On the stability of cold drawn, two-phase wires

Hong, Sun Ig; Hill, Mary Ann; Sakai, Yoshikazu; Wood, Jeffrey; Embury, J.D.

doi:10.1016/0956-7151(95)00050-6

Cited by 68 publications

(35 citation statements)

References 11 publications

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“…Nb being a bcc material, has the major slip components in the temperature range under consideration of {110}<111> [20]. The extrusion and drawing textures in Nb are predominantly the {110} textures, which are widely reported in the literature [21][22][23]. Our best Cu-Nb results were obtained with the finer grain size (20-60 µm) ECAE processed sample.…”

Section: Discussionsupporting

confidence: 71%

FINE GRAINED NB FOR INTERNAL TIN NB[sub 3]SN CONDUCTORS

Balachandran¹,

Barber²,

Huang³

et al. 2010

AIP Conference Proceedings

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The push to drive superconductor strand technology to reach higher critical current density (J c ) values and reduce production costs has led to innovative approaches in manufacturing technology. The Restacked Rod Process (RRP®) by Oxford Instruments is one such process which involves Nb bar extrusions in a Cu sheath. Commercially available Nb used in the initial RRP extrusion leads to nonuniform deformations of the Nb bar which in turn leads to a jagged Cu-Nb interface. This report presents a feasible methodology to remedy the problem of nonuniform deformation of Nb through severe plastic deformation (SPD) of precursor Nb to obtain smaller grains in starting Nb. Cu-Nb monocore extrusion and drawing experiments were accomplished at Oxford Instruments using Nb bars of nominal dimensions 45mm diameter by and 78mm long and with grain sizes in the range of µm to mm. Results of Cu-Nb interface roughness measurements show that a finer starting grain size gives a significantly lower roughness and better Nb core conformance to initial shape. Our experiments indicate that refinement of the initial Nb grain size to below ~50µm could enable fabrication of RRP conductor with improved wire yield.

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Section: Discussionsupporting

confidence: 71%

FINE GRAINED NB FOR INTERNAL TIN NB[sub 3]SN CONDUCTORS

Balachandran¹,

Barber²,

Huang³

et al. 2010

AIP Conference Proceedings

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“…[30] The increase of the strength due to precipitates was reported to be 127 MPa for the bundled Cu-15.6 vol pct Nb microcomposite wire. [16] Since Nb precipitates were suggested to result from the redistribu- tion of Nb across the migrating grain boundaries [15,16,24,31] during the high-temperature bundling process, the interaction between Nb filaments and migrating grain boundaries would increase with increasing Nb content. Hence, Nb prewith increasing Nb content.…”

Section: Resultsmentioning

confidence: 99%

Strength and ductility of heavily drawn bundled Cu-Nb filamentary microcomposite wires with various Nb contents

Hong

Kim

Hill

2000

Metall Mater Trans A

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The strength and ductility of heavily drawn bundled Cu-Nb filamentary microcomposite was examined as a function of Nb content. In order to predict the variation of the yield strength (YS) with Nb content, the interfilamentary spacing was calculated as a function of Nb content based on the assumption that Nb filaments are distributed regularly along the sides of a triangular unit cell in the transverse section. The yield stress can be described as the sum of the substructure strengthening component due to elongated grains, subgrains and/or cells, the phase boundary strengthening term associated with the Hall-Petch type interaction between dislocations and phase boundaries, and the precipitate strengthening component. The contributions from phase boundary strengthening, PB (Cu-Nb), and precipitate strengthening, ppt , increase with increasing Nb content. However, the contribution from substructure strengthening, sub (Cu-Nb), decreases with increasing Nb content since more grain or subgrain boundaries are absorbed at Cu/Nb phase boundaries with increasing Nb content. The good agreement between the prediction and the experimental data suggests that the increase of the strength in Cu-Nb filamentary microcomposite with increasing Nb content results mostly from an increasing volume fraction of Nb filaments, which act as barriers to plastic flow.

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“…At high temperatures, however, the initial as-processed microstructure was not stable, and equiaxed dislocation cells and substructures, a typical microstructure after high-temperature creep deformation of pure metals, was observed. At high temperatures, the initial as-swaged microstructure was completely replaced through recrystallization, as observed in other Cu-based microcomposites, [21,27] and newly generated dislocations during creep may have transformed into dislocation cells through glide, cross slip, and climb. In this case, climb could be a rate-controlling process, as mentioned earlier.…”

Section: B Creep Deformationmentioning

confidence: 78%

Creep behavior of copper-chromium in-situ composite

Lee

Whitehouse

Hong

et al. 2004

Metall Mater Trans A

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Creep deformation and fracture behaviors were investigated on a deformation-processed Cu-Cr in-situ composite over a temperature range of 200 °C to 650 °C. It was found that the creep resistance increases significantly with the introduction of Cr fibers into Cu. The stress exponent and the activation energy for creep of the composite at high temperatures (≥400 °C) were observed to be 5.5 and 180 to 216 kJ/mol, respectively. The observation that the stress exponent and the activation energy for creep of the composite at high temperatures (≥400 °C) are close to those of pure Cu suggests that the creep deformation of the composite is dominated by the deformation of the Cu matrix. The high stress exponent at low temperatures (200 °C and 300 °C) is thought be associated with the as-swaged microstructure, which contains elongated dislocation cells and subgrains that are stable and act as strong athermal obstacles at low temperatures. The mechanism of damage was found to be similar for all the creep tests performed, but the distribution and extent of damage were found to be very sensitive to the test temperature. Creep deformation and fracture behaviors were investigated on a deformation-processed Cu-Cr in-situ composite over a temperature range of 200°C to 650°C. It was found that the creep resistance increases significantly with the introduction of Cr fibers into Cu. The stress exponent and the activation energy for creep of the composite at high temperatures (Ն400°C) were observed to be 5.5 and 180 to 216 kJ/mol, respectively. The observation that the stress exponent and the activation energy for creep of the composite at high temperatures (Ն400°C) are close to those of pure Cu suggests that the creep deformation of the composite is dominated by the deformation of the Cu matrix. The high stress exponent at low temperatures (200°C and 300°C) is thought be associated with the as-swaged microstructure, which contains elongated dislocation cells and subgrains that are stable and act as strong athermal obstacles at low temperatures. The mechanism of damage was found to be similar for all the creep tests performed, but the distribution and extent of damage were found to be very sensitive to the test temperature. Disciplines Materials Science and Engineering | Metallurgy

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On the stability of cold drawn, two-phase wires

Cited by 68 publications

References 11 publications

FINE GRAINED NB FOR INTERNAL TIN NB[sub 3]SN CONDUCTORS

FINE GRAINED NB FOR INTERNAL TIN NB[sub 3]SN CONDUCTORS

Strength and ductility of heavily drawn bundled Cu-Nb filamentary microcomposite wires with various Nb contents

Creep behavior of copper-chromium in-situ composite

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