Crack initiation at dislocation cell boundaries in the ductile fracture of metals

Gardner, R. N.; Pollock, Thomas Clark; Wilsdorf, H.G.F.

doi:10.1016/0025-5416(77)90123-9

Cited by 87 publications

(6 citation statements)

References 22 publications

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“…The current observations are reminiscent of the 1977 study by Gardener, Pollock, and Wilsdorf where crack nucleation in beryllium was found to occur at subgrain boundaries. [25] Although, the current observations suggest the possibility that not all voids nucleate at subgrain boundaries (see arrow in Figure 7(f)). …”

Section: Discussionmentioning

confidence: 55%

The Morphology of Tensile Failure in Tantalum

Boyce

Clark

et al. 2013

Metall Mater Trans A

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The deformation, crack nucleation, coalescence, and rupture process of pure tantalum (99.9 pct) were studied under room temperature quasistatic loading using several in situ and ex-situ techniques including optical metallography, scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission-electron microscopy (TEM). The fracture surface of tantalum forms a ridge-and-valley morphology that is distinct from conventional notions of ductile dimple microvoid coalescence, and also distinct from spall damage formed during dynamic shock conditions. Failure proceeds by void nucleation at a dislocation cell wall or in subgrain interiors. Coalescence appears to involve a two-stage damage progression: first individual voids coalesce along the tensile axis forming diamond-shaped multivoid cavities; then cavities link-up by intercavity necking. Final rupture occurs when the intercavity necks thin tõ 100-nm films and fail by crystallographic cleavage. This final tearing process was observed using in situ TEM tensile deformation of a thin tantalum film. The detailed microstructural and morphological observations of the current study can be used to guide the development of improved models for tearing of ductile metals.

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Section: Discussionmentioning

confidence: 55%

The Morphology of Tensile Failure in Tantalum

Boyce

Clark

et al. 2013

Metall Mater Trans A

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“…He observed walls with large dislocation densities at the PFZ boundaries (i.e., the interface between PFZ and precipitate strengthened grain), and suggested that these may serve as void initiation sites when impinged by slip bands from the grain interiors. This suggestion was motivated by observations of Gardner et al [12] and Wilsdorf et al [13] who showed how dislocation structures can serve as nucleation sites for voids in pure metals. More recent studies on pure tantalum crystals support this idea, and attribute such void formation to vacancy condensation at dislocation cell boundary block walls [14].…”

Section: Introductionmentioning

confidence: 92%

Lattice rotations in precipitate free zones in an Al-Mg-Si alloy

Christiansen

Marioara

Marthinsen

et al. 2018

Materials Characterization

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Scanning precession electron diffraction and automated crystal orientation mapping in a transmission electron microscope (TEM) have been applied to quantitatively study the crystal orientation of precipitate free zones (PFZs) of four GB regions in an AA6060 alloy in peak aged condition (temper T6) after uniaxial compression to 20% engineering strain. The PFZ width in the alloy is found to be w = 170 ± 40 nm. The results show that some PFZs develop significant misorientations relative to their parent grain, and represent, to the best knowledge of the authors, the first quantitative evidence of this. This misorientation may either be constant inside a particular PFZ, making it appear like a band or a very elongated subgrain, or be partitioned in discrete regions with a diameter comparable to the PFZ width, making the former PFZ into a collection of small grains. The band-like PFZ observed in this work had a misorientation relative to its parent grain of ∼ 7°, while the grain-like PFZ had grains with misorientations between ∼ 12°and ∼ 20°r elative to its parent grain. The other PFZs that were observed had only limited misorientations relative to their parent grains, and had either dislocations perpendicular to the GB plane or a dislocation wall at the transition region. A general TEM study of the material at various engineering strains was also conducted and suggests that grain-like PFZs are more frequent for larger strains, indicating that the different PFZ features are likely due to different strain localisation in individual PFZs. This localisation is expected to be influenced by the orientation of the loading axis relative to crystal orientations and GB planes. It is also suggested that the different PFZ features engender different work hardening rates and possibly affect nucleation of intergranular fracture. The results support previous studies on the microstructure evolution of PFZs in age-hardenable aluminium alloys during deformation.

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“…void nucleation, growth and coalescence. Upon deformation, microvoids have been reported to nucleate and grow from: second-phase particles through matrix particle decohesion and particle cracking (Puttick, 1959); triple junctions between grains of identical phases (Tan et al, 2007); interfaces between different phases (Greenfield and Margolin, 1972); slipband intersections (Gysler et al, 1974); dislocation cell boundaries (Gardner et al, 1977); etc. The anisotropic nature of these mechanisms is clearly shown (Benzerga et al, 2004).…”

Section: Introductionmentioning

confidence: 99%