Characterisation of Microstructure in model ODS Alloys

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Indira Gandhi Centre for Atomic Research

Kalpakkam – 603 102, India

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Physical Metallurgy Division, PMD

Characterisation of Microstructure in model ODS Alloys

Arup Dasgupta

Physical Metallurgy DivisionIndira Gandhi Centre for Atomic Research

Kalpakkam – 603102, INDIA

A collaborative work between IGCAR, Kalpakkam and International Advanced Research Centre for Powder

Metallurgy and New Materials, Hyderabad

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SCHEME

• The Issue– What kind of alloy is under development

– Processing Scheme

– Importance of microstructure and microchemistry investigations in alloy development

• This Talk– Types of samples studies so far

– Results and Discussion

– Summary

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The Alloy under development

9Cr-0.12C-2W-0.2Ti-0.35Y2O3 Ferritic/Martensitic steel chosenbecause of advantages over austenitic stainless steels:

• Higher thermal conductivity

• Lower thermal expansion

• Lower void swelling during irradiation

• Excellent high temperature creep resistance

• W Mo replacement for solid solution strengthening; reduced activation

• Ti Helps to get finer dispersoids

Mandate: Clad Tubes (6.6mm OD, 0.45mm thick, 2.65 m long)

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Processing Scheme

Courtesy: IGCAR ODS Task force, ARCI - Hyderabad

Extr. Rods Mother Tubes Clad TubesMult. Pass CWInt. Heat Trtmt.

Machining

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Importance of Microstructural & Microchemical Investigations MA systems

• Grain morphology• Phase stability• Microstructural Uniformity • Mechanical Interdiffusion

(Microchemical Uniformity) Milling process

+

Subsequent Annealing Steps

Dispersoid Large strain fields• Shape• Size• Distribution• Interface with matrix• Dislocations, other defects

Impurities Microstr. Mech. Prop.• Microstructure / Microchemistry

Purity of feed powders, containers, milling conditions

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Samples Studied

#ODS 0: 48h Milled Fe-0.2Ti-0.35Y2O3 Powder

#ODS 1: Fe-0.35Y2O3

Fe (150µm) and Y2O3 (1.33µm) ball milled / 30h, annealed at 973K / vacuum , double compacted, double sintered at 1323K / H2

#ODS 2: Fe-0.2Ti-0.35Y2O3

Fe (150µm), Ti (105µm) and Y2O3 (1.33µm) ball milled / 30h, annealed at 973K / vac., double compacted, double sintered at 1323K / H2

#ODS 3: Fe-0.2Ti-0.35Y2O3 - Forged

Fe (150µm), Ti (105µm) and Y2O3 (10-20nm) attritor milled / 20h, degassed at 723K & sealed. Can hipped/ forged at 1323K/ 1000MPa

#ODS 4: Fe-0.12C-9Cr-2W-0.2Ti – Pre-alloyed Powder – SEM Only

#ODS 5: Yttria Powder

#ODS 6: Fe-9Cr-2W-0.2Ti-0.35Y2O3-0.12C – Milled Powder

#ODS 7: Fe-9Cr-2W-0.2Ti-0.35Y2O3-0.12C – Extruded at 1050oCB1-ODS-S150-Z04-C46-D04-E1050-ER09

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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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3 size ranges:

(a) large, facetted (Fe-Co)

(b) 50 – 75 nm (Fe-Ti)

(c) sub-10 nm (Fe)

FeCo

Courtesy: Institute Nano-science Initiative IISc, Bangalore- Tecnai F-30

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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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Pore Size Distribution

0

20

40

60

80

100

120

140

2 4 8 MorePore dia. (mm)

Freq

uenc

y

Porosity ~ 1%

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SADP

Selection RuleFCC : (h k l) all odd / evenBCC : h + k + l even

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0

5

10

15

20

25

30

35

40

20 30 40 50 60 70 80

Size (nm)

Fre

qu

en

cy

DF

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IMPURITY

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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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3 4 5 6 7 8 9 10

WL

FeK

FeK

CrK

CrK

Cou

nts

Energy (keV)

TiK

Element Wt. %

Ti 0.57

Cr 9.78

Fe 87.18

W 2.46

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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3




#ODS 4: Fe-9Cr-2W-0.2Ti – Pre-alloyed Powder – SEM Only




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1 2 3 14 15 16 17 18 19 20

YK

OK

YK

Cou

nts

(arb

.un.

)

Energy (keV)

YL

EDS: Yttria Powder, as received

Av. Particle Size (XRD) : 42 nm

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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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Samples Studied


#ODS 1: Fe-0.35Y2O3


#ODS 2: Fe-0.2Ti-0.35Y2O3








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Pore Density ~0.3% aligned along Extrusion direction Tears

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Y L : 0.63 %Ti K : 0.36 %Cr K : 8.95 %Fe K : 87.6 %W L : 2.44 %

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0

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Summary

Seven sets of model materials studied (powders, milled, compacted products)

Higher Milling Duration Agglomeration

The sintered products were porous, 14-20% but forged material had a porosity ~1%. Extruded material had porosity ~0.3% only!

Yttria bcc with a=10.6 Å

Forged sample fine bcc yttria particles with an av. size ~ 10-20 nm; some were ~ 5-7 nm and some were agglomerated; there appeared to be an orientation between the Yttria and the rextallised ferrite grains

Prealloyed powder & yttria powder desired sizes + quite pure

The extruded ODS steel desired composition, fine martensite laths (~100 nm wide) within the elongated grains, very fine (~ 3nm) yttria.

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ContributorsIGCAR, Kalpakkam ARCI, Hyderabad

Arup Dasgupta*, R Divakar, S Saroja, E Mohandas, M Vijayalakshmi, PV Sivaprasad,

KBS Rao & Baldev Raj

R Vijay, S Sudhakara Sarma, A Venugopala Reddy

Characterisation of Microstructure in model ODS Alloys

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