Microstructural Refinement of Niobium for Superconducting RF Cavities

Hartwig, K. T.; Wang, Jyhwen; Baars, D.; Bieler, T. R.; Mathaudhu, Suveen; Barber, R. E.

doi:10.1109/tasc.2007.899893

Cited by 11 publications

(9 citation statements)

References 6 publications

(6 reference statements)

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“…4) [7]. This supports the notion that SPD processing of precursor bulk material enables fabrication of sheet with improved deformation characteristics.…”

Section: Deformation Behaviorsupporting

confidence: 81%

Fine Grained Tantalum for Composite ${\rm Nb}_{3}{\rm Sn}$ Superconductor Diffusion Barrier Sheet

Mathaudhu

Hartwig

Barber

2007

IEEE Trans. Appl. Supercond.

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Poor deformation behavior of commercial polycrystalline Ta sheet used for Sn diffusion barriers in Nb 3 Sn composite superconductors leads to the use of more Ta than may be necessary in these conductors, and to strand fracture during wire drawing. These problems arise because of nonuniform deformation of the Ta layer when co-drawn with Cu. The origin of the problem resides in the microstructure of the Ta and the code formation mechanics of relatively strong BCC Ta with weaker and more ductile adjacent FCC Cu. In an attempt to remedy this problem, we have processed 25 mm square bars of Ta by multi-axis severe plastic deformation (SPD) via equal channel angular extrusion, then rolled the bars to sheet and annealed the as-worked sheet. The processing is done to refine the microstructure and reduce nonuniformities in grain size and texture. Measurements of hardness, microstructure and mechanical properties are reported for bulk and sheet Ta. The results of SPD processing are encouraging.

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“…4) [7]. This supports the notion that SPD processing of precursor bulk material enables fabrication of sheet with improved deformation characteristics.…”

Section: Deformation Behaviorsupporting

confidence: 81%

Fine Grained Tantalum for Composite ${\rm Nb}_{3}{\rm Sn}$ Superconductor Diffusion Barrier Sheet

Mathaudhu

Hartwig

Barber

2007

IEEE Trans. Appl. Supercond.

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“…A pair of OIM scans approximately 1.5 mm apart and extending about two-thirds into the thickness from either surface of the sheet were taken of two samples with different deformation histories to evaluate microstructure and texture (Figure 4). 7 The recrystallized grain size varied somewhat due to the different deformation histories, but the average grain size for six different deformation histories was 18±3 m, as illustrated in Figure 5, which is much smaller than the commercially rolled material. While the average grain size was similar for both samples, the textures were completely different.…”

Section: Commercially Processed Sheetmentioning

confidence: 90%

“…7 To put these newer ideas into context, some relationships between texture, microstructure, and properties of conventionally processed sheet niobium are first illustrated. [7][8][9][10][11][12][13][14][15] …”

Section: Introductionmentioning

confidence: 99%

Processing strategies for niobium sheet used in advanced superconducting particle accelerator cavities

Baars

Bieler

Hartwig

et al. 2007

JOM

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Ultra-high-purity niobium sheet is used to fabricate radio frequency cavities for use in future linear accelerators. The complexity of the shapes requires the electron-beam welding of deep-drawn components , but diffi culties with inconsistent formability, springback, and surface roughness have been traced to non-uniform microstructures and texture gradients that are common in commercial niobium sheet. Two approaches under study to overcome these problems are the development of fi ne-grained favorably textured polycrystalline sheet, and the use of a properly oriented and nearly

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“…This involved refining the microstructure by severe plastic deformation (SPD) through multi pass equal channel angular extrusion (ECAE) [14] and subsequent recrystallization heat treatments. This process has been previously demonstrated to effectively refine as-cast Nb [15,16]. TABLE 1 provides details of the starting Nb bars used in the mono core experiments.…”

Section: Starting Materials and Processing Of Precursor Nbmentioning

confidence: 99%

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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Microstructural Refinement of Niobium for Superconducting RF Cavities

Cited by 11 publications

References 6 publications

Fine Grained Tantalum for Composite ${\rm Nb}_{3}{\rm Sn}$ Superconductor Diffusion Barrier Sheet

Fine Grained Tantalum for Composite ${\rm Nb}_{3}{\rm Sn}$ Superconductor Diffusion Barrier Sheet

Processing strategies for niobium sheet used in advanced superconducting particle accelerator cavities

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

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