2005-10-06 Neumann Herbstschule - AG Kristallographiecrysta.physik.hu-berlin.de/as2005/pdf/as2005_talk_13_Glatzel.pdf · University Bayreuth Uwe Gl4 atzel, Metals and Alloys Superalloys

2University Bayreuth Uwe Glatzel, Metals and Alloys

Single Crystal Nickel Based Superalloys

for High Temperature Applications- Microstructure, Properties, Anisotropy -

Uwe GlatzelUwe GlatzelMetals and Alloys

University Bayreuth


Content• motivation: history, application field

• processing

• microstructure, misfit

• anisotropic properties(modulos, creep behavior)

• dislocations, stress induced diffusion

• Outlook (alloys with reduced density, platinum basedsuperalloys)

TU-Berlin (SFB 339)Uni Jena


Superalloys for Extreme Demands

Single crystal nickel based superalloys as material for firstrotating blades after thecombustioncombustion chamberchamber in aircraft flight engines.

fan(thrust)

compressor (titanium)

gas temp.: 1500°C

material: 1100°C

⇒ const. stress of about 100 MPa

(≈ 1 car/cm2)

20.000 rpm


Big, Single Crystal Blade

Blade forstationarygas turbinefor powerproduction

≈ $ 40.000


Coefficient of Efficiency

in

outinmax.theor T

TT −=η

regular fuel car engine: 23%

diesel car engine: 27%

aircraft turbine: 30-35%

stationary gasturbine: 40%

gas and steam generation: 54%

gas + steam + long distance heating: 87%

increase of Tin increasescoefficient of efficiency


Increase in Temperature due to Improved Construction and Material

constantimprovement5-10°C/year

ceramics??platinumbase alloys?

year1950 1960 1970 1980 1990 2000

tem

pera

ture

[°

C]

500

1000

1500

2000

improved materials

improved coolingcivilianmilitary

material temperature

gas temperature

polycrystalline

directional solidified

single crystal

iron base

nickel base alloys


Why nickel based superalloys?Anomalous flow stress behavior of the

intermetallic phase Ni3Al:

temperature [°C]

0 200 400 600 800 1000

flow

str

ess

[M

Pa]

0

100

200

300

400

500

superalloy as cast

superalloy heat treated

Ni3Al

nickel solid solution0 %

100 %

70 %

Copley and Kear, Trans. AIMEVol. 239 (1967), 984-992


History

≈ 1980: Inconel 738 (polycrystalline) => 738 LC (single crystal)50-60vol.% γ' phase, 3wt.% W, 0% Re

SRR 99, CMSX-6 (first generation)60-70% γ', 9% W, 0% Re

≈ 1990: CMSX-4 (second generation)> 70 % γ', 6% W, 3% Re

≈ 1995: CMSX-10 (third generation)> 70 % γ', 6% W, 6% Re

Costly and time intensive heat treatment:3-stage homogenization, controlled rapid cooling2-stage aging



• processing






Single Crystal Growing

R = ∆T/∆x

v = ∆x/∆tR⋅v = ∆T/∆t

determines the dendrite spacing

[001] crystaldirection

alternative: seeding technique


Heat Treatment

example: CMSX-4 standard heat treatment

homogenization:1 h @ 1280°C, 2 h @ 1290°C, 6 h @ 1300°Ccooling rate 150-400°C/min.

aging6 h @ 1140°C für 6 h, 870°C für 16 h

if possible, combined with coating treatment



• processing






Microstructuretwo-phase, single crystal:

face-centred-cubicmatrix(nickel solid solution)

Ni3Al => fcc, but superlatticeordering, L12 or γ' Phase dislocation free


Ni3Al ⇔ nickel solid solution

nickel atoms in face centre

aluminium atoms on cube corners

in nickel solid solution statistical distribution of atoms

dNi3Al = 358,0 pm dnickel solid sol. = 358,7 pm


Optimal Precipitation Hardening

• round particles(better than needle-shaped)

• high volume fraction• finely dispersed• small particles ( )• hard precipitates,

soft matrix

500 nm

in text books no information given on optimum misfit


Constrained ↔ UnconstrainedMisfit

Matrix

γ' Phase

Matrix

γ' Phase

high compression stresses in matrix parallel to interface

Small difference in lattice parameter, ∆d/d ≈ - (1 – 3)·10-3

resulting in a coherent interface and internal stresses:

MPa300100d

dE −≈∆

=σ

isotropic misfitmisfit dependent of planes taken for Bragg reflection


Two-Phase but 100% Coherent=> Internal Stresses


Stress Distribution

two views of 1/8 of the γ' cube with surrounding matrix

stress σxx [MPa]


Stress Distribution Schematical

compressiontension

in matrix

in γ' phase


"Macrostructure"

single crystal,but no hgomogeneousdistribution of tungstenand rhenium

[001][010]

dendrite spacing≈ 1/4 mm

⇒ therefore local variation of misfit


Variation of Misfit due to Dendritic Segregation

• negative misfit in dendrite

• close to zero in interdendritic region

[10-3]

-5

-4

-3

-2

-1

0

1

DendritInterdendrit Interdendrit

Fehlpassung gemessen mit CBED

Neutronenstreuung

Völkl, Glatzel, Feller-Kniepmeier; Acta mat. 46 (1998) 4395


200 400 600 800

-300

-250

-200

-150

-100

-50

Local Stress Variation

up to 300 MPa compression stress in matrix channels in dendrite

Spa

nnun

g [

MP

a]

spacing ≈ 250 µm

dendrite

interdendritic region

5 10 15 20

-17.5-15

-12.5-10-7.5-5

-2.5

spacing ≈ 0,5 µm



• processing






Elastic Anisotropy togetherwith Misfit:

Explanation for cuboidal γ' precipitates, with {100} phase boundary planes

thereby very high volume fractionsachievable


Temperature Dependence of Elastic Constants

T [K]

200 300 400 500 600 700 800 900 1000 1100 1200 1300

E<

100>

[

GP

a]

80

90

100

110

120

130

140

E<100>

γ'

MatrixCMSX-4

ultrasonic speed measurements at RTMatrix

CMSX-4

Siebörger, Knake, Glatzel; Mat. Sci. Eng. A298 (2001) 26

Important: anisotropy stays on the same high level of ≈ 2.8

T [K]

200 300 400 500 600 700 800 900 1000 1100 1200 1300

G[1

00]

85

90

95

100

105

110

115

120

125

130

135

140

145

150

G<100>

CMSX-4

Matrix

γ'

[GPa

]

ultrasonic speed measurements at RT


Creep Deformation


High TemperatureDeformation up to 1400°C

temperature and load are kept constant


Orientation Dependenceat 850°C

(T = 850°C) l0

Single crystal with load axis parallel to [001]

constant load of 500 MPa

"horizontal" / "vertical" matrix channels

CMSX-41123K, 500MPa

Strain [%]0 1 2 3

Str

ain

Rat

e [

1/s]

10-8

10-7

10-6

+

A 1

A 2B 1

M

+

B 2

C 1

+ Fracture

C1

[001] [011]

[111]

A 1

A 2M

B 2

B 1

→ [001] orientation shows best creep performance


Orientation Dependenceat 980°C

A

C

C

A

anisotropy has less influence at higher temperatures

strain

stra

inra

te [

s-1]


Changes in Morphology980°C, 350 MPa, 28 h

[001]

[100][010]

[100][110]

[110]

rafts with planes normal to theexternal [001] load axis

bars with long axisparallel to <100>

σ σ


[001] crystal orientation:

• fastest growing direction +

• elastic soft +

• leads to {001} phase boundaries of the cuboidal γ' particles +

• direction of best creep properties +



• processing






FEM calculation of stress distribution (pure elastic)

No external loadhigh compression stresses in

matrix channels parallel to thephase boundaries

With an external load (500 MPa)high stress levels in horizontal

channels; low stress levels in vertical channels

compressiontensionσ

pure elastic at time t = 0


FEM calculations of stress distributionafter creep (plastic deformation)

(Matrix according to Norton creep, γ' phase yields plastisch)

tension

dislocations networks:

horizontaler channel:High density of edgedislocations with additional half plane within γ' phase

hydrostatic tension p ≈ σext.

vertical channel:network of LH- and RH-screw dislocations,1/3 density

σext.


TEM Dislocation Structure:

load axis

longitudinal sectionε = 1 %

cross section, ε = 2.1 %external load normal to view plane

look onto horizontal matrixchannels, vertical channels edge-on.

horizontal

channel


Stress Induced Diffusion (EDX-TEM)

Large atoms diffuse from vertical to horizontal channel.

σext. ≈ 500 MPa

channelverticaltungsten

channelhorizontaltungsten c2.1c ⋅=

Schmidt and Feller-Kniepmeier, 1993 (SRR99, 760°C)


additionally: compostion variation dendrite – interdendritic regionand morphology changes

γ'FEM+

TEM

TEM + FEM

γ'

W

W

W W

Re

Re Re

TEM +

EDX

γ'

+

-

neutron diffr.

dislocation networks in phase boundaries(plastic deformationaccording to localstress distribution)

=> high hydrostatic stress level in horizontal channel

=> stress induceddiffusion

change in latticeparameter (misfit). Change and reduction of stress level.

σext

Summary:changes occuring durig creep



• processing






Outlook

• International patent (Glatzel, Mack, Wöllmer, Wortmann):Reduce W and Re content reduced density, improved phase stability, larger temperature window for solution heat treatment, cheaper LEK 94.Within GP 7000 engine for Airbus A 380.

• DFG-Project "Platinbasissuperlegierungen":Pt-Al-Cr-Ni (+ Ta, + Ti) alloys can copy successful system of nickel based superalloys (coherent L12 ordered, cuboidal γ' particles withhigh volume fraction embedded in fcc-matrix)


LEK 94

Larsen-Miller-ParameterP = (T+273) [20+log tB] 10-3

25 26 27 28 29 30 31 32

stre

ss

[MP

a]

120

230

500CMSX-6 [Wortmann 88] 8.0 g/cm3

CMSX-4 [Erickson 94] 8.7 g/cm3

CMSX-4 [Frasier 90] 8.7 g/cm3

LEK-2 8.5 g/cm3

LEK-4 8.2 g/cm3

LEK-5 8.2 g/cm3

LEK-3 8.1 g/cm3

LEK-6 8.3 g/cm3

LEK-1C 8.4 g/cm3

LEK-1B 8.3 g/cm3

LEK-1A 8.2 g/cm3

∆T = 10 K

24 K

10 K

29 K

not corrected withdensity!

Patente: D, Europa, USA, Kanada, Japan


MicrostructurePlatinum Based Superalloy

Pt77Al14Cr6Ni6

12h @1500°C + 120h @1000°C

CMSX-4, samemagnification

Hüller et al., Met.Mat.Trans. A, 36A (2005), 681


MisfitPlatinum Based Superalloys

Pt80Al11Cr3Ni6

Pt84Al11Cr3Ni2

Pt77Al10Cr3Ni10


Creep PropertiesPlatinum Based Superalloys

Maximum Stress inCompression withStrain Rate 10-5 s-1

Temperature [°C]

700 800 900 1000 1100 1200 1300 1400

Str

ess

10

100

1000

Pt82Al7Cr6+Ta5

Pt82Al7Cr6+Ti5

CMSX-4 (single crystal !)

Pt77Al12Cr6+Ni5Pt77Al12Cr6+Fe5

Pt77Al12Cr6+Co5

γ' precipitate dissolutionin Ni-base alloys

γ' precipitate dissolutionin Pt-base alloys


Juni 2005 Bayreuth

Documents

2005-10-06 Neumann Herbstschule - AG Kristallographiecrysta.physik.hu-berlin.de/as2005/pdf/as2005_talk_13_Glatzel.pdf · University Bayreuth Uwe Gl4 atzel, Metals and Alloys Superalloys