NASA/TM--2001-210814

High Temperature Fatigue Crack

Growth Behavior of Alloy 10

John Gayda

Glenn Research Center, Cleveland, Ohio

National Aeronautics and

Space Administration

Glenn Research Center

April 2001
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INTRODUCTION

Gas turbine engines for future subsonic aircraft will probably have higher pressure ratios

which require nickel-base superalloy disks with 1300 to 1400°F temperature capability.

Several advanced disk alloys are being developed to fill this need. Under NASA's AST

Program, manufacturing technologies for two advanced disk alloys were studied by a

team representing four engine companies, GEAE, PWA, Honeywell (Allied Signal), and

Allison. GEAE and PWA focused their attention on an advanced disk alloy suitable for

large engine applications developed under NASA's HSR Program, while Honeywell and

Allison opted to focus their attention on Alloy 10, a high strength nickel-base disk alloy,

which was developed by Honeywell for application in smaller gas turbine engines. The

initial evaluation, i.e. tensile and creep properties, of Alloy 10 were run under the AST

Disk Program (Reference 1). However, due to funding limitations, fatigue and crack

growth evaluation were moved to NASA's Ultrasafe and UEET Programs.

This paper describes Alloy 10 crack growth studies conducted under Ultrasafe and

UEET. The crack growth program was divided into two parts. The first part of this study

was designed to evaluate the effects of solution temperature, cooling rate, and

stabilization on crack growth. The second part of this study was designed to evaluate the

effects of niobium and tantalum on crack growth. Previous work under NASA's HSR

Program has shown that heat treatment and alloying additions can have dramatic effects

on crack growth rates of nickel-base superaUoys at elevated temperatures.

MATERIAL AND PROCEDURES

Alloy 10 is a high strength nickel-base superalloy, with a gamma prime content of about

55%. Evaluation of heat treat parameters on crack growth rates were run using existing

forgings from the AST Program, while alloying effects were studied using small

extrusions to stay within overall budget constraints. The compositions of baseline Alloy

10 and the Alloy 10 mods are presented in Table I.

The forgings were produced from argon atomized powder which was HIPed and extruded

to 6" diameter billet. Mults were cut from the billet and isothermally forged into

"pancake" shapes about 14" in diameter and 2" thick. Six forgings were given different

heat treatments, defined in Table II. As previously stated, these heat treat options were

designed to study the effect of solution temperature, cooling rate, and stabilization. Three

solution temperatures were employed, 2125, 2160, and 2190°F. These solution

temperatures were intended to produce target grain sizes of ASTM 11, 8, and 6

respectively. As cooling rate from the solution temperature can impact mechanical

properties it was varied as follows. Fan cooling, which gives moderately fast cooling

rates, was applied at all three solution temperatures. A faster cooling rate, produced by oil

quenching, was also tried at 2125°F. The effect of a stabilization treatment, 1550°F for 4

hours, was studied for oil quenched forgings with the 2125°F solution treatment and fan

cooled forgings with the 2190°F solution treatment. Stabilization treatments are used to

minimize residual stresses, but are also known to impact mechanical properties by

NASA/TM 2001-210814 1
coarsening gamma prime precipitates and promoting the formation of Cr23C6 carbides. A

final age, 1400°F for 16 hours, was also applied as the last step in all heat treatments.

The Alloy 10 modifications listed in Table I were designed to study the effects of

changes in the niobium and tantalum content on crack growth, especially dwell crack

growth. Compared to the baseline chemistry, tantalum levels were increased while

niobium levels were decreased. The rationale for these choices were tied to the opinion

that niobium accelerates crack growth while tantalum retards crack growth. As previously

stated, material for this part of the study was obtained from small extrusions, produced

from argon atomized powder which was compacted and extruded to 3" diameter billet.

EDM was used to prepare heat treat blanks, 0.5"diameter by 3" long. These blanks were

then solutioned at 2100F to obtain a fine grain, subsolvus microstructure or 2190F to

obtain a coarse grain, supersolvus microstructure. The small blanks were air cooled and

subsequently aged at 1400F for 16 hours.

Crack growth rates were determined using a surface-notched specimen shown in Figure

1. The details of the test procedure are described in Reference 2. However, in brief,

testing consisted of precracking the specimen at room temperature followed by elevated

temperature crack growth measurement using a potential drop system for accurate

determination of crack growth rates. As high temperature dwell crack growth rates of

nickel-base superalloys often limit disk life, comparison of heat treat and composition

effects on crack growth were made at 1300F with a 90 second dwell at peak load

employing an R-ratio of 0.1. For the heat treat study the crack growth specimens were

machined from the outer rim of the forgings such that the length of the test bar was

parallel to the hoop direction. For the composition study, the crack growth specimens

were machined such that the length of the test bar was parallel to the extrusion direction.

RESULTS AND DISCUSSION

Heat Treat Study. AS heat treat also affects tensile properties, a short discussion of this

topic is warranted. The 1300F tensile data are summarized in Table 111. One can see

increasing solution temperature (coarser grain size) results in less strength, while higher

cooling rates increase strength. Both of these trends are expected, however, stabilization

has little effect on strength, unlike other nickel-base disk alloys where stabilization often

causes a pronounced drop in tensile strength (Reference 3).

Before comparing the effect of heat treatment on crack growth, an examination of the

relation between temperature, dwell time, and crack growth rates for Alloy 10 will be

made for the subsolvus, fine grain microstructure. Figure 2 shows that going from borelike temperatures, 750F, to rim-like temperatures, 1300F, produce about a ten fold

increase in cyclic crack growth rates. The addition of a 90 second dwell at 1300F

produces a fifteen fold increase in cyclic crack growth rates. Further, the temperature

dependency of the dwell cycle is quite dramatic, as shown in Figure 3, decreasing the

temperature from 1300F to 1200F decreases dwell crack growth rate about ten fold. The

high temperature dwell cycle simulates conditions encountered at the rim of a turbine

NASA/TM--2001-210814 2
disk during takeoff and landing of commercial jets. Therefore improving high

temperature dwell crack growth resistance can enhance disk life.

The effect of heat treatment on 1300F dwell crack growth for Alloy 10 is presented in

Figure 4. Several trends are immediately obvious. First, higher solution temperature

(coarser grain size) produces a tremendous improvement. Second, stabilization produces

a significant improvement for the supersolvus, coarse grain microstucture, and a modest

improvement for the subsolvus, fine grain microstructure. Finally, increasing cooling rate

(fan versus oil) for the subsoivus material is seen to have a somewhat detrimental effect

on dwell crack growth rates. It appears that a supersolvus heat treatment with a

stabilization cycle would be the preferred heat treatment for Alloy 10 from a crack

growth standpoint. Further, adopting this philosophy does not appear to have a negative

impact on crack growth rates at bore-like temperatures, as seen in Figure 5. However,

coarse grain sizes decrease tensile strength, while stabilization is known to reduce creep

properties of Alloy 10 (Reference 1). With these observations in mind, the use of

advanced processing technologies, which can produce a coarse grain rim and a fine grain

bore, would be the preferred option for Alloy I0 to obtain the optimal balance between

tensile, creep, and crack growth requirements for turbine disks.

Composition Study. While heat treat offers options for improving crack growth resistance

of Alloy 10, changes in composition may also provide improved crack growth resistance.

With this in mind, niobium and tantalum effects were studied. As seen in Figure 6,

significant changes in the alloy's niobium:tantalum ratio had minimal impact on

subsolvus dwell crack growth resistance, although decreasing the ratio does appear to

produce a small benefit. For the supersolvus, coarse grain microstructure the effect is

more pronounced, although the maximum benefit is only about a two fold decrease in

dwell crack growth rate on decreasing the niobium:tantalum ratio. It is interesting to note,

that stripping all niobium from the alloy had very little effect, suggesting that increasing

tantalum content was probably more important with respect to improving dwell crack

growth resistance. Further, as shown in Table IV, removing all niobium from the alloy

produces a significant drop in tensile strength.

SUMMARY AND CONCLUSIONS

Methods to improve the high temperature, dwell crack growth resistance of Alloy 10, a

high strength, nickel-base disk alloy, were studied. Two approaches, heat treat variations

and composition modifications, were investigated. Under the heat treat approach, solution

temperature, cooling rates, and stabilization, were studied. It was found that higher

solution temperatures, which promote coarser grain sizes, coupled with a 1550F

stabilization treatment were found to significantly reduce dwell crack growth rates at

1300F. Changes in the niobium and tantalum content were found to have a much smaller

impact on crack growth behavior. Lowering the niobium:tantalum ratio did improve

crack growth resistance and this effect was most pronounced for coarse grain

microstructures.

NASA/TM--2001-210814 3
Based on these findings, a coarse grain microstrucmre for Alloy 10 appears to be the best

option for improving dwell crack growth resistance, especially in the rim of a disk where

temperatures can reach or exceed 1300F. Further, the use of advanced processing

technologies, which can produce a coarse grain rim and fine grain bore, would be the

preferred option for Alloy 10 to obtain the optimal balance between tensile, creep, and

crack growth requirements for small gas turbine engines.

REFERENCES

1. S. K. Jain, "High OPR Core Material (AoI 4.2.4), Regional Engine Disk

Development", Final Report, NAS3-27720, November 1999.

2. R. H. Vanstone and T. L. Richardson, Potential-Drop Monitoring of Cracks in

Surface Flawed Specimens, ASTM STP 877, 1985, pp. 148-166.

3. J.C. Chesnutt, R. G. Tolbert, and D. P. Mourer, "High OPR Core Materials (AoI

4.2.5), Forging Process Definition - Alloy 2", Final Report, NAS3-27720,

November 1999.

NASA/TM--2001-210814 4
TABLE I. COMPOSITION OF ALLOY 10 AND MODS.

Co Cr AI Ti Mo W Nb Ta C B Zr N|

MOD1 15.0 11.0 3.8 3.8 2.5 5.7 0.g 0.9 0.04,0.03 0.10 56.23

MOD2 15.0 11.0 3.8 3.8 2.5 5.7 0.9 1.8 0.04 0.03 0.10 55.33

MoD3 15.0 11.0 3.8 3.8 2.5 5.7 0.07 i.8 0:04!0.03 0.10 56.23

ALLOY10 15.0 11.0 3.8 3.8 2.5 5.7 1.8 0.9 0.04 0.03 0.10 55.33

NASAfrM--2001-210814 5
TABLE II. HEAT TREAT MATRIX FOR ALLOY 10 FORGINGS.

ID

SUB/FAN

SOLUTION STABILIZE AGE

2125F/2.5HR/FAN 1400F/16HR/AC

SUB/OIL 2125F/2.5HPJOIL

SUB/OIL/STAB 2125F/2.5HR/OIL

NEAR/FAN 2160F/2.5HR/FAN

NONE

NONE"

GRAIN SIZE

ASTM 11.3

1400F/16HR/AC

1400FI16HRJAC ASTM 11.5

1550F/4HR/AC 1400F/16HR/AC ASTM 11.5

NONE

NONE

ASTM 7.9

SUP/FAN 2075FIIHR+2190F/2.5HR/FAN 1400F116HR/AC ASTM 6.1

SUP/FAN/STAB 2075FIIHR+2190F/2.5HR/FAN 1550FI4HR/AC 1400F/16HPJAC ASTM 6.4

NASA/TM--2001-210814 6
TABLE Iil. 1300F TENSILE DATA FORALLOY 10 FORGINGS.

ID q

SUB/FAN

SUB/OIL

SUB/OIL/STAB

!NF__AR/FA'N

SUP/FAN '

SUP/FAN/STAB

0.2% YiELD(KSI)

163

175

i74

- i59

i51

152

UTS (KSl),,

193

203

202

lg7

195

195

ELONG(%)

9

8

8

16

17

19

GRAIN SIZE

ASTM 11.3

ASTM 11.5

ASTM 11.5

ASTM 7.9

ASTM 6.1

ASTM 6.4

NASA/TM_2001-210814 7
TABLE IV. 1300F TENSILE DATA FOR ALLOY 10 MODS.

Nb:Ta RATIO

1.7

0.8

0.4

0.0

1.7

0.2% YIELD(KSI)

172

167

169

164

167

UTS (KSI)

203

199

201

196

212

0.8 160 204

0.4 162 207

0.0 156 200

ELONG(%) GRAIN SIZE

9 ASTM 11,8

11 ASTM 11.4

10

12

ASTM 12.0

ASTM 11.6

16 ASTM 7.7

"i8 ASTM 7.6

17 ._STM 7.9

19 ASTM 8.1

NASA/TM--2001-210814 8
FIGURE 1. DESIGN OF CRACK GROWTH SPECIMEN.

.'5t2

.508

2 PL_cr_;

.172

.t68

.086

.084

.;_0!

.199

_25 o

.015 '"

7J_

P

--j •50l n]4.

A9')

2 PLACES

101ki :000,51

SEE NOTCH--.%

DETAIl.

1. \

5-

.49

II I_.ACCS

INR

pt _.,ccs

_n 3 ¢0¢11[It mlU.

____ ,. N'_

NOTCH DETAIL _ , NOTCH DETAIL (VIEW SECT

.' i!

NOTCH CEHTER TO BE VlrH[N .003" OF ]BOI'H CENTERLIflE_;

I

A-A)

NASA/TM--2001-210814 9
FIGURE 2. CYCLIC CRACK GROWTH DATA FOR

SUBSOLVUS/FAN COOLED HEAT TREAT.

le-2 --

le-3 -,

....

0

0

r-

_ le-4 - -

Z

le-5 -

le-6 -

f.

.... " " I

v 1300°F/NO DWE

® 750°F/NO DWELL

© 1300°F/90 SEC UWELL

_T T 1

10 15 20 25 30 35 40 50

DELTA K (KSI SQRT IN)

NASA/TM--2001-210814 10
FIGURE 3. TEMPERATURE EFFECT ON DWELL

CRACK GROWTH DATA FOR SUBSOLVUS

MICROSTRUCTURE.

O

(D

r/)

r'-

o_

V

(0

"O

le-4 -

le-5 -

le-6 -

I

le-7 -

10

• i ....

'1 '"

.... I _=="

15 2O

0

A

25 30 35 40

Kmax (ksi sqrt in)

1300°F

1300°F

1200°F

5O

NASA/TM_2001-210814 11
FIGURE 4. EFFECT OF HEAT TREATMENT ON DWELL

CRACK GROWTH DATA FOR ALLOY 10.

le-4

le-5 -

O

m

._c le-6

N

le-7

le-8

10

1300F

,,

• sUB/FAN

O SUB/OIL

/_ SUP/FAN/STAB

SUP/FAN

* NEAR/FAN

15 2O 25 30 35 40 5O

Kmax (ksi sqrt in)

NASA/TM--2001-210814 12
FIGURE 5. EFFECT OF HEAT TREATMENT ON

CYCLIC CRACK GROWTH DATA FOR ALLOY 10.

le-4 -

0

o_

tZ

"0

(_

"0

le-5 -

le-6 -

750F

le-7 - --_

10 15 20 25 30

DELTA K (KSI SQRT IN)

SUB/OIL/STAB

NEAR/FAN

SUP/FAN/STAB

35 40 50

NASA/TM--2001-210814 13
FIGURE 6. EFFECT OF NIOBIUM: TANTALUM RATIO

ON DWELL CRACK GROWTH DATA.

O

(D

r-

"O

"10

le-4 -

le-5 -

le-6 -

le-7 -

10

I'll

1300F

15 2O 25 30 35

(ASTI_)/Nb:Ta

• SUP(7.7)/1.7

• SUP(7.6)/0.8

• SUP(7.9)/0.4

• SUP(; 1)/0.0

[] SUB(11.8)/1.7

A SUB( 1.4)/0._

_7 SUB(12.0)/0A

O SUB(11.6)/0.C

T l

40 50

Kmax (ksi sqrt in)

NASA/TM--2001-210814 14

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April 2001 Technical Memorandum

4. TITLE AND SUBTITLE

High Temperature Fatigue Crack Growth Behavior of Alloy 10

S. AUTHOR(S)

John Gayda

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

John H. Glenn Research Center at Lewis Field

Cleveland, Ohio 44135-3191

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration

Washington, DC 20546-0001

11. SUPPLEMENTARY NUII::S

5. FUNDING NUMBERS

WU-708-24-I 3-00

8. PERFORMING ORGANIZATION

REPORT NUMBER

E-12729

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AGENCY REPORTNUMBER

NASA TM--2001-210814

Responsible person, John Gayda, organization code 5120, 216--433-3273.

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This publication is available from the NASA Center for AeroSpace Information. 301--621-0390.

13. ABSTRACT (Maximum 200 words)

12b. DISTRIBUTION CODE

Methods to improve the high temperature, dwell crack growth resistance of Alloy 10, a high strength, nickel-base disk

alloy, were studied. Two approaches, heat treat variations and composition modifications, were investigated. Under the

heat treat approach, solution temperature, cooling rates, and stabilization, were studied. It was found that higher solution

temperatures, which promote coarser grain sizes, coupled with a 1550 °F stabilization treatment were found to significantly reduce dwell crack growth rates at 1300 °F. Changes in the niobium and tantalum content were found to have a

much smaller impact on crack growth behavior. Lowering the niobium:tantalum ratio did improve crack growth resistance and this effect was most pronounced for coarse grain microstructures. Based on these findings, a coarse grain

microstructure for Alloy 10 appears to be the best option for improving dwell crack growth resistance, especially in the

rim of a disk where temperatures can reach or exceed 1300 °E Further, the use of advanced processing technologies,

which can produce a coarse grain rim and fine grain bore, would be the preferred option for Alloy 10 to obtain the

optimal balance between tensile, creep, and crack growth requirements for small gas turbine engines.

14. SUBJECT II'_HMS

Superalloy; Crack growth

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