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Aniruddh Das | ODISSEUS Workshop 2015| 24.03.15 Fracture behavior and mechanisms of ODS steels.

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Presentation on theme: "Aniruddh Das | ODISSEUS Workshop 2015| 24.03.15 Fracture behavior and mechanisms of ODS steels."— Presentation transcript:

1 Aniruddh Das | ODISSEUS Workshop 2015| Fracture behavior and mechanisms of ODS steels

2 Member of the Helmholtz Association Page 2 Aniruddh Das | ODISSEUS Workshop 2015| Content History of ODS alloys Motivation Fracture toughness analysis methods Preliminary results Conclusion

3 Member of the Helmholtz Association Page 3 Aniruddh Das | ODISSEUS Workshop 2015| History of ODS alloys

4 Member of the Helmholtz Association Page 4 Aniruddh Das | ODISSEUS Workshop 2015| Need for advanced materials Use at high temperatures  higher efficiency Good mechanical properties at high temperature Simplification of design Reduced activation and swelling Thermal efficiency of sodium fast reactors

5 Member of the Helmholtz Association Page 5 Aniruddh Das | ODISSEUS Workshop 2015| Gen IV Reactors YearReactor typeEfficiencyMaterialTemperature Gen I-IIILow (15-30%)Ferritic /Martensitic, Austenitic < 500°C YearReactor typeEfficiencyMaterialTemperature after 2014Gen IVHigh (38%)ODS/NFA< 650°C Advantages of Gen-IV reactor Better use of nuclear fuel Faster decay of radioactive waste Ability to consume nuclear waste for electricity Improved operating safety

6 Member of the Helmholtz Association Page 6 Aniruddh Das | ODISSEUS Workshop 2015| Candidate materials for high temperature nuclear application Ni SuperalloysFerritic/Martensitic Steels ODS steels Temperature range< 1200°C< 600°C< 800°C Tensile strength (at RT) MPa MPa MPa Ductility (at RT)up to 6%about 20%up to 26% Creep rupture strength (10 5 h)125 MPa (700°C)50 MPa (650°C)180 MPa (650°C) DBTTAlways ductile-100°C to 0°C Fracture toughness (RT)70-90 MPa-m 1/ MPa-m 1/ MPa-m 1/2 ActivationNi, Co  60 CoLow Irradiation swelling5-10 % (100 dpa, °C) LowVery low High temperature corrosionAl Oxidation protection layer Cr oxidation protection layer

7 Member of the Helmholtz Association Page 7 Aniruddh Das | ODISSEUS Workshop 2015| Ferritic ODS steels: Nuclear applications AlloyFeCrWTiMoMnVTaCY2O3Y2O3 Other ODS Eurofer 97Bal N 12Y1Bal Ni 12YWTBal YWTBal MA 957Bal PM 2000Bal Al MA 956Bal Al

8 Member of the Helmholtz Association Page 8 Aniruddh Das | ODISSEUS Workshop 2015| History of ODS alloys High strength Ti,Y,O nano particles Stable creep Low fracture toughness Chaouadi et al2010Thak Sang Byun et al Klueh et al Byun et al Klueh et al. 2002

9 Member of the Helmholtz Association Page 9 Aniruddh Das | ODISSEUS Workshop 2015| Motivation

10 Member of the Helmholtz Association Page 10 Aniruddh Das | ODISSEUS Workshop 2015| Why is fracture toughness of ODS important? Normal operation gives rise to stresses (pressure, vibrations, temperature) + presence of microcracks from manufacturing  Fracture Accidental conditions can result in additional thermal shock Low fracture toughness is detrimental for machinability of ODS steels. Fracture toughness is a well-defined generally accepted quality parameter, which helps for qualitative ranking of materials and design of components.

11 Member of the Helmholtz Association Page 11 Aniruddh Das | ODISSEUS Workshop 2015| Motivation No clear systematic fracture toughness data of ODS steels from RT to 800 ° C Ductile-to-brittle transition: Master Curve approach Ductile region : determination of J R Curves Understanding of fracture mechanisms from RT to 800 ° C Understanding the role of selected process parameters on fracture toughness Effect of bulk microstructure of ODS on fracture toughness Relation between fracture surfaces and fracture toughness Development of small specimen methods Development of high temperature testing

12 Member of the Helmholtz Association Page 12 Aniruddh Das | ODISSEUS Workshop 2015| Small scale specimens Less amount of material required More specimens irradiated Less activity to handle Difficulty in COD measurement Experimental setup challenging Some validity criteria in ASTM E1820 are not fulfilled 1T C(T) Inner Knife 0.16T C(T) Outer Knife 0.25T C(T) Front Face

13 Member of the Helmholtz Association Page 13 Aniruddh Das | ODISSEUS Workshop 2015| Fracture toughness analysis methods

14 Member of the Helmholtz Association Page 14 Aniruddh Das | ODISSEUS Workshop 2015| Fracture toughness analysis Multiple specimen method Potential drop method Unloading compliance method Normalization method Most common specimens Analysis methods Most common orientations

15 Member of the Helmholtz Association Page 15 Aniruddh Das | ODISSEUS Workshop 2015| Fracture toughness analysis methods Simple procedure Multiple specimen method Single specimen method Convenient and time saving Unloading Compliance (UC) Single specimen method Initial and final crack length required for J R curve Normalization method Requires multiple specimen Time consuming Needs high accuracy in COD measurement High temperature COD measurement needs special arrangement Empirical method of estimation Needs to be combined with another method for validation

16 Member of the Helmholtz Association Page 16 Aniruddh Das | ODISSEUS Workshop 2015| Single specimen method Only monotonic loading needed Can be used at high temperatures Requires specimen isolation from machine Has to be coupled with a COD measurement device for J integral calculation Needs to be validated with other techniques such as Unloading Compliance Advantages Disadvantages Fracture toughness analysis methods Potential drop method (PD): Approximate linear relation of crack extension with potential difference

17 Member of the Helmholtz Association Page 17 Aniruddh Das | ODISSEUS Workshop 2015| Preliminary Results

18 Member of the Helmholtz Association Page 18 Aniruddh Das | ODISSEUS Workshop 2015| Our ODS material SourceCompositionProduction method iFAM/HZDR (Ms Hilger) KIT (LT & TL) 14Cr ODS bar (GETMAT) ODS PM 2000 (Plansee) Fe14Cr1W0,4Ti0,3Si0,3Mn0,15Ni Fe14Cr1W0,4Ti0,3Si0,3Mn0,15Ni + 0,3 Y 2 O 3 Fe14Cr1W0,4Ti0,3Si0,3Mn0,15Ni + 0,6 Y 2 O 3 Fe 13Cr 1W 0,3Ti + 0,3Y 2 O 3 Fe 13.98Cr, 1.03W, 0.39Ti,0.29Mn, 0.32Si, 0.17Ni + 0.3Y 2 O 3 Fe 20Cr, 0.5Ti, 0.01C, 5.5Al + 0.5Y 2 O 3 MA + SPS (1050°C + 247KN) MA+HIP (1100°C/100MPa)+ HR(1100°C) Hot extruded (1100°C) + Annealed (1050°C,1.5 hrs) Hot Rolled Total elongation / % Temperature / °C  C

19 Member of the Helmholtz Association Page 19 Aniruddh Das | ODISSEUS Workshop 2015| Fracture surface macrostructure of ODS-KIT (LT 0.25T C(T)specimen) RT-1 RT-2 100°C 200°C L S T Heat tinting and Liq. N 2 fracture Advanced cracks Larger crack front at 200°C T S

20 Member of the Helmholtz Association Page 20 Aniruddh Das | ODISSEUS Workshop 2015| Preliminary results Fracture toughness of 0.25T C(T) specimen ODS KIT Load drop

21 Member of the Helmholtz Association Page 21 Aniruddh Das | ODISSEUS Workshop 2015| Preliminary results Fracture toughness of 0.25T C(T) specimen ODS KIT

22 Member of the Helmholtz Association Page 22 Aniruddh Das | ODISSEUS Workshop 2015| ODS fracture surface microstructure at 20°C Presence of sharp cracks 4  Residual fracture 3  Fatigue post-cracking 2  Crack growth region 1  Fatigue pre-cracking Dimple formation at micro level T S

23 Member of the Helmholtz Association Page 23 Aniruddh Das | ODISSEUS Workshop 2015| Pre-fatigue cracks in ODS-KIT at 20°C 1 Presence of similar crack advancement in fatigue pre-crack region T S

24 Member of the Helmholtz Association Page 24 Aniruddh Das | ODISSEUS Workshop 2015| ODS fracture surface microstructure at 200°C T S

25 Member of the Helmholtz Association Page 25 Aniruddh Das | ODISSEUS Workshop 2015| Porosity in ODS KIT As-hipped material TS Plane LS Plane Hot Rolling The pores are elongated after hot rolling The pores are linearly arranged More elongation in L than in T direction L T

26 Member of the Helmholtz Association Page 26 Aniruddh Das | ODISSEUS Workshop 2015| Delamination Fracture between weak interfaces (matrix- inclusions or matrix-pores) Higher plastic deformation in the S-direction than in the T-direction Delamination perpendicular to notch base  LT Delamination parallel to notch base  LS Relaxation of triaxial towards biaxial tension Lowering the DBTT and reducing the upper- shelf energy. Chao et al 2013 Kimura et al. 2010

27 Member of the Helmholtz Association Page 27 Aniruddh Das | ODISSEUS Workshop 2015| Delamination of ODS KIT (LT) L S T Delamination similar to crack divider geometry Existing linearly arranged pores act as weak interfaces along L and T directions Energy absorption variation in crack front  Non- uniform crack front Non-uniform crack front makes ASTM J IC evaluation complicated ODS-KIT cutting scheme LT Orientation RT200°C

28 Member of the Helmholtz Association Page 28 Aniruddh Das | ODISSEUS Workshop 2015| GETMAT ODS fracture surface microstructure (C-L direction at RT)

29 Member of the Helmholtz Association Page 29 Aniruddh Das | ODISSEUS Workshop 2015| Porosity in GETMAT as-extruded microstructure (C-L direction) 2000X5000X L-R Plane 2000X5000X C-R Plane L C R Extrusion direction

30 Member of the Helmholtz Association Page 30 Aniruddh Das | ODISSEUS Workshop 2015| Conclusion

31 Member of the Helmholtz Association Page 31 Aniruddh Das | ODISSEUS Workshop 2015| Conclusion Linear arrangement of existing pores in material lead to delamination and advanced cracks Load drops due to advanced cracks? Fracture toughness decreases with increase in temperature More dimple formation and larger crack front at 200°C than at 100°C Production method critical for presence and arrangement of pores

32 Member of the Helmholtz Association Page 32 Aniruddh Das | ODISSEUS Workshop 2015| Current challenges Adaptation of testing methods required Limited ODS material : use of small specimen Small specimen setup adaptation: 0.25T C(T) and 0.16T C(T) Pre-cracking of ODS (GETMAT) difficult High temperature COD measurement (UC) Mechanical clip on gauge (only up to 200°C) LSE accuracy needs to be improved Potential drop method development Isolation of specimen Adaptation to small specimen Development of analysis methods UC, Normalization and PD method Modification for load line offset and outer knife measurement locations

33 Member of the Helmholtz Association Page 33 Aniruddh Das | ODISSEUS Workshop 2015| Thank You! Sources Busby et al, Economic benefits of advanced materials in nuclear power systems (2009) ASTM E1820 – 2013 Standard Test Method for Measurement of Fracture Toughness T.L. Anderon, Fracture Mechanics fundamentals and applications Amir Shirzadi and Susan Jackson, Structural alloys for power plants Oh Young Jin, PhD thesis, Development of modified normalization method using blunt notch specimen for J-R test of nuclear piping material Chao et al, Notch Impact Behavior of Oxide-Dispersion-Strengthened (ODS) Fe20Cr5Al Alloys Kimura et al.,Delamination Toughening of Ultrafine Grain Structure Steels Processed through Tempforming at Elevated Temperatures

34 Member of the Helmholtz Association Page 34 Aniruddh Das | ODISSEUS Workshop 2015| Brief overview of the first six months P91, Biblis-C reactor pressure vessel steel and ODS material fracture toughness testing using UC, multiple specimen and PD methods Microstructural examination under SEM of ODS and P91 Development of analysis software for fracture toughness Development of machine setups for small specimen and high temperature measurements Literature survey of microstructure and mechanical properties of ODS steels at RT and high temperature

35 Member of the Helmholtz Association Page 35 Aniruddh Das | ODISSEUS Workshop 2015| Plan of action Evaluation of Fracture Toughness of ODS steel and P91 Scale down 1T C(T)  0.16T C(T); check influence of specimen dimension on fracture toughness at RT Development of experimental set up to determine J R curves from RT to 800°C Study the fracture surfaces Optical microscope SEM combined with EBSD and EDX Interpretation of J IC values using fractography and determination of fracture mechanisms Comparison of different ODS steels and P91 w.r.t. fracture toughness and microstructure Accompanied by investigations using small punch testing


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