Rezultate 2008
METHOD FOR IN SITU OBSERVATION OF STRESS-INDUCED MARTENSITE FORMATION
AND EVOLUTION IN SHAPE MEMORY ALLOYS
BY
SERGIU STANCIU, LEANDRU-GHEORGHE BUJOREANU, NICANOR CIMPOEŞU, MONICA NICOLETA
LOHAN
Abstract The recent development of shape memory alloys (SMAs) led to the conclusion that no shape
memory effect (SME) exists unless a “cold shape” (characteristic to martensitic domain) different to
initial “hot shape” (characteristic to austenitic domain) can be induced to a SMA specimen. The
microstructural phase that accompanies cold shape obtainment is termed stress-induced martensite
(SIM). To observe SIM during in situ experiments, special devices are necessary in order to keep the
specimens in deformed state. The present paper describes an original method for in situ observation
of SIM by means of two experimental devices. The former is adapted to optical microscopes table. It
is applicable for lamellar specimens which are elongated while being examined under microscope.
This allows good in situ observation of SIM formation. The latter is used in conjunction with a tensile
testing machine and is meant to “freeze” elongated specimens in tensioned state, in order to be
analyzed by X-ray diffraction. The structure and functionality of the two devices are introduced in the
paper together with corresponding examples of in situ observation of SIM formation and evolution
with increasing applied stress.
Keywords: shape memory alloys, stress-induced martensite, microstructure, optical microscopy, X-
ray diffraction
2000 Mathematics Subject Classification: 53B25, 53C15
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4. Conclusions
1. Two experimental devices for in situ observation of stress-induced martensite formation, in SMAs
were introduced.
2. Two examples were presented of the study of stress-induced martensite formation in the specific
case of a Cu-Al-Ni SMA, illustrating OM micrographs and XRD profiles recorded using the two
experimental devices.
Acknowledgements Financial support was granted by UEFISCU, by means of the research grant PN
II-ID 616-PCE-2007-1, contract no. 83/ 01.10.2007
Submitted: “Gh. Asachi” Technical University from Iaşi,
Accepted: Faculty of Materials Science and Engineering
Bd. D. Mangeron 61A, 700050 Iaşi, Romania
e-mail: sergiustanciu2003@yahoo.com
R E F E R E N C E S
1. B u j o r e a n u L. G, Intelligent Materials (in Romanian), Editura Junimea, Iaşi, 2002
2. D u e r i g T. W., Z a d n o R., An Engineer’s Perspective of Pseudoelasticity, In Engineering .
Aspects of Shape Memory Alloys (Duerig T.W., Melton K.N., Stöckel D., Wayman C.M Eds.) Butterworth-
Heinemann, 369, 1990
3. ., S t a n c i u S., B u j o r e a n u L. G., Formation of stress-induced martensite in the presence of γ
phase in a Cu-Al-Ni-Mn-Fe shape memory alloy, Materials Science and Engineering A, 481-482, 494-
499, (2008)
METODĂ PENTRU STUDIUL IN SITU AL FORMĂRII ŞI EVOLUŢIEI MARTENSITEI INDUSE PRIN TENSIUNE
ÎN ALIAJELE CU MEMORIA FORMEI
(Rezumat)
Dezvoltarea recentă a aliajelor cu memoria formei (AMF) a dus la concluzia că nu se poate obţine
efect simplu de memoria formei (EMF) dacă unei probe din AMF nu i se poate induce o “formă rece”
(caracteristică domeniului martensitic) diferită de “forma caldă“ iniţială (caracteristică domeniului
martensitic). Faza microstructurală care însoţeşte obţinerea formei reci este numită martensită
indusă orin tensiune (MIT). Pentru a observa MIT, în timpul experimentelor in situ, sunt necesare
dispozitive speciale pentru a păstra probele în stare deformată. Lucrarea de faţă descrie o metodă
orginală de observare in situ a MIT, prin intermediul a două dispozitive experimentale. Primul este
adaptat la masa microscoapelor optice. Este aplicabil pentru probele lamelare care sunt alungite în
timp ce sunt examinate sub microscop. Acest lucru permite o bună observare in situ a formării MIT.
Cel de-al doilea este utilizat împreună cu o maşină de încercat la tracţiune şi are rolul de a „îngheţa”
proble alungite în stare tensionată, pentru a fi analizate prin difracţie de raze X. Lucrarea descrie
structura şi funcţionalitatea celor două dispozitive, împreună cu exemple corespunzătoare de
observare in situ a formării şi evoluţiei MIT la creşterea tensiunii aplicate
Lucrarea a fost publicata in Buletinul Institutului Politehnic Iaşi, tomul LIV(LVIII), fascicula 1, Construcţii
de Maşini, pp. 357-362, 2008, ISSN 1011-2855
Lucrarea format pdf. se gaseste aici
