Twinning stress prediction in bcc metals and alloys

Ojha, A.; Şehitoğlu, Hüseyin

doi:10.1080/09500839.2014.955547

Cited by 53 publications

(19 citation statements)

References 63 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The potential was already used for the simulation of tensile and compressive deformation of α‐Fe . Previous simulations also showed that twinning is the dominant deformation mode for α‐Fe nanowires under tension, which is consistent with our simulations where twinning always nucleates from the tensile region of the sample under bending. The potential correctly predicted the sixfold core structure of screw dislocation as confirmed by DFT calculations .…”

Section: Methodssupporting

confidence: 90%

“…The generalized stacking fault energy, interstitial and vacancy formation energy, thermal expansion, and dislocation properties predicted by the potential are in good agreement with density functional theory (DFT) calculations . The potential was already used for the simulation of tensile and compressive deformation of α‐Fe . Previous simulations also showed that twinning is the dominant deformation mode for α‐Fe nanowires under tension, which is consistent with our simulations where twinning always nucleates from the tensile region of the sample under bending.…”

Section: Methodssupporting

confidence: 88%

“…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%

See 2 more Smart Citations

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Yang

Ding

et al. 2015

Adv Funct Materials

View full text Add to dashboard Cite

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...

show abstract

Section: Methodssupporting

confidence: 90%

Section: Methodssupporting

confidence: 88%

See 1 more Smart Citation

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Yang

Ding

et al. 2015

Adv Funct Materials

View full text Add to dashboard Cite

show abstract

“…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

View full text Add to dashboard Cite

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.

show abstract

“…This process requires overcoming the twinning energy barrier represented by the generalized planar fault energy (GPFE). The GPFE is the energy per unit area required to nucleate a twin [13][14][15] and will be discussed later. Upon subsequent heating above the austenite finish (A f ) temperature, the detwinned martensite reverts back to austenite, giving rise to shape memory effect.…”

Section: Introductionmentioning

confidence: 99%

Critical Stresses for Twinning, Slip, and Transformation in Ti-Based Shape Memory Alloys

Ojha

Şehitoğlu

2016

Shap. Mem. Superelasticity

View full text Add to dashboard Cite

We investigate the effect of Nb and Ta contents on the (i) critical resolved shear stress (CRSS) for the ba 00 transformation, (ii) the CRSS for austenite slip, and (iii) the CRSS for twin nucleation in martensite (a 00 phase) that govern shape memory and superelasticity in Ti-based alloys. The critical stresses for slip and twinning are achieved with a modified Peierls Nabarro formalism utilizing generalized stacking fault energy and the generalized planar fault energy (GPFE), respectively, obtained from first-principles density functional theory (DFT) calculations. During the calculation of the twinning stress, we show the importance of the shuffling process in stabilizing and lowering the GPFE curve. Similarly, the transformation stress is obtained with heterogeneous martensite nucleation mechanism incorporating the energy barriers associated with the transformation process. Here, we point to the role of dislocations in the shuffling process during the early stage of transformation. We show that the increase of Ta content raises the CRSS more effectively for the case of slip compared to twinning or transformation. The slip stress and twin stress magnitudes increase with an increase in the unstable fault energy c us ð Þ and unstable twinning fault energy c ut ð Þ; respectively. In summary, as the Ta composition increases, the difference between martensite/austenite slip resistance and the transformation/ twinning stress widens showing the efficacy of Ta alloying additions.

show abstract

Twinning stress prediction in bcc metals and alloys

Cited by 53 publications

References 63 publications

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

Interface Driven Pseudo‐Elasticity in a‐Fe Nanowires

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

Critical Stresses for Twinning, Slip, and Transformation in Ti-Based Shape Memory Alloys

Contact Info

Product

Resources

About