Fatigue behavior of columnar-grained Cu with preferentially oriented nanoscale twins

Pan, Qingsong; Lu, Qian; Lü, Lei

doi:10.1016/j.actamat.2012.11.015

Cited by 89 publications

(47 citation statements)

References 47 publications

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“…Cross-sectional scanning electron microscopy (SEM) observations of the as-fatigued nt-Cu samples have revealed that the slip bands are mutually parallel to each other in the grain interiors, but inclined to TBs [8,9]. The slip bands on both sides of TBs are mirror symmetric relative to TBs, which implies that they come from a single slip system with the slip planes inclined to TBs.…”

Section: Lettersmentioning

confidence: 98%

“…Furthermore, the stable microstructure of nt-Cu under strain-controlled fatigue is also different from the unstable structures associated with detwinning in nt-Cu films [6,7].Schmid factor analysis reveals that threading dislocations with the Burgers vector parallel to TBs but the slip plane inclined to TBs would be preferentially activated in the nanoscale twin lamellar channels when the twin plane is parallel to the loading axis [8,9]. However, the direct characterization of the threading dislocation by the conventional bright/dark field image under transmission electron microscope (TEM) is quite difficult.…”

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confidence: 99%

“…The twin lamellae thickness has a broad distribution from several tens to ~500 nanometers, but majority of them are in the nanometer scale, with an average value of ~75 nm. More details about the sample preparation and microstructures of the nt-Cu sample are described in [8,9]. Tensile tests reveal that nt-Cu sample displays a yield strength (σ y ) of 302 MPa and an ultimate tensile strength (σ uts ) of 360 MPa, much higher than that (σ y ~ 69 MPa, σ uts ~160 MPa) of twin-free CG-Cu with an average grain size of 9 μm.…”

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confidence: 99%

“…From view of engineering application, apart from tensile properties, fatigue properties and cyclic deformation of nanotwinned materials are of vital importance. Actually, investigations on the fatigue properties and cyclic deformation of nanotwinned metals under cyclic loading were carried out gradually in recent years [5][6][7][8]. Stress-controlled tension-tension fatigue tests of nanotwinned Cu (nt-Cu) film synthesized by magnetron sputtering have shown that their high-cycle fatigue life and fatigue limit are greatly improved over that of coarse grained Cu (CG-Cu) [5].…”

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Dislocation characterization in fatigued Cu with nanoscale twins

Pan

Lü

2015

Sci. China Mater.

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loops is maintained in nt-Cu, which is fundamentally distinct from cyclic softening of UFG [12,13] and cyclic hardening of CG counterparts [14][15][16]. Furthermore, the stable microstructure of nt-Cu under strain-controlled fatigue is also different from the unstable structures associated with detwinning in nt-Cu films [6,7].Schmid factor analysis reveals that threading dislocations with the Burgers vector parallel to TBs but the slip plane inclined to TBs would be preferentially activated in the nanoscale twin lamellar channels when the twin plane is parallel to the loading axis [8,9]. However, the direct characterization of the threading dislocation by the conventional bright/dark field image under transmission electron microscope (TEM) is quite difficult. On one hand, no trace of threading dislocations will be left behind on coherent TBs, due to their Burgers vector parallel to TBs. On the other hand, threading dislocations within twin/matrix layers at nanometer scale will overlap with the edge-on coherent TBs and become invisible in TEM under a perfect [110] incident electron beam. This is because threading dislocations are severely curved under the confinement of the twin/matrix layer at nanometer scale. In this study, the Burgers vector and morphology of threading dislocations in strain-controlled polycrystalline Cu with highly oriented nanoscale twins will be specifically characterized with an unique observation direction with respect to TBs by means of TEM analysis, i.e., under two-beam diffraction condition.Bulk (~3.4 mm in thickness) high-purity copper plates containing highly oriented nanoscale growth twins were synthesized by a direct-current electro-deposition technique in an electrolyte of CuSO 4 . Microstructural observations indicated that the as-deposited nt-Cu sample was composed of numerous columnar-shaped grains separated by clear grain boundaries (GBs). The grain size displays a wide distribution from 1 to 20 μm, with an average value of ~7 μm, which is approximately an order of magnitude Previous studies have shown that strain-controlled cyclic stability was maintained in bulk Cu samples with highly oriented nanoscale twins. In order to explore the underlying fatigue mechanism, transmission electron microscopy observations under two-beam diffraction condition were utilized to characterize the dislocation configurations in the twin/matrix layers of as-fatigued nanotwinned Cu. It was clarified that the threading dislocations with Burgers vector parallel to twin boundaries are mainly active during fatigue. A three-dimensional stereo projection was re-configured for demonstrating the special structure of dislocations in nanoscale twins.

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Section: Lettersmentioning

confidence: 98%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Dislocation characterization in fatigued Cu with nanoscale twins

Pan

Lü

2015

Sci. China Mater.

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“…[16,31,32] Besides, the formation of twins with low excess energy, the interaction between Al atoms with GBs and the formation of short-range order (SRO) are also beneficial to the improvement of microstructures stability. [16,33,34] Although the formation mechanism of the shear bands during cyclic deformation is not well understood, this kind of surface damage was significantly lessened with lowering of the SFE as well, which could be attributed to the changed GB natures stemming from the lowered SFE. [35] Additionally, the nature of planar slip in the materials with low SFE and SRO will facilitate reducing the strain localizations as well.…”

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Improved Fatigue Strengths of Nanocrystalline Cu and Cu–Al Alloys

Lin

Sheng

et al. 2015

Materials Research Letters

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Effect of Strain Rate on Tensile Ductility and Fracture Behavior of Bulk Nanotwinned Copper

You

Lü

2015

Adv Eng Mater

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A bulk columnar-grained copper with preferentially oriented nanoscale growth twins is prepared by means of direct-current electrodeposition. Tensile tests at different strain rates reveal a significant influence of strain rate on the tensile ductility and fracture behavior. The ductility, especially the postnecking elongation, reduces dramatically at low strain rates, which is associated with evident intergranular fracture. The results suggest that the grain size as well as the grain boundary microstructural evolution exert a strong influence on the intrinsic fracture mode in the nanotwinned structure.Hierarchical microstructure with nanoscale twin boundaries (TBs) incorporated into polycrystalline metals has attracted world-wide attention over the past decade, as the nanotwinned structure simultaneously exhibits several superior mechanical properties, including ultra-high strength, good ductility, and enhanced work hardening. [1][2][3][4][5][6] It has been accepted that the coherent TBs at the nanoscale play an essential role in generating the outstanding properties not only by obstructing motion of dislocations but also by providing ample space for dislocation storage. [1,7] Intrinsic microstructure characteristics, including twin length (i.e., grain size) and twin thickness, affect the mechanical properties as well as the plastic deformation mechanisms. [8][9][10] Recently, via a columnar-grained Cu with nanoscale growth TBs preferentially oriented parallel to the deposition plane, it is further instructive to detect the fact that TB orientation with respect to the loading direction could substantially affect the dominating dislocation mechanism for both monotonic and cyclic deformation. [11][12][13] For instance, if TBs are mostly aligned with tensile direction, the plastic deformation is mainly accomplished by threading dislocations nucleating from grain boundaries (GBs) and bowing out under the constraint of neighboring TBs. [12,14] Strain rate effect on plastic flow behavior is generally studied in order to reveal the intrinsic deformation mechanism of metallic materials. [15][16][17] Through systematically investigating the strain rate sensitivity of nanotwinned Cu (nt-Cu) with randomly oriented nanoscale twins, Lu et al. demonstrated an substantially elevated strain rate sensitivity contributed by strong dislocation-TB interactions as the twin thickness was reduced down to tens of nanometer. [18][19][20] For the nt-Cu with highly oriented nanoscale twins, Ye et al. demonstrated a TB orientation dependence of strain rate sensitivity, a reflection of the intrinsic plastic anisotropy. [21] On the other hand, tensile tests at different strain rates only revealed a slightly enhanced ductility with increasing strain rate. [18,22] The previous studies of strain rate effect on the mechanical response of nanotwinned structure have mainly dealt with samples with grains in the nanometer and submicron meter scale ( 500 nm). However, it has also been demonstrated that GBs can interact with impinging dislocations, lea...

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Fatigue behavior of columnar-grained Cu with preferentially oriented nanoscale twins

Cited by 89 publications

References 47 publications

Dislocation characterization in fatigued Cu with nanoscale twins

Dislocation characterization in fatigued Cu with nanoscale twins

Improved Fatigue Strengths of Nanocrystalline Cu and Cu–Al Alloys

Effect of Strain Rate on Tensile Ductility and Fracture Behavior of Bulk Nanotwinned Copper

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