RD-0158 444 ONE STEP INTERNAL TIN N83SN SUPERCONDUCTOR FABRICATION V

RD95 4 (U) OXFORD SUPERCONDUCTING TECHNOLOGY CARTERET NJI N NRANCIC MAR 85 AFURL-TR-85-2087 F336i5-93-C-2324pUNCLASSIFIED F/ 13/8 NL

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AFWAL-TR-85-2007

ONE-STEP INTERNAL-TIN Nb 3 Sn SUPERCONDUCTOR FABRICATION

Irw

I Dan Pattanayak"- William G. Marancik

SOXFORD SUPERCONDUCTING TECHNOLOGY600 MILIK STREETCARTERET, NEW JERSEY 07008

MARCH 1985

FINAL REPORT FOR PERIOD JUNE 1983 - AUGUST 1984

APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

AUG.A 91985

AERO PROPULSION LABORATORYAIR FORCE WRIGHT AERONAUTICAL LABORATORIES

C.J AIR FORCE SYSTEMS COMMAND

p- WRIGHT-PATTERSON AIR FORCE BASE, OHIO 45433

85 8 26 072

. NOTICE

When Government drawings, specifications, or other data are used for any pur-pose other than in connection with a definitely related Government procurement.operation, the United States Government thereby incurs no responsibility nor anyobligation whatsoever; and the fact that the government may have formulated,furnished, or in any way supplied the said drawings, specifications, or otherdata, is not to be regarded by implication or otherwise as in any manner licen-

.' sing the holder or any other person or corporation, or conveying any rights orpermission to manufacture, use, or sell any patented invention that may in anyway be related thereto.

* This report has been reviewed by the Information Office (O) and is releasable*to the National Tecl.nical Information Service (NTIS). At NTIS, it will be avail-

able to the general public, including foreign nations.

This technical report has been reviewed and is approved for publication.

.- NEAL C. HAROLD, CAPT, USAF PAUL R. BERTHEAUDPower Components Branch Chief, Power Components BranchAerospace Power Division Aerospace Power DivisionAero Propulsion Laboratory Aero Propulsion Laboratory

'* FOR THE COMMANDER

ROBERT E. COCHOY, T COL, USAFDeputy Director, Aerospace Power DivisionAero Propulsion Laboratory

"If your address has changed, if you wish to be removed from our mailing list,or if the addressee is no longer employed by your organization please notify

AWA! aPo(i. w-PAFB, OH 45433 to help us maintain a current mailing list".

Copies of this report should not be returned unless return is required by se-curity co.j--,erations, contractual obligations, or notice on a 1pecific document.

S"

'UffASIFIED j . i iSECURITY' C6ASSIPICATION OF TN'S PAGE f~) ~ ~ (~.L

REPORT DOCUMENTATION PAGEI& REPORT SECURITY CL.ASSIFICATION Ia. RESTRICTIVEk MARKINGSUNCLASSIFIED NIA

21LSECURITY CLASSIFICATION AUTHORI1TY 3. OISTRIBUTiONIAVAII.ABILIT? OP REPORTNA Approved.-for jpublic release; distri-

lb. OCCLASSIPICATIONOCOWNGRAOING, SCHE1DULE but ion unl imi ted.

4. FERPORMiNG ORGANIZATION REPORT NUMBERIS) S. MONITORING ORGANIZATION REPORT NuMBER(S%)

AFWAL-TR-85-2007

B.NAME Of PERFORMING ORGANIZATION IL OFFICE SYMBOL 7e. NAME OF MONITORING ORGANIZATION

OxfordAircoAero Propulsion Laboratory

Ed. ADDRESS (CICY. S44111 and ZIP Cu.d*) 7Lb ADDRESS (Cily.3.. eaand ZIP Caddo

600 Milik Street AFWAL /POOS-2Carteret, NJ 07008 Wright-Patterson AFB, OH 45433-656 3

G& AMFOUFNINGIP0NORINPIftCOFICESYOOZ *. PROCURIEMENT INSTRUMENT .0ENTIFiCAT;ON NUMBERORGANIZATION i ,Appliu.OI.)

AeoPropulsion Lab AFWALIPOOS-21 F33615-83-C-2324Bk ADDRESS (City, State od ZIP Caddo 10. SOURCE OF F UND01 N NOS

AFWAL/POOS-2 PROGRAM PROJECT TASKC W0RIK UNITELEMENT NO. NO. NO0. NO.Wright-Patterson AFB, OH 45433-6563 62203F ILIR P3 05

11. ?ITLIE (include SirteanlY Ciae,t.1cguoai Onel .Z Lep 7nLLerTn.Tin Nb3Sn Superconductor Fabrication

12. PERSONAL AUTHOR(S) WlimMrni

1,3& TYPE OP REPORT 13t& TIME COVEnev 14, DATE OF REPORT) , I..D, , 5 PAGE COUNTFinal IPRtOMiJune 83T0 Aug 84 1985 March 25

19. SUPPLEMENTAY NCTATION

N/A

17. COSATI COOSS It SUBJECTr TERMS iC0011u0u.. an Npte i f,9tI@ear and identifty by 610CAb iiintiter

PIeLO GROUP $us. ot. Superconductor Niobium Tin14 04 internal Tin

IS, ABSTRNACT (Casolie. onvi ow" 'IMw 0111il00Vd .deuifY b7 6eo 110u40011100A.twd; (2) inch diameter extrusion was packed with about 2,000 filaments by anovel technique.

Niobium Tin plated copper wires, each .010 inch diameter, were co-wound into asingle layer along solenoid with copper toil on both the inside and outside.This was compacted and slit .longitudinally to produce a ribbon with .010" Nbwires separated by 0.010" dia. Cu wire.

This contiquration was Jelley rolled into a cylinder with the Nb wires parallel

NealeraC.rHad (513). 255383 copoit cud nlLb/ranPhrug0evrade

M DST111GUIONAVILAILT VOf^41STACT31 ABTRCT SECURITY CLASSIFICATION OP145P E

................. toa d SAM . k P..1 ~cLsesUCASFE32&. . .NAM Of 111P N.L IN IID A 22.E E H N dAOG 2 F IK Y

FOREWORD

This work was an effort to produce a Nb 3Sn multifilamentsuperconductor with internal tin. In addition, an attempt was made to -1start with very small diameter Nb to reduce the effect of workhardening. Also, the tin was distributed uniformly between filaments topermit faster homogenizati.on of the tin prior to reaction, and also toavoid large area not available for Nb filaments. The techniques employedwere a radical departure from the conventional billet packing.

I wish to thank Frank Lewicki for his excellent skill in implementingthese radical techniques and the many suggestions which allowed us toaccomplish as much as we did.

IPV~cf

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* - * *

** . - - *. .. S .

SUMMARY

This program investigated the feasibility of fabricating a Nb 3Snsuperconductor with internal tin and employing only a single extrusion.

The starting materials were 0.010" dia. Nb wire and 0.010" dia. tinplated copper wire. These were co-wound into a solenoid, slitlongitudinal, and packed into an extrusion can. The billet was thenextruded and drawn.

The program demonstrated that the technique employed has potential tomeet the above requirements. Although, more work is required to producea useful product.

""

TABLE. OF CONTENTS

SECTION PAGE

I INTRODUCTION 1

11 TIN PLATING LINEI

III RIBBON FABRICATION2

IV EXTRUSION2

V WIRE DRAWING

VI HEAT TREATMENT

VII DISCUSSION

SECTION I

~INTRODUCTION

object of this research is to demonstrate the feasibility ofproducing a Nb3Sn superconductor in a single extrusion process with alarge number of filaments with internal tin. .r.

The technique chosen fE;tJLnd-4-n --i-gurc -ar2L-) uses .01'diameterNb and tin plated Cu wires formed into a solenoid. The solenoi-d iscovered with tin plated copper foil and isostatically compacted to apressure of 17,000 psi. The solenoid is slit along its length. thisresults in a ribbon about 40 inches long by about 5 inches wide, with theNb wires running across the 5 inch width.

The ribbon is then rolled up (Jelly Roll) around a 0.5 inch diameterTa covered copper rod to produce a composite of about 1.5 inches indiameter by 5 inches long. The composite geometry is now a cylindrialbundle of 0.010 inch diameter Nb wire separated from each other by tinplated copper. Each Nb wire is aligned with the axis of cylinder. Thecylinder is slid into a Ta lines copper extrusion can which is evacuatedand sealed.

The can is extruded at a low temperature and drawn to final wire sizewithout intermediate annealing.

The advantage of the process is that it is an internal tin processwith the tin uniformly distributed through the matrix. The Nb is in arelatively soft state having been fully annealed at 0.020 inch diameter.Only one extrusion is required since the bundling technique allows alarge number of wires to be precisely aligned and spaced in the matrix.

SECTION II

TIN PLATING LINE

The OAP plating line was set up to plate tin on the copper wires andfoils which were used to assemble the extrusion billet. A schematic ofthe line is shown in Figure 3.

The plating solution was made up using a commercial plating additive,as shown in Figure 4.

The plating of the wire was performed at about 10 ft./min. with adeposit thickness of 0.015 mm. No problems were encountered in thecontinuous plating of 500 ft. of 0.25 mm wire used for the billetassembly.

a.

.: .. : ~~~~~~~~~~~~~~~. :. . .] .. >...... ........... ..-..........-.... ......... ,.-....

SECTION III

RIBBON FABRICATION

The .010" Sn plated copper wire and .010" diameter Nb wire wereco-wound over a tin plated copper foil covered 1.5" diameter by 40" longmandrel. This single layer solenoid of alternate copper and niobiumwires was then overlaid with two layers of tin plated .001" thick copperfoil.

The assembly was wrapped in a protective layer of copper foil (to beremoved later), and this, in turn, painted with a plastic to seal againstleakage during isostatic compaction.

The plastic sealed assembly was then isostatically compacted to17000 psi. The compaction is required to remove the majority of voids inthe composite.

After compaction, the plastic sealant and outer layer of copper foilwas removed, and the remainder of the assembly was heated at 330 0C forS minutes to bond the assembly together.

After heating, the copper clad solenoid (Figure 5 and 6) was slitlongitudinally and slid off the steel mandrel. The slit solenoid wasflattened to form a ribbon about 4.5" wide, 0.018" thick, and 40" long.The ribbon contained about 2,000 wires of Nb separated by copper.

This was then wound around a 0.5" diameter Ta clad copper core rod.This was slid into a Ta line copper extrusion billet. The billet waswelded, evacuated, and sealed.

SECTION IV

EXTRUSION

Prior to extrusion of the multifilament billet, two solid copperbillets were extruded. The first was extruded at approximately 2000C,and the second at 1000C. Based on the extrusion pressure and thetemperature of the exiting rod, it was decided to extrude themultifilament billet at room temperature.

The multifilament Jelly Roll billet was extruded at roomtemperature. The extrusion went very well, and no external defects couldbe seen. The filament size distribution is large, as shown in Figure 7.

This is due to an excessive void fraction in the filament area in thebillet prior to extrusion. An isostatic compaction of the billet willeliminate this defect.

2.

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SECTION V

WIRE DRAWING

The extruded rod was cut into approximately 15 cm long pieces fordrawing experiment. The initial drawing was made on a 20% area reductionschedule. The piece was drawn as extruded with the entire outer copperstabilizer in place. Only two draw passes could be made before the outersurface of the rod showed indications of center burst.

A second piece of the extruded rod was machined to reduce the amountof copper in an attempt to get a more equitable distribution of work intothe rod during the drawing process. This, too, resulted in center burstafter a few die passes.

A third attempt to draw a piece of the extrusion was made byincreasing the area reduction per pass to approximately 27%. This gavethe same results as the previous drawing experiments.

SECTION VI

HEAT TREATMENT AND DIFFUSION STUDIES

Cold drawings of the Oxford Jelly Roll billet was abandoned becauseof non-uniform deformation in Nb-Cu warped portion of the billet. Someof the broken rods had been heat treated at below the melting point of Snand then subsequently annealed at 2200 and 750 0 C for several hours.The diffusion of Sn into Cu and Sn from bronze to Nb interface wasstudied. Three specimens have been used for S.E.M. investigation.

SPECIMENS

1) Diameter of spec. 0.475" diameter. (As received).

2) 220OC/40 hours.

3) 220oC/48 hrs. + 250oC/50 hrs. + 340oC/200 hrs. +550oC/l00 hrs. + 750oC/100 hrs.

The transversal section of these specimens were polished andsubsequently etched. The micrograph of the Specimen 1 (Figure 8 and 8a)shows a large number of voids are present between the Nb-Cu wire layerand Sn plated Cu layer. The voids were not removed even after isostaticpressure. These voids have been developed due to uneven distribution ofSn on Cu surface. Some of the Nb wire showed no bonding with thesurrounding region (Figure 9). These defect structures, which arepresent from the initial stage of process, could lead to internalfracture in subsequent cold drawing.

The Speciment 2 (Figure 10 and 10a) shows microstructure after the48 hour heat treatment at 220 0 C. It seems the bonding gaps around theNh wire has become wider. No bronze layer was found between Sn and Cuinterface by S.E.M. studies, but the wider gap around Nb indicated thatSn diffusion has taken place - Sn has gone into solution in Cu, leavingbehind Sn vacancies, which is the cause of wider gap around Nb.

Specimen 3 (Figure 11) shows the reaction at 7500C has produced1.5 - 2 micrometers thickness of Nb 3Sn. Also, Sn has diffused intoCu. (Figure 12) shows the bonding between Cu-Cu interface.

3,

SECTION VII

DISCUSSION

Center burst, an effect due to excessive strain developed along theentral axis of the rod, is a result of the inhomogeneous forceistribution in the die area during drawing. The effect is a function ofrea reduction, die angle, configuration of the rod, and relative tensiletrength of the various components making up the rod.

Cross sections taken at about 1/8" internals (Figure 13) shows theffect of the non-uniform distribution of work into the rod. Voidscenter burst) have developed in or around the copper core. In some(reas the core is missing.

Various steps can be taken to minimize or eliminate the problem.hey are as follows:

0 Isostatically compact the billet to eliminate all voids prior toextrusion. This will result in a more uniform distribution of thefilaments, and this produce better drawing characteristics in theextruded rod.

'' Change the geometery of the packed billet by eliminating the coppercore and reducing the amount of copper on the outer surface.

:) Substitute Sn 7 w/o Cu alloy in place of the pure tin plating on thecopper wires and foils used to assemble the billet. This will resultin a better yield strength compatability of the various components.

In general, it appears with better compacting and electroplatingrSn + 7 Wt. % Cu) on Cu, a better result can be achieved. Hydrostaticextrusion at elevated temperature would further improve the soundworkability of the billet. Probably, Nb + Cu wire of rectangularcross-section would decrease the void density. An improvement in rodsand bonding gaps could be achieved if compacting is carried out at220 0 C.

At new attempt should be made wit the above mentioned modification tonake this Jelly Roll an alternative and economically feasible process.

4

LIST OF ILLUSTRATIONS

[GURE NUMBER PAGE

1. Single Extrusion Process For Multifilament Tin 7 & 8

2. Assembly Into Extrusion Can 9 & 10

3. Tin Plating Line 11

4. Plating Solution 12

5. Copper Clad Solenoid After Heating 13

6. loX Magnification Of Solenoid 13

7. Extruded Billet Showing Filament Size Distribution 14

8. 200X Cross Section Of Extruded Billet 15

8a. 480X Cross Section Of Extruded Billet is

9. 480X Cross Section Of Extruded Billet 16

10. 300X After 48 Hours At 200 0 C 16

10a. 1500X After 48 Hours At 200 0C 17

11. 800X After Heat Treatment At 7500C 17

12. Bonding At Cu-Cu Interface 18

13. Center Burst Of Conductor 19 20

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7- 7 7.7

Stannous Sulfate 30 g/L

Sulfuric Acid 60 gIL

*Starter P 50 ml/L

Temperature 200C

Agitation None

Cathode Current 50 Amps/ft2

Density

Filtration Continuous 2 micrometers

Anodes 99.95% Tin

* Product of Lea Ronal, Freeport, New York

Fig. 4 Plating Solution

S Fig. 5 Copper Clad Solenoid After Heating

Fig. 6 lox Magnification Of Solenoid

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i Fig. 7 Extruded Billet Showing

Filament Size Distribution1

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