Workshop on Steels

1
Hot Dip Aluminizing Process for TBM
applications- An Overview

• Nirav I. Jamnapara, S. Mukherjee, P. M. Raole, E.
  Rajendrakumar
• INSTITUTE FOR PLASMA RESEARCH
• Gandhinagar 382044, India

2
About LLCB

• Solid Liquid Breeder Concept
• Li2TiO3 pebbles as solid breeder Pb-17Li
  Eutectic as liquid breeder.

Fig 1 Open view of LLCB TBM
3
Schematic
450-900 ?C
460 ?C PbLi out
325 ?C PbLi in
2
4
Environment Challenges

• Liquid Pb-17Li _at_ 1.2 MPa, 325-460 ?C, 0.5-1 m/s
  velocities 1 Hot Corrosion-erosion
• T generation in CB Pb-Li circuits 1
• Tritium permeation through FMS
• Thermal Cycles 1
• MHD effects 1 Insulation needed

5
Why coating?
Fig 3 T permeation into coolant from Pb-17Li
blanket by Reiter 2
Fig 4 Permeability of several metals by P.S.
Korinko 3
Crsn
6
Ideal Coating Should

• Protect FMS against corrosion from Pb-17Li (gt
  10,000 hrs) 5, 6
• Resist Tritium permeation through FMS (PRF gt 75
  in Pb-17Li conditions) 4
• Maintain thermal compatibility (?)
• be Electrically insulating (to resist MHD
  effects)
• not affect heat transfer
• be easy to apply on substrates

7
Candidate coatings
8
Why Aluminide coating?

• Good resistance to T permeation
• Good corrosion resistance of FMS against liquid
  Pb-Li (480 550 ?C)
• Thermally compatible
• Electrically Insulating top layer (Al2O3)
• Volume resistivity 0.01 ? m
• EU Fusion Technology Program has considered
  aluminide coatings as reference coating (HDA
  CVD) as tritium permeation barriers.
• Ref 09 J. Konys et. al., FZK Germany

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Comparison
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Why Hot Dip Aluminizing?

• Aluminizing possible by solid, liquid gas
  processing 3
• Better PRFs with H2 as compared to CVD (J. Konys
  FZK, Germany, 4)
• Ease of processing complex geometries
• Scalable
• Adherent alumina by oxidation of surface

11
Targeted Aluminide Coating

• Intermetallic Fe-Al Al2O3

1-10 ?m Al2O3 (for resistance to corrosion, MHD
and Erosion)
150-180 ?m Intermetallic Fe-Al (for Tritium
Permeation Resistance)
Ref J. Konys et. al., FZK 4,5
12
Targeted Microstructures
Parameters for hot dipping temperature at 700C
and dipping time of 30 s
Microstructure of hot dipped surface
Microstructure after heat treatment
Al
Fe2Al5
F82H-mod.
The alloyed surface layer consists of brittle
Fe2Al5, covered by solidified Al
Heat treatment at 1040C/0.5 h 750C/1 h and an
applied pressure of gt250 bar (HIPing) reduces
porosity and transforms the brittle Fe2Al5-phase
into the more ductile phases FeAl and ?-Fe(Al)
Ref J. Konys et. al., FZK 4,5
13
HDA Setup - proposed
Al2O3 - crucible
Sample
Holding chamber with protective environment
Al-melt
Furnace
Melting chamber
Coating conditions 4,5 Temperature 700 750
C Melt Al or Al-Si (7-11 Si) Sample
dimensions 50 mm (l) x 30 mm (w) x 5 mm
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HDA PROCESS
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Steel sample (sheet or tube)
Grinding
Cleaning in acetone
Coating, aq. flux-solution
Pre-drying 100C
Glove-box (Ar-5H2)
Heat Treatment (Standard process)
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Coated sample
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HIP-process (advanced process)
Cleaning in water
?
?
Ref Voltrag, et. al. FZK 4,5
Hot-dip-aluminizing, 700C
15
Challenges

• Wettability of sample in Al melt
• Melt Composition (alloying, viz. Si)
• Surface Activation (fluxes etc.)
• Case composition tailored (Fe-Al)
• Post treatment (HIPing), dipping time, batch
  composition
• No porosities (HIPing), Case depth
• Adherent Al2O3 layer on top
• Plasma oxidation process
• Qualify for validation (performance related)

16
Plans for development

• Development of homogenous aluminized coating
  after HDA
• Generation of desired compositional profile by
  heat treatment plasma oxidation
• Hot Isostatic Pressing of aluminized samples
• (To be worked out in collaboration with other
  national insitutes)

Hot Dip aluminizing 700 750 ?C
HIPing 1050 ?C, 250 Bar 1 hr
Validation
Plasma Oxidation H/T 1050 ?C
17
Validation

• Pb-17Li Loop testing
• H2 / T permeation
• Initially the sample will be tested for Hydrogen
  permeation
• Susequently the sample will be validated for
  Tritium permeation in Pb-Li environment

Ref Schematic of Permeation testing facility at
ENEA, Italy
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Present status

• Design generation of specs for furnace
• Fabrication installation of furnace
• Preliminary trials for HDA wettability
  uniformity
• Heat treatment optimization
• Characterization
• Hot Isostatic Pressing
• Validation

19
Thank You
20
References

• Design Description Document for Indian Lead
  Lithium cooled ceramic breeder (LLCB) Blanket
• G. W. Hollenberg et. al., Tritium / Hydrogen
  Barrier Development, June 1994, 3rd Intl.
  Symposium on Fusion Nuclear Technologies, LA,
  California
• P.S. Korinko et. al., Dev. of aluminide coatings
  for Hydrogen isotope permeation resistance,
  Tritium 2001, Tsukaba, Japan, 11-16 Nov, 2001
• J. Konys et. al., ITER TBM Project Meeting, UCLA,
  Feb 23-25, 2004.
• J. Konys et. al., J. Nucl. Mat. 367-370 (2007)
  1144-1149
• H. Glasbrenner et. al., J. Nucl. Mat. 307-311
  (2002) 1360-1363

BACK
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Corrosion data
Ref W. Krauss et. al., Intl. workshop on breeder
blankets, Russia June, 2006
BACK
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Results of permeation testing in H2gas in
different facilitiesat ENEA Brasimone, Italy
(PERI, CORELLI)Permeation Reduction Factors
(PRF)
cancelled
pH2 1 bar, steel F82H-mod., Ref J. Konys et.
al. 4
BACK
23
WHY HIPPING?
Microstructure after heat treatment
Microstructure after HIP
Heat treatment at 1040C/0.5 h 750C/1 h and an
applied pressure of gt250 bar (HIPing) reduces
porosity and transforms the brittle Fe2Al5-phase
into the more ductile phases FeAl and ?-Fe(Al)
Heat treatment at 1040C/0.5 h 750C/1
h incorporates the solidified Al and transforms
the brittle Fe2Al5-phase into the more ductile
phases FeAl and ?-Fe(Al)
BACK
Ref J. Konys et. al. 4