Temperature-induced transformations and martensitic reorientation processes in ultra-fine-grained Ni rich pseudoelastic NiTi wires studied by electrical resistance

JOURNAL OF ALLOYS AND COMPOUNDS

卷:735

Article

Pelegrina, J. L.^1,2  Olbricht, J.^3,4  Yawny, A.^1,2  Eggeler, G.³ 

[1] Inst Balseiro, Ctr Atom Bariloche, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina

[2] Consejo Nacl Invest Cient & Tecn, RA-8400 San Carlos De Bariloche, Rio Negro, Argentina

[3] Ruhr Univ Bochum, Inst Mat, D-44780 Bochum, Germany

[4] BAM Fed Inst Mat Res & Testing, D-12200 Berlin, Germany

关键词: Shape memory alloys;    NiTi;    Martensitic transformation;    Electrical resistance;   

DOI  :  10.1016/j.jallcom.2017.12.009

来源: Elsevier

【 摘 要 】

Temperature-induced, stress-induced martensitic phase transitions and martensite reorientation process in Ni rich (50.9 at.%) NiTi pseudoelastic NiTi wires with ultra-fine grained (UFG) microstructure were studied by electrical resistance measurements. Measurements of the electrical resistance as a function of temperature at different constant mechanical loads accompanied by complementary experiments with variable loads at constant temperature were performed. Results show that the transformation mechanisms in UFG microstructures exhibit a higher level of complexity when compared with those characterizing the behavior of other microstructures (e.g., recrystallized or larger grains size). It was found that a threshold stress level below 150 MPa delimits the transition from a homogeneous (low stress) to localized but reversible Luders type transformation (high stress) when the transformations are induced under constant applied stress and that reorientation processes require stresses of 100 MPa in the present UFG wires. Even though the strain evolutions do not always show two distinct yielding events during cooling or heating, electrical resistance measurements proved that a two-step transformation involving R-phase and B19' martensite was always present in the extended range of temperatures and stresses investigated here. (C) 2017 Elsevier B.V. All rights reserved.

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