COMPARISON OF A15 STOICHIOMETRY AND GRAIN MORPHOLOGY IN INTERNAL Sn AND TUBE TYPE STRANDS; INFLUENCE OF STRAND DESIGN, HTs AND ALLOYING

Bhartiya, S.; Sumption, M.D.; Peng, Xuan; Gregory, E.; Tomsic, M.; Doll, David; Collings, E. W.

doi:10.1063/1.3402298

Cited by 3 publications

(2 citation statements)

References 16 publications

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“…At present, Hyper Tech Research Inc (HTR) has successfully produced 1387-subelement tube type strands, reducing the subelement diameter to 12 µm [14]. In spite of its advantages of small d eff and stability the present tube type strand has a lower non-Cu J c than its RIT counterpart [15]. This report addresses the cause of the discrepancy and offers a solution.…”

Section: Introductionmentioning

confidence: 96%

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

Sumption

Bhartiya

et al. 2013

Supercond. Sci. Technol.

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In this work, the transport and magnetization properties of distributed-barrier Rod-inTube (RIT) strands and Tube Type strands are studied. While Tube Type strands had smaller magnetizations and thus better stabilities in the low field region, their 12 T non-Cu J c s were somewhat smaller than those of the RIT strands. Microstructures were investigated in order to find out the reasons for the difference in non-Cu J c values. Their grain size and stoichiometry were found to be comparable, leading to similar layer J c s. Accordingly it was determined that the lower A15 area fraction rather than the quality of A15 layer was the cause of the discrepancy in non-Cu J c . Subsequently, the area utilizations of subelements were investigated. While for a RIT strand the fine grain (FG) A15 area occupies ~60% of a subelement, for a Tube Type strand it is no more than 40%. Further analysis indicates that the low FG area fraction in a Tube Type strand is attributed to its much larger unreacted Nb area fraction. Finally, a simple change in strand architecture is proposed to reduce the unreacted Nb area fraction.

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Section: Introductionmentioning

confidence: 96%

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

Sumption

Bhartiya

et al. 2013

Supercond. Sci. Technol.

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“…Gregory [8,9] showed the transport values of the early tube type conductors. In recent work, we have looked at higher filament count strands, and have reported non-Cu J c as high as ∼2500 A mm −2 at 12 T [10][11][12][13][14].…”

Section: Introductionmentioning

confidence: 99%

A model for phase evolution and volume expansion in tube type Nb₃Sn conductors

Sumption²,

Collings³

2013

Supercond. Sci. Technol.

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In this work, an analytic model for phase formation and volume expansion during heat treatment in tube type Nb 3 Sn strands is presented. Tube type Nb 3 Sn conductors consist of Nb or Nb-Ta alloy tube with a simple Cu/Sn binary metal insert to form the basic subelement (filament). A number of these elements, each with an outer Cu jacket, are restacked to form a multifilamentary strand. The present tube type conductors, with 4.2 K, 12 T non-Cu critical current density (J c ) in the 2000-2500 A mm −2 range and effective subelement diameters (d eff ) in the 12-36 µm range, are of interest for a number of applications. During the reaction of typical tube type strands, the Sn-Cu becomes molten and reacts with the Nb tube first to form NbSn 2 , then Nb 6 Sn 5 . At later times in the reaction sequence, all of the NbSn 2 and Nb 6 Sn 5 is converted to Nb 3 Sn. Some of the Nb 3 Sn is formed by a Nb-Sn reaction and has a fine grain (FG) structure, while some is converted from Nb 6 Sn 5 , which results in a coarse grain (CG) region. The fractions of FG and CG A15 are important in determining the final conductor properties. In this work we develop an analytic model to predict the radial extents of the various phases, and in particular the final FG and CG fractions based on the starting Nb, Cu, and Sn amounts in the subelements. The model is then compared to experimental results and seen to give reasonable agreement. By virtue of this model we outline an approach to minimize the CG regions in tube type and PIT strands and maximize the final FG area fractions. Furthermore, the volume change during the various reaction stages was also studied. It is proposed that the Sn content in the Cu-Sn alloy has a crucial influence on the radial expansion.

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Structure of superconducting layers in bronze-processed and internal-tin Nb3Sn-based wires of various designs

Deryagina

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Патраков

et al. 2017

Journal of Applied Physics

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The microstructure of Nb3Sn layers in multifilamentary composites manufactured by bronze technology and the internal-tin (IT) method differing in the strand design has been studied. The IT strands of International Thermonuclear Experimental Reactor (ITER) type and high-Jc type are characterized by both the higher Sn concentration and the higher fraction of equiaxed grains than bronze-route composites. In all the samples under study, the fraction of equiaxed grains correlates with the average concentration of Sn in Nb3Sn layers. The Ti doping of the bronze matrix in the bronze-processed wires results in the reduction in average grain sizes of Nb3Sn grains and in a higher fraction of equiaxed grains with a higher Sn concentration, which leads to a higher non-Cu Jc (calculated as a ratio of critical current Ic to a cross-sectional area of a strand without stabilizing Cu), 997 A/mm2 at 12 T, 4.2 K, compared to a composite of the same design with artificially Ti-doped Nb filaments. The ITER type IT strand demonstrates a somewhat higher fraction of equiaxed Nb3Sn grains with much larger average grain sizes (120 nm). The grain coarsening in this IT strand results in a decrease in Jc compared to other ITER type strands studied. The highest values of Jc are ensured in the high-Jc type of IT wires with 7 extended tin sources by the highest fraction (92%) of equiaxed Nb3Sn grains despite their coarser sizes (92 nm).

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COMPARISON OF A15 STOICHIOMETRY AND GRAIN MORPHOLOGY IN INTERNAL Sn AND TUBE TYPE STRANDS; INFLUENCE OF STRAND DESIGN, HTs AND ALLOYING

Cited by 3 publications

References 16 publications

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

A model for phase evolution and volume expansion in tube type Nb₃Sn conductors

Structure of superconducting layers in bronze-processed and internal-tin Nb3Sn-based wires of various designs

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COMPARISON OF A15 STOICHIOMETRY AND GRAIN MORPHOLOGY IN INTERNAL Sn AND TUBE TYPE STRANDS; INFLUENCE OF STRAND DESIGN, HTs AND ALLOYING

Cited by 3 publications

References 16 publications

Critical current densities and microstructures in rod-in-tube and tube type Nb3Sn strands—present status and prospects for improvement

Critical current densities and microstructures in rod-in-tube and tube type Nb3Sn strands—present status and prospects for improvement

A model for phase evolution and volume expansion in tube type Nb3Sn conductors

Structure of superconducting layers in bronze-processed and internal-tin Nb3Sn-based wires of various designs

Contact Info

Product

Resources

About

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

Critical current densities and microstructures in rod-in-tube and tube type Nb₃Sn strands—present status and prospects for improvement

A model for phase evolution and volume expansion in tube type Nb₃Sn conductors