In situ TEM study of dislocation slip in a metastable β titanium alloy

Castany, Philippe; Besse, Magali; Gloriant, T.

doi:10.1016/j.scriptamat.2011.11.036

Cited by 76 publications

(39 citation statements)

References 16 publications

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“…9). This domain thus corresponds to the plastic domain wherein dislocation slip and twinning are mainly operating in this alloy [7] and more generally in this alloy family [5,[36][37][38]. As the SIM transformation is not fully reversible from 2% of applied strain (Fig.…”

Section: Correlation Between Sxrd Results and Tensile Curvesmentioning

confidence: 89%

In situ synchrotron X-ray diffraction study of the martensitic transformation in superelastic Ti-24Nb-0.5N and Ti-24Nb-0.5O alloys

et al. 2015

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Mechanisms of superelasticity were investigated by in situ cyclic tensile tests performed under synchrotron X-ray radiation on Ti-24Nb-0.5N and Ti-24Nb-0.5O compositions of metastable b titanium alloys. Analyses of diffraction patterns acquired under load and after unloading for each cycle were used to determine the characteristics of the potential mechanisms of deformation in both alloys. The Ti-24Nb-0.5N alloy exhibits the conventional behavior of superelastic b titanium alloys. Synchrotron X-ray diffraction (SXRD) experiments proved that superelasticity is exclusively due to the occurrence of a stress-induced martensitic (SIM) transformation from the b phase to the a 00 phase. The evolution of volume fraction of a 00 martensite corresponds exactly to the variation of the recovery strain of the cyclic tensile curve. Conversely, the Ti-24Nb-0.5O alloy displays a nonconventional behavior. SXRD experiments showed a huge ability of the b phase to deform elastically until 2.1%. Surprisingly, a reversible SIM transformation also occurs in this alloy but starts after 1% of applied strain that corresponds to the yield point of the stress-strain curve. Although the SIM transformation occurs, the b phase simultaneously continues to deform elastically. The superelasticity of this alloy is unexpectedly due to a combination of a high elastic deformability of the b phase and a reversible SIM transformation. In both alloys, the lattice parameters of the a 00 martensite evolve similarly in accordance with the initial texture of the b phase and the crystallography of the transformation.

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Section: Correlation Between Sxrd Results and Tensile Curvesmentioning

confidence: 89%

In situ synchrotron X-ray diffraction study of the martensitic transformation in superelastic Ti-24Nb-0.5N and Ti-24Nb-0.5O alloys

et al. 2015

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“…The dislocation slip has been investigated in b-titanium alloy using TEM analysis [16]. The dislocations with Burgers vector b = a/2h111i are observed to glide on the {110}, {112}, and {123} planes similar to bcc metals, and the deformation is largely governed by the motion of screw segments.…”

Section: Discussion Of the Resultsmentioning

confidence: 99%

“…In order to achieve high transformation strains, it is desirable to minimize plastic strain accumulating through austenite slip. The slip in bTi-based alloys occur on {110}h111i system similar to bcc metals [16,37], and we are interested in obtaining the energy barriers (GSFE) required to nucleate a h111i dislocation on {110} plane. The GSFE can be obtained by rigidly shearing one half of the crystal relative to the other half on the {110} plane along h111i direction by displacement of u = nb, where b is the magnitude of the Burgers vector of the slip dislocation and n is the parameter ranging from 0 to 1 [29].…”

Section: Generalized Stacking Fault Energy and Austenite Slipmentioning

confidence: 99%

“…Both class of studies uncovered the physical mechanisms governing the deformation utilizing microscopic tools such as transmission electron microscopy (TEM) and with experiments at macroscale. The works on slip and twinning using TEM investigations [16] have revealed the similarities between b Tibased alloys and pure bcc metals. The TEM analysis on Ti-4.4Ta-1.9Nb alloy [17] investigated the role of the microstructural variations, slip, and twinning, and the role of austenite/martensite interface on the strength and ductility.…”

Section: Introductionmentioning

confidence: 99%

“…The TEM analysis on Ti-4.4Ta-1.9Nb alloy [17] investigated the role of the microstructural variations, slip, and twinning, and the role of austenite/martensite interface on the strength and ductility. Experiments [16] have successfully revealed the slip systems in b Ti-based alloys allowing an in-depth understanding on the mobility of slip dislocations, cross-slip mechanism, and dislocation-interstitial interactions. Specially, the role of interstitials such as Si and O on the strength of Ti-based alloys has been discussed in detail.…”

Section: Introductionmentioning

confidence: 99%

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

Ojha

Şehitoğlu

2016

Shap. Mem. Superelasticity

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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.

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