Microstructure and superelastic properties of free forged Ti–Ni shape-memory alloy

Bahador, Abdollah and Hamzah, Esah and Kondoh, Katsuyoshi and Asma Abubakar, Tuty and Yusof, Farazila and Umeda, Junko and Saud, Safaa N. and Ibrahim, Mustafa K. (2018) Microstructure and superelastic properties of free forged Ti–Ni shape-memory alloy. Transactions of Nonferrous Metals Society of China, 28 (3). pp. 502-514. ISSN 1003-6326, DOI https://doi.org/10.1016/S1003-6326(18)64683-7.

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Official URL: https://doi.org/10.1016/S1003-6326(18)64683-7


Elemental titanium (Ti) and nickel (Ni) powders were consolidated by spark plasma sintering (SPS) to fabricate Ti–51%Ni (mole fraction) shape-memory alloys (SMAs). The objective of this study is to enhance the superelasticity of SPS produced Ti–Ni alloy using free forging as a secondary process. Products from two processes (with and without free forging) were compared in terms of microstructure, transformation temperature and superelasticity. The results showed that, free forging effectively improved the tensile and shape-memory properties. Ductility increased from 6.8% to 9.2% after forging. The maximum strain during superelasticity increased from 5% to 7.5% and the strain recovery rate increased from 72% to 92%. The microstructure of produced Ti–51%Ni SMA consists of the cubic austenite (B2) matrix, monoclinic martensite (B19′), secondary phases (Ti3Ni4, Ti2Ni and TiNi3) and oxides (Ti4Ni2O and Ti3O5). There was a shift towards higher temperatures in the martensitic transformation of free forged specimen (aged at 500 °C) due to the decrease in Ni content of B2 matrix. This is related to the presence of Ti3Ni4 precipitates, which were observed using transmission electron microscope (TEM). In conclusion, free forging could improve superelasticity and mechanical properties of Ti–51%Ni SMA.

Item Type: Article
Funders: Ministry of Higher Education of Malaysia: the Malaysian International Scholarship and research funding under FRGS vote No. R.J13000.7824.4F810
Uncontrolled Keywords: shape-memory alloy; superelasticity; spark-plasma sintering; free forging
Subjects: T Technology > TJ Mechanical engineering and machinery
Divisions: Faculty of Engineering
Depositing User: Ms. Juhaida Abd Rahim
Date Deposited: 17 Sep 2019 06:44
Last Modified: 17 Sep 2019 06:44
URI: http://eprints.um.edu.my/id/eprint/22375

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