Ods steels part i manufacture mechanical properties and oxidation behaviour
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ODS steels – part I : manufacture, mechanical properties and oxidation behaviour. Yann de Carlan, Jean Henry, Ana Alamo Arnaud Monnier Raphael Couturier, Emmanuel Rigal Céline Cabet Commissariat à l’Energie Atomique CEA, FRANCE. Overview. Why ODS steels? Manufacture

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ODS steels – part I : manufacture, mechanical properties and oxidation behaviour

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ODS steels – part I :manufacture, mechanical properties and oxidation behaviour

Yann de Carlan, Jean Henry, Ana Alamo

Arnaud Monnier

Raphael Couturier, Emmanuel Rigal

Céline Cabet

Commissariat à l’Energie Atomique CEA, FRANCE


Why ODS steels?


Observation and analysis

Microstructure control

Mechanical properties (+ radiation stability)

Welding techniques

Oxidation properties

Why ODS ?

Why ferritic ODS?

  • Radiation resistance at high temperature

M. Inoue, JAEA, MATGENIV, 2007

Strengthening of alloys: ODS principle

  • Increase obstacles to dislocation glide

    • Precipitates or other dislocations

    • Finer dispersoides and higher number density


Ds 


Clement, CEA


Overview of the powder metallurgy process


Mechanical Alloying


Raw materialpowder

High IsostaticPressure

Elemental orprealloyed powder

soft steel can

MA powder

Y2O3 powder

Attrition Mill

Hot/cold Rolling

Hot Extrusion


Mother tube



Intermediateheat treatment

Atomisation of an alloy

R. Lindau, FZK, GETMAT project

P91 steel

SEM of atomized powder

Powder sieving

Photo attritor + parameters

R. Lindau, FZK, GETMAT project

alloying parameters - powder to ball ratio - milling energy (-> rpm, cycling) - milling time

Hot extrusion

Y de Carlan, CEA

Hot extrusion

ODS steel

soft steel

What happens during the process ?

Mechanical alloying


12h milling – With Ti


12h millingno Ti

Before milling

nano clusters< 10 nm

After milling

Fe-18Cr-Ti Y2O3 , Y. De Carlan et al., ICRFM13, 2007

What happens during the process ?

Study by X Ray diffraction : Pre-alloyed powder + 10% of yttria

M. Ratti et al., Boston, MRS 2008




48h milling with titanium


48h milling without titanium

Nombre de coups





Angle 2.Théta







What happens during the process?

Study by X Ray diffraction : Pre-alloyed powder + 10% of yttria

Fe peak

After MA

After MA

After 1h @950°C

M. Ratti et al., Boston, MRS 2008

Characterization by Tomographic Atom Probe

Consolidation 1100°C

M.K. Miller, D.T. Hoelzer, E.A. Kenik, K.F. Russell, Nanometer scale precipitation in ferritic MA/ODS alloy MA957,Journal of nuclear materials 2004


O ak Ridge National Laboratory, U .S . Department of Energy

D. Hoelzer

After mechanical alloying

After consolidation


Alternative process routes

M. Inoue, JAEA

Alternative process routes

OCAS, GETMAT project


Optical microscopy

  • General microstructure

Optical micrographs of the general microstructure of MA957 in the

(a) as- received condition and after annealing at 1300°C for (b) 1 h and (c) 24 h

M.K. Miller et al., JNM 329–333 (2004) 338–341

0.85 W

0.46 Y

0.3 Ti

SEM, EDX and microprobe

  • Grain size and morphology

  • Structure homogeneity

SEM picture of MA957 recrystallized grains obtained after deformation by cold-drawing and recrystallization heat treatment at 1100°C

Microprobe analysis of as-manufactured Fe-18Cr-Ti-Y2O3 alloy

Y de Carlan, CEA

A. Alamo et al., JNM 329–333 (2004) 333–337, CEA


12Y1 ODS steel: bright- and dark-field TEM micrographs taken near beam direction B ~(1 2 2)

Y2O3 particle sizes are in the

range of a few tens of nanometers in diameter

I.-S. Kim et al., JNM 280 (2000) 264-274

Atom Probe

Nanometer scale precipitation in ferritic MA/ODS alloy MA957 after hot consolidation

M.K. Miller et al., JNM, 2004


Analysis by XRD and SANS

  • Nature of crystallized phases

  • Particles size and distribution

SANS of ODS steels with 0.3%Y2O3 and 10%Ti at RT under magnetic field (2 Teslas) perpendicular to the incident neutron beam direction, in a range of scattering vectors going from 0 to 0.16 nm-1

XRD of ODS steels with 0.3%Y2O3 and 10% Ti

major peak of Fe according to ICDD db

M. Ratti et al., Boston, MRS, 2008, CEA

M. Ratti et al., ICRFM13, 2007

Microstructure control

Ti is the most effective element to refine the dispersoid sizes

Precipitation of Ti-Y-O (C) nanoscale clusters

Chemical composition: Minor Alloying Elements

Refinement of dispersoids size by Minor Alloying Elements

AP-FIM with 3D mapping MA/ODS12-YWT

Larson D.J. et al., Scripta Mater. 44 (2001) 359-364, ORNL

Inoue M., JAEA, MATGENIV, 2007

Chemical composition: Y2O3 content

  • Effect of addition of Y2O3 in 13Cr-3W-0.5Ti on tensile properties at 650°C

  • Effect of addition of Y2O3 in 13Cr-3W-0.5Ti on creep rupture strength at 650°C

Ukai S., JNM 204 (1993) 65-73

Chemical composition: Minor Alloying Elements

  • Effect of addition of Ti in 13Cr-3W-0.5Y2O3 on creep rupture strength at 650°C

Fig 4 Ukai JNM 1993

Ukai S., JNM 204 (1993) 65-73

Chemical composition: Excess of oxygen

  • Effect of excess O in 13Cr-3W-0.5Ti-0.5Y2O3 on creep rupture strength at 650°C

Ukai S., JNM 204 (1993) 65-73

Effect of the grain size

  • Effect of MA957 ODS-alloy microstructure on

    • the impact properties

    • the tensile properties

fine grain

A. Alamo et al. , JNM 329–333 (2004) 333–337

Mechanical properties

Creep properties (creep rupture time)

A. Alamo et al., JNM 329–333 (2004) 333–337

Creep of high strength ODS alloys


Basis of welding

  • Welding of two metallic pieces= creation of a metal bond between the atoms of the 2 parts

  • Weld must be as mechanically strong as the base metal

  • HT strength is due to the uniform dispersion of nanoscale oxide particles welding operation has to retain the nanostructure

    • no reallocation of the dispersoids

    • no aggregation of the dispersoids

    • no change in the initial microstructure

liquid state welding

solid state welding

[email protected]

Liquid state welding

melting of the base metal

change in the microstructure

  • Arc welding:

    • GTAW (Gas Tungsten Arc Welding)

    • GMAW (Gas Metal Arc Welding):MIG (Metal Inert Gas) or MAG (Metal Active Gas)

  • Electron beam welding, laser welding

GTAW welder (2)

GTAW principle (2)

GTAW equipment (1)

GMAW (1)


(2) www.wikipedia.com

GTAW weld in narrow gap (1)

electron beam equipment (1)

Solid state wedling

Solid state welding

retain the microstructure

  • Solid state welding+ nuclear constraints: large scale, glove box working

    • HIP (Hot Isostatic Pressing)

    • SPS (Spark Plasma Sintering)

    • Friction Stir Welding, Resistance Welding

FSW principle (6)

Resistance welding principle (4)

SPS principle (3)

(3) www.ceramicindustry.com

(4) www.swantec.com

Resistance welding operation (5)

(5) www.plasmo.eu

(6) www.wikipedia.com

Hot Isostatic Pressure

  • Surface conditioning:

    • Degreasing, acid cleaning, mechanical cleaning, ionic sputtering, coating…

  • Canning:

    • in a steel capsule (welded by GTAW)

  • Degassing of the can (P ~ 10-5 mbar)

  • Closing of the can, gas-tightness

  • HIP cycling : ~1000 °C/1000 bar/1 h

  • Removal of the can:

    • machining, chemical dissolution

[email protected]

High Isostatic Pressing

Mockup: upper plate

[email protected]

Mockup: first wall

Mockup: cooling plate

Eurofer joint

Spark Plasma Sintering (SPS)

[email protected], CEA

Université de Bourgogne

SPS principle


Resistance welding


Resistance welding device of CEA/DEN/DANS/DM2S/SEMT/LTA

[email protected]

Resistance welding – characterization of the weld

  • hardness of the weld = hardness of the base metal

  • needs for accurate analysis of the dispersoid size and allocation

[email protected]

Characterization of ODS weld

  • How to characterize an ODS weld?

  • Usual methods to characterize a weld

    • SEM, EDS analysis, hardness profile

    • Do not allow observing nanoscale dispersoids

  • Methods to characterize an ODS

    • TEM, nano-indentation, SANS

    • Do not allow checking for the weld homogeneity

    • + technically difficult to perform

Oxidation properties

Example of commercial ODS



Y is a RE !!!

  • Improve the oxidation and corrosion properties longer service life

  • RE = Reactive Elementeffective when added as

    • metal or alloy

    • oxide dispersoids (ODS)

    • ionic implantation

    • surface coating


800°C, air

alumina scale spalls out

protection is lost

12Cr-2W ODS (0.24 Y2O3)

FMS 12Cr-2W

Oxidation in dry air at 650°C for 2000hrs

Improvement of the oxidation properties

  • Surface oxide thickness

  • Mass gain

  • Spallation

Influence on the scale formation

Chromia forming

Alumina forming

  • Decrease of the critical Cr% for chromia formation

  • Promote -Al2O3 (no transitory θ-Al2O3)

  • Decreases the duration of transitory oxidation(reduces the base metal oxidation)

12Cr steel oxidized at 1300°C in dry air for 50h





no Y

Wagner theory








Influence on the scale growth

Chromia forming

Alumina forming

  • Supress outward diffusion of metal cation

  • Decrease the oxidation rate (parabolic constant)

  • Possible change in the oxidation kinetics (from parabolic to subparabolic)


Influence on the scale microstructure and adhesion

Chromia forming

Alumina forming

  • Increase adhesion spallation resistance

  • Increase the scale compacity and decrease the oxide grain size

  • Supress the pores at the alloy/scale interface

FeCrAl oxidized at 1300°C for 100h

Al2O3 dispersion

Tb4O7 dispersion

Which is the optimum RE quantity?

  • No practical rule

  • It depends on

    • Chemical nature of the RE

    • Size and distribution

    • Chemical interactionwith Ti, C, N

    • Fabrication technique

Temperature range for ODS use










oxidation rate



breakaway oxidation

breakaway oxidation



PM2000 tested in air at 1200°C for 1825 h, cycling at RT every 48h


  • Gen IV systems are highly demanding toward structural materials:high temperature, extended service life, high neutron dose, corrosive environment…

  • ODS steels and alloys could met these high level requirements especially for

    • SFR cladding

    • VHTR heat exchanger or GT-MHR turbine

    • GFR cladding

  • Oxide dispersion strengthening

    • Nanoscale particles = obstacle to dislocation glide

    • Superior HT strength

Conclusion cont.

  • ODS can be produced via powder metallurgy processes

    • Fabrication route and parameters impact microstructure and properties of the final ODS product

  • ODS can be characterized by

    • Microscopy, SEM, microprobe analysis  global microstructure

    • TEM, AP-FIM, DRX, SANS  dispersoids

  • ODS welding

    • Solid state welding processes are to be used (resistance welding)

  • ODS oxidation properties

    • Y is a Reactive Element that improves HT oxidation properties

    • Chromia-forming alloy: lower oxidation rate

    • Alumina forming alloys: improved spallation resistance

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