Microstructural evolution and strain-hardening in TWIP Ti alloys

Zhao, Guohua; Xu, Xin; Dye, David; Rivera-Dı́az-del-Castillo, P.E.J.

doi:10.1016/j.actamat.2019.11.009

Cited by 139 publications

(33 citation statements)

References 39 publications

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“…So far, the total twinned fraction has been used as the main consistent variable to characterize the twinning behavior for different TWIP alloys. However, recent researches by Zhao et al (2019Zhao et al ( , 2020 confirmed that the key microstructural parameter determining the TWIPbased hardenability is the dynamically reduced intertwin spacing, which is as a function of both the twin-density and twin-fraction. This raises new fundamental questions closely related to twin evolution mode upon loading, that is, nucleation versus growth of twins as dominant mechanism to reach a given fraction of twins.…”

Section: Introductionmentioning

confidence: 99%

The Influence of Twinning on the Strain–Hardenability in TRIP/TWIP Titanium Alloys: Role of Solute–Solution Strengthening

et al. 2020

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Transformation Induced Plasticity and Twinning Induced Plasticity (TWIP) titanium alloys are well-known to display a good combination of strain-hardenability and ductility. However, a large range of strain-hardening rates, which cannot be predicted by the actual design method based on electronic parameters, is obtained. In order to explain this wide range of properties, two different alloys displaying a large difference of strain-hardening rates, but similar chemical stability, have been studied and compared: Ti-12Mo and Ti-8.5Cr-1.5Sn (in wt%). Evolution of both twin size and density during in situ tensile tests has been followed by SEM/electron backscatter diffraction mapping, and two distinct behaviors can be highlighted: the growth of existing twins (Ti-12Mo) and the nucleation of new twins (Ti-8.5Cr-1.5Sn) upon loading. The last one may lead to an improvement of the dynamic Hall-Petch effect by multiplication of twin/matrix interfaces, with subsequent improvement of the macroscopic strain-hardening. It is thought that this competition may be related to the crystal lattice distortion induced by the alloying elements and the subsequent reduction of the migration velocity of the twin/matrix interfaces. Impact Statement: This work reports on distinct behaviors of mechanical twins in TRIP/TWIP titanium alloys, highlighting for the first time a competition between growth of existing twins and nucleation of additional twins upon loading. This effect is assumed to be due to the solute-strengthening effect in the studied alloys and modify, as a consequence, the strain-hardenability of the TRIP/TWIP alloys.

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Section: Introductionmentioning

confidence: 99%

The Influence of Twinning on the Strain–Hardenability in TRIP/TWIP Titanium Alloys: Role of Solute–Solution Strengthening

et al. 2020

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“…It should be noted, however, that in the interval of strain from 15% to 40%, there was no observed noticeable increase in the density of kink bands; that is quite similar to the deformation twinning exhausting in BCC beta titanium alloys or HCP alpha titanium with an increase in plastic strain. [19,20] At ε th ¼ 60%, strain localization due to shear bands formation was observed; meanwhile, the microstructure of the adjacent regions was found to be almost intact ( Figure 1e). An increase in strain resulted in the involvement of the whole microstructure into shear deformation so that after rolling to ε th ¼ 80% the EBSD map (not shown) comprised a very small fraction of dots with a high-enough confidence index (i.e., CI ≥ 0.1).…”

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confidence: 99%

Microstructure and Mechanical Properties Evolution in HfNbTaTiZr Refractory High‐Entropy Alloy During Cold Rolling

et al. 2020

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The effect of cold rolling on the structure and mechanical properties of the HfNbTaTiZr refractory high‐entropy alloy with a single body‐centered cubic (BCC) phase structure is studied. The microhardness evolution during cold rolling to the thickness strain εth = 80% shows three distinct stages: an increase till εth ≈ 15%, a plato in the interval ≈15–40%, and again some increase at εth ≥ 40%. This behavior is found to be associated with an increase in dislocation density at the first stage, the formation of kink bands at the second stage, and the development of shear bands with fine lamellar internal substructure at the third stage. After cold rolling to 80%, the alloy demonstrates the yield strength of 1220 MPa, peak strength 1320 MPa, and elongation to fracture 3.4%. A short steady‐state flow stage is observed on the engineering stress–strain curve that can also be associated with kinking.

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“…The formation of the ω phase always leads to a significant improved strength with a decreased elongation of the titanium alloy [ 30 , 31 ]. The formation of deformation twinning not only induces the strengthening but also has a twinning-induced plasticity (TWIP) effect [ 32 , 33 ]. Therefore, the increase in strength is due to the co-work of deformation twinning and the ω phase.…”

Section: Resultsmentioning

confidence: 99%

Strength-Ductility Synergy in a Metastable β Titanium Alloy by Stress Induced Interfacial Twin Boundary ω Phase at Cryogenic Temperatures

Liao

Zhang

et al. 2020

Materials

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A β titanium alloy is an excellent candidate for cryogenic applications. In this study, the deformation behavior of Ti-36Nb-2Ta-3Zr-0.35O with cold swaging was investigated at cryogenic temperatures to verify its practical application value. The microstructure after tensile tests was observed by transmission electron microscope in order to reveal the cryogenic deformation mechanism. The results show that the mechanical properties of this alloy have a strong temperature dependence: an increase in strength with a non-monotonic trend (first increase and then decrease) in elongation is found when the temperature decreases from 297 K to 77 K. At 200 K, a strength-ductility synergy is obtained and is mainly due to the occurrence of {211} <11> mechanical twinning accompanied with the ω plate located at the twin boundaries, which is the first time it is detected in titanium alloy at a cryogenic temperature. However, at 77 K, martensitic transformation (β phase to α phase) is induced by the tensile deformation, leading to the increase of strength with a massive sacrifice of elongation. These findings provide insights for understanding the deformation mechanisms and optimizing the mechanical properties of titanium alloys at a cryogenic temperature.

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Microstructural evolution and strain-hardening in TWIP Ti alloys

Cited by 139 publications

References 39 publications

The Influence of Twinning on the Strain–Hardenability in TRIP/TWIP Titanium Alloys: Role of Solute–Solution Strengthening

The Influence of Twinning on the Strain–Hardenability in TRIP/TWIP Titanium Alloys: Role of Solute–Solution Strengthening

Microstructure and Mechanical Properties Evolution in HfNbTaTiZr Refractory High‐Entropy Alloy During Cold Rolling

Strength-Ductility Synergy in a Metastable β Titanium Alloy by Stress Induced Interfacial Twin Boundary ω Phase at Cryogenic Temperatures

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