TUNGSTEN ALLOY DEVELOPMENT AS ADVANCED TARGET MATERIAL

FOR HIGH-POWER PROTON ACCELERATOR

Muon, MLF, J-PARC Center IMSS, KEKShunsuke MakimuraHiroaki Kurishita

Metal Technology Co., LTDKoichi NiikuraHun-Chea Jung Masahiro OnoiYutaka Nagasawa

RaDIATE_CM@CERN (Through TV meeting system) 20th. December 2018

History of this research

2

Tohoku University (by Prof. Kurishita till 2013) Ultra Fine Grained Recrystallized WNot ductile at RT

Toughened Fine-Grained Recrystallized (TFGR) WDuctile at RT, With Grain Boundary Sliding Based Microstructural Modification

KEK-MTC (since 2016) Revival of TFGR W with GSMM Further progress of the material development. Application to Industry

Technology & Patent transfer

GSMM

till 2008

till 2013

Collaboration

3

Collaborative researchKEKMetal Technology Co., LTD

Supply to some venders,,, Economical manufacturing Increment of sizeApplication to industry

Ehime University National Institute of Fusion

Science CERNAdvanced material research

Thanks to everyone Your collaboration is welcome.

Tungsten as Target Material

Why, Tungsten as target material?e.g. MLF 2nd target station

Candidates of target

Liquid metal (Pb-Bi, Hg)

Tantalum clad tungsten

Tungsten rotating target

Current MLF facility: tandem target

MLF 2nd target station: common target

Will be submitted as next Master plan to Science Council of JapanCommon target for muons & neutronsproduction10 times higher brightness of muons & neutrons

Density Totalheat load

Heat density(a.u.)

g/cc kW@1MW

W 19.3 476 1.557

Hg 13.5 402 1.000

Pb 11.4 368 0.764

PbBi 10.6 357 0.704

Fe 7.87 331 0.591

Rotating Tungsten target at ESS

Tungsten as target materialFrom Yongjoong san’s slides at HPTW 2016

• 2 GeV/ 2.5 mA avg. (5 MW)• Long pulse: 2.86 ms/14 Hz

6mm Diameter Tungsten target

Mu2e target at Fermi Lab (Developed by STFC)

From Peter Loveridge ’s slides at HPTW2016

• 8 GeV/ 1 μA avg. (8 kW)• Radius of Beam spot: 1mm (1 sigma)• Thermal radiation cooling (560 W on target)

J-PARC/COMET phase 2 W targetISIS, ORNL-SNS2, C-ADS,,,

Toughened Fine-Grained Recrystallized Tungsten (TFGR W),developed at Tohoku University

load

J.Reiser et al. JNM, 423 (2012) 1.

tough

brittle

Pure W foil : ductile

loadRecrystallized grain structure by heating at and above Tr

Fiber grain structure by heavy plastic working

GB fracture :

Current structure modification to mitigate GB fracture

Equiaxed, especially after recrystallization

The use of W is limited below Tr (Tr : ~0.4Tm for stress relieved pure W )

PLANSEE

Radiation embrittlement : caused by radiation induced lattice defects whichimpede the movement of dislocations (radiation hardening)

Accumulation of radiation induced point defects can be suppressed byintroducing sinks : Dispersoids (precipitates) and GBs

The use of W as target material is limited by1. Recrystallization embrittlement2. Radiation-induced embrittlement

8

In general,

Equiaxed, fine grains with TiCprecipitates

GB reinforced by TiC enrichment Recrystallized state High sink density DBTT (nil-ductility tem.) < RT

9

Toughened Fine-Grained Recrystallized Tungsten

(TFGR W)Originally developed for fusion reactor material at Tohoku Univ. by Prof. Kurishita

H. Kurishita et al. Mater. Trans. 54 (2013) 456-465.

50 nm

500 nm

Before GSMM After GSMM

GSMM: Slow deformation at High Temperature

Toughened Fine-Grained Recrystallized Tungsten

(TFGR W-TiC)

Stre

ss(M

Pa)

1500

500

1000

2000

2500

1320 1230

Strain

840 870

250 320

Z

10 mm t

0

XY

Number is fracture strength

W-1.1TiC/H2

0

1000

2000

3000

4000

5000

0 0.005 0.01 0.015 0.02 0.025

StrainSt

ress

(MPa

)

σy

1650 degC GSMMFracture strength: 3200 MPa

TFGR~W at RT

5 μm

2150

1.5 mm t

1100

Y

Ductility is improved with orientation by heavy plastic working.But, Brittle after anneal.

As-received1240˚C x 1 hr anneal

Z

XW plate (hot rolling)

Y

H. Kurishita et al. Mater. Trans. 54 (2013) 456-465.

In 3-point bending testing of TFGR at RT, ductility is shown after annealing . 10

H. Noto et al., 2013

Pure hot-rolled W

Insufficient research for irradiation effect of W-TiC

11

600

800

1000

1200

Before irr. After irr.

521

1039

1164 1108

1034

619

HV

Nanostructured W-0.5TiC/Ar)

Nanostructured W-0.5TiC/H

Pure W (Commercially available, SR）

Vickers microhardness

・ No radiation hardeningΔHV = 98

H.Kurishita et al. JNM 377 (2008) 34.

Tirr = 873K, 2×1024n/m2 (En >1 MeV), 0.08 dpa, JMTR

W/O GSMM H.Kurishita et al. Phys. Scr. T159(2014)014032

TFGR-W

Tirr = RT, 1-2×1019ions/m2 (2.4 MeV Cu2+), 2-4 dpa, Tohoku Univ. IMRTirr = RT, 1×1021D2+/m2 (2.0 keV D2+)

Thermal Desorption Spectroscopy of D2

The D retention in pure W is significantly increased by Cu2+ irradiation, while that in TFGR is relatively insensitive to the damage level.

Irradiation effect research of TFGR is mainly for D retention.

Current Status of TFGR W Development(KEK-MTC collaboration)

Current status of W development (1)Preparation and handling of purified powders

Setup of High-purity glove box (GB)with vacuum chamber/furnace forhanding highly pure powders withoutgaseous contaminations• Purification and (remote) handling

of starting powders (W, TiCx,) andMAed powders (W-Ti-C)

• Fully degassing of MA vessels andballs, HIP capsule etc. before use

High-Purity GB, KEK/MTCWith Baking system

Typical GB

Impurity O N Mo O N MoContent(wt%) 0.091 0.009 1.98 1.0 0.18 1.25

Powders inTa boat forpurification

Comparison of impurity content in MAed powder

Current status of W development (2)Mechanical Alloying (MA) in vacuum

Setup of 3MPDA high energy ball mill withcooling system (~ -20ºC) to prevent strongadhesion of MAed powder to the vessel inner walls

MA: Introduction of ultrafine grains (~20 nm) andalloying by using high energy ball milling

Mo impurity (~ 2%)coming from TZMballs and vessels

3MPDA

(a) SEM, (b) EDS(Ti)mapping for MAedW-1.2%TiC powder

Powder with hard ballsin a vessel (TZM)

(a)

(b)

The MA Vessel is filled withPrevious work: Hydrogen, This work: Vacuum

3MPDA: 3 Mutually Perpendicular Directions Agitation

Current status of W development (3)HIP (Hot Isostatic Pressing)

HIP: Densification of MAed powder without exposure to airDensified compacts with equiaxed, ultra-fine grains

HIPed W-1.2wt%TiC compactDensity : 17.92 g/cm3

Ti C O N Mo

HIPed compact 0.88 0.23 0.038 0.010 ---MAed powder --- --- 0.091 0.009 1.98

Chemical compositions (wt%) of W-1.2%TiC before and after HIP

Steel capsule filled with MAed W-1.2%TiC powder

3h

GSMM (Grain boundary sliding-based microstructural modification) process

GSMM : Reinforcement of intrinsically weak GBs in W by enhancement and optimization of TiC precipitation and their segregationRemoval of the residual bubbles/pores through GB diffusion

γ (shear strain) γ = 0 γ = 1 γ = 2

Shear stress

N. Wakai, Materia 45 (2006) 644.

8φ x 20 mm

Reduction ratio: 85.3%1650ºC

Superplastic deformation by GB sliding at high temperature

The number of GSMM operationsat 1650ºC attempted to date is 10times with various final loads

by using superplastic deformation, driven by GB sliding, where the recrystallized,equiaxed grain geometry is maintained and active grain rotation and extensiverelative displacement of the adjacent grains are operative.

Three point bend (3PB) testing at RT3PB testing : Demonstrate that the fabricated W alloys exhibit very high fracture strength ( > 2~3 GPa) and appreciable ductility at RT in the nanostructured, recrystallized state

Specimen deflection during 3PB testing

3PB specimen1.1 mm x 0.9 mm x 15 mm

3PB test fixture usedOverview of 3PB testing at RT and 0.3mm/min

3PB test results at RTW-1.2wt%TiC in the nanostructured, recrystallized state#8 specimen: MA-HIP-GSMM (RR : 82. 9%)

Very high fracture strengthof 2590 MPa and slightductility at RT→ TFGR (Toughened, FineGrained, Recrystallized) W-1.2%TiC alloy

#8 specimen brokenin two pieces aftertesting

In order to manufacture muchmore ductile W-1.2%TiCalloys, the microstructure ofthe #8 specimen hasthoroughly been examined.

SEM

Microstructures of #8 specimen SEM, EDS

Ti

EDS

OC

3 μm

A large precipitate of titanium oxy-carbide with approximately 1 μm diameterobserved is attributable to locally insufficient progress of the MA process; thestarting TiC phase has not completely been decomposed into Ti and C solutes in theW matrix by MA. The optimization of the MA process is required for ductilityenhancement of W-1.2%TiC alloy.

TEM analysis by Prof. Sakamoto at Ehime University will come soon.

Thermal shock experiment of TFGR W at CERN-HiRadMat (HRT48 PROTAD, Sep. 28, 2018)

Thanks to CERN team and Ishida-san

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Beam ParametersBeam energy 440 GeV

Max. bunch intensity 1.2 x 1011

No. of bunches 1 – 288

Max. pulse intensity 3.5 x 1013 ppp

Max. pulse length 7.2 µs

Gaussian beam size 1σ: 0.1 – 2 mm

Current achievement and future plan

21

High fracture strength of 2590 MPa and slight ductility at RT. But not enough.

TFGR W at Tohoku Univ. TFGR W at KEK-MTC

H. Kurishita et al. Phys. Scr. T159 (2014) 014032.

Future plan: Economical manufacturing and Increment of size Further advanced research

Requirement: Proton Irradiation Opportunity

MA process should be optimized. Gas impurity should be reduced.

We are here

SUMMARY

22

1. Tungsten is expected as target material.2. Use of tungsten is limited by Recrystallized and Radiation-

induced embrittlement.3. Toughened Fine-Grained Recrystallized Tungsten (TFGR W-

TiC), developed at Tohoku University has a possibility to solve these embrittlement.

4. The development of TFGR is transferred to KEK-MTC collaboration.

5. High fracture strength and slight ductility is confirmed.6. Further development is expected.

Thank you for your attention!!