctu ra l A n aly sis ......................................................................................................................................... 2 1
2.2.1 Encapsulation ................................................................................................................ 21
2.2.2 Annealing and Quenching ............................................................................................. 21
2.2.3 M ounting and Polishing ................................................................................................ 22
2.2.4 Etching and Imaging ..................................................................................................... 22
2 .3 C o m p o sitio n al A n alysis ........................................................................................................................................... 2 2
2.4 Differential Scanning Calorimetry (DSC) ......................................................................................................... 22
2.5 Dynamic Mechanical Analysis (DMA) ................................................................................................................ 22
3. Results and Discussion ............................................................................................................. 23
3 .1 A n n ealin g C o n d itio n s ............................................................................................................................................... 2 3
3. 1. 1 Inconsistent M icrostructural Results ............................................................................. 27
3.2 Transition Temperatures ........................................................................................................................................ 29
3 .3 Stra in R eco v e ry ........................................................................................................................................................... 3 2
4. Conclusions ............................................................................................................................... 33
5. Future W ork ............................................................................................................................. 34
6. References ................................................................................................................................ 37
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List of Figures
1.1. A hysteretic loop showing the change in length, or strain, as a shape memory material is
heated and cooled through its transformation temperatures. .................................................... 12
1.2. A hysteretic loop depicting the recoverable strains of shape memory materials held at a
temperature above the austenite finish temperature.................................................................... 13
1.3. Schematic showing the crystallographic transformations of shape memory materials
undergoing heating, cooling, and mechanical deformation. The horizontal green arrow
corresponds to the shape memory effect and the vertical green arrow corresponds to
sup erelasticity . .............................................................................................................................. 14
1.4. This schematic shows the heat flow of a shape memory material as it is heated and cooled
through its transform ation tem peratures. .................................................................................. 15
1.5. A schematic of a wire with oligocrystalline structure, which consists of columnar grains
parallel to the longitudinal axis................................................................................................. 18
1.6. Stress-strain plots showing the amount of recoverable strain for Cu-Al-Ni samples...... 19
2.1. This schematic shows the melt-spin technique where the alloy is pushed out of the crucible
and rapidly solidified in a water-coated wheel. ......................................................................... 20
2.2. The microwires obtained after melt-spinning ................................................................... 20
2.3. The wire encapsulated inside a quartz tube pressurized with argon.................................. 21
3.1. These plots show the relationship between the aspect ratio and the (a)temperature and
(b)annealing time where the threshold time and temperature is 4 hours and 9000C.. ............ 24
3.2. This optical image of the highly oligocrystalline sample annealed at 9000C for 4 hours...... 24
3.3. The images above depict the microstructure of three samples annealed at 9500C for (a) 2
hours, (b) 3 hours, and (c) 4 hours............................................................................................ 25
3.4. The images above depict the more oligocrystalline microstructure of three samples annealed
at 950"C for (a) 2 hours, (b) 3 hours, and (c) 4 hours but cooled to 9000C before quenching. .... 26
3.5. A subsequent trial of heat treatment at 9000C for 4 hours produced a non-oligocrystalline
w ire .. ............................................................................................................................................. 2 6
3.6. Plot showing the ternary phase diagram for Cu-Al-Ni alloys at 900'C with low Mn samples
m arked at the crosshairs................................................................................................................ 29
3.7. These plots show (a) exothermic and (b) endothermic the heat flow of wire samples as they
are heated from -800C to 800C and undergo phase transformations......................... 30
3.8. The microstructures of samples annealed at 9000C for (a) 2 hours, (b) 3 hours, and (c) 5
h o u rs.............................................................................................................................................. 3 1
3.9. A stress-strain plot that shows strain recovery of the sample in Figure 3.2 which underwent
heat treatm ent at 9000C for 4 hours.. ........................................................................................ 33
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List of Tables
2.1. The various combinations of annealing times and temperatures tested in various trials....... 21
3.1. The atomic percent of each element in the Cu-Al-Ni-Mn alloys shown in Figures 3.2, 3.3,
3 .4 , an d 3 .5 .................................................................................................................................... 2 8
3.2. A chart showing the transformation temperatures and aspect ratio for each sample shown in
F igu re 3 .8 ...................................................................................................................................... 3 2
List of Equations
3.1. C alculating A spect R atio ................................................................................................... 23
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