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Analysis of Multi-Step Transformations in Single Crystal NiTi

Wagoner Johnson, A. und Hamilton, R. und Sehitoglu, H. und Biallas, G. und Maier, H.J. und Chumlyakov, Y.I. und Woo, H.S. (2005) Analysis of Multi-Step Transformations in Single Crystal NiTi. Metallurgical and Materials Transactions A, 36A (4), Seiten 919-928.

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Kurzfassung

The effects of composition and heat treatment on the thermally induced phase-transformation behavior of single-crystal NiTi with compositions of 50.1, 50.4, 50.8, and 51.5 at. pct Ni are presented in this article. Differential scanning calorimetry (DSC) experiments reveal that a heat-treated 50.1 at. pct Ni alloy exhibits an unprecedented multiple-step transformation (MST) on both heating and cooling, with up to four peaks. This behavior is absent in the higher-Ni-content alloys. In polycrystalline NiTi alloys, MSTs have been attributed to microstructure heterogeneities such as grain boundaries and dislocations, which influence precipitation. In-situ scanning electron microscopy (SEM) results show that the MST in the 50.1 at. pct Ni alloy is associated with single-crystal defects such as dendrites and low-angle boundaries. A heterogeneous precipitate distribution is observed in transmission electron microscopy (TEM) images of the same low-Ni alloy, also associated with the defects, creating conditions that have been shown in other studies to promote the MST in polycrystals. These MSTs are not observed for high-Ni single-crystal alloys containing the same defects. In this article, we describe the origin of the extraordinary forward and reverse MSTs in the low-Ni alloy and the absence of the MST in high-Ni alloys. Transformation sequences are proposed based on the contrasting precipitate microstructures.

Dokumentart:Zeitschriftenbeitrag
Titel:Analysis of Multi-Step Transformations in Single Crystal NiTi
Autoren:
AutorenInstitution oder E-Mail-Adresse der Autoren
Wagoner Johnson, A.University of Illinois
Hamilton, R.University of Illinois
Sehitoglu, H.University of Illinois
Biallas, G.NICHT SPEZIFIZIERT
Maier, H.J.Universität Paderborn
Chumlyakov, Y.I.Siberian Physical and Technical Institute
Woo, H.S.Dongguk University
Datum:2005
Erschienen in:Metallurgical and Materials Transactions A
Referierte Publikation:Ja
In ISI Web of Science:Ja
Band:36A
Seitenbereich:Seiten 919-928
Status:veröffentlicht
Stichwörter:shape memory alloys, phase transformation, NiTi, scanning electron microscopy, transmission electron microscopy, differential scanning calorimetry, microstructure
HGF - Forschungsbereich:Verkehr und Weltraum (alt)
HGF - Programm:Luftfahrt
HGF - Programmthema:Starrflügler
DLR - Schwerpunkt:Luftfahrt
DLR - Forschungsgebiet:L AR - Starrflüglerforschung
DLR - Teilgebiet (Projekt, Vorhaben):L - Strukturen & Werkstoffe
Standort: Köln-Porz
Institute & Einrichtungen:Institut für Werkstoff-Forschung > Werkstoffmechanische Prüfung
Hinterlegt von: Dr.-Ing. Gerhard Biallas
Hinterlegt am:27 Jan 2006
Letzte Änderung:27 Apr 2009 04:55

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