Effect of Convection on Primary Dendrites: Observations from Ground-Based and Space Station Processed Samples

ASGSR/ISPS–Orlando,2013

EffectofConvectiononPrimaryDendrites:

ObservationsfromGroundbasedandSpace

StationProcessedSamples.

Masoud Ghods – ClevelandStateUniversity

MarkLauer– TheUniversityofArizona

Surendra N. Tewari – Cleveland State University

Surendra N.Tewari

ClevelandStateUniversity

RichardN.Grugel– MarshallSpaceFlightCenter

RobertE.Erdman– TheUniversityofArizona

D

id R P i i

Th U i

it

f A i

DavidR.Poirier– TheUniversityofArizona

CollaborativeEffortbetweenNASAandEuropeanSpaceAgency:Program

MICAST

(Microstructure Formation in Castings of Technical Alloys under Diffusive and

(MicrostructureFormationinCastingsofTechnicalAlloysunderDiffusiveand

MagneticallyControlledConvectiveConditions)

Outline

¾Introduction:Directionalsolidification(DS)

¾Dendritic array(why“lowgravity”?)

¾Previouslowgdendritic arrayDS

¾Purpose

¾Groundbasedandlowgravityresults

¾Primarydendritespacing

¾Primarydendritetrunkdiameter

¾Radialmacrosegregation

¾Surprises

Dendritic arraymorphologydependsuponDS

processing parameters: G

_l

, R, C

_o

,

Convection

??

processingparameters:G

_l

,R,C

_o

,

Convection

??

1 Primary dendrite arm

Primary dendrite

_{1. Primarydendritearm}

spacing(

O)

:Extensive

literature(SCN/Metals)

2 Secondary/tertiary arm

Primarydendrite

spacing(

O)

2. Secondary/tertiaryarm

spacing:Extensive

SCN/Metals

3. Dendritetipradius:SCN/

p

/

limited(AlCu,PbAu,Pb

Pd)

4. Primarydendritetrunk

diameter(

))

:Limited

(Esaka:Thesis86,Grugel:

92/95)

Primarydendrite

trunk diameter (

))

trunkdiameter(

))

Primarydendritearrayduringdirectional

solidification in a positive thermal gradient

solidificationinapositivethermalgradient

•Thermalprofile:stabilizing •Solutal profile: d bili i ( l i h d d i E 0) Pb 6Sb) a. destabilizing(soluteenrichmentreducesdensity,E_c>0):Pb6Sb) E

Naturalconvectionisinevitableduring

dendritic DSonearth

Th ll t bl Thermallystable Solutally unstable (Pb5.8Sb:40Kcm1_,10Pms1₎

Felicelli Poirier Heinrich (1998)

Axialmacrosegregation

Radialmacrosegregation (Freckle)

Severalnumericalmodels

(Poirieretal.,Beckermann etal.) Felicelli,Poirier,Heinrich(1998)

Naturalconvectionisinevitableduring

dendritic DSonearth

Thermallystable Solutally stable (Al19Cu:81Kcm1_,10Pms1₎ Radialmacrosegregation Dendritesteepling

Noanalyticalornumericalmodels

Naturalconvectiondecreasesprimarydendritespacing

Al26.5wt%Cu

,30K cm1 _{4 2 m s}1 (M.D.Dupouy,D.CamelandJ.J.Favier,Acta.Metall.Mater.Vol.37,No.4,pp.11431157,1989) Al26.5wt%Cu,30Kcm1_, 4.2Pms1 cm1_,4.2Pms1 Al26.5wt%Cu,25Kcm1_, 4.2Pms1 Terrestrial:Solutally unstable, thermally stable mode Terrestrial:Solutally stable, thermallystablemode Microgravity: thermallystablemode 1540± 10Pm 340± 10Pm PrimaryspacingÎ 450± 20Pm

Purpose

MICAST

:Asystematicanalysisoftheeffectofconvectiononthemicrostructural

evolutionincastbinary,ternaryandcommercialAlSibasedalloys.

MICAST6

MICAST 7

RemeltandDSterrestriallygrowndendritic monocrystalsofAl7

wt% Si (9 mm dia 25 cm long) in

Pg

MICAST6

MICAST7

wt%Si(9mmdia,25cmlong)in

Pg.

Advantages: Minimize Thermo-Solutal Convection

Intent: Produce Segregation Free Samples Grown Underg g p Diffusion-Controlled Conditions

Purpose: Better Understand the Relationship between Processing and Microstructure-Development

1.Primarydendritespacing

2.Primarydendritetrunkdiameter

3.Radialmacrosegregation

Microgravityprocessing:

Partiallyremelt andthenDSfrom

terrestriallygrowndendritic monocrystalin

Pg.

MicrogravityprocessedsampleMICAST7

XrayradiographofMICAST7

EutecticMeltBack /Isotherm

MICAST6:ESALowGradientFurnace(1hrheatup,5hr

hold G

_l

~ 20 K cm

1

): 3 8 cm at 5

Pm s

1

11 3 cm at 50

Pm s

1

MICAST6:ESALowGradientFurnace(1hrheatup,5hr

hold G

_l

~ 20 K cm

1

): 3 8 cm at 5

Pm s

1

11 3 cm at 50

Pm s

1

hold,G

_l

20Kcm ):3.8cmat5

Pms ,11.3cmat50Pms

MICAST611

MICAST69

MICAST611

MICAST61

Terrestrialprocessing

Graphitecrucible(~9mmID,~19mmOD),104 _{torr vacuum}

Thermal Gradient at the liquidus temperature

(Al-7%Si, Graphite Crucible, 3 TCs located along crucible length)

700 u re, o C 660 680 TC1_4.2Pm s-1 TC2_4.2 Pm s-1 TC3_85Pm s-1 Temp erat u 620 640 G 42 K cm-1 Translation Distance, cm 0 2 4 6 8 10 12 600 Gl= 42 K cm Gl= 41 K cm-1

Don’t have terrestrial samples which are processed in LGF or LGFQ equivalent

Don thaveterrestrialsampleswhichareprocessedinLGForLGFQequivalent

Comparisonofmicrostructures:Al7%Sidirectionally

solidifiedongroundandonISS(MICAST6)

5Pms1 _50Pms1 MICAST6:20Kcm1 MICAST6SEED 41Kcm1_,22Pms1 TerrestrialDS: 15 K cm1Î 15Kcm Î Convectioncausesdendrite clustering(steepling) and

radial macrosegregation at low radialmacrosegregation atlow thermalgradientandgrowth speedsduringterrestrialDS.

Comparisonofmicrostructures:Al7%Sidirectionally

solidifiedongroundandonISS(MICAST7)

MICAST7SEED 41Kcm1_,22Pms1 21Pms1 _11Pms1 MICAST7:26Kcm1 TerrestrialDS: 24Kcm1Î

Theoreticalmodels:Primarydendritearmspacing

(Diffusioncontrolledgrowth)

(

g

)

•Trivedi (1984)

•HuntLu (1996)

Hunt Lu(1996)

J.D.HuntandS.Z.Lu,MMT,1996

Measured:, G,V

,

,

AlloyProperties:

T

_o

=sol’dn.temp.range,K

 = Gibbs Thomson coefficient m K

 = Gibbs-Thomson coefficient, m K

k = equilibrium partition ratio

TheoreticalModel:PrimaryDendriteTrunkDiameter( )

DendriteTipRadius RapidGrowth “Initial”TrunkDiameter(I₀) Determination Initial Trunk Diameter,I₀ p 12 0 5Ac Esaka(1986Ph.D.Thesis) SuccinonitrileAcetone “alloys” CoarseningRegime e r/ T ip Ra dius 8 10 0.5Ac 1.3Ac 3.6Ac 9.2Ac T runk Di amet e 4 6 FinalTrunk Diameter,I Dl Gl k/(ml R Co (k-1))

1e-5 1e-4 1e-3 1e-2 1e-1 2

= 6 59 ± 1 3 r

Primarydendritetrunkdiameter(

model

After

I

₀

thetrunkdiameterincreasesvia

dissolutionofsecondaryarmsandredepo

iti

th t

k

til th

t

ti

sition onthetrunkuntiltheeutectic.

Kirkwoodripeningmodel(1985)isused.

Assumptions:

1. Secondaryarmmeltsbackbecauseof

itscurvature.

2. Mass of the melted arm deposits on

2. Massofthemeltedarmdepositson

trunksurfacewherethereisnegative

curvature.

Primarydendritearmspacingcomparedwith

HuntLuModel

ical), P m 1600 1800 Hunt-Lu calculations Terrestrial ISS a cing (empir i 1200 1400 Dendrite steepling d ri te arm sp a 800 1000 P rimary den d 400 600 ¾ISSDS:GoodagreementwithpredictionsfromHuntLumodel.

Primary dendrite arm spacing (no convection), Pm

200 400 600 800 1000 1200 1400 1600 1800

P ₂₀₀

¾ TerrestrialDS(“Notsteepled”):GoodagreementwithpredictionsfromHuntLumodel. ¾TerrestrialDS(“steepled”):Convectiondecreases primarydendritearmspacing.

Primarydendritetrunkdiametercomparedwith

trunk diameter model (using r (HuntLu))

trunkdiametermodel(usingr

_t

(Hunt Lu))

ical), P m 300 m eter (empir i 200 250 ite tr unk dia m 100 150 rimary dendr 0 50

Trunk dia model calculations using Hunt-Lu tip radius

Terrestrial ISS

Dendrite steepling

¾ISSDS:Goodagreementwithpredictionsfromthetrunkdiametermodel.

Primary dendrite trunk diameter (no convection), Pm

0 50 100 150 200 250 300

P

r ₀

(M.D.Dupouy,D.CamelandJ.J.Favier,Acta.Metall.Mater.Vol.37,No.4,pp.11431157,1989)

TrunkdiameterfromDupouy etal.Micrographs(Al26.5Cu)

Al26.5wt%Cu,30Kcm1_, 4.2Pms1 Al26.5wt%Cu,30Kcm1_, 4.2Pms1 ( p y, , , , pp , ) Al26.5wt%Cu,25Kcm1_, 4.2Pms1

Terrestrial: Solutally stable

120± 18Pm? 122± 18Pm? 92± 11Pm? TrunkdiameterÎ Terrestrial:Solutally unstable, thermallystablemode Terrestrial:Solutally stable, thermallystablemode Microgravity: 21 21

Naturalconvectionappearstoincreaseprimarydendritetrunk

Radialmacrosegregation measurementinDSAl7%Si

Measure Fraction Eutectic (f

_E

) vs. Fraction Solidified

() wrt steeplecenterofmass.

L

l S l t C t t C

r

_{1 094 + 11 60f}

Local Solute Content: C

₀r

_{= 1.094 + 11.60f}

Comparisonofradialmacrosegregation:Al7%Si

directionally solidified on ground and on ISS

directionallysolidifiedongroundandonISS

Extensiveradialmacrosegregation associatedwith“dendritesteepling”in

terrestrialsamplesisnearlyabsentinISSprocessedsamples.

Numericalmodelingofradialmacrosegregation

during directional solidification of Al7Si alloy

duringdirectionalsolidificationofAl 7Sialloy

MICAST6:GrainseliminationandformationalongDSlength

Surprises??

5

Pms

1

_5>50

_Pms

_1

SEED

Conclusions

d

d

f l

%

ll

• Primarydendritearmspacings ofAl7wt%Sialloy

directionallysolidifiedinlowgravityenvironmentofspace

(

MICAST6 and MICAST7: Thermal gradient ~ 19 to 26 K cm

1

_{, Growth}

(

MICAST 6andMICAST 7:Thermalgradient 19to26Kcm ,Growth

speedsvaryingfrom5to50

Pms

1

)showagoodagreementwith

predictionsfromHuntLuandTrivedi models.

• PrimarydendritetrunkdiametersoftheISSprocessed

samplesshowagoodfitwithasimpleanalyticalmodel

based on Kirkwood’s approach proposed here

basedonKirkwood sapproach,proposedhere.

• Naturalconvection,

decreases primary dendrite arm spacing

– decreasesprimarydendritearmspacing.

– appearstoincreaseprimarydendritetrunkdiameter.

– produces radial macrosegregation

producesradialmacrosegregation.

Canwepredictmicrostructural inhomogeneity induced

bynaturalconvectionduringterrestrialDSofindustrial

y

g

components?

Processingparameters

Î DiffusivetransportÎMicrostructureÎProperties

•Well understood

(Al19Cu:81Kcm1_,10Pms1₎ (Pb5.8Sb:40Kcm1_,10Pms1₎

•Wellunderstood

P

i

t

Î N t

l

ti

Î Mi

t

t

Processingparameters

Î Naturalconvection

Î Microstructure

•Notunderstood

G t f l f

t f

Gratefulforsupportfrom

• NASA

• NASA

• ESA

• DLRMUSC

• ALCOA