ods alloy development...ods alloy development ian wright , bruce pint, claudette mckamey oak ridge...

1

OAK RIDGE NATIONAL LABORATORYU. S. DEPARTMENT OF ENERGY

ODS Alloy Development

Ian Wright , Bruce Pint, Claudette McKameyOak Ridge National Laboratory

17th Annual Fossil Energy Materials ConferenceBaltimore, Maryland, April 22-24, 2003

2


Barriers:• Joining• Highly-directional properties: for tubes, transverse strength << axial• Unusual mechanical behavior; strain-rate sensitivity/mode of failure• Cost

Options:• Unconventional joining approaches• Innovative processing to obtain the desired microstructure• Improved quantification of alloy properties and characteristics so that there are no surprises

Scientific approach:• Understand and quantify all available routes for joining• Develop mechanistic understanding for understanding how to control the alloy microstructure; and of the oxidation behavior

Goal: Facilitate the Exploitation of ODS Alloys

3


• Creep strength to temperatures > conventional high-temperature alloys• Potential for use to temperatures where typically ceramics are considered • Excellent oxidation resistance• Resistance to sulfidation; steam oxidation• Current Focus: ODS-FeCrAl alloys

Related work:• Special Metals Inc: ODS tubing• European COST programs• SBIR at MER Corp.• ARM programs:

–Foster Wheeler–UCSD–U. Liverpool

• ORNL: ‘nano-clusters’

Why ODS Alloys?

1

10

100

1000

600 700 800 900 1000 1100 1200

Ave

rage

100

kh S

tress

Rup

ture

Stre

ngth

, MP

a

Metal Temperature,°C

CurrentAverage

TheoreticalMaximum

ODS-FeCrAls(longitudinal)

USC

HT-HX

Afte

r Sta

rr &

Shi

bli,

2002

4


Alloys of Interest

ORNL developmentY2O3-Al2O3Ti,Si15.92.2BalODS-Fe3Al

oxidation comparator‘ZrO2-Al2O3’Ti,Si5.520BalKanthal APM

Dour MetalY2O3-Al2O3Ti4.516.5BalODM751

PlanseeY2O3-Al2O3Ti5.520BalPM2000

956 modificationY2O3-Al2O3Ti,Si5.721.6BalMA956H

Special Metals Inc.Y2O3-Al2O3Ti4.520BalMA956

REotherAlCrFeRemarksComposition, weight percentAlloy

5


Presentation Content

• Joining

• Temperature limits– fireside/steam-side compatibility

• Mechanical properties– transverse (hoop) strength

• ODS-specific issues– strain-sensitivity/mode of failure

6


Joining of ODS Alloys•Joining must avoid

– redistributing the Y2O3 dispersed phase– changing the grain structure size/shape/orientation

•Challenges:– fusion processes: probably a last resort

brazing in COST-522 program– friction/inertia welding: distortion of microstructure– diffusion bonding

TLP: successfully demonstrated on other ODSplasma-assisted diffusion bonding: MER Corp

– others:explosive bonding: successfully demonstrated (COST-501) pulsed magnetic weldingmechanical--threading + brazing

7


Tested Configurations for ODS Joints

Bayonet tubes (COST-522)

ODS tube

Ceramic tube

Joints

HeaderAIR INAIR OUT

ODS tube

Header

‘Safe’ end

Explosive bond

British Gas ‘Harp’ Joint

Conventional weld

ODS Corner block

ODS tubes

TLP bond

TLP joint: HiPPS program

8


Other Possible Configurations for ODS Joints

Reinforced joints

Threaded & brazed Overlapped and brazed Inertial welded

tube-to-flange joint

9


Inertia welding of MA-956 tubes

• 63.5 mm diam. x 7 mm wall thickness, unrecrystallized MA-956 tube

• mechanically robust joints have be produced in using inertia welding

• process window was determined based on the integrity of the joint in bend tests in coupons cut from joined tubes

• reproducibility of joining parameters is excellent

B. Kad/Interface Welding

10


Very sharp demarcation of deformed microstructure after inertia welding

JOINT

Tube outer surface

B. K

ad, 2

003

11


Plasma-Assisted Diffusion Bonding

MA956

• MER Corp-SBIR-II

• ‘clean’ joint

• thin joined zone

• apparent grain continuity

Bond line

12


Bond line

AlTi

Y

O

BSE

SE

• EPMA suggests an accumulation of Ti, Al, Y, and O along the bond line

• predominantly Ti• alloy contains approx. 0.5 %Ti

Bond-line exhibits Ti-rich precipitates

13

TEM indicates discrete particles

Grain/Side 1

Imag

e K

arre

n M

ore

(853

)

BoundaryParticles alongboundary

0.5 µm

Grain/Side 2

14

Particles are TiC and Al2O3

Al2O3 particles at boundary

TiC particles at boundary

Al O

Ti C

0.25 µmImage Karren More (858 + maps 859…)

15


TLP Joining: Collaborative Effort

J. Hurley/N.A. Bornstein, 2003

MA956

•EERC-N.A. Bornstein-ORNL

•TLP approach based on concepts demonstrated for HiPPS joints

•special considerations for application to an alumina scale-forming alloy

•proof-of-concept TLP alloy

Bond line

Extent of interdiffusion

16


Temperature LimitsThe basis for modeling the oxidation-limited lifetimes of these alloys is

relatively straightforward, since:

• they form essentially Al2O3 scales that are uniform in thickness

• there is negligible internal attack (life can’t be equated to section thinning)

• the Al concentration gradient in the alloy is flat until very near the end of life

As a result, it is possible simply to equate the oxidation lifetime to the rate of consumption of the available Al to form the alumina scale:

Life = Al available for oxidation/oxidation rate

17


The oxidation kinetics of these alloys have a characteristic form

P1 P2

0

5

10

15

20

0 200 400 600 800 1000 1200 1400 160

MA956H1300°C

Tota

l Mas

s Cha

nge,

mg/

cm2

Time (hr, in 100 hr cycles)

'Breakaway'(end of life)

Parabolic oxidation 'stage 2'

Linear oxidation'stage 3'

18


Current ModelThe current expression of the model is:

tb = {[S*10-4*ρA*Aτ*e-Qτ/(1.987*T)]2/(3600*A2*e-Q2/(1.987*T))} + {[1/(3600*M)*(V/A)*(ρM/(A3*e-Q3/(1.987*T)))*[(CBo-CBb) – M*S*10-4*(A/V)*(ρA/ρM)*Aτ*e-Qτ/(1.987*T)]} hours

Input required is:1. Alloy data: ρM; CBo; CBb (need to measure CBb)2. Oxide data: ρA; M; S; (constants based on oxide/alloy stoichiometry)3. Alloy oxidation descriptors: Arrhenius data A2, Q2; A3, Q3, and Aτ, Qτ

4. The metal temperature (T), and the component size (V/A)

19


Summary of Oxidation Kinetics

P1 P2

-13.5

-13

-12.5

-12

-11.5

-11

-10.5

-10

0.6 0.65 0.7 0.75 0.8

log

k 2

1000/T°K

ODS-Fe3Al

MA956

MA956: k2 = 53 x e -86,600/RT

ODS-Fe3Al: k

2 = 28 x e -85,554/RT

13001250 1200 1100 1000Temperature, °C

Parabolic oxidation ‘stage 2’

-10.5

-10

-9.5

-9

-8.5

-8

0.6 0.65 0.7 0.75 0.8

log

k 3

1000/T°K

ODS-Fe3Al

MA956H

MA956H: k3 = 0.2 x e -56,900/RT

ODS-Fe3Al: k

3 = 3 x e -62,436/RT

13001250 1200 1100 1000Temperature, °C

Linear oxidation ‘stage 3’

Some alloys haven’t run long enough to establish the Stage 3 oxidation rate

20


Calculated Lifetimes

P1 P2

100

1000

104

105

0.2 0.4 0.6 0.8 1

V/A, mm

1200°C

1300°C

1100°C

1000°C

1250°C

Oxi

datio

n Li

fetim

e, h

Dashed Lines: predicted lives for MA956H using 2-stage model

21


Calculated vs Observed Lifetimes

P1 P2

100

1000

104

105

0.2 0.4 0.6 0.8 1

V/A, mm

Dashed Lines: predicted lives (2-stage model )

1200°C

1300°C

Data Points: observed lifetimes

1100°C1000°C

1250°C

Data for MA956H

22


Calculated vs Observed Lifetimes

P1 P2 Reasonable predictions for 1100-1300°C

100

1000

104

105

0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Oxi

datio

n-Li

mite

d Li

fetim

e, h

r

V/A, mm

Dashed Lines: predicted lives (2-stage model)

1200°C

1300°C

Data Points: Observed Lifetimes

1100°C

1000°C

1250°C

Data for MA956

23


Calculated Lifetimes at 1100°C

P1 P2TUBE 1in OD x 0.1in (25.4 x 2.54 mm), V/A = 0.64 mm

6000

8000

104

3 104

5 104

0.2 0.4 0.6 0.8 1

V/A, mm

ODM751

MA956MA956H

ODS-Fe3Al

Data for 1100°C/2012°F

PM2000

KanthalAPM

Based on CBb values:

FeCrAls--0.001

Fe3Al--0.056

• CBb is difficult to measure

• don’t know if it is T-dependent

24

Cross section of scale on MA956H

Karren More (875 + 876)

Al2O3 scale

1 µm

Alloy substrate

voids in Al2O3 scale(not many)

100h, 1200°C, air

25

Alloy-oxide interface on MA956H

Ti-enriched at interface

Ti

Y-containing particles in alloyThere is also Y-enrichment at Al2O3

grain boundaries (not shown)

Y

0.25 µm

Karren More (879 + maps 880…)

26

Scale cross section on MA956

thicker Al2O3 scale than on 956H

Karren More (881 + 882)

1 µm

voids in Al2O3 scale(many more )

TiC particleat interface

elongated Y-Ti-Si-C grain(no oxygen!) ~4 mm longbetween Al2O3 grains (red bars show ends of grain)

Alloy substrate

100h, 1200°C, air

27


Current approach under-predicts oxidation lifetime

• Predictions should be conservative!

• Are lab results overly affected by specimen shape?

• V/A is a ‘shape factor,’ but doesn’t discriminate among parallelepipeds

• Other shapes:

0.80

0.64

1.13

0.67

V/A mm

452400523Cylinder

46068612.5231.6Standard parallelepiped

28043512.5141.6Parallelepiped-2

283

Volume mm3

353

Surface area mm2

151.6Disc

Width mm

Length mm

Thickness mm

Shape

28


Effect of Specimen Shape

P1 P2

0

5

10

15

20

25

30

35

0 500 1000 1500 2000 2500 3000

MA956, 1250°C

Tota

l Mas

s Gai

n, m

g/cm

2

Time, h

Large p'ped

P'piped(square)

Disc

Cylinder

PLAN

CROSS SECTION

some shapes make less efficient use of the Al reservoir?

29


Possible Shape Factors

Shortest diffusion path from center of specimen thickness to outer surface (dmin) is given by locus of surface of a sphere of radius = d/2

dDe = diffusion length to an edge

dDc = diffusion length into a corner

Longest diffusion path is from the center of mass (= dDcm)

ddDc

dDcmdDe

center of mass

l

w

dmin = d/2d/2

30


Shape Factors: Diffusion Lengths

0.707 x d

—

0.707 x d

EdgedDe

0.5 x sqrt(d2 + diam2)0.707 x dDisc

0.5 x sqrt(l2 + diam2)0.707 x diamCylinder0.866 x d

CornerdDc

0.5 x sqrt(l2 + w2 + d2)

Center of MassdDcm

P’piped

Shape

d = specimen thickness I = specimen lengthw = specimen width

31


Summary

• Joining–3 routes are being evaluated

– inertia welding--controlled microstructural distortion– plasma-assisted diffusion--clean joints (?); examining reinforced design– TLP bonding--questions about amount of residual elements and their effects

–significant effort on other techniques in the Vision 21-SM project–Temperature limits

–generating data for all available ODS-FeCrAls–have an initial working model for life prediction

– continuing long-term exposures to validate and improve the model– issues of over-prediction, and the influence of shape

– lifetimes of 30-70kh at 1100°C in air for typical tube sizes–continuing to generate data in steam, other environments

32


Sensitivity to CBb

P1 P2Don’t know if CBb is T-dependent

104

105

0.2 0.4 0.6 0.8 1

V/A, mm

Data for ODS-Fe3Al, 1100°C/2012°F

PM2000

KanthalAPM

CBb

1%2%3%4%5%

Tube2.5 mm (0.1 in)wall thickness

PM2000, APM: CBb

= 0.1%

ods alloy development...ods alloy development ian wright , bruce pint, claudette mckamey oak ridge...

Documents