Xi. The origin of fatigue fracture in copper

Thompson, N.; Wadsworth, N. J.; Louat, N.

doi:10.1080/14786435608238086

Cited by 406 publications

(85 citation statements)

References 5 publications

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“…Due to the activation of cross slip, the arrangement of dislocations is characterized by the formation of dislocation walls and cells. During cyclic deformation, slip localization occurs in form of so-called PSBs [94], which are characterized by the well-known "ladder-like" structure of the arrangement of dislocation dense walls [95,96]. PSBs emerging at the specimen surface cause so-called persistent slip markings (PSMs) forming a pronounced surface relief composed of extrusions and intrusions [97,98], which are preferred locations for crack initiation.…”

Section: Ecci and The Slip Activity Of Psbsmentioning

confidence: 99%

Case studies on the application of high-resolution electron channelling contrast imaging – investigation of defects and defect arrangements in metallic materials

Weidner

Biermann

2015

Philosophical Magazine

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In 1967, Coates discovered the electron channelling contrast of backscattered electrons (BSEs) in scanning electron microscopy, and by this the possibility to investigate arrangements of lattice defects in deformed microstructures of materials. Since that time, a straightforward development of the scanning electron microscopes as well as of the electron channelling contrast technique took place. Nowadays, the performance of scanning electron microscopes is high enough that the resolution of electron channelling contrast imaging (ECCI) micrographs is comparable with conventional bright field transmission electron microscopy (TEM) micrographs. In the first part of the present paper, a historical review on the development of the ECCI technique starting from its discovery more than 45 years ago up to the combination with other advanced methods of scanning electron microscopy like electron backscatter diffraction or high-resolution selected area channelling patterning in the last few years is given. Major important investigations using this technique for the visualization of individual lattice defects like stacking faults (SFs) and dislocations or dislocation arrangements are chronologically summarized. The second part demonstrates that nowadays, ECCI micrographs taken in high-resolution scanning electron microscopes can be called high-resolution ECCI (HR-ECCI). It is shown that the resolution of individual SFs and dislocations in the HR-ECCI micrographs is comparable to that of conventional TEM (about 15 nm defect image width). Furthermore, the paper is demonstrating that HR-ECCI micrographs can be obtained for various types of materials after different mechanical loadings and different grain sizes ranging from large grain size of 500 μm (cast steel) down to less than 2 μm (γ-TiAl).

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Section: Ecci and The Slip Activity Of Psbsmentioning

confidence: 99%

Case studies on the application of high-resolution electron channelling contrast imaging – investigation of defects and defect arrangements in metallic materials

Weidner

Biermann

2015

Philosophical Magazine

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“…Room temperature fatigue testing in this alloy at low stresses also revealed that microcracks initiated near and parallel to annealing twin boundaries in surface large grains, as described above for internal initiation at 593°C. Similarly, fatigue crack initiation in the region close to annealing twin boundaries has been observed in other FCC materials [17,18]. Annealing twin boundaries are thought to be important locations for cyclic strain localization and fatigue crack initiation in FCC materials due to elastic anisotropy between the twin and matrix [19].…”

Section: Fatigue Crackmentioning

confidence: 92%

Fatigue Crack Initiation in Nickel-Based Superalloy Ren� 88 DT at 593�C

Miao¹,

Pollock²,

Jones³

2008

Superalloys 2008 (Eleventh International Symposium)

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Fatigue crack initiation in the polycrystalline nickel-based superalloy, René 88 DT, was investigated at 593 °C in air using an ultrasonic fatigue testing instrument. Within the testing stress range of 500 -760MPa, all fatigue failures initiated from internal regions. Large crystallographic facets were observed at the crack initiation sites in most failed fatigue samples. Critical microstructure features controlling fatigue crack initiation and the early stage of small crack growth were identified by the combination of serial sectioning, orientation imaging microscopy (OIM) and quantitative fractographic analysis. Large crystallographic facets at crack initiation sites were formed in regions close to Σ 3 annealing twin boundaries within favorably oriented large grains. The facet planes are parallel to Σ 3 annealing twin boundaries and are of {111} type. Cyclic deformation substructures were studied by transmission electron microscopy. At the low cyclic stresses and long lives examined, fatigue failure at 593°C is controlled by strain localization in large, favorably oriented grains and subsequent propagation of small cracks through neighborhoods of favorably oriented grains. Annealing twin boundaries, prevalent in the microstructure, appear to be important in cyclic strain localization.

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“…48,58) However, since grain size is very small and since the unstable dislocation wall structure is formed only in selected grains of UFG Al, the dislocation walls do not appear to cause the extensive formation of persistent slip bands. From this viewpoint, the present unstable dislocation walls formed in UFG Al at 77 K may not be so harmful to the fatigue resistance.…”

Section: Relationship Between Monotonic Tensile Deformationmentioning

confidence: 99%

Stability of Fatigued Dislocation Wall Structure in Coarse-Grained and Ultrafine-Grained Aluminum against Monotonic Tensile Deformation

et al. 2013

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Coarse-grained (CG) and ultrafine-grained (UFG) pure aluminum samples fabricated by equal channel angular pressing (ECAP) were cyclically deformed at 77 K under constant plastic strain amplitude. Monotonic tensile tests were performed at 300 and 77 K soon after the fatigue tests. In spite of the increase in the tensile strength of fatigued CG Al, tensile ductility decreased remarkably in comparison to that of as-annealed CG Al. On the other hand, the ultimate tensile strength (UTS) and tensile ductility of UFG Al were much higher at 77 K than those at 300 K. Furthermore, UFG Al at 77 K maintained high UTS and high tensile ductility even after fatigue tests. Microstructural observation has revealed that dislocation wall structure formed in fatigued CG Al persists after the monotonic tensile tests. However, dislocation wall structure formed in fatigued UFG Al disappeared during early stages of monotonic tensile tests at both 300 and 77 K. These results indicate that the dislocation wall structure in UFG Al is unstable against succeeding monotonic tensile deformation.

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Xi. The origin of fatigue fracture in copper

Cited by 406 publications

References 5 publications

Case studies on the application of high-resolution electron channelling contrast imaging – investigation of defects and defect arrangements in metallic materials

Case studies on the application of high-resolution electron channelling contrast imaging – investigation of defects and defect arrangements in metallic materials

Fatigue Crack Initiation in Nickel-Based Superalloy Ren� 88 DT at 593�C

Stability of Fatigued Dislocation Wall Structure in Coarse-Grained and Ultrafine-Grained Aluminum against Monotonic Tensile Deformation

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