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Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016 Presentation title – Presenter/ref. - 26 May 2016 - p.1

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Failure Analysis of Alloy 718 Hold Down Springs Mahendra Punatar Jacqueline Stevens AREVA, Inc., Lynchburg, VA, USA Keith J. Leonard, Maxim N. Gussev Oak Ridge National Laboratory, Oak Ridge, TN, USA Gabriel Ilevbare EPRI, Palo Alto, CA, USA J. Lawrence Nelson JLN Consulting, Mills River, NC, USA 2016 International LWR Material Reliability Conference and Exhibition August 1 – 4, 2016

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Outline

Background Examination Results Discussion Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Outline

Background Examination Results Discussion Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Background (1/2)

Alloy 718 material to AMS 5596 HDS under high stress state during operation PWR conditions – 2, 24-month cycles Approximately 0.5 dpa

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Background (2/2)

Archive materials also investigated: Archive A – Representative of HDS which failed during operation, same

manufacturing lot as irradiated samples Archive B – Representative of HDS which completed operational life

without damage

Both archives manufactured from same alloy 718 ingot

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

Archive and irradiated samples examined at ORNL

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Outline

Background

Examination Results Discussion Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Examination Results (1/4)

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Examination Results (2/4)

Sample surface after oxide removal Extensive slip lines around major cracks Slip line oxidation Secondary cracks (red arrows)

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Examination Results (3/4)

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

Delta phase

Twin Boundary

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Examination Results (4/4)

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

Archive A Archive B

Following 3.7% Bulk Strain

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Outline

Background Examination Results

Discussion Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Discussion (1/2)

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Discussion (2/2)

Precipitation Heat Treat Differences

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

0

100

200

300

400

500

600

700

800

0 100 200 300 400 500 600 700 800 900 1000

Tem

pera

ture

(°C

)

Time (minutes)

Archive A / Irradiated Samples

Archive B Samples

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Outline

Background Examination Results Discussion

Conclusion

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Conclusion (1/1)

Failed HDS (Archive A) 2, 24-month cycles – PWR

chemistry High Stress Approximately 0.5 dpa Negligible δ phase

precipitation on GBs

Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

Non-Damaged HDS (Archive B) 3, 18-month cycles – PWR

chemistry High Stress Approximately 0.5 dpa Substantial δ phase precipitation

on GBs

δ precipitates on the grain boundaries of alloy 718 produce a PFZ which facilitates cross-slip leading to localized stress reduction

In the absence of a PFZ, the build up of slip bands at GBs under a high bulk stress state will initiate cracks

Cracks then readily propagate in alloy 718 in a PWR environment

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Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016

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Failure Analysis of Alloy 718 Hold Down Springs – M. Punatar - 11 May 2016 Presentation title – Presenter/ref. - 26 May 2016 - p.18