Evaluation of Neutron Irradiated Additively- Manufactured Zircaloy … · 2019. 6. 26. · 5...
Transcript of Evaluation of Neutron Irradiated Additively- Manufactured Zircaloy … · 2019. 6. 26. · 5...
Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights Reserved.
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Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights Reserved.
Jonna M. Partezana, William T. Cleary, Peng Xu
Westinghouse Electric Company LLC
Evaluation of Neutron Irradiated Additively-
Manufactured Zircaloy-2
Zirconium in the Nuclear Industry: 19th International Symposium,
May 20-23, 2019, Manchester, UK
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Outline
• Motivation of Study
• Laser Powder Bed Fusion Technique
• Characterization of Additively-Manufactured (AM) Zircaloy-2
• Results and Discussion
• Conclusions
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“Throne” by Kohei Nawa
• Displayed under Pyramid of Musée du Louvre from July 2018 – January 2019
• 3D printed piece made of stainless steel and fiber-reinforced plastic; gilded with gold leaf
• Artist invites viewer to “reflect on rapid advances in computer science and artificial intelligence, and questions the idea of absolute power”
• Example of intricate geometries 3D printer can make Additive manufacturing - a new era for
manufacturing!
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Motivation for Study of Additive Manufacturing
• Unique capability to generate complex geometries
• Fabricate near net shape product with reduced processing
(machining, metal forming, and welding) and tooling costs
• Assess the feasibility of applying AM to Zr-based alloys
• Potential applications of AM Zr components to enhance
performance of fuel assemblies
– Spacer grids
– Intermediate flow mixers (IFM)
– Debris filters
AM not widely applied to nuclear
industry, especially Zr!
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• Printed with an EOS M280
with 400W laser
• Zircaloy-2 powder from ATI
Specialty Alloys and
Components
– Made by a hydride/dehydride
process (HDH) followed by
plasma spheroidization
• Printing Process Conditions:
– Layer thickness: 40 µm
– Chamber gas: Argon
– Build plate: Zircaloy-4
– Build time: ~ 21 hours
– Build height: 55.760 mm
AM Zircaloy-2 Printed by Laser Powder Bed Fusion
Top Surface During Build-up Process
Final AM Zircaloy-2 Printed Block
Powder Layer
Laser for
Fusion
Block
Build
Plate
Image courtesy of ATI
Powder
Bed
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AM Zircloy-2 Build for EDM Tensile Quads
Block 2
Block 1
Block 3
Block 4
Z
X
Y
Miniature tensile quads were
machined by EDM
Quads were 1 mm thick
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MIT-R Test Conditions
Images courtesy of MIT (G. Koshe)
Nominal reactor conditions:
• 573 K at 10.3 MPa
• PWR water chemistry
– 1400 PPM B; 4 PPM Li
– 50 cc/kg H2
• Flux (E > 1.0 MeV):
– 4.8 x 1013 n/cm2/s
• Approximate dpa:
– Cycle 1: 0.9
– Cycle 2: 1.6
– Cycle 3: ~3 (target)
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Characterization of AM Zircaloy-2 Materials
• Chemistry
• Density
• Microstructure
• Crystallographic Texture
• Mechanical Properties– Hardness
– Tensile (Room Temp. and 573 K)
• Corrosion
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Chemistry
• Major alloying elements remained constant
• O higher than 1200 PPM in reference Zircaloy-2 plate
• N and H higher than ASTM Zircaloy-2 spec.
Sample Process
Composition
Weight Percent wPPM
Sn Fe Cr Ni O N H
Zircaloy-2 powder
(ATI)HDH 1.41 0.126 0.086 0.052 0.16 110 -
AM Zircaloy-2 block
(EWI)AM 1.38 0.128 0.079 0.052 0.17 85 33
Zircaloy-2 plate
(ATI)RXA 1.52 0.188 0.104 0.074 0.12 22 4
Zircaloy-2 plate
(SMT)
RXA 1.35 0.168 0.104 0.066 0.12 20 <3
BQ 1.36 0.180 0.108 0.070 0.13 29 3
ASTM B352
Zircaloy-2-
1.2 –
1.7
0.07 –
0.20
0.05 –
0.15
0.03 –
0.08* 80
max
25
max
* As specified by customer PO
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Density of AM Zircaloy-2
• Nearly 100% dense
• Results from immersion
density and light optical
microscopy are consistent
(99.9% dense)
• Metallography shows voids– Make up about 0.1%
– Angular voids present
– Spherical voids present
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Microstructure of AM Zircaloy-2
X
Y
• Equiaxed grains are observed
normal to the build direction
• Elongated grains are
observed in the build (Z)
direction
Y
Z
X
Z
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Microstructure of AM Zircaloy-2
• Beta-quenched microstructure (as expected)
• Fine alpha lathe microstructure indicative of rapid cooling
• Lathe size less than 1 µm (greater than 500 K/sec.)
• Rapid cooling suggests the microstructure is martensitic
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Random Crystallographic Texture
• Isotropic
as
expected
Texture Parameters
Specimen fX fY fZ ∑f
AM Y Block 0.321 0.330 0.348 0.999
Calculated Pole Figures
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Mechanical: Microhardness
• Vickers indentations with
500 gram-force load
• Data are similar for the
three directions in the AM
Zr material
• Hardness increased with
increasing irradiation
• RXA Zircaloy-2 plate is
significantly softer
Sample and Load DirectionMicrohardness
Avg. HV (SD)
AM Zry-2 Quad
(0 dpa)
X 263 (6)
261 (5)Y 258 (5)
Z 260 (2)
1-cycle AM Zry-2
Quad (0.9 dpa)
X 307 (4)
306 (5)Y -
Z 306 (5)
2-cycle AM Zry-2
Quad (1.6 dpa)
X -
324 (8)Y 320 (8)
Z 327 (6)
Zircaloy-2 Plate
(RXA/ATI)
T 188 (8)
L 170 (4)
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Mechanical: Summary of Tensile Test Results
RT = Room Temperature
ET = Elevated Temperature of 573 K
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Fracture Surfaces of Unirradiated Zircaloy-2
• Pores observed
on AM fracture
surfaces
• Result of
porosity found in
as-printed
material
RXA Zircaloy-2
Room
Temp.
573 K
57% RA
76% RA
47% RA
67% RA
AM Zircaloy-2
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Fracture Surfaces of Irradiated AM Zircaloy-2
15% RA 10% RA
• % reduction in
area (RA)
decreased with
radiation
exposure
• Large pores not
observed on RT
samples (low
%RA)
Cycle 1: 0.9 dpa Cycle 2: 1.6 dpa
Room
Temp.
573 K
60% RA 47% RA
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In-reactor Corrosion of AM Zircaloy-2
• Tensile quads
lost weight
suggesting oxide
spallation
• Possible causes:– EDM surface
contamination
(Zn and Cu)
– Poor
microstructure
• High hydrogen
content
Oxide thicknessOxide thickness
Cycle 1: 0.9 dpa
Hydrogen: 408 PPM
Cycle 2: 1.6 dpa
Hydrogen: 468 PPM
Hydrogen normalized to sample thickness of 0.5 mm
573 K in PWR Water Chemistry
AM Zircaloy-2 AM Zircaloy-2
Hydrides Hydrides
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Autoclave Corrosion of AM Zircaloy-2
Ni Plating Ni Plating
• Corrosion of Zr alloys requires optimization of thermo-mechanical processing to achieve desired microstructure, e.g. second phase particle (SPP) size
• Martensitic microstructure of AM Zircaloy-2 not optimum due to rapid quenching and expected extremely fine SPPs
• Coupons of AM Zircaloy-2 prepared for autoclave testing – Removed EDM surface by grinding– Annealed coupons at 1033 K/ 2 hours to nucleate and
coarsen SPPs
• Short-term autoclave testing performed– 700 K steam, 10.3 MPa– 9-10 days exposure
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Autoclave Results (700 K, 10.3 MPa Steam)
MaterialTime
(days)Process
Weight gain
(mg/dm2)
H Pickup
Norm. to 0.5 mm
thick (PPM)
H Pickup
% theoretical
AM Zircaloy-2 9
as-printed130 260 24
159 - -
1033 K/2 h50 98 24
52 - -
Zircaloy-2
Plate10
RXA/ATI 42 - -
RXA/SMT 47 - -
BQ/SMT 58 - -
• Annealed AM Zircaloy-2 resulted in significant reduction in weight gain
• Annealed AM Zircaloy-2 weight gain was comparable to conventionally-
processed materials
• HPF in annealed AM Zircaloy-2 results from lower weight gain
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Autoclave Results (700 K, 10.3 MPa, 9 Days)
• Anneal at 1033 K
for 2 hours
recrystallized the
martensitic
microstructure
• Reduced oxide
thickness on
annealed AM
Zircaloy-2
• Annealing of AM
material provides
a possible way to
restore corrosion
resistance
Zr Metal
Zr Oxide
Ni Plating
Zr Metal
Zr Oxide
Ni Plating
AM Zircaloy-2 AM Zircaloy-2 + Anneal
HV: 261; Wt. Gain: 130 mg/dm2 HV: 204; Wt. Gain: 50 mg/dm2
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Recrystallization of As-printed AM Zircaloy-2
• The anneal was performed to nucleate and coarsen SPPs
• Unexpected result was recrystallization of the martensitic
microstructure
• Observation is reminiscent of ‘blocky’ alpha grain growth– Observed following low cold work (3-10%)
– Anneal in high temperature alpha region
– Bimodal grain size
• Appears that stresses in the martensitic structure (not cold
work) provided the driving force for recrystallization
• The impact of the anneal on SPP size is planned
• Expect random texture in the annealed AM material
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Conclusions of Exploratory Study
• Achieved nearly 100% dense material with no meaningful chemistry change (no loss of alloying elements or pickup of O/N)
• Material is isotropic (texture, hardness, tensile properties)
• Tensile properties:– Significantly higher 0.2% YS and UTS than RXA plate – Lower % EL and % RA than RXA plate– Strength increased and ductility decreased with irradiation dose
• Corrosion properties of as-printed AM material were poor
• Annealing as-printed AM material restores corrosion properties– Recrystallizes microstructure– Impact on SPPs is planned– Anticipate random crystallographic texture
• Potential path forward has been identified for application of AM zirconium alloy components in LWRs
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Acknowledgements
• PIE work funded by NSUF under contract 194396; CINR FOA Award 13016
• Noah Philips from ATI Specialty Alloys and Components
• Gordon Koshe from MIT
• Zeses Karoutas from Westinghouse
• Robert J. Comstock from Westinghouse (Retiree)
Thank you for your attention!
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Backup Slides
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AM by Laser Powder Bed Fusion Technique
• Deposit a layer of powder across a build plate within the printing chamber
• Following a CAD file, a laser rasters across the powder and melts it in the required geometry
• Another layer of new powder is deposited across the build plate and the process is repeated
• After final powder layer is laser melted, the powder is removed and the printed component is cut away from build plate
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Mechanical: Room Temperature Tensile Tests
• UTS and 0.2%
YS increased
with radiation
exposure
• % EL
decreased with
radiation
exposure
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Annealing AM Zircaloy-2
• Post processing of AM material is limited to thermal treatments
• Selected high temperature (1033 K) alpha anneal for two hours in an effort to nucleate and coarsen SPPs
• Quantified anneal by A-parameter (A = t e(-Q/RT))
• Note: A-parameter calculated for comparison to conventional processing
ParameterReactor Type
PWR BWR
Alloy Zircaloy-4 Zircaloy-2
Q/R 40,000 K 31,700 K
A target for conventional processing 1 x 10-17 h 0.6 x 10-14 h
A for AM anneal (2h at 1033K) 3 x 10-17 h 9.4 x 10-14 h