In situ observation of individual variant transformations in polycrystalline NiTi

Raghunathan, S.L.; Azeem, Mohammed Abdul; Collins, David M.; Dye, David

doi:10.1016/j.scriptamat.2008.07.014

Cited by 34 publications

(22 citation statements)

References 17 publications

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“…However, the (010) pole figure for the same cycle in Ref. [15] also showed a significant texturing towards the tensile axis, consistent with the current work and recent in situ studies investigating the stress induced formation of the B19 0 from the B2 at room temperature [26,28]. Each of the 24 martensitic variant pairs, which can form from a given B2 parent grain, offer a different transformation strain in a chosen parent direction and so parent orientation to the loading axis will influence the specific variant self accommodation in each grain.…”

Section: Effect Of a Single Thermal Cycle Under Loadsupporting

confidence: 91%

Martensite evolution in a NiTi shape memory alloy when thermal cycling under an applied load

Jones

Dye

2011

Intermetallics

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Section: Effect Of a Single Thermal Cycle Under Loadsupporting

confidence: 91%

Martensite evolution in a NiTi shape memory alloy when thermal cycling under an applied load

Jones

Dye

2011

Intermetallics

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“…[27,28] Full Debye-Scherrer diffraction rings were collected from the monochromated X-ray beam (300 9 300 lm, k = 0.14291 Å ) every 2 seconds by a Pixium 4700 2D area detector. Thermal cycling was achieved by resistance heating using an Instron electrothermal mechanical tester (ETMT), [29,30] controlled by an R-type thermocouple, spot welded to the sample directly above the X-ray beam.…”

Section: Methodsmentioning

confidence: 99%

In-Situ Synchrotron Characterization of Transformation Sequences in TiNi-Based Shape Memory Alloys during Thermal Cycling

Jones

Raghunathan

Dye

2010

Metall Mater Trans A

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In-situ synchrotron radiation has been used to provide direct analysis of the transformation sequences in TiNi-based shape memory alloys during thermal cycling. The high resolution, narrow peak width Debye-Scherrer diffraction spectra enabled positive identification and quantification of the phase transformation sequences, which is not possible through normal laboratory studies. The results facilitate a clearer understanding of the development and influence of intermediate phases such as R or B19 on sequential martensitic transformations. Ti 50.2 Ni 49.8 transformed predominately via a single-step B2 M B19¢ transformation, although evidence of the R phase was found during cooling in every cycle. The martensitic start temperature was depressed by~0.6°C per cycle, while the R-phase start temperature was found to be unaffected. Ti 50 Ni 41 Cu 9 transformed through a two-step B2 M B19 M B19¢ sequence, with the B2 fi B19 transformation reaching completion prior to the formation of any B19¢. The transformation temperatures of Ti 50 Ni 41 Cu 9 were found to be insensitive to thermal cycling, remaining constant over the studied cycle range.

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“…The lattice strain behavior of austenite has also been examined using neutron diffraction in pseudoelastic NiTi during compressive loading [34,36], where no localized deformation was observed. Raghunathan et al [38] examined individual texture components in B2 and B19 0 phases of NiTi rolled sheet during in situ tensile loading using synchrotron X-ray diffraction. Finally, it should be mentioned here that synchrotron Xray diffraction has been used to examine the R phase only during thermal heating and cooling, where Kulkov and Mironov [22] observed lattice parameter changes in NiTi with 50.1 at.% Ni, and Khalil Allafi et al [50] describe the spontaneous strain evolution of R phase with temperature in the framework of the Landau theory.…”

Section: Introductionmentioning

confidence: 99%

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

et al. 2010

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An ultrafine-grained pseudoelastic NiTi shape-memory alloy wire with 50.9 at.% Ni was examined using synchrotron X-ray diffraction during in situ uniaxial tensile loading (up to 1 GPa) and unloading. Both macroscopic stress-strain measurements and volume-averaged lattice strains are reported and discussed. The loading behavior is described in terms of elasto-plastic deformation of austenite, emergence of R phase, stress-induced martensitic transformation, and elasto-plastic deformation, grain reorientation and detwinning of martensite. The unloading behavior is described in terms of stress relaxation and reverse plasticity of martensite, reverse transformation of martensite to austenite due to stress relaxation, and stress relaxation of austenite. Microscopically, lattice strains in various crystallographic directions in the austenitic B2, martensitic R, and martensitic B19 0 phases are examined during loading and unloading. It is shown that the phase transformation occurs in a localized manner along the gage length at the plateau stress. Phase volume fractions and lattice strains in various crystallographic reflections in the austenite and martensite phases are examined over two transition regions between austenite and martensite, which have a width on the order of the wire diameter. Anisotropic effects observed in various crystallographic reflections of the austenitic phase are also discussed. The results contribute to a better understanding of the tensile loading behavior, both macroscopically and microscopically, of NiTi shape-memory alloys.

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In situ observation of individual variant transformations in polycrystalline NiTi

Cited by 34 publications

References 17 publications

Martensite evolution in a NiTi shape memory alloy when thermal cycling under an applied load

Martensite evolution in a NiTi shape memory alloy when thermal cycling under an applied load

In-Situ Synchrotron Characterization of Transformation Sequences in TiNi-Based Shape Memory Alloys during Thermal Cycling

Phase volume fractions and strain measurements in an ultrafine-grained NiTi shape-memory alloy during tensile loading

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