Evaluation of Neutron Irradiated Additively- Manufactured Zircaloy … · 2019. 6. 26. · 5 Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights

Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights Reserved.

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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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Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights Reserved.Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights Reserved.

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

Documents

Evaluation of Neutron Irradiated Additively- Manufactured Zircaloy … · 2019. 6. 26. · 5 Westinghouse Non-Proprietary Class 3 © 2019 Westinghouse Electric Company LLC. All Rights