Twin nucleation in Fe-based bcc alloys—modeling and experiments

Ojha, A.; Şehitoğlu, Hüseyin; Patriarca, L.; Maier, Hans Jürgen

doi:10.1088/0965-0393/22/7/075010

Cited by 45 publications

(19 citation statements)

References 54 publications

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“…However, when the size reduces from the micro to the nanoscale, the material strength increases dramatically, and dislocations become rare . Previous simulations and experiments on nanoscale α‐Fe under tension already showed that twinning dominates …”

Section: Resultsmentioning

confidence: 99%

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Yang

Ding

et al. 2015

Adv Funct Materials

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wileyonlinelibrary.comwill specify exactly the conditions under which the formation of nanostructures is reversible after bending the nanowire.Reversibility is typically related to the shape memory effect and pseudo-elasticity in shape memory alloys (SMAs). [5][6][7] The shape recovery is achieved by thermoelastic martensitic phase transformations and domain switching. The driving force for the shape recovery arises from the free energy difference between the martensite and parent phase. This effect is strongly size-dependent and it is not obvious how SMAs operate in thin wires. [ 8,9 ] The fundamental question is whether a different shape memory effect exists at the nanoscale and if so by which mechanism. This is important because many traditional SMAs fail under nanoscale bending and it becomes important to search for alternative functional materials to replace the traditional SMAs for such nanoscale applications. We show by molecular dynamics simulations that α-Fe, which is not a shape memory alloy, also shows shape recovery (or pseudo-elasticity) after bending. Large bending in α-Fe occurs via the formation of interfaces between domains of different orientation and twinning. The deformed nanowire completely recovers under unloading. The mechanism is shown to be very different from the classic pseudo-elasticity, and is related to high-energy interfaces in the nanowire and not the martensite-austenite phase transformation. This result has implications more widely for shape-dependent SMAs that are used in microelectromechanical systems (MEMS) technology. This is also an example of the emerging fi eld of domain boundary engineering where functionality (namely the shape recovery) is linked to domain boundaries and interfaces, but not to bulk properties (such as the martensite-austenite phase transformation). [10][11][12] Previous molecular dynamics (MD) simulations have identifi ed a class of metallic nanowires with both face-centered cubic (fcc) and body-centered cubic (bcc) structures that show pseudo-elasticity and shape memory effects. [13][14][15][16][17][18][19] This pseudoelastic behavior was achieved under uniaxial tension while little is known whether such unique behavior can still exist when a wire is bent. Under tension, the shape recovery relates to the reversibility of conventional twinning. The driving force for the recoverable deformation stems from the minimization of the surface energy. [ 14,15,17,18 ] The total recoverable strain is very large and can exceed 40%. A large inelastic deformation mediated by conventional twinning has been confi rmed experimentally in fcc palladium and bcc tungsten. [ 20,21 ] Here we also show that the shape recovery effect under bending in α -Fe relates to the formation of nonconventional interfaces between domains of different orientations. Unlike conventional <111>/{112}-type Interface Driven Pseudo-Elasticity in α-Fe Nanowires Yang Yang , Suzhi Li , * Xiangdong Ding , * Jun Sun , and Ekhard K. H. Salje * Molecular dynamics simulations of bent [100] α-Fe nanowires...

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Section: Resultsmentioning

confidence: 99%

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Yang

Ding

et al. 2015

Adv Funct Materials

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“…8. Plasticity via formation of twins has previously been reported for both single crystal [40][41][42][43] and polycrystalline iron [44]. It has been shown, for sc-iron, that twinning occurs as a results of disassociation of [111] core of an (a/2) h111i dislocation into three (a/6) h111i fractional dislocations.…”

Section: Plastic Deformation During the Scratching Stagementioning

confidence: 93%

Atomistic Insights on the Wear/Friction Behavior of Nanocrystalline Ferrite During Nanoscratching as Revealed by Molecular Dynamics

et al. 2017

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Using embedded atom method potential, extensive large-scale molecular dynamics (MD) simulations of nanoindentation/nanoscratching of nanocrystalline (nc) iron have been carried out to explore grain size dependence of wear response. MD results show no clear dependence of the frictional and normal forces on the grain size, and the single-crystal (sc) iron has higher frictional and normal force compared to nc-samples. For all samples, the dislocation-mediated mechanism is the primary cause of plastic deformation in both nanoindentation/nanoscratch. However, secondary cooperative mechanisms are varied significantly according to grain size. Pileup formation was observed in the front of and sideways of the tool, and they exhibit strong dependence on grain orientation rather than grain size. Tip size has significant impact on nanoscratch characteristics; both frictional and normal forces monotonically increase as tip radii increase, while the friction coefficient value drops by about 38%. Additionally, the increase in scratch depth leads to an increase in frictional and normal forces as well as friction coefficient. To elucidate the relevance of indentation/scratch results with mechanical properties, uniaxial tensile test was performed for nc-samples, and the result indicates the existence of both the regular and inverse Hall-Petch relations at critical grain size of 110.9 Å . The present results suggest that indentation/scratch hardness has no apparent correlation with the mechanical properties of the substrate, whereas the plastic deformation has.

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“…Based on this slip system, the Burgers vector (b) for B19 Ti-6.25Zr-25Nb lattice is equal to 3.24 Å , for example. The GSFE is obtained by shearing one half (001) plane of the crystal with respect to another half by continuous rigid displacements of u x = nb along [100] direction, where b is the magnitude of the Burgers vector and n is a parameter ranging from 0 to 1 [18][19][20]. Similarly, Fig.…”

Section: Slip and Gsfe Curves In B19 Ti-based Alloysmentioning

confidence: 99%

Slip Resistance of Ti-Based High-Temperature Shape Memory Alloys

Ojha

Şehitoğlu

2016

Shap. Mem. Superelasticity

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Titanium with Nb, Zr, and Ta alloying substitutions possesses high plastic slip resistance and high transformation strains upon bcc (b) to orthorhombic ða 00 Þ transformation. In the current study, we determine the critical resolved shear stress (CRSS) for slip in Ti alloyed for a wide composition range of Nb, Ta, and Zr. The CRSS is obtained with a proposed Peierls-Nabarro formalism incorporating the generalized stacking fault energy barrier profile for slip obtained from the first-principles Density Functional Theory (DFT) calculations. The CRSS for slip of the orthorhombic martensite increases from 80 to 280 MPa linearly with increasing unstable fault energy. The addition of tantalum is most effective in raising the energy barriers. We also demonstrate the composition dependence of the lattice parameters of both b and a 00 crystal structures as a function of Nb, Ta, and Zr additions showing agreement with experiments. Using the lattice constants, the transformation strain is determined as high as 11 % in the [011] pole and its magnitude increases mainly with Zr addition.

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Twin nucleation in Fe-based bcc alloys—modeling and experiments

Cited by 45 publications

References 54 publications

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Atomistic Insights on the Wear/Friction Behavior of Nanocrystalline Ferrite During Nanoscratching as Revealed by Molecular Dynamics

Slip Resistance of Ti-Based High-Temperature Shape Memory Alloys

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