Status and perspective of the Nb3Al development in Japan

Workshop on Accelerator Magnet Superconductors, Mar. 22-24, 2004

T. TakeuchiNat. Inst. Materials Sci. (NIMS)

K. TsuchiyaHigh Energy Accel. Res. Organ. (KEK)

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8

0.8

0.9

1.0B*

c2/B*c2m

Nb3Ge

V3Si Nb3Sn(Ta,H)

Nb3Sn(Ti,Hf,Ga)

V3Ga

Nb3Al

by EkinIntrinsic Strain (%)

better strain tolerancehigher Bc2(4.2K): 30 T

Advantages of RHQT Nb3Al over Nb3Sn

Large scale applicationFusion, Accelerator

Advantages of RHQT Nb3Al over HTS

• Easy superconducting joint• Large n-value• Tolerance to stress and strain

• High-field NMR spectroscopy

Application

Specification of Nb3Al conductor for NMR uses

• Rectangular • Stabilizer (Cu clad)• Nb matrix (superconducting) • DC (filament diameter, spacing)• Optimization of Jc (4.2K) at 21 T

Explored processes to achieve stoichiometrywithout grain coarsening

∼55

2600

600

1000

1400

1800

2200

100 20 30 40 50 60 70 80 90 100

Nb

Nb 3

Al

Nb2Al

NbA

l 3Tem

pera

ture

(° C

)Atomic Percent AluminumNb Al

∼28

2469°C

2060°C±10

1940°C

1680°C1590°C

42

661.4°C

660.45°C

32

II

I II'

Manufacture: binary reaction, Al dimension: < 100nm

Cu or Nb rodNb sheet

Al sheet

Diffusion process (750oC x 50h)

RHQT process (1900oC + 800oCx10h) New process (TRUQ, DRHQ)

11-14 T, off-stoichiometryCu-matrix JR

12-23 T, stacking faultsNb-matrix JR

21-25 T

Advanced A15 Compounds• Nb3Al• Nb3Ga• Nb3(Al,Ge)

Off-stoichiometry at LT

RHQT technique(rapid-heating, quenching and transformation)

stoichiometrywithout grain growth

Case of Nb3Al

New approachNew approach

Joule Heating+

Quenching

Precursor：Nb/JR Nb/Al

Nb/Nb(Al)ss

Winding+

Transformation

Cu/Nb/Nb(Al)ss

Cu cladding

Cu/Nb/Nb3Al

Extrusion + Drawing

bcc supersaturated solid solution

stoichiometryfine grain

Cu or Nb rodNb sheet

Al sheet

Jelly-roll

Nb rod

Rapid Heating, Quenching and Transformation process

Long-length of RHQ processing

• Plateau region (150oC): optimum• Insensitivity to unwanted

temperature scatter• Uniformity of SC properties along a

long-length of wire

1.00 1.05 1.101

10

100

17.0

17.5

18.0

18.5

4.2 K

24T

23T

22T

21T

20T

19T

Crit

ical

Cur

rent

Den

sity

(A/

mm

2 )

Normalized Heating Current iRHQ

M9-4Current: 30mA

Crit

ical

Tem

pera

ture

(K)

bccA15+σ bcc Al-poor bcc + liquidbrittle ductile (not brittle) ductile

two phase extendedsolid solution

partialmelting

completemelting

→ Tmax

1910oC 2060oC10.5 A

25at%Al

20 25 30

98

100

102

104

106

108

110

I RHQ(T

max

) (A)

at.% Al

bcc

Liquid

optimum

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0 200 400 600 800 10000

2

4

6

8

10

12

Wire diam.: 1.35 mmφNb/Nb3Al ratio: 0.81Fil. No.: 132Fil. diam.: 89 µm

RHQ Duration (s)

(a) Current variation

Shun

t Vol

tage

(V)

(b) Voltage variation

Volta

ge b

etw

een

Elec

trode

s (V

)

Nb matrix

Filament

0 50 100 150 200 250 300

100

150

200

250

300

17.0

17.2

17.4

17.6

17.8

18.0

Crit

ical

Tem

pera

ture

(K)

Crit

ical

Cur

rent

(A)

Position along a 300 m length of conductor (m)

Ic@4.2 K 21T 20T 19T

Tc

Distributions of Tc and Jc along a 300 m length of wire

Standard deviation of Jc (4.2K&21T) : 5 %

・Constant current power supply

Deformability of Nb(Al)ss at RT

0 2 4 6 8 10 12 140

200

400

600

800

1000

1200600oC 500oC

400oC300oC

without pre-annealing

Sample #1 (1.275mmφ, 0%RA) Temperature: 20oC Strain Rate: 6.25 x 10-4 sec-1

Stre

ss (M

Pa)

Tensile Strain (%)

Cu

Nb(Al)ss

Nb sheath

0.3mm

0 20 40 600

100

200

300

400

Cu-cladding JR Nb 3Al

Jc21T

J c (A

/mm

2 )

Reduction in Area, R.A. (%)

0

100

200

300

21 T4.2 K

I c (A

)

Ic21T

Incorporation of Cu stabilizerby mechanical cladding

Jc improvement

Tensile test at room temperature

Temperature ramp-up rate at transformation annealing

19 20 21 22 23 24 25

4.2 K

40%RA800oCx10h

B (T)

Ramp Rate 1h/800oC 2h/800oC 4h/800oC 6h/800oC 10h/800oC

19 20 21 22 23 24 25

0

100

200

300

400

500

600

4.2 K

Ramp Rate 1h/800oC 2h/800oC 4h/800oC 6h/800oC 10h/800oC

core

Jc

(A/m

m2 )

B (T)

0% RA800oCx10h

0 2 4 6 8 10 12 14 1617.3

17.4

17.5

17.6

17.7

17.8

0% RA

40% RA

T c (K

)

Ramp-Up Time to 800oC, t (h)

M9-4

M9-4 M9-4

DeformationJc enhancementLess sensitive to ramp rate

-10 -5 0 5 10 15 200

200

400

600

800

1000Transformation HT profilefor a W&R coil

Tem

pera

ture

(o C

)

Heat Treatment Time (h)

TABLE I SPECIFICATIONS OF WIND & REACT NB3AL SOLENOID COILS

Previous M11-1

Present ME332

Present ME356

RHQT JR Nb3Al con-ductor

Stabilizer Cu-clad Cu-clad Cu-clad Piece length (m) 35 370 370

Cross section (mm2) 1.61x0.71 1.82x0.84 1.81x0.80 Filament diameter 70 74 75.5 Number of filaments 84 132 132 Cu/non-Cu ratio 0.45 0.38 0.39 Insulator Al2O3 fiber Al2O3 fiber Al2O3 fiber

Winding Inner diameter (mm) 19.7 90.2 64.6 Outer diameter (mm) 40.8 111.8 99.3 Height (mm) 49.7 200 132.4 Number of turns 311 949 988 Total length of wire 30 300.5 254

Coil Impregnation Beeswax Beeswax Beeswax Transformation RT? (5h) ? 800oC? (10h) ? 800oC? RT Coil constant (T/A) 0.00106 0.00562 0.00797

Coil specifications

n-value (10-5 – 10-4 V/m)

Consistency of Icpoint, tail of 370 m

n-value25@21T,4.2K

0.3 mm(e)

CuNb

17 18 19 20 21 22 23 24 25 260

100

200

300

400

500

0

50

100

150

200

250

300

17 18 19 20 21 22 23 24 25 26

0

5

10

15

20

25

30

35

0

100

200

300

400

500

4.2 K

0.1 µV/cm criterion

370 m length of Cu-clad conductor

I c

(A)

B (T)

Ic_point Ic_tail

overall J

c (A/mm2)

voltage taps specing:25cmfitting range: 2.5µV-25µV

V = Const.In

n-in

dex

n value_point n value_tail

J c (A/mm2)

Iq (coil) > 0.9 Ic (short samples)

Uniformity of a long-length of RHQ operation over 300 m

・Loading test

14 16 18 20 22 24 260

100

200

300

400

50014 16 18 20 22 24 26

0

100

200

300

400

500

0

50

100

150

200

250

300

0

50

100

150

200

250

300

3.2 T

1.8 K

4.2 K (b)

ME365 64.6I.D.x99.3O.D.x132H mm3

254 m, 988 turns

C

urre

nt, I

(A)

Magnetic Field, B (T)

Ic_point Ic_tail Quench Current load line

2.3 T

4.2 K (a)

90.2I.D.x111.8O.D.x200H mm3

300.5 m, 949 turnsME332

Cur

rent

, I (A

)

Ic_point Ic_tail Quench Current load line

Ove

rall

J (A

/mm

2 ) O

vera

ll J

(A/m

m2 )

NMR coil Jc

・RHQT Nb3Al is really reliable for practical coil application.

0

500

1000

1500

2000

2500

6 8 10 12 14 16 18

M13-1-80.6(0.69)M13-2-79.3(0.69)M13-2-80.6(0.69)M13-3-79.3(0.69)M13-3-80.6(0.69)M13-4-79.3(0.69)M13-4-80.6(0.69)M13-5-81.8(0.69)

Jc n

on C

u (A

/mm

2 )

B (T)

KEK

• 1 kA Ic probe• Measurement of Jc of round wire

electroplated with Cu in fields from 8 to 17 T

• Optimizationwire diameter: 0.8 0.69 mmRA: 20% (< 40% for 21T)transformation HT: 775oC15h

• Highest Jc:1730 A/mm2 at 10 T

Sample length: 300 mmLarge cross section of Cu: 72 mm2

Heating at 1000 A: < 80 mW/lead(∆T < 10 mK)

Internal Stabilization

0 10 20 30 40 500

20

40

60

80

100

120

140

160

180

200

RR

R

Stabilizer/Non-stabilizer Ratio

Cu Ag Ta/Cu (no stabilizer)

1. Less expensive2. Round cross section of wire3. Possible high current conductors (CICC,

Rutherford cables, etc)4. No contamination of Ag with Ga5. Large RRR (200)6. Applicability to high temperature

transformation (TRUQ, DRHQ)

5mm

The 1st triplet: a Nb3Al, two Cu

0.8 mmΦAg/non-Ag:0.17

CableCable--inin--Conduit ConductorConduit Conductorfor Fusion Usesfor Fusion Uses

The third stage cable: 3 x 4 x 4

SUS conduit

CuNb3Al

SUS tape

Trial Manufactureof High-Current RHQT Nb3Al Conductors

12 14 16 18 20 22 240

1000

2000

3000

4000

5000

6000

Ic_point strand Ic_tail strand Ic_tail strand Ic_point x 16 Ic_tail x 16 Ic_tail x16 CIC conductor

4.2 K

Crit

ical

Cur

rent

, Ic (

A)

Magnetic Field, B (T)

Measure: 3.49 kADesign (Ic, strand x 16): 3.7 – 4.3 kA

Ic at 14 T

7% degradationInternally stabilized Nb3Al strand

Measurement_1

V taps spacing: 100 mm, 375 mmCurrent ramp rate: 30A/sec, 60A/sec

0 500 1000 1500 2000 2500 3000 3500 4000-50

0

50

100

150

200

V taps spacing: 375 mm

V taps spacing: 100 mm

4.2 K

14T, 30A/sec,1st

Vol

tage

(µV

)Current (A)

Table 1 Specifications of measured JR Nb3Al wires.

Sample #1 #2 #3

Diameter of wire (mm) 0.507 0.89 1.275

Number of filaments 36 84 84

Diameter of filament

(µm)

55 76 108

Average thickness

between filaments (µm)2.8 6 9.4

Nb/Non-Nb ratio 1.5 1.39 0.59

• bridging• proximity effect

AC Loss

Matrix: NbFlux jump

Not desirable for fusion and accelerator magnets

RHQT JR Nb3Al

Manufacture of Ta matrix JR Nb3Al wire

Ta tube (sheath)Ta dummy

Ta barrier

Ta core

Nb/AlJerry-roll

2 other filament structures

Ta core-Nb barrier Nb core-Nb barrier(conventional)

Ta core-Ta barrier

by Tatsumi et al

Workability

1.5φ65μm66Φ0.8mm

Matrix ratio(non JR / JR)

Filament diameter

No of filaments

Wire Diamete

r

Good (no breakage)

Good (no breakage)

Very Good(no breakage until

φ0.5mm)

Workability

Cross sectio

n

Nb core-Nb barrier(ﾌｨﾗﾒﾝﾄ間:Nb

JRｺｱ:Nb)

Ta core-Nb barrier(ﾌｨﾗﾒﾝﾄ間:Nb

JRｺｱ:Ta)

Ta core-Ta barrier(ﾌｨﾗﾒﾝﾄ間:Ta

JRｺｱ:Ta)

Structure

Magnetization curve

-10000 -5000 0 5000 10000

-0.1

0.0

0.1

Ta/Nb3Al ratio:1.53Fil. diam:64.7µm

Ta matrix 4.2K Ta matrix 10K

m (e

mu/

mm

3 )

H (Oe)-10000 -5000 0 5000 10000

-0.3

-0.2

-0.1

0.0

0.1

0.2

0.3 Nb matrix 4.2K Nb matrix 10K

m (e

mu/

mm

3 )H (Oe)

Nb/Nb3Al ratio:0.59Fil. diam:79.7µm

Ta matrix suppression of flux jump

Other advantages・high strength at high temperature・no formation of Ga-rich compound

on a surface・less induced-radioactivity

Potential of RHQT Nb3Al

20 22 24 26 280

100

200

300

400

4.2 K

no

n C

u J c

(A/m

m2 )

B (T)

RHQT Nb3Al TRUQ Nb3Al DRHQ Nb3Al RRP Nb3Sn (OST) 16 % Sn Bronze Nb3Sn 14 % Sn Bronze Nb3Sn

A15-typeNb3Al

bcc Nb(Al)ss

1 200

1 000

800

600

400

200

0

10 sec~10 min

trans

form

atio

nhe

at

free energyTe

mpe

ratu

re (°

C)

Time

10 h

TRUQ:time for 1 to 3 steps < 0.3 sec

(b)

(c)

propagation of heat

untransformedparttransformed

part

(a)sample

1

2

3

4

TRUQ (TRansformation-heat-based Up-Quenching)

1. ignition (nucleation of transformation)2. thermal explosion ·propagation of the transformation interface ·trasform to A15 via highly disordered bcc phase low long-range order free from stacking faults3. self-turn down to ambient temperature4. annealing for long-range order

similar to a combustion synthesis

TRUQ

Microstructure

40 nm40 nm40 nm40 nm

TRUQ

RHQT

SF

SF

TEM像

SGB

SGB

0 20 40 60

Ave. 8.8 nm

Ave. 19.7 nm

Distance between Adjacent Stacking Faults

19.7 nm

8.8 nm

TRUQ

RHQT

0 20 40 60

Ave.34 nm

Ave. 52 nm

Subgrain Diameter (nm)

52 nm

34 nmTRUQ

RHQT

By N. Banno et al.

Non-uniformity

10 12 14 16 18 20

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

norm

aliz

ed χ

', χ"

Temperature (K)

TRUQ χ' TRUQ χ" 700C-10h/800C-10h χ' 700C-10h/800C-10h χ" 800C-10h χ' 800C-10h χ"

16.0 16.5 17.0 17.5 18.0 18.50.00

0.05

0.10

0.15

0.37

0.350.24

χ"

Temp (K)

Microchemical homogeneity in filaments

↓Sharp transition

↓Enhancement in Jc

a) as-quenched wire at 1.27 mm and b) after Cu-cladding and forming into tape.

Microstructure by FESEM by P. Lee

Optimization for Jc

• Wire diameter• Nb matrix ratio• No. of JR filaments• Filament diameter• Inter-filament spacing• Nb/Al ratio• layer thickness• Alloying

• Joule heating current density

• Heating distance• Wire speed at RHQ• R.A. after RHQ• Transformation HT

under the condition of ordinary transformationthat enables W&R coil (～800oC, ramp rate of 1-5 h/800oC)

Parameters

MicrochemistryCrystal imperfection

bcc grain, orderingA15 grainStacking faults

Ongoing improvement of JR Nb3Al

by Iijima and Takeuchi20 22 24 26 28

0

100

200

300

400

230

1864.2 K

non

Cu

J c (A

/mm

2 )

B (T)

RHQT Nb3Al TRUQ Nb3Al DRHQ Nb3Al RRP Nb3Sn (OST) 16 % Sn Bronze Nb3Sn (Kobe) 14 % Sn Bronze Nb3Sn optimaization ongoing RHQT Nb3Al

Development Schedule

• Long-length of precursor (>2km)large billet

• Long-length of RHQ processing (>2km)large-scale RHQ apparatus: under construction

• Reel-to-reel Cu ion platinginstallation, trial operation

Target: piece length of more than 2 km for 1.35 mmφ wire

Multifilament billet (50kg)

Piece-length: 2.6 km for Φ 1.35 mm wire

Φ 2. 9 mm Φ 1. 75 mm

Φ 1. 50 mm

Φ 8. 4 mm Φ 5.9 mm

No breaking during drawing of wire

(corresponding to 9.7 km for Φ 0.7 mm wire)

Prototype RHQ-apparatus

• >2 km length of 1.35mmΦ precursor-wire

Prototype reel-to-reel ion plating apparatus

Reel-to-reel Cu ion plating apparatus_2

Summary• Large multifilament billet: 52 kg • Piece length of precursor (1.35 mm): 2.6 km• RHQ apparatus: just installed

300 m ? km• Non-Cu Jc improvement (21T): Ongoing• Stabilization of a round wire

internal stabilizationCu ion plating and electroplating