TEM analysis of deformation bands created by tensile deformation of superelastic NiTi wires

0531993 - ÚJF 2021 RIV US eng J - Journal Article
Molnárová, O. - Šittner, Petr - Veselý, J. - Cieslar, M.
TEM analysis of deformation bands created by tensile deformation of superelastic NiTi wires.
Materials Characterization. Roč. 167, SEP (2020), č. článku 110470. ISSN 1044-5803. E-ISSN 1873-4189
R&D Projects: GA MŠMT EF16_013/0001794
Institutional support: RVO:61389005
Keywords : Shape memory alloy * Martensitic phase transformation * NiTi * Transmission electron microscopy * Selected area electron diffraction * Dark field imaging
OECD category: Materials engineering
Impact factor: 4.342, year: 2020
Method of publishing: Limited access
https://doi.org/10.1016/j.matchar.2020.110470

Deformation processes derived from martensitic transformation in shape memory alloys are theoretically fully recoverable in a complete thermomechanical loading cycle across transformation range and do not leave any lattice defects in the microstructure. In reality, this is rarely the case in NiTi, since plastic deformation tends to accompany the martensitic transformation, particularly if it proceeds under large stress. Lattice defects observed in the microstructure of deformed NiTi wires (slip dislocations and deformation bands) attract the attention of researchers, since they are linked to unrecovered strains and play significant role in functional fatigue, shape setting or two-way shape memory effect. In this work, we present an experimental approach allowing for analysis of deformation bands in deformed NiTi consisting in: i) preparation of superelastic NiTi wires with recrystallized, small grained microstructure, ii) subjecting these wires to desired tensile test (e.g. superelastic or shape memory cycle) and iii) characterizing the deformation bands in TEM using selected area electron diffraction combined with dark field imaging following simple rules described in this work. If the deformed microstructure becomes too complex due to the high density and small size of deformation bands, ASTAR orientation mapping can be beneficially applied to reveal the refinement of the microstructure through the introduction of deformation bands.
Permanent Link: http://hdl.handle.net/11104/0310605