Crack-tip dislocation emission arrangements for equilibrium —I. In situ TEM observations of Fe2wt%Si

Zieliński, W.; Lii, Mirng-Ji; Gerberich, William W

doi:10.1016/0956-7151(92)90451-j

Cited by 75 publications

(20 citation statements)

References 33 publications

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“…4. In such cases, different levels of crack tip shielding than at isolated cracks may be expected due to the interaction of dislocation densities surrounding neighbouring cracks [42][43][44] . This interaction may include-among other possibilities-enhanced annihilation of opposite sign dislocations 45 , generation of a greater number of statistically stored 'redundant' dislocations 46 , repulsion of like-signed dislocations and modified levels of cross-slip.…”

Section: Discussionmentioning

confidence: 99%

The dual role of coherent twin boundaries in hydrogen embrittlement

et al. 2015

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Hydrogen embrittlement (HE) causes engineering alloys to fracture unexpectedly, often at considerable economic or environmental cost. Inaccurate predictions of component lifetimes arise from inadequate understanding of how alloy microstructure affects HE. Here we investigate hydrogen-assisted fracture of a Ni-base superalloy and identify coherent twin boundaries (CTBs) as the microstructural features most susceptible to crack initiation. This is a surprising result considering the renowned beneficial effect of CTBs on mechanical strength and corrosion resistance of many engineering alloys. Remarkably, we also find that CTBs are resistant to crack propagation, implying that hydrogen-assisted crack initiation and propagation are governed by distinct physical mechanisms in Ni-base alloys. This finding motivates a re-evaluation of current lifetime models in light of the dual role of CTBs. It also indicates new paths to designing materials with HE-resistant microstructures.

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Section: Discussionmentioning

confidence: 99%

The dual role of coherent twin boundaries in hydrogen embrittlement

et al. 2015

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“…[8] The prevailing view on cleavage fracture is that there is a competition between the emission of dislocations and the propagation of a Griffith crack from the crack tip. [4,[9][10][11][12][13][14][15][16][17][18][19][20] The limiting stage in the dislocation emission process can either be the nucleation of dislocations at the crack tip [4,[9][10][11][12][13][14][15][16][17][18][19][20] or, once nucleated, the mobility of the dislocations propagating away from the crack tip. [21,22,23] In both cases, dislocation emission leads to shielding of the crack tip that results in an enhancement of fracture resistance.…”

Section: Introductionmentioning

confidence: 99%

Effects of Ti addition on cleavage fracture in Nb-Cr-Ti solid-solution alloys

Chan

Davidson

1999

Metall Mater Trans A

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The fracture toughness of Nb-Cr-Ti solid-solution alloys has been shown to be greatly improved by Ti addition, but the mechanism of toughness enhancement has not been established. In this study, critical experiments were performed on the tough Nb-Cr-Ti alloy to characterize the crack-tip fracture process and to investigate the origin of fracture toughness. In addition, theoretical calculations of the unstable stacking energy (USE) and the Peierls-Nabarro (P-N) energy and stress were performed as a function of Ti content in the Nb-Cr-Ti alloys. The experimental results indicate that the fracture toughness in the tough Nb-Cr-Ti alloy originates from extensive dislocation emission that suppresses cleavage crack propagation from the crack tip. The theoretical calculation indicates that Ti addition lowers the P-N energy and stress, but has little effect on the USE. These results are used to elucidate the effects of Ti addition on cleavage fracture in Nb-Cr-Ti alloys by considering the influence of the P-N energy and stress values on (1) dislocation mobility, (2) crack-tip dislocation emission, (3) fracture toughness, and (4) brittle-to-ductile fracture transition. It is concluded that dislocation emission in the Nb-Cr-Ti alloys appears to be controlled by the P-N energy, which influences dislocation mobility, rather than by the USE, which influences dislocation nucleation. Ti increases the fracture toughness of Nb-Cr-Ti alloys by increasing dislocation mobility and dislocation emission from the crack tip through a reduction of the P-N energy and stress.

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“…3. Zielinski [6] reported an observation of a step-by-step crack growth for Fe-2 wt.% silicon and showed that the cleavage crack left 3.5 slip traces of residual dislocations for every 100 nm of crack growth, with an average of 18.6 dislocations per trace. Zhu et al [7] defined a Crack Tip Opening Angle (CTOA) where full dislocation emissions along the slip plane were assumed, omitting the slip deformation caused by incomplete dislocations.…”

Section: Resultsmentioning

confidence: 98%

An experimental observation of dislocation nucleation based on the peierls concept

2001

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The HREM-moiré method developed by Dai and Xing [1] is an experimental technique which allows for the direct measurement of such parameters as displacement, strain and dislocation in the nanoscopic range. This technique was used to measure the nanoscopic deformation field near the tip of a quasi-cleavage crack in silicon. A process of dislocation nucleation was observed. A long dislocation extending about 600 burgers vectors was found at the crack tip and the slip distribution along it was measured. This distributed dislocation has a similar slip structure to the one based on the Peierls concept described by Rice [2], but has a much longer slip range. The nanoscopic strain distribution near the crack tip was obtained. There is a strain field controlled by linear elastic fracture mechanics at the very vicinity of the crack tip.

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Crack-tip dislocation emission arrangements for equilibrium —I. In situ TEM observations of Fe2wt%Si

Cited by 75 publications

References 33 publications

The dual role of coherent twin boundaries in hydrogen embrittlement

The dual role of coherent twin boundaries in hydrogen embrittlement

Effects of Ti addition on cleavage fracture in Nb-Cr-Ti solid-solution alloys

An experimental observation of dislocation nucleation based on the peierls concept

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