In-situ synchrotron x-ray diffraction texture analysis of tensile deformation of nanocrystalline superelastic NiTi wire at various temperatures

Bian, Xiaobing; Heller, Luděk; Tyc, Ondřej; Kadeřávek, Lukáš; Šittner, Petr

doi:10.1016/j.msea.2022.143725

Cited by 22 publications

(2 citation statements)

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“…Nevertheless, deformation mechanism of the 14 ms NiTi wire at elevated temperatures cannot be deduced from experiments reported in this work. The reader is referred to article [24], in which deformation mechanism of superelastic NiTi wire deforming at elevated temperature is thoroughly discussed based on the results of the analysis of texture evolution in austenite and martensite phases during the tensile tests at elevated temperatures.…”

Section: Fracture Of Niti Wires Via Neckingmentioning

confidence: 99%

“…When NiTi is loaded beyond the yield stress for plastic deformation, the martensite is assumed to deform by dislocation slip and deformation twinning [15][16][17][18], unrecovered strains are observed on subsequent unloading and heating and lattice defects are generated [16,[19][20][21]. Recently, we have reported that plastic deformation of the B19' oriented martensite proceeds via a peculiar deformation mechanism [22][23][24][25][26][27] involving combination of deformation twinning and dislocation slip-based kinking called ''kwinking.'' Kwinking deformation can be induced not just by mechanical loading [27] but also by cooling or heating NiTi wires under large applied stress [25].…”

Section: Introductionmentioning

confidence: 99%

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Localized Plastic Deformation of Superelastic NiTi Wires in Tension

Kadeřávek

Šittner

Molnárová

et al. 2023

Shap. Mem. Superelasticity

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Tensile deformation of superelastic NiTi shape memory alloy wires at temperatures above austenite finish temperature proceeds via stress-induced martensitic transformation followed by plastic deformation of oriented martensite. While superelastic deformation tends to proceed in localized manner, plastic deformation of martensite is considered to be homogeneous. In this work, we have investigated strain localization patterns in tensile tests on superelastic NiTi wires deformed until fracture in wide temperature range from 10 to 400 °C using in situ digital image correlation analysis of local strains and analyzed lattice defects created during the deformation in TEM. We have found that plastic deformation of oriented martensite can be either homogeneous or localized, depending on the yield stress and strain hardening rate (on the Considere criterion for stability of tensile deformation). Plastic deformation of martensite proceeds via peculiar deformation mode involving combination of deformation twinning and dislocation-based kinking. Strain localization takes the form of either necking leading to wire fracture at 13–15% strain or via propagation of macroscopic deformation band fronts at constant stress. Regardless the deformation is homogeneous or localized, plastic strains at fracture reach ~ 50%. Strain localized within the propagating band front as large as ~ 40% was observed in tensile tests test on NiTi wires having specific microstructures (grain size ~ 230 nm) in a narrow temperature range (~ 10–60 °C).

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Section: Fracture Of Niti Wires Via Neckingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Localized Plastic Deformation of Superelastic NiTi Wires in Tension

Kadeřávek

Šittner

Molnárová

et al. 2023

Shap. Mem. Superelasticity

Self Cite

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Tensile Deformation of B19′ Martensite in Nanocrystalline NiTi Wires

Šittner

Molnárová

Bian

et al. 2023

Shap. Mem. Superelasticity

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Deformation mechanisms activated during tensile deformation of nanocrystalline NiTi wire in martensite state were investigated by combination of two experimental methods: (i) analysis of the evolution of martensite-variant microstructures in grains of deformed wire by TEM and (ii) analysis of the evolution of martensite texture by in situ synchrotron X-ray diffraction. The obtained results are linked to the activity of various twinning processes in martensite. It is concluded that martensite reorientation proceeds via motion of interdomain interfaces, gives rise to reoriented martensite with microstructure consisting of single (001) compound-twinned domain in each grain and results in sharp two-fiber texture of the martensite. The reorientation process leaves behind only very small unrecovered strains and very few dislocation defects in the austenitic microstructure of the deformed wire after unloading and heating. Plastic deformation of B19′ martensite proceeds via peculiar deformation mechanism which combines (100) deformation twinning with [100]/(011) dislocation slip based kinking. It gives rise to very special martensite variant microstructures consisting of deformation twin bands and kink bands containing martensite lattice aligned with [010] direction and characteristic two-fiber martensite texture. Reverse martensitic transformation of plastically deformed martensite upon unloading and heating leaves behind large unrecovered strains and high density of lattice defects in austenite. But there are also significant recoverable strains up to 10%. While the martensite matrix in grains of plastically deformed wire transforms into parent austenite matrix, (20-1) deformation twins transform into {114} austenite twins.

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