In situ monitoring of the deformation mechanisms in titanium with different oxygen contents

Barkia, Bassem; Doquet, Véronique; Couzinié, Jean-Philippe; Guillot, Ivan; Héripré, Eva

doi:10.1016/j.msea.2015.03.044

Cited by 112 publications

(47 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Frequent cross-slip of hc + ai dislocations can occur in early stage, room temperature deformation (10-15). However, the propensity and nature of hc + ai cross-slip differ among different materials and can also depend on the applied stress and temperature in the same material (12,(16)(17)(18)(19)(20)(21)(22) (Fig. 2 and refs.…”

mentioning

confidence: 99%

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Curtin

2016

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

Hexagonal close-packed (hcp) metals such as Mg, Ti, and Zr are lightweight and/or durable metals with critical structural applications in the automotive (Mg), aerospace (Ti), and nuclear (Zr) industries. The hcp structure, however, brings significant complications in the mechanisms of plastic deformation, strengthening, and ductility, and these complications pose significant challenges in advancing the science and engineering of these metals. In hcp metals, generalized plasticity requires the activation of slip on pyramidal planes, but the structure, motion, and cross-slip of the associated 〈c + a〉 dislocations are not well established even though they determine ductility and influence strengthening. Here, atomistic simulations in Mg reveal the unusual mechanism of 〈c + a〉 dislocation cross-slip between pyramidal I and II planes, which occurs by cross-slip of the individual partial dislocations. The energy barrier is controlled by a fundamental step/ jog energy and the near-core energy difference between pyramidal 〈c + a〉 dislocations. The near-core energy difference can be changed by nonglide stresses, leading to tension-compression asymmetry and even a switch in absolute stability from one glide plane to the other, both features observed experimentally in Mg, Ti, and their alloys. The unique cross-slip mechanism is governed by common features of the generalized stacking fault energy surfaces of hcp pyramidal planes and is thus expected to be generic to all hcp metals. An analytical model is developed to predict the cross-slip barrier as a function of the near-core energy difference and applied stresses and quantifies the controlling features of cross-slip and pyramidal I/II stability across the family of hcp metals.P lastic deformation of crystalline materials occurs mainly by slip along low-index atomic planes. Slip regions are bounded by line defects called dislocations (1), which are characterized by the crystallographic slip increment known as the Burgers vector b and the local line direction ξ. The transition from slipped to unslipped regions is resolved at the atomic scale by local atomic rearrangements creating a dislocation "core" structure. Slip occurs by motion of this core, and the surrounding elastic fields, driven by an applied stress. Plasticity is thus controlled by the details of the core region, which differ significantly among face-centered cubic (fcc), bodycentered cubic (bcc), and hexagonal close-packed (hcp) metals (2). The motion of the dislocation core is usually confined to glide within the slip plane defined by the normal vector n = b × ξ. Screw dislocations have b × ξ = 0, however, and so do not have a unique slip plane and can therefore "cross-slip" among glide planes that share a common Burgers vector. Cross-slip is a crucial process in plasticity, acting to spread slip spatially on multiple nonparallel planes and to enable dislocation multiplication and annihilation processes; all of these processes affect ductility and ultimate strength of the material. Whereas the atomistic mecha...

show abstract

mentioning

confidence: 99%

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Curtin

2016

Proc. Natl. Acad. Sci. U.S.A.

View full text Add to dashboard Cite

show abstract

“…In the present work, high resolution techniques based on the AE and local strain-rate fields were applied, on the one hand, to verify the hypothesis of dislocation mechanism of the non-monotonous work hardening of α-Ti polycrystals deformed by tension [9][10][11][12] and, on the other hand, investigate the deformation processes on finer scales relevant to the so-called collective processes in the dislocation dynamics. The analysis of the AE average count rate allowed, first of all, to corroborate the presence of nonmonotonous trends during the elastoplastic transition.…”

Section: Discussionmentioning

confidence: 99%

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry

Lebyodkin

Amouzou

Lebedkina

et al. 2018

Preprint

View full text Add to dashboard Cite

Current progress in the prediction of mechanical behavior of solids requires understanding of spatiotemporal complexity of plastic flow caused by self-organization of crystal defects. It may be particularly important in hexagonal materials because of their strong anisotropy and combination of different mechanisms of plasticity, such as dislocation glide and twinning. These materials often display complex behavior even on the macroscopic scale of deformation curves, e.g., a peculiar three-stage elastoplastic transition, the origin of which is a matter of debates. The present work is devoted to a multiscale study of plastic flow in α-Ti, based on simultaneous recording of deformation curves, 1D local strain field, and acoustic emission (AE). It is found that the average AE activity also reveals three-stage behavior, but in a qualitatively different way depending on the crystallographic orientation of the sample axis. On the finer scale, the statistical analysis of AE events and local strain rates testifies to an avalanche-like character of dislocation processes, reflected in power-law probability distribution functions. The results are discussed from the viewpoint of collective dislocation dynamics and are confronted to predictions of a recent micromechanical model of Ti strain hardening.

show abstract

“…In addition, Khan et al [43] increased the YS of Ti-6Al-4V alloy in 65.8 MPa by varying the oxygen content from 0.2 to 0.5 wt.%. As also mentioned by [44], this fact could be directly related to its higher oxygen content, which acts as an interstitial strengthening element in the crystal lattice by increasing the critical resolved shear stresses (CRSS) necessary for the grain boundary sliding to happen.…”

Section: Materials Characterisationmentioning

confidence: 91%

Influence of oxygen content on the machinability of Ti-6Al-4V alloy

Sacristan

Garay

Hormaetxe

et al. 2016

Int J Adv Manuf Technol

View full text Add to dashboard Cite

Titanium alloys are widely employed in many aerospace components due to their high strength-toweight ratio, good corrosion resistance and fatigue properties, maintained at relatively high temperatures. Nevertheless, machining these materials efficiently has become a challenge in a sector that demands high productivity rates and minimal manufacturing times. This work analyses the machinability of the α + β Ti-6Al-4V alloy in rough turning. Since oxygen is one of the elements that most affects the mechanical properties of titanium alloys, the aim is to understand its influence on the machinability of these materials. To do so, two different oxygen contents of 1200 and 2000 ppm are tested. A comprehensive material characterisation of both materials is carried out in order to clearly establish their differences: chemical composition, microstructure and mechanical properties (yield strength and hardness of the phases by nanoindentation). Machining trials consist of (i) tool life tests, which include a tool wear analysis, and (ii) cutting fundamental turning tests, in which the cutting forces and the chip form are studied. The work concludes that Ti-6Al-4V alloy with the highest oxygen content has the worst machinability (~15 % lower compared to lowO), due to its higher volume fraction of β + α s phase, slightly harder α p and greater yield strength, which generates higher mechanical and thermal tool wear. Thus, oxygen is a key composition element that should be controlled in machining titanium alloys, if robust results in tool life are expected to be obtained. Nomenclature Symbol Description UnitsMaterial characterisation T β Beta-transus temperature (phase transition) ºC ε True strain () σ True stress MPa UTS Ultimate tensile strength MPa YS Yield stress MPa YS 0.2 Yield stress for a plastic deformation of 0.2 % MPa Machining tests E Activation energy J mol −1 V b Average flank wear mm α Clearance angle°A c Contact area on the rake face mm 2 Q Cooling flow l min −1 P Cooling pressure bar * Irantzu Sacristan isacristan@mondragon.edu;

show abstract

In situ monitoring of the deformation mechanisms in titanium with different oxygen contents

Cited by 112 publications

References 37 publications

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry

Influence of oxygen content on the machinability of Ti-6Al-4V alloy

Contact Info

Product

Resources

About

In situ monitoring of the deformation mechanisms in titanium with different oxygen contents

Cited by 112 publications

References 37 publications

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Mechanism and energetics of 〈c + a〉 dislocation cross-slip in hcp metals

Complexity and Anisotropy of Plastic Flow of &alpha;-Ti Probed by Acoustic Emission and Local Extensometry

Influence of oxygen content on the machinability of Ti-6Al-4V alloy

Contact Info

Product

Resources

About

Complexity and Anisotropy of Plastic Flow of α-Ti Probed by Acoustic Emission and Local Extensometry