Strain rate and oxidation effects on crack initiation at 600 and 650 °C in a nickel-based superalloy

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Strain rate and oxidation effects on crack initiation at

600 and 650 °C in a nickel-based superalloy

Maxime Perrais, Alexandre Seror, A. Burteau, Eric Andrieu, Dominique

Poquillon

To cite this version:

Maxime Perrais, Alexandre Seror, A. Burteau, Eric Andrieu, Dominique Poquillon. Strain rate and

oxidation effects on crack initiation at 600 and 650 °C in a nickel-based superalloy. Materials at

High Temperatures, Taylor and Francis, 2016, 33 (3), pp.241-247. �10.1080/09603409.2016.1169665�.

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This is an author-deposited version published in :

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Eprints ID : 19781

To link to this article : DOI:10.1080/09603409.2016.1169665

URL :

http://dx.doi.org/10.1080/09603409.2016.1169665

To cite this version :

Perrais, Maxime and Seror, Alexandre and

Burteau, A. and Andrieu, Eric and Poquillon, Dominique Strain rate

and oxidation effects on crack initiation at 600 and 650 °C in a

nickel-based superalloy. (2016) Materials at High Temperatures,

vol. 33 (n° 3). pp. 241-247. ISSN 0960-3409

Any correspondence concerning this service should be sent to the repository

administrator:

staff-oatao@listes-diff.inp-toulouse.fr

Strain rate and oxidation effects on crack

initiation at 600 and 650 °C in a nickel-based

superalloy

M. Perrais

1,2

_{, A. Seror}

2

_{, A. Burteau}

3

_{, E. Andrieu}

1

_{and D. Poquillon}

1

 

Nickel-based superalloys are sensitive to an oxidation-assisted intergranular crack (OAIC) growth

mechanism. Crack initiation during slow strain rate tensile tests is investigated at 600 and 650 °C, at

different strain rates, with or without oxidation on a direct-aged material. A V-shaped sample geometry

is used to promote damage initiation for a specific stress triaxiality. The critical mechanical loading paths

inducing intergranular crack initiation as well as the effect of oxidation are discussed.

Keywords: Ni-based superalloys, Direct aged alloy 718, Oxidation, Environment assisted cracking

Introduction

Alloy 718 is a nickel-based superalloy used for a wide range RI DSSOLFDWLRQV LQ ¿HOGV LQFOXGLQJ DHURVSDFH FKHPLFDO DQG QXFOHDUHQJLQHHULQJ0DQ\VWXGLHVKDYHEHHQGHYRWHGWRLWV PHFKDQLFDOEHKDYLRXUGXULQJIDWLJXHWHVWV1–4 _{creep tests}5–7 _and

creep- fatigue tests.8–12+RZHYHUPRVWRIWKHPKDYHIRFXVHGRQ

standard solution-treated and aged condition 718 alloys (STD  ZKRVH PLFURVWUXFWXUH1012 GLIIHUV IURP WKH GLUHFWDJHG

PDWHULDO'$7KLVVWXG\LVGHYRWHGWR'$XVHGLQ ORZSUHVVXUHWXUELQHGLVFVRIDLUFUDIWHQJLQHV7KHHOHYDWHGWHP-SHUDWXUHIDWLJXHFUDFNJURZWKEHKDYLRXULQ67'GHSHQGV RQWKHHQYLURQPHQWDQGOLNHPDQ\RWKHUQLFNHOEDVHGVXSHU-DOOR\VLVVHQVLWLYHWRR[LGDWLRQDVVLVWHGLQWHUJUDQXODUFUDFNLQJ (OAIC).±+RZHYHUIHZHUVWXGLHVDUHGHYRWHGWR$OOR\ IRUWHPSHUDWXUHVDERYHƒ&EXWVRPHSDSHUVKRZHGWKDW WKHDOOR\LVVHQVLWLYHWRLQWHUJUDQXODUFUDFNLQJDWƒ&17 0HFKDQLFDOWHVWLQJVKRZVWKDW'$H[KLELWVDKLJKHU WHQVLOHVWUHQJWKWKDQ67'10,QWKHSUHVHQWZRUNFUDFN

initiation in DA 718 during slow strain rate tensile tests is LQYHVWLJDWHGDWDQGƒ&ZLWKRUZLWKRXWR[LGDWLRQ7KH SXUSRVHLVWRFKHFNWKHHIIHFWVRIVWUDLQUDWHGRZQWRí _sí₎ DQGR[LGDWLRQRQGDPDJHLQLWLDWLRQ 7KHFULWLFDOPHFKDQLFDOORDGLQJSDWKVLQGXFLQJLQWHUJUDQX- ODUFUDFNLQLWLDWLRQDUHGHWHUPLQHGYLDDGXDODSSURDFKREVHU-YDWLRQRIFUDFNLQLWLDWLRQORFDWLRQVRQ9VKDSHGVSHFLPHQV (Fig. 1DQGVXSSRUWLQJ¿QLWHHOHPHQW)(VWUHVVDQGVWUDLQ FDOFXODWLRQV7RDVVHVVWKHUROHRIR[LGDWLRQLQFUDFNIRUPD- WLRQWHVWVZHUHFRQGXFWHGXVLQJHLWKHUDODERUDWRU\DLURUYDF-XXPHQYLURQPHQW)XUWKHUPRUHVRPHSUHR[LGLVHGVDPSOHV ZHUHDOVRWHVWHG0HFKDQLFDOWHVWVZHUHVWRSSHGDWDGLIIHUHQW VWUDLQOHYHOVVXEVHTXHQWO\GDPDJHLQLWLDWLRQVLWHVDQGWKHLU FRUUHVSRQGLQJ RFFXUUHQFH IUHTXHQFLHV ZHUH LGHQWL¿HG DQG UHFRUGHGWKDQNVWRGHWDLOHG6(0REVHUYDWLRQV

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Material and samples

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QPZLGHDQGFDQUHDFKVHYHUDOKXQGUHGQDQRPHWUHVORQJ 7KLVW\SHRISUHFLSLWDWLRQLVRIWHQREVHUYHGEXWQRWV\VWHP-DWLF)XUWKHUPRUHDSUHFLSLWDWHIUHH]RQH±QPZLWKLV DOZD\VREVHUYHGDURXQGWKHVHWKLQįSKDVHSUHFLSLWDWHV:KHQ DOOR\LVVXEPLWWHGWRVROXWLRQDQQHDOHGKHDWWUHDWPHQW DIWHUIRUJLQJVXFKSUHFLSLWDWLRQDQG3)=RQJUDLQERXQGD-ULHVLVQHYHUREVHUYHG7KLVYHU\SDUWLFXODUPLFURVWUXFWXUHRI JUDLQERXQGDULHVLQ'$LVDNH\HOHPHQWIRUXQGHUVWDQG-LQJLQWHUJUDQXODUFUDFNVLQLWLDWLRQ'XULQJVDPSOHSUHSDUDWLRQ SDUWLFXODUFDUHZDVWDNHQQRWWRFKDQJHWKHPLFURVWUXFWXUH especially in surface. DOI 10.1080/09603409.2016.1169665

*Corresponding author, email Dominique.Poquillon@ensiacet.fr

1_{CIRIMAT, Université de Toulouse, CNRS, INPT, UPS, 4 allée Emile Monso –}

BP 44362 – 31030 TOULOUSE cedex 04, France

2_{SNECMA – Rond-Point René Ravaud – 77550 Moissy–Cramayel, France} 3_{TURBOMECA – Avenue Joseph Szydlowski 64511 Bordes, France}

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Experimental procedures

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1 Typical microstructure of the alloy of this work. Optical microscopy etched using Kalling’s reagent

Table 1 Chemical composition of 718 alloy (weight %)

Ni Cr Fe Nb (+Ta) Mo Ti Al

50–55 17–21 Bal. 4.75–5.5 2.8–3.3 0.65–1.15 0.2–0.8

phase

PFZ

2 TEM observation of DA 718 grain boundary with thin

ͣ phase on the GB and a precipitate-free zone (PFZ)

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Results

Finite element simulations

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corresponded to a reference strain rate of 10í sí9DOXHVRI 10í and 10í síFRUUHVSRQGHGWRDQGȝPVí.

SEM observations of crack initiations

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3 Sketch of V-shaped specimens

Crack initiated on a carbide

4a SEM observations examples of crack initiation on carbide. The tensile stress direction is indicated by the white arrow

Intergranular crack

4b SEM observations examples of intergranular crack initiation. The tensile stress direction is indicated by the white arrow

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Discussion

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5 Comparison between experimental data and FE results for force / displacement curves obtained during the opening of the V at 650 °C. Tests carried out at in imposed displacement rate of 0.2 μm/s (res. 20 μm/s) corresponds to a reference strain rate of 10−6_s−1 _{(res. 10}−4_s−1₎

6 Comparison between of cumulative strain fields between DIC results. (a) Experimental results at 600 °C, after 5 mm elongation at in imposed displacement rate of 0.2 μm/s. The sample thickness is 1 mm. (b) FE simulations results in the centre of the intrados of the V, at 600 and 650 °C, after 5  mm elongation at in imposed displacement rate of 0.2 μm/s

7 Diagram showing the results obtained for crack initiations on carbides or carbonitrides. Metallographic analysis of the material showed an average of 134 particles (carbides or carbonitrides) per mm2 _{with very large heterogeneities}

8 Diagram showing the results obtained for intergranular crack initiations as a function of the strain rate in the centre of the area where SEM observations were performed

9 Diagram showing the results obtained for intergranular crack initiations for the slowest reference strain rate (10−6_s−1

corresponding to an imposed displacement rate of 0.2 μm/s). Results are plotted as a function of the maximum cumulative strain in the center of the area where SEM observations were performed

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Conclusion

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Crack initiation due to carbide or carbonitride is widely rep RUWHG89 _{especially for fatigue tests on DA 718 alloys. Strain}

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10 Diagram showing the results obtained for intergranular crack initiations for a 5  mm elongation (corresponding to 7% of cumulative strain in the centre of the V), for the slowest reference strain rate (10−6_s−1 _{corresponding to an imposed}

displacement rate of 0.2 μm/s). Results are plotted as a function of experimental conditions. Tests are performed under air or vacuum, with or without 8 h of pre-oxidation at the test temperature

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References

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