Creep Behaviour of NearEquiatomic Nickel-Titanium Wires

Aysegul Akdogan Eker; Deniz Sonmez; Bedri Onur Kucukyildirim

doi:10.3139/120.110411

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Creep Behaviour of NearEquiatomic Nickel-Titanium Wires

Aysegul Akdogan Eker , Deniz Sonmez and Bedri Onur Kucukyildirim

Published/Copyright: May 26, 2013

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From the journal Materials Testing Volume 55 Issue 2

Abstract

The creep behaviour of near-equiatomic (50.8 at.-% Ni) NiTi wire with a diameter of 0.49 mm is studied between 82 MPa and 127 MPa tensile stress as well as in a temperature range of 575 °C to 650 °C. For 600 °C and between 82–107 MPa a stress exponent of n = 4.5 as well as for 82 MPa between 600–625 °C an activation energy of Q = 300 kJ mol^-1 have been found, these results have been compared with previous creep studies. In contrast to previous studies, this investigation has been performed with high stresses for thin NiTi wires. Moreover, fracture surfaces and ductility of wires have been investigated. The main reasons for the various results are discussed.

Kurzfassung

Das Kriechverhalten von nahezu äquiatomigen (50.8 at.-% Ni) NiTi-Drähten mit einem Durchmesser von 0,49 mm wurde zwischen Zugspannungen von 82 MPa und 127 MPa und im Temperaturbereich von 575 °C bis 650 °C untersucht. Für 600 °C und zwischen 82–107 MPa wurden ein Spannungsexponent von n = 4,5 und für 82 MPa zwischen 600–625 °C eine Aktivierungsenergie von Q = 300 kJ mol^-1 bestimmt sowie mit früheren Kriechuntersuchungen verglichen. Im Gegensatz zu früheren Studien wurden diese Untersuchungen unter hohen Belastungen der NiTi-Drähte durchgeführt. Darüber hinaus wurden die Bruchoberflächen und die Duktilität der Drähte untersucht. Die Hauptursachen für die verschiedenen Ergebnisse werden diskutiert.

Prof. Aysegul Akdogan Eker, PhD, was born in 1957, studied chemical engineering in I.D.M.M. Academy, Istanbul, Turkey, which was the older name of Yildiz Technical University. She finished her MSc at Istanbul Technical University in 1981 and PhD at Yildiz Technical University in mechanical engineering in 1987, where Akdogan Eker is working as professor. Shape memory alloys, composites, nanomaterials and corrosion topics are in her area of interest. Prof. Akdogan Eker is the Head of Mechanical Engineering Department in Yildiz Technical University, Istanbul, Turkey since 2010.

Deniz Sonmez, MSc, was born in 1980, studied mechanical engineering in Trakya University, Turkey. He finished his MSc at Yildiz Technical University in 2010. He is working in an industrial organization located in Istanbul, Turkey.

Bedri Onur Kucukyildirim, PhD, was born in 1983, studied mechanical engineering in Yildiz Technical University. He finished his MSc in 2007 and PhD in 2012 in the same department where Kucukyildirim is researcher since 2005. Composites, carbon nanotubes and corrosion are his reseach areas.

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Published Online: 2013-05-26

Published in Print: 2013-02-01

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https://doi.org/10.3139/120.110411