NASA/TM--2002-211868

Burst Testing of a Superalloy

With a Dual Grain Structure

Disk

John Gayda

Glenn Research Center, Cleveland, Ohio

Pete Kantzos

Ohio Aerospace Institute, Brook Park, Ohio

August 2002
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NASA/TM--2002-211868

Burst Testing of a Superalloy

With a Dual Grain Structure

Disk

John Gayda

Glenn Research Center, Cleveland, Ohio

Pete Kantzos

Ohio Aerospace Institute, Brook Park, Ohio

National Aeronautics and

Space Administration

Glenn Research Center

August 2002
The Aerospace Propulsion and Power Program at

NASA Glenn Research Center sponsored this work.

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

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Available electronically at _sa. _ov
Burst Testing of a Superalloy Disk With a Dual Grain Structure

John Gayda

National Aeronautics and Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Pete Kantzos

Ohio Aerospace Institute

Brook Park, Ohio 44142

Introduction

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

require nickel-base disk alloys with temperature capability in excess of 1300 °F. NASA's Advanced

Subsonic Technology Program initiated a task to develop manufacturing technologies for advanced disk

alloys in the 1990's. Under this program, Honeywell and Allison focused their attention on Alloy 10, a

high strength nickel-based disk alloy, developed by Honeywell for application in regional gas turbine

engines. Since tensile, creep, and fatigue are strongly influenced by grain size, the effect of heat treatment

on grain size and the attendant properties were studied in detail (refs. 1 and 2). It was observed that a fine

grained material offered the best tensile and fatigue properties while a coarse grained material offered the

best creep and crack growth properties. Therefore a disk with a dual microstructure, fine grain bore and

coarse grain rim, should have a high potential for optimal performance.

Additional disk work, funded by NASA's Ultrasafe and Ultra Efficient Engine Technology Programs,

was initiated to assess the feasibility of producing a disk from Alloy 10 with a dual grain structure. The

objectives of these programs were twofold. First, existing Dual Microstructure Heat Treatment (DMHT)

technology was refined and subsequently employed to produce a dual grain structure in full scale disks of

Alloy 10 (ref. 3). Second, key mechanical properties from specimens machined from the bore and rim of

the DMHT Alloy 10 disk were measured and compared to "traditional" solution heat treatments to assess

the benefits of DMHT technology (ref. 4). The results of these tests showed the DMHT disk had a fine

grain, high strength bore similar to that found in subsolvus heat treated disks, and a coarse grain, creep

resistant rim similar to that found in supersolvus heat treated disks.

While test data on small coupons machined from DMHT disks was encouraging, the benefit of the

dual grain structure on the entire disk needed to be demonstrated. To address this issue spin testing of

Alloy 10 disks with a dual grain structure was required. Previous work (ref. 5) has demonstrated the

advantage of a DMHT disk, with a fine grain bore and coarse grain rim, under creep loading versus a

traditional subsolvus disk, with a fine grain structure in the bore and rim. The results of these tests showed

that the DMHT disk exhibited significantly lower growth at 1500 °F compared to a subsolvus disk.

In this paper the results of a room temperature burst test run on the DMHT Alloy 10 disk, which was

previously spun at 1500 °F, will be examined. The burst data will be analyzed using finite element methods to obtain a better understanding of the deformation characteristics of the DMHT disk during the burst

event.

NASA/TM--2002-211868 1
Materials and Procedures

Material Processing

While a complete description of the processing history of the forgings used in this study can be found

elsewhere (refs. 1 and 3), a brief description is presented here for the convenience of the reader. Alloy 10

powder of the composition shown in table 1 was produced by argon atomization. The powder was

screened, canned, HIPed, and extruded to billet. The billet was subsequently cut to mults and isoforged as

"pancake" shapes 14 in. in diameter and 2 in. thick. These forgings were then machined to the shape

shown in figure 1 for heat treatment.

An existing DMHT process was applied to two forgings, one for spin testing and one for coupon testing. The DMHT process was refined for Alloy 10 by Wyman-Gordon based on earlier work described in

U. S. Patent 5,527,020 (ref. 6). It consists of a thermally insulated box that encloses the bore of the disk

but allows the rim to be exposed. The assembly is placed in a furnace at a temperature above the solvus

of Alloy 10. Prior to insertion into the furnace an air flow is begun. This air flow is maintained at a rate

which keeps that portion of the disk inside the insulated box below the solvus. The temperature differential between the bore and rim produces a dual grain structure in the disk. Removal of the disk is a rather

slow process, which necessitated a subsolvus resolution step. Two DMHT forgings were solution heat

treated at 2125 °F for 2 hr, followed by fan cooling and aging at 1400 °F for 16 hr to obtain the high

strength required for disk applications. Visual inspection of the disks revealed no evidence of quench

cracking or other abnormalities after heat treatment. One of the forgings was used to obtain creep and

tensile data while the other was used for spin/burst testing.

Test Procedure

In order to test the entire disk in a spin pit the DMHT forging was machined to the configuration

shown in figure 2. The design was developed to produce a uniformly high stress region in the web of the

disk while minimizing stress in the bore. This philosophy maximizes the deformation in the web, which

encompasses the grain size transition zone of the DMHT disk.

All spin testing was performed utilizing facilities of the Balancing Company located in Dayton, Ohio.

As previously stated, the DMHT disk, which was burst at room temperature, was the same disk tested

in reference 5. The disk was spun at 20 000 rpm and 1500 °F for 24 hr before burst testing at room

temperature. As a result of the previous spin testing at 1500 °F, creep deformation caused the diameter

of the disk to grow by about 0.025 in. and produced the residual stress distribution shown in figure 3.

Spin pit facilities used for this program employed "off-the-shelf' technology with the exception of

the arbor. The arbor used in this test program utilized the design shown in figure 4. Two clamping mechanisms were employed in this design to hold the disk. The primary clamping mechanism was provided by

a 9 in. stretch bolt, while a secondary clamping mechanism was provided by capture flanges. In this

design, the clamping force exerted by the capture flanges increases as the disk grows and therefore tends

to counteract any decrease in clamping force provided by the stretch bolt. As with any spin test, the disk

and arbor were balanced before testing.

Burst testing at room temperature was conducted by increasing the speed of the drive turbine until the

disk failed. Rotational speed was increased at a rate of about 5000 rpm every minute. Disk growth was

monitored with a single proximity gage positioned at the outer diameter of the disk with a 0.1 in. standoff.

NASA/TM--2002- 211868 2
FiniteElement Analysis

Analysis of the burst trial was performed with Algor's finite element package using the 2-D

axisymmetric finite element model shown in figure 5. Also shown in that figure is the grain size distribution used in the analysis. As the stresses exceed the yield strength of Alloy 10 in the burst test an elasticplastic material response with a bilinear stress-strain curve was employed for both fine and coarse grain

sections of the disk with an elastic and plastic moduli of 30 000 ksi and 1000 ksi respectively. For the fine

grain section, at the center of the disk, a yield strength of 180 ksi was used. For the coarse grain section,

at the periphery of the disk, a yield strength of 160 ksi was used. Theses values were picked based on

room temperature tensile data obtained from the companion disk, table 2. As previously stated, an initial

residual stress distribution shown in figure 3 was also employed in this analysis. This residual stress

distribution is based on the analysis of prior creep deformation more fully described in reference 5.

Results and Discussion

DMHT Microstructure

A dual grain structure was successfully produced in two Alloy 10 disks used in this study. The bore of

each disk has a fine grain size, about ASTM 12, while the rim has a coarse grain size, about ASTM 6 to 7.

Both grain sizes are typical of subsolvus and supersolvus heat treatments respectively. The transition

region is located about 4 in. from the center of the disk and is remarkably symmetric. This structural transition is fully documented in figure 6 and was used to determine the boundary location between the fine

grain region and the coarse grain region in the finite element model, figure 5.

Burst Testing

After initial balancing, the DMHT disk was successfully burst on the first attempt. Output from

the proximity gage, which provided a measure of disk growth, was steady except for the critical speed,

between 15 000 and 20 000 rpm, where significant vibration of the disk/arbor assembly was recorded.

Above 30 000 rpm growth of the disk increased dramatically, as seen in figure 7, saturating the output

from the proximity gage around 38 000 rpm. At 39 190 rpm the disk burst in the web as seen in figure 8.

Additional fragmentation of the rim occurred upon impact with the steel liner in the spin pit. Photographic documentation of the disk at burst was attempted, but revealed no useful information as "flashing" obscured the image.

Finite element analysis of the burst trial was performed to understand the deformation behavior of the

DMHT disk. As previously stated, an initial residual stress distribution shown in figure 3 was the starting

point for the analysis. As the disk exhibits a complex multiaxial stress pattern, the Von Mises stress was

employed to provide an overview of the stress distribution within the disk in a single plot. The stress

distribution shown in figure 3 is a result of prior creep deformation associated with spin testing of the

DMHT disk at 1500 °F and was obtained from a 2-D viscoelastic finite element analysis described in

reference 5. Starting with the initial residual stress distribution, the analysis of the burst trial proceeds

by increasing the centrifugal speed of the disk until the ultimate strength of Alloy 10 is exceeded at

any given location within the disk. This occurred at approximately 38 000 rpm in the model as seen in

figure 9. At this speed the stress in the web approaches 250 ksi, which is representative of ultimate

strength values for Alloy 10 as measured in room temperature tensile tests. It is interesting to note the

reversal of the peak stress location in the web, from the coarse grain region at the start of the test to the

NASA/TM--2002-211868 3
finegrainregionattheendof thetest.Thisreflectstheenhancedcreepresistanceofthecoarsegrain

microstructureatelevatedtemperatures, andtheenhancedstrengthof thefinegrainmicrostructureat

lowertemperatures. Diskgrowthduringtheburstrialcanalsobeobtainedanalyticallyandappearedto

verifythemeasureddataasshowninfigure7.

Finally,examinationofthediskfragmentsrevealedthefractureprocessstartedinthewebatasmall

indentation, asshowninfigure10.Several indentationswereintentionallymadeusingahardnesstester

atvariouslocationsonthefaceofthediskandwereusedasadditional"markers"toassessdiskgrowthin

previouspintestingofthisdisk.Nevertheless, thefractureoriginwasrelativelyclosetothehighstress

locationshowninfigure9.Thisfactcoupledwiththegoodagreement betweenmeasuredandpredicted

valuesofburstspeedanddiskgrowthindicatedtheDMHTprocessdidnotcompromisethedurabilityor

reliabilityofthedisk.

Summary and Conclusions

Room temperature burst testing of an advanced nickel-base superalloy disk with a dual grain structure

was conducted. The disk had a fine grain bore and a coarse grain rim. The results of this test showed

that the disk burst at 39 100 rpm in line with predictions based on a 2-D finite element analysis. Further,

significant growth of the disk was observed before failure which was also in line with predictions.

The burst results and previous work documenting the growth of the disk at elevated temperature

have demonstrated the benefits and reliability of DMHT technology for superalloy disks under monotonic

loading, however, additional work is needed to assess the cyclic durability of this materials technology.

.

2.

3.

4.

5.

6.

References

S. K. Jain, "High OPR Core Materials, AOI 4.2.4, Regional Engine Disk Development", Final

Report NAS3-27720, November 1999.

J. Gayda, P. Kantzos and J. Telesman, "The Effect of Heat Treatment on the Fatigue Behavior of

Alloy 10", NASA AST Report 32, February 2000.

A. S. Watwe and H. F. Merrick, "Dual Microstructure Heat Treat Technology", Honeywell Report

21-11619A, May 2001.

J. Gayda, "Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy", NASA/TM--2001-

211168, November 2001.

J. Gayda and P Kantzos, "High Temperature Spin Testing of a Superalloy Disk with a Dual Grain

Structure", NASA/TM--2002-211684, June 2002.

S. Ganesh and R. C. Tolbert, "Differentially Heat Treated Article and Apparatus and Process for the

Manufacture Thereof", U. S. Patent 5,527,020, June 18, 1996.

TABLE 1.--COMPOSITION OF ALLOY 10 IN WEIGHT PERCENT

Cr Co Mo W A1 Ti Nb Ta C B Zr Ni

10.2 15 2.8 6.2 3.7 3.8 1.9 0.9 0.03 0.03 0.1 BAL

NASA/TM--2002- 211868 4
TABLE 2.--ROOM TEMPERATURE TENSILE

PROPERTIES OF ALLOY 10

Heat treat

Subsolvus

DMHT bore

Transition

DMHT rim

Supersolvus

Yield,

ksi ksi

193 257

186 256

176 245

163 231

165 227

Ultimate, Elongation,

percent

18

20

17

19

18

1.50

J

--_" 1,50

5,00

iq 7.00

Full diameter

Full thickness

• I/i

"i

Figure 1 .--Machining plan for heat treat shape of Alloy 10 forgings. All dimensions in inches.

2.75

5.50 ID

6.45

Figure 2.--Machining plan for finished disk used in spin testing. All dimensions in inches.

,j

yon MJses,

psi

58567.2

_ 39501.5

_ 20485.8

Figure &--Initial residual stress distribution in the DMHT disk.

NASA/TM--2002-211868 5
H230

"capture"

flanges

\\

"_ Upper arbor

_ Alloy I 0

stretch bolt

"-- Disk

"-- Lower arbor

i

Figure 4,--Design of the arbor used for spin testing,

Fine grain bore

,,,_ t .......... o["_ _._"T"7- ,j_._._.). .'_

lz l--Fr7-,<x_.x"-A,-.>,,,

.................... y CL:[:[...T..:-_:::I-_.LJ-..z:_[-.J ....

X

Coarse grain rim

Figure &--Assumed distribution of grain size used for modeling the DMHT disk.

NASA/TM--2002- 211868 6
Bore Transition at R = 4 in.

Rim

Figure 6.--Actual grain size in DMHT disk.

NASA/TM--2002-211868 7
0.12

0.10

0.08

L

o 0.06

0.04

O FEA (38,000 rpm prediction)

• EXP (39,190 rpm actual)

O

- O

E

0

0

00

oo

0,02

0.00 .... © .... I.,, _ _ ..... t,, _ _

0 10,000 20,000 30,000 40,000 50,000

Speed, rpm

Figure 7.--Growth of the DMHT disk during the room tennperature

burst trial.

Figure 8.--Major disk fragments after room

temperature burst test.

NASAFFM--2002- 211868 8
(a)

yon Mises,

psi

r---T 58,567.2

_ 20,485.8

yon Mises,

psi

I----T 249,773

_.._ 195,777

141,781

(b)

Figure 9.--Calculated stress distribution in the DMHT disk at the start of the test (a) 0 rpm, and the end of

the test (b) 38,000 rpm.

Figure lO.--Fracture surface showing initiation site in burst test.

NASAFFM--2002-211868 9
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August 2002 Technical Memorandum

4. TITLE AND SUBTITLE 5. FUNDING NUMBERS

Burst Testing of a Superalloy Disk With a Dual Grain Structure

6. AUTHOR(S)

John Gayda and Pete Kantzos

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

WU-708-24-13-00

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NASA TM--2002-211868

11. SUPPLEMENTARY NOTES

John Gayda, NASA Glenn Research Center, and Pete Kantzos, Ohio Aerospace Institute, Brook Park, Ohio 44142.

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

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13. ABSTRACT (Maximum 200 words)

Room temperature burst testing of an advanced nickel-base superalloy disk with a dual grain structure was conducted.

The disk had a fine grain bore and a coarse grain rim. The results of this test showed that the disk burst at 39 100 rpm

in line with predictions based on a 2-D finite element analysis. Further, significant growth of the disk was observed

before failure which was also in line with predictions.

14. SUBJECT TERMS

Superalloy disk

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