The Dislocation Mechanism of Stress Corrosion Embrittlement in Ti-6Al-2Sn-4Zr-6Mo

Chapman, T.P.; Vorontsov, V.A.; Sankaran, A.; Rugg, David; Lindley, T.C.; Dye, David

doi:10.1007/s11661-015-3181-0

Cited by 17 publications

(9 citation statements)

References 55 publications

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“…2c), is below 2 at.%, which mostly originates from the residual gas in the ultra-high vacuum chamber of the APT microscope 25,33 . In the specimens of the two-phase Ti6246 alloy, prepared by conventional FIB milling, no hydride was detected, consistent with the observations of Ding and Jones 23 on dual-phase Ti-6Al-4V (Ti64, wt%) or β-phase Ti–5Al–5Mo–5V–3Cr (Ti-5553, wt%) TEM lamellae, and with our previous work 34–37 . However, a much higher amount of dissolved H was detected, 2–6 at.% H in the hexagonal α phase and 13–19 at.% H in the body-centred cubic β phase, consistent with our previous report 25 .…”

Section: Resultssupporting

confidence: 90%

Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials

et al. 2019

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Hydrogen pick-up leading to hydride formation is often observed in commercially pure Ti (CP-Ti) and Ti-based alloys prepared for microscopic observation by conventional methods, such as electro-polishing and room temperature focused ion beam (FIB) milling. Here, we demonstrate that cryogenic FIB milling can effectively prevent undesired hydrogen pick-up. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, in wt.%) were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage reaching −135 °C. Transmission electron microscopy (TEM), selected area electron diffraction, and scanning TEM indicated no hydride formation in cryo-milled CP-Ti lamellae. Atom probe tomography further demonstrated that cryo-FIB significantly reduces hydrogen levels within the Ti6246 matrix compared with conventional methods. Supported by molecular dynamics simulations, we show that significantly lowering the thermal activation for H diffusion inhibits undesired environmental hydrogen pick-up during preparation and prevents pre-charged hydrogen from diffusing out of the sample, allowing for hydrogen embrittlement mechanisms of Ti-based alloys to be investigated at the nanoscale.

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Section: Resultssupporting

confidence: 90%

Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials

et al. 2019

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“…The cleavage-like crack appearance in the α phase was observed in this work, which is similar to the previous findings on NaCl HSSCC of Ti-6246 [12,15]. It has been proposed that both HELP and AIDE could lead to a transgranular fracture appearance [13,17,37]. However, dense dislocation structures were normally found a few µm below the α facets in previous TEM studies [17,37], in comparison with the observation of high dislocation density near the fracture surface (< 1 µm) in this case.…”

Section: Crack Propagationsupporting

confidence: 91%

“…TEM investigation on a cleavage-fractured primary α grain displayed a large amount of long and straight dislocation segments on basal and pyramidal planes. This high dislocation density across the whole grain was not observed in previous study on NaCl HSSCC of Ti-6246, especially not adjacent to the fracture surface within 1 µm distance [37]. Also, less dislocation entanglements were seen in this case, which could imply a change of the embrittlement mechanism ahead of crack tips for AgCl HSSCC.…”

Section: Main Experimental Observationscontrasting

confidence: 59%

AgCl-induced hot salt stress corrosion cracking in a titanium alloy

Shi

Joseph

Saunders

et al. 2020

Preprint

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The mechanism of AgCl-induced stress corrosion cracking of Ti-6246 was examined at 500 MPa and 380 °C for 24 h exposures. SEM and STEM-EDX examination of a FIB-sectioned blister and crack showed that metallic Ag was formed and migrated along the crack. TEM analysis also revealed the presence of SnO 2 and Al 2 O 3 corrosion products mixed into TiO 2 . The fracture surface has a transgranular and brittle appearance with cleavage-like cracking of the α phase. Long, straight and non-interacting dislocations were observed in a cleavage-fractured primary α grain, with basal and pyramidal traces. This is consistent with a dislocation emission view of the the cracking mechanism.

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“…Further, Beachem [88] reported a reduction in fracture toughness during hydrogen-assisted cracking, and suggested that hydrogen unlocks, rather than pins, dislocations, thus providing further support for two apparently contradicting mechanisms occurring at different length scales. For full details of hydrogen enhanced dislocation motion in an HSSCC scenario, the reader is referred to [89].…”

Section: (D) Experimental Evidence Of Hydrogen Embrittlement In Hsscc Mechanismmentioning

confidence: 99%

Hydrogen in Ti and Zr alloys: industrial perspective, failure modes and mechanistic understanding

Chapman

Dye²,

Rugg

2017

Phil. Trans. R. Soc. A.

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Titanium is widely used in demanding applications, such as in aerospace. Its strength-to-weight ratio and corrosion resistance make it well suited to highly stressed rotating components. Zirconium has a no less critical application where its low neutron capture cross section and good corrosion resistance in hot water and steam make it well suited to reactor core use, including fuel cladding and structures. The similar metallurgical behaviour of these alloy systems makes it alluring to compare and contrast their behaviour. This is rarely undertaken, mostly because the industrial and academic communities studying these alloys have little overlap. The similarities with respect to hydrogen are remarkable, albeit potentially unsurprising, and so this paper aims to provide an overview of the role hydrogen has to play through the material life cycle. This includes the relationship between alloy design and manufacturing process windows, the role of hydrogen in degradation and failure mechanisms and some of the underpinning metallurgy. The potential role of some advanced experimental and modelling techniques will also be explored to give a tentative view of potential for advances in this field in the next decade or so.This article is part of the themed issue 'The challenges of hydrogen and metals'.

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The Dislocation Mechanism of Stress Corrosion Embrittlement in Ti-6Al-2Sn-4Zr-6Mo

Cited by 17 publications

References 55 publications

Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials

Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials

AgCl-induced hot salt stress corrosion cracking in a titanium alloy

Hydrogen in Ti and Zr alloys: industrial perspective, failure modes and mechanistic understanding

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