John Gayda

Glenn Research Center, Cleveland, Ohio

Dual Microstructure Heat Treatment

of a Nickel-Base Disk Alloy

NASA/TM—2001-211168

November 2001
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NASA/TM—2001-211168

November 2001

National Aeronautics and

Space Administration

Glenn Research Center

John Gayda

Glenn Research Center, Cleveland, Ohio

Dual Microstructure Heat Treatment

of a Nickel-Base Disk Alloy
Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

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Available electronically at http://gltrs.grc.nasa.gov/GLTRS
NASA/TM—2001-211168 1 

DUAL MICROSTRUCTURE HEAT TREATMENT 

OF A NICKEL-BASE DISK ALLOY 

John Gayda 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

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. The AST Disk Progam was initiated to develop manufacturing 

technologies for advanced disk alloys. 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 (Ref. 1). 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. 

A NASA funded disk program was initiated to assess the feasibility of producing a dual 

microstructure disk using Alloy 10. The objectives of this program were twofold. First, 

existing Dual Microstructure Heat Treatment (DMHT) technology would be applied and 

refined as necessary for Alloy 10 to yield the desired grain structure in full scale forgings 

for use in regional gas turbine engines. Second, key mechanical properties from the bore 

and rim of a DMHT Alloy 10 disk would be measured and compared to “traditional”

subsolvus and supersolvus heat treatments to assess the benefits of DMHT technology. 

This paper describes the results of that property comparison. A previous report (Ref. 2) 

describes the DMHT process and resulting microstructure, however, for the reader’s 

convenience the main points of that report are also summarized herein. 

Material & Procedures. Alloy 10 powder of the composition shown in Table 1 was 

produced by argon atomization. The powder was then canned, HIPed, and extruded to 

billet. The billet was cut to mults and isoforged to “pancake” shapes 14” in diameter and 

2” thick. These forgings were machined to the shape shown in Figure 1 for DMHT 

conversion. 

The DMHT process, for Alloy 10, was designed and developed by Wyman-Gordon. It 

consists of a thermally insulated box that holds 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. 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 size in the disk 

as shown in Figure 2. The transition zone between the fine grain region and the coarse 
NASA/TM—2001-211168 2 

grain region in the DMHT disk occurs near the periphery of the thermally insulated box, 

about 3” from the center of the disk. Removal of the disk is a rather slow process which 

necessitated a subsolvus resolution step, at 2125°F/2Hr, followed by an oil quench and 

age at 1400°F/16Hr to obtain the high strength required for disk applications. Visual 

inspection of the disk revealed no evidence of quench cracking or other abnormalities 

after heat treatment. 

The heat treated disk was then sectioned as shown in Figure 3 so that key mechanical 

properties could be measured. Tensile specimens were cut from the bore, transition 

region, and rim of the disk. Creep and crack growth specimens were cut from the bore 

and rim. Fatigue specimens were cut from the bore of the disk. Test temperature and 

other test parameters were identical to those used in previous studies on Alloy 10 (Ref. 3 

and 4) so the DMHT test data could be compared with existing data for “traditional” heat 

treatments. 

Results & Discussion. Since the DMHT disk was oil quenched after resolutioning, the 

DMHT test data will be compared with subsolvus, oil quenched data. However, as 

supersolvus oil quenching is generally not employed on Alloy 10 due to quench cracking 

concerns, the DMHT data will be compared to supersolvus, fan quenched data. For all 

three conditions, subsolvus, DMHT, and supersolvus, data comparison will be limited to 

material given a 1400°F/16Hr age. 

As previously stated, a dual grain structure is produced by the DMHT process. The bore 

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 3” from the center of the disk and is 

remarkably symmetric. The morphology of γ ′ precipitates in the bore of the DMHT disk 

is similar to that observed in most subsolvus heat treatments. However, the rim of the 

DMHT disk contains a significant amount of relatively coarse γ ′, about 1 μm in diameter, 

which is not observed in most supersolvus heat treatments. A more detailed examination 

of DMHT microstructure can be found in Ref. 2. 

Comparison of tensile properties can be found in Table 2 and Figure 4. At room 

temperature and 1300°F, the DMHT properties show bore data is equivalent to subsolvus 

data, while rim data is equivalent to supersolvus data. Further, the DMHT tensile 

properties through the transition region is intermediate in terms of strength and ductility, 

which indicates the grain size transition zone is not acting as a “weak link” in the disk. A 

key difference between DMHT and “traditional” heat treatments is seen in the strength 

gradient from bore to rim. For subsolvus or supersolvus heat treatments the strongest 

material is found at the rim of the disk due to cooling rate effects, however, with DMHT 

the reverse trend is observed, i.e. the bore is stronger than the rim. This is a direct result 

of the grain size gradient in the DMHT disk. 

Creep times to 0.2% strain were measured at 1300°F/100KSI and 1500°F/50KSI in both 

the bore and rim of the DMHT disk. At 1300°F both bore and rim creep times were 

equivalent, running between 700 and 1000 hours. However, at 1500°F creep times of less 
NASA/TM—2001-211168 3 

than 5 hours were measured in the bore, while creep times approached 100 hours in the 

rim. Comparison of the DMHT creep data with subsolvus and supersolvus data is 

presented in Figure 5 using a Larson-Miller approach. As seen in this plot, coarse grain 

microstructures, DMHT rim or supersolvus, yield significant improvements at higher 

temperatures compared to fine grain microstructures, DMHT bore or subsolvus. 

Minimum fatigue life of disks is often observed at intermediate temperatures, between 

700 and 1000°F, and high stresses produced in the bore. For this reason, low cycle 

fatigue tests were run on DMHT bore specimens at 750°F. A strain controlled, 0.3Hz 

sinusoidal waveform with an R-ratio of 0.0 was employed in these tests (Ref. 3). The 

results of these tests are presented in Figure 6. Fatigue lives from subsolvus and 

supersolvus heat treatments are also plotted. As seen in this plot the fine grain 

microstructures, DMHT bore or subsolvus, have superior fatigue lives compared to the 

coarse grain, supersolvus microstructure. This trend is especially pronounced at 0.6%, an 

important design point for disk alloys. 

The last property to be evaluated in this paper was crack growth. Kb bar crack growth 

tests were employed in this study using the same procedures outlined in Ref. 4. Cyclic 

crack growth tests were run at 750°F and 0.3Hz on DMHT bore specimens, while 

90 second dwell crack growth tests were run at 1300°F on DMHT rim specimens. This 

choice reflects design limiting, crack growth criteria for modern disk applications. The 

cyclic crack growth results for the DMHT bore are plotted in Figure 7 along with data 

from subsolvus and supersolvus heat treatments. Very little difference in crack growth 

rates is observed for all three heat treatments. This is typical of crack growth data at 

temperatures below 1000°F, but it does show that DMHT technology does not adversely 

affect cyclic crack growth rates under these conditions. The dwell crack growth results 

for the DMHT rim are plotted in Figure 8 along with data from subsolvus and 

supersolvus heat treatments. Unlike cyclic crack growth, the dwell results at 1300°F 

show significant differences among heat treatments. While the DMHT rim crack growth 

rate is less than that for subsolvus material, it is significantly higher than that for the 

supersolvus material. It is felt that the slow cool after the DMHT conversion and/or the 

subsolvus resolution step may be responsible for the relatively rapid dwell crack growth 

rates in the rim of the DMHT disk. Both these factors would have a significant affect on 

γ ′ morphology and minimal impact on grain size. Recall the grain size of the DMHT rim 

is equivalent to that of supersolvus material, but their γ ′ morphologies exhibited 

significant differences. Additional research is planned to understand and hopefully 

remedy the shortfall of DMHT rim crack growth performance. 

Summary & Conclusions. Existing DMHT technology was successfully applied to Alloy 

10, a high strength, nickel-base disk alloy, to produce a disk with a fine grain bore and 

coarse grain rim. Specimens were extracted from the DMHT disk and tested in tension, 

creep, fatigue, and crack growth using conditions pertinent to disk applications. These 

data were then compared with data from “traditional” subsolvus and supersolvus heat 

treatments for Alloy 10. 
NASA/TM—2001-211168 4 

The results showed the DMHT disk to have a high strength, fatigue resistant bore 

comparable to that of subsolvus Alloy 10. Further, creep resistance of the DMHT rim was 

comparable to that of supersolvus Alloy 10. Crack growth resistance in the DMHT rim, 

while better than that for subsolvus, was inferior to that of supersolvus Alloy 10. The 

slow cool at the end of the DMHT conversion and/or the subsolvus resolution step are 

thought to be responsible for degrading rim DMHT crack growth resistance. 

REFERENCES 

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

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

2. A. S. Watwe and H. F. Merrick, “Dual Microstructure Heat Treat Technology”, 

Honeywell Report 21-11619A, May 2001. 

3. 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. 

4. J. Gayda, “High Temperature Fatigue Crack Growth Behavior of Alloy 10”, 

NASA TM 210814, April 2001. 
NASA/TM—2001-211168 5

Figure 1.—DMHT disk shape.
NASA/TM—2001-211168 6

Figure 2.

—Microstructure of DMHT disk.
NASA/TM—2001-211168 7

Figure 3.—DMHT cut-up plan.
NASA/TM—2001-211168 8

Figure 4.—Comparison of yield strength.
NASA/TM—2001-211168 9

Figure 5.—Comparison of 0.2 percent creep life.
NASA/TM—2001-211168 10

Figure 6.—Comparison of 750 °F fatigue life.
NASA/TM—2001-211168 11

Figure 7.—Comparison of 750 °F cyclic crack growth rate.
NASA/TM—2001-211168 12

Figure 8.—Comparison of 1300 °F dwell crack growth rate.
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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November 2001

NASA TM—2001-211168

E–13033

WU–708–24–13–00

18

Dual Microstructure Heat Treatment of a Nickel-Base Disk Alloy

John Gayda

Superalloy; Disk

Unclassified -Unlimited

Subject Category: 26 Distribution: Nonstandard

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

Existing Dual Microstructure Heat Treat (DMHT) technology was successfully applied to Alloy 10, a high strength,

nickel-base disk alloy, to produce a disk with a fine grain bore and coarse grain rim. Specimens were extracted from

the DMHT disk and tested in tension, creep, fatigue, and crack growth using conditions pertinent to disk applications.

These data were then compared with data from “traditional” subsolvus and supersolvus heat treatments for Alloy 10.

The results showed the DMHT disk to have a high strength, fatigue resistant bore comparable to that of subsolvus

Alloy 10. Further, creep resistance of the DMHT rim was comparable to that of supersolvus Alloy 10. Crack growth

resistance in the DMHT rim, while better than that for subsolvus, was inferior to that of supersolvus Alloy 10. The slow

cool at the end of the DMHT conversion and/or the subsolvus resolution step are thought to be responsible for degrading rim DMHT crack growth resistance.