On elastic moduli and elastic anisotropy in polycrystalline martensitic NiTi

Qiu, Shipeng; Clausen, B.; Padula, Santo; Noebe, Ronald D.; Vaidyanathan, R.

doi:10.1016/j.actamat.2011.04.018

Cited by 101 publications

(79 citation statements)

References 19 publications

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“…[12,13]). This assumption is erroneous since both experiments [55,56] and first principle calculations [34,51] show that martensite is stiffer than austenite (Table 1). A more compliant martensite increases E T by increasing the elastic strain and texturing in the martensite; the former is deduced from the unloading path from A to A 0 in Fig.…”

Section: Assumptions Concerning Martensite Elastic Moduli and Thermalmentioning

confidence: 97%

Thermal cycling and isothermal deformation response of polycrystalline NiTi: Simulations vs. experiment

et al. 2011

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A recent microstructure-based FEM model that couples crystal-based plasticity, the B2 M B19 0 phase transformation and anisotropic elasticity at the grain scale is calibrated to recent data for polycrystalline NiTi (49.9 at.% Ni). Inputs include anisotropic elastic properties, texture and differential scanning calorimetry data, as well as a subset of recent isothermal deformation and load-biased thermal cycling data. The model is assessed against additional experimental data. Several experimental trends are captured -in particular, the transformation strain during thermal cycling monotonically increases and reaches a peak with increasing bias stress. This is achieved, in part, by modifying the martensite hardening matrix proposed by Patoor et al. [Patoor E, Eberhardt A, Berveiller M. J Phys IV 1996;6:277]. Some experimental trends are underestimated -in particular, the ratcheting of macrostrain during thermal cycling. This may reflect a model limitation that transformation-plasticity coupling is captured on a coarse (grain) scale but not on a fine (martensitic plate) scale.

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Section: Assumptions Concerning Martensite Elastic Moduli and Thermalmentioning

confidence: 97%

Thermal cycling and isothermal deformation response of polycrystalline NiTi: Simulations vs. experiment

et al. 2011

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“…The initial nucleation and growth of these variants in regions I and II along the loading direction were captured in detail in Ref. 28. As observed in Fig.…”

Section: -3mentioning

confidence: 99%

“…The microstructural response of NiTi during the initial loading up to 6% strain has been thoroughly investigated in Ref. 28 and hence omitted in this study. After straining each sample to a predetermined value, it was then unloaded to 0 MPa and thermally cycled 10-times through the phase transformation between room temperature and 200 C using a heating rate of 20 C/min (while holding the stress constant at 0 MPa).…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…Various physical and thermomechanical properties of this alloy are available in the literature. 7,28,[35][36][37][38] Prior to testing, two no-load thermal cycles between room temperature and 200 C at a rate of 20 C/min were performed on the as-machined samples to relieve any residual stresses resulting from the machining operation. Stress-free transformation temperatures: martensite start (M s ), martensite finish (M f ), austenite start (A s ), and austenite finish (A f ) were measured from the second mechanical no-load thermal cycle using the intercept method and were found to be 71, 55, 92, and 105 6 2 C, respectively.…”

Section: Experimental Techniquesmentioning

confidence: 99%

“…28 These latter processes are responsible for the non-linearity observed in the initial loading response of NiTi and the often deflated values of modulus reported from mechanical test data. With increasing strain (region II), a broad stress plateau is obtained where the deformation is mainly dominated by variant reorientation and detwinning of the initial [011] type II and (1 11) type I twinning modes.…”

Section: Introductionmentioning

confidence: 99%

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Role of B19′ martensite deformation in stabilizing two-way shape memory behavior in NiTi

Benafan

Padula

Noebe

et al. 2012

Journal of Applied Physics

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Deformation of a B19′ martensitic, polycrystalline Ni49.9Ti50.1 (at. %) shape memory alloy and its influence on the magnitude and stability of the ensuing two-way shape memory effect (TWSME) was investigated by combined ex situ mechanical experimentation and in situ neutron diffraction measurements at stress and temperature. The microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were captured and compared to the bulk macroscopic response of the alloy. With increasing uniaxial strain, it was observed that B19′ martensite deformed by reorientation and detwinning with preferred selection of the (1¯50)M and (010)M variants, (201¯)B19′ deformation twinning, and dislocation activity. These mechanisms were indicated by changes in bulk texture from the neutron diffraction measurements. Partial reversibility of the reoriented variants and deformation twins was also captured upon load removal and thermal cycling, which after isothermal deformation to strains between 6% and 22% resulted in a strong TWSME. Consequently, TWSME functional parameters including TWSME strain, strain reduction, and transformation temperatures were characterized and it was found that prior martensite deformation to 14% strain provided the optimum condition for the TWSME, resulting in a stable two-way shape memory strain of 2.2%. Thus, isothermal deformation of martensite was found to be a quick and efficient method for creating a strong and stable TWSME in Ni49.9Ti50.1.

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Mapping of Texture and Phase Fractions in Heterogeneous Stress States during Multiaxial Loading of Biomedical Superelastic NiTi

et al. 2020

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Thermoelastic deformation mechanisms in polycrystalline biomedical‐grade superelastic NiTi are spatially mapped using in situ neutron diffraction during multiaxial loading and heating. The trigonal R‐phase is formed from the cubic phase during cooling to room temperature and subsequently deforms in compression, tension, and torsion. The resulting R‐phase variant microstructure from the variant reorientation and detwinning processes are equivalent for the corresponding strain in tension and compression, and the variant microstructure is reversible by isothermal loading. The R‐phase variant microstructure is consistent between uniaxial and torsional loading when the principal stress directions of the stress state are considered (for the crystallographic directions observed here). The variant microstructure evolution is tracked and the similarity in general behavior between uniaxial and torsional loading, in spite of the implicit heterogeneous stress state associated with torsional loading, pointed to the ability of the reversible thermoelastic transformation in NiTi to accommodate stress and strain mismatch with deformation. This ability of the R‐phase, despite its limited variants, to accommodate stress and strain and satisfy strain incompatibility in addition to the existing internal stresses has significance for reducing irrecoverable deformation mechanisms during loading and cycling through the phase transformation.

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On elastic moduli and elastic anisotropy in polycrystalline martensitic NiTi

Cited by 101 publications

References 19 publications

Thermal cycling and isothermal deformation response of polycrystalline NiTi: Simulations vs. experiment

Thermal cycling and isothermal deformation response of polycrystalline NiTi: Simulations vs. experiment

Role of B19′ martensite deformation in stabilizing two-way shape memory behavior in NiTi

Mapping of Texture and Phase Fractions in Heterogeneous Stress States during Multiaxial Loading of Biomedical Superelastic NiTi

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