John Gayda and Pete Kantzos

Glenn Research Center, Cleveland, Ohio

Burst Testing and Analysis of Superalloy Disks

With a Dual Grain Microstructure

NASA/TM—2006-214462

October 2006
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John Gayda and Pete Kantzos

Glenn Research Center, Cleveland, Ohio

Burst Testing and Analysis of Superalloy Disks

With a Dual Grain Microstructure

NASA/TM—2006-214462

October 2006
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NASA/TM—2006-214462 1 

Burst Testing and Analysis of Superalloy Disks 

With a Dual Grain Microstructure 

John Gayda and Pete Kantzos 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Introduction 

As operating temperatures of gas turbine engines increase, there is a need for superalloy turbine disks 

which can operate with rim temperatures in excess of 1300 °F. To meet this need, a new generation of 

nickel-base superalloys, such as Rene 104 (initially designated ME3, General Electric Aircraft Engines), 

Alloy 10 (Honeywell Engines & Systems), and Low Solvus High Refractory (LSHR), have been 

developed (refs. 1 to 3). These alloys all contain a high percentage of gamma prime precipitates, Ni3Al, 

and refractory element additions to achieve strength at temperature. Although they provide advantages 

over older alloys, the continuing need for high tensile strength at intermediate temperatures in the bore of 

a disk, which runs much cooler than the rim, as well as high creep strength in the rim also demands 

innovative heat treatments which can optimize bore and rim properties. Traditional heat treatments 

produce fine grain disks when the solution temperature is maintained below the gamma prime solvus, or 

coarse grain disks when the solution temperature is maintained above the gamma prime solvus. Fine grain 

disks yield high strength at intermediate temperatures, while coarse grain disks yield high creep strength 

at elevated temperatures. Recently, several advanced heat treatment technologies (refs. 4 to 6) have been 

developed which can produce a superalloy disk with fine grain bore and coarse grain rim. Trade studies 

by General Electric Aircraft Engines (GEAE) (ref. 7) and Allison Advanced Development Company 

(AADC) (ref. 8) have identified potential advantages offered by superalloy disks which employ a dual 

grain structure for advanced gas turbine engine application. The GEAE report cited a fatigue benefit for a 

disk with a dual grain structure when compared with a coarse grain disk, while the AADC report cited a 

creep benefit for a disk with a dual grain structure when compared with a fine grain disk. 

A two year program between AADC, GEAE, and NASA was undertaken to develop/refine design 

methodologies for yield and burst criteria of superalloy disks with dual grain structures. Previous spin 

testing of disks with dual grain structures were conducted to rigorously test the integrity of the grain size 

transition zone with unusually high web stresses. In this study, room temperature burst testing and 

analysis of four superalloy disks were performed with moderate web stresses more typical of real 

production disks in gas turbine engines. AADC chose to study Alloy 10 disks with a dual grain structure 

and a uniform fine grain structure. GEAE chose to study Rene 104 disks with a dual grain structure and a 

uniform coarse grain structure. The chose of alloy and disk microstructure comparison reflected current 

design interest of each company. A final report on testing and analysis by each company can be found in 

references 9 and 10. The purpose of this report is to compare the results of all four burst tests using a 

common analysis run by NASA which employed a simplified elastic-plastic finite element technique. 

Materials and Procedures 

In this program a generic disk shape based on AADC’s AE2100 stage-3 turbine disk, nominally 14 in. 

in diameter and 2 in. thick, was employed as depicted in figure 1. The disks were isothermally forged by 

the Ladish Company using extruded mults of Alloy 10 and Rene 104 supplied by AADC and GEAE, 

respectively. After forging, the Ladish Company heat treated the Alloy 10 forgings producing two disks 

with a dual grain structure and one disk with a uniform fine grain structure, ASTM 11-12. The disks with 

a dual grain microstructure were produced using NASA’s patented Dual Microstructure Heat Treatment 

(DMHT) process (ref. 6). GEAE chose to have the Rene 104 forgings heat treated at the Wyman-Gordon 
NASA/TM—2006-214462 2 

facility in Houston, Texas. Two dual grain structure disks were produced using GEAE’s patented process 

(ref. 5) and a third disk was processed to produce a uniform coarse grain structure, ASTM 7. The 

transition radius of the Alloy 10 dual grain structure disk was determined to be 5.3 in. while that of the 

Rene 104 dual grain structure disk was determined to be 4.5 in., both in line with expectations. The 

bore/rim sections of the dual grain structure disks had a grain size of ASTM 11/6 and ASTM 12/5 for the 

Alloy 10 and Rene 104, respectively. More details on the processing history and resulting microstructures 

can be found in the individual contractor reports (refs. 9 and 10). 

After heat treatment, one of the Alloy 10 and Rene 104 disks with the dual grain structure were 

sectioned to provide tensile, notch tensile, and fatigue test bars. The cut-up plan and test results are 

documented in the contractor reports. Room temperature tensile data used in the subsequent NASA 

analysis is summarized in table I. The remaining disks were machined by Douglas Machining of 

Evendale, Ohio using the machining plan shown in figure 2. As seen in this figure the final disk shape 

was designed with rim slot features to simulate blade loading. This design was intended to produce the 

highest stresses, and therefore failure at the bottom of the rim holes. For both the Alloy 10 and Rene 104 

disks, the critical location was outboard of the transition zone well into the coarse grain region of the 

disks with the dual grain structure. After machining at Douglas, each company was free to pursue any 

inspection or any additional surface treatment deemed critical for their alloy. A photo of a machined disk 

is presented in figure 3 after acceptance by both companies. 

Room temperature spin testing of the four machined disks was performed by Test Devices, Inc. of 

Hudson, Massachusetts. During each test, the disk was connected to the air turbine/spindle drive via a 

stainless steel arbor attached to the bore flange on the disk with 24 bolts. Radial proximity probes were 

used to monitor disk growth to failure. High speed video and eight channels of strain data were recorded 

in each test as described in the contractor reports (refs. 9 and 10). Redundant strain gages (2) were 

employed at the critical disk location, i.e., bottom of rim holes at the 0 and 180° position. A photo of the 

spin pit with the disk is presented in figure 4. 

Experimental Results 

Each of the four spin tests were run in three segments. During the first segment the disk was spun to a 

maximum speed of 21000 rpm before returning to rest. At this speed, the response of all four disks was 

intended and found to be largely elastic, as strain gage and proximity probe data returned to near-zero 

readings upon completion. The response, of all four disks for this segment of the tests, is summarized in 

table II. As expected the strain gage at the bottom of the rim hole produced the largest strain. 

For the next test segment, the disks were spun to a maximum speed which produced 3 percent total 

strain at the bottom of the rim hole before returning to rest. The resulting readings at maximum speed and 

rest for all four disks are summarized in table III. Significant flow and growth of the disks are evident by 

non-zero readings upon completion of this test segment. 

The final test segment, for all four disks, was run to burst. As most of the strain gage signals were lost 

before burst, only the burst speeds and radial growth are presented in table IV. High speed video clearly 

showed failure initiated from the base of the rim holes in all tests. A series of photos showing the 

progression of crack propagation for one of the tests is shown in figure 5. As seen in table IV, the Rene 

104 burst speeds and radial growth data were significantly higher than that for Alloy 10. Further, the burst 

speed for the dual grain Rene 104 disk was greater than that of the coarse grain Rene 104 disk, while the 

burst speed for the dual grain Alloy 10 disk was less than that of the fine grain Alloy 10 disk. 

Finite Element Analysis 

To understand and compare the results of all four spin tests, NASA utilized a simplified finite element 

analysis employing a commercial platform from Algor, Inc., MES with Nonlinear Material Models 

Version 12.28. As all tests were conducted at room temperature to burst, an elastic-plastic, bilinear 

material model with isotropic hardening was employed using the data presented in table I. When an 
NASA/TM—2006-214462 3 

element’s von Mises stress exceeded the yield strength, its stiffness was set equal to a plastic modulus, 

which was defined by the following formula: 

 Eplastic = (Ultimate Tensile Strength-Yield Strength)/Tensile Elongation 

The disks with dual grain structures were divided into two material groups. Inside the transition zone 

fine grain properties were employed. Outside the transition zone coarse grain properties were employed. 

The three-dimensional meshed model of a dual grain disk is presented in figure 6. The analysis mimicked 

the three test segments, i.e., the disk was spun to 21000 rpm, unloaded, spun to 3 percent rim strain, 

unloaded, and finally spun to burst. Analytically, disk burst was assumed to occur when the von Mises 

stress equaled the ultimate tensile strength of the alloy. As expected this occurred at the base of the rim 

holes in all analyses, a typical run is shown in figure 7. Comparative plots of the radial growth for all four 

disks, based on the aforementioned analysis procedure, are presented in figure 8 showing all test 

segments. Note that the time scale is artificial and was chosen for analytical convenience as the elasticplastic analysis employed in this study yields a time-independent solution. The peak values in these plots 

do, however, correspond to maximum and zero rpm levels in the three segment test procedure. All four 

analyses showed very little plastic flow after segment 1, loading to 21000 rpm, and significant plastic 

flow after segment 2, loading to 3 percent strain at the base of rim holes, as evident by the level of 

permanent radial growth after unloading to zero rpm. The maximum speed and radial growth of the final 

segment was determined using an iterative process, that is, the maximum rpm was varied until the von 

Mises stress at the base of the rim hole equaled the ultimate tensile strength of the alloy. 

A comparison between the analytical and experimental growth rates of all four disks is presented in 

figure 9. The predicted growth rates prior to burst are fairly accurate for all tests considering the 

simplifying assumptions used in the analysis. However, the differences in growth at burst between 

experiment and analysis as well as between the alloys are significant. Analytically the predicted 

differences in growth at burst are relatively modest between all four disks, with a low of 0.086 in. and a 

high of 0.103 in., the experimental data however, shows the Rene 104 disks averaging about 0.14 in., 

which is significantly higher than the Alloy 10 disks which averaged about 0.07 in. Looking at the same 

data from another perspective, the analytical growth rate at burst of the Alloy 10 disks are greater than the 

experimental data, while the analytical growth rate at burst of the Rene 104 disks are less than the 

experimental data. A comparison of analytical and experimental burst speeds of all four disks is presented 

in table V. As with growth at burst, the predicted burst speeds show only modest differences, high of 

25200 rpm for fine grain Alloy 10 and a low of 24800 rpm for coarse grain Rene 104, while the 

experimental results, as previously stated, show the Rene 104 disks to have failed at significantly higher 

speeds than the Alloy 10 disks. Taken as a whole, the burst data, both growth and speed, suggest 

differences in alloy behavior were more pronounced than differences between heat treat option, i.e. dual 

grain versus uniform grain structure. Finally, it should be noted, for each alloy the ranking of burst speed 

between dual grain and uniform grain structure was correctly predicted. The burst speed for fine grain 

Alloy 10 was greater than dual grain Alloy 10, and the burst speed for coarse grain Rene 104 was less 

than dual grain Rene 104. 

Fractographic Analysis 

Failure analysis of the burst disks was performed in order to confirm failure locations and to 

determine possible differences in failure modes or microstructure that may explain the observed 

discrepancies in behavior between the alloys. The failed disks were reconstructed as shown in figure 10. 

With the aid of the high speed test video and paint pattern on the disk, the initiation location and 

progression of failure was identified. As expected, all disks failures initiated at the root of the rim hole. 

Fractography of several primary and secondary initiation sites on all the disks revealed that a common 

location of failure was approximately 4 mm from the bottom of the disk (fig. 11). The conjugate location 
NASA/TM—2006-214462 4 

from the top side of the disk was also a prevalent initiation site. As shown in figure 11, the failure 

location was accurately predicted by the three-dimensional elasto-plastic FEA models generated by both 

GEAE and AADC. 

The failure mode for both alloys was typical of tensile fracture as shown in figure 12. Also, none of 

the initiation sites, primary or secondary, revealed any material related defects that may have attributed to 

the observed differences in burst behavior. Furthermore, metallography did not reveal any abnormal 

microstructure. The disk grain sizes in the region were failure occurred were also as expected for both 

alloys and heat treatments. One obvious difference was the deformation present at the surface of the hole 

for the Alloy 10 DMHT disk (fig. 13). (This type of localized surface deformation is likely to represent 

cold work from a machining operation.) The R104 disks did not show any surface deformation. 

Subsequent examination of the surface of intact rim holes adjacent to holes that initiated failure also 

revealed differences in the nature and extent of damage. As seen in figure 14, in comparison to the R104 

DMHT disk, the Alloy 10 DMHT disk revealed significantly more microcracking. Furthermore, most of 

the microcracks in the Alloy 10 disk have coalesced into long cracks. This behavior may be a 

manifestation of surface cold work suggesting lack of ductility and premature cracking. Since only the 

surface material is deformed, the premature cracking was limited to the surface layer. Premature surface 

cracking, even if shallow, can hasten the failure process and may explain the smaller radial growth at 

burst observed for the Alloy 10 disks. 

Summary and Conclusions 

Elastic-plastic finite element analyses of room temperature burst tests on four superalloy disks were 

conducted and reported in this paper. Two alloys, Rene 104 and Alloy 10, were studied. For both alloys 

an advanced dual microstructure disk, fine grain bore and coarse grain rim, were analyzed and compared 

with conventional disks with uniform microstructures, coarse grain for Rene 104 and fine grain for 

Alloy 10. The analysis and experimental data were in good agreement up to burst. At burst, the analysis 

underestimated the speed and growth of the Rene 104 disks, but overestimated the speed and growth of 

the Alloy 10 disks. Fractography revealed that the Alloy 10 disks displayed significant surface 

microcracking and coalescence in comparison to Rene 104 disks. This phenomenon may help explain the 

differences between the Alloy 10 disks and the Rene 104 disks, as well as the observed deviations 

between analytical and experimental data at burst. 

In conclusion, this work, coupled with previous efforts by NASA, extends DMHT maturity to a level 

where industry can utilize this technology in advanced engine designs. Both the performance and analysis 

capability for DMHT technology is firmly established and documented. 

References 

1. T. Gabb, J. Telesman, P. Kantzos, and K. O’Connor, “Characterization of the Temperature Capability 

of Advanced Disk Alloy ME3,” NASA/TM—2002-211796, August 2002. 

 2. S. Jain, “Regional Engine Disk Process Development,” NASA Contract NAS3–27720, September 

1999. 

 3. T. Gabb, J. Gayda, J. Telesman, “Realistic Subscale Evaluation of the Mechanical Properties of 

Advanced Disk Superalloys,” NASA/TM—2003-212086, January 2003. 

 4. G. Mathey, “Method of Making Superalloy Turbine Disks Having Graded Coarse and Fine Grains,” 

U.S. Patent 5,312,497, May 17, 1994. 

 5. S. Ganesh and R. Tolbert, “Differentially Heat Treated Article and Apparatus and Manufacture 

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

 6. J. Gayda, T. Gabb, and P. Kantzos, “Heat Treatment Technology for Production of Dual 

Microstructure Superalloy Disks,” NASA/TM—2002-211558, April 2002. 

 7. J. Williams, “Dual Heat Treat Superalloy Disk Design Trade Study,” NASA/CR—2004-212949, 

February 2004. 
NASA/TM—2006-214462 5 

 8. K. Green, “Trade Study on Dual Microstructure Heat Treat Technology,” NASA/CR—2004-212948, 

February 2004. 

 9. T. Heffernan, “Spin Testing of Superalloy Disks with Dual Grain Structure,” NASA/CR—2006-

214338, May 2006. 

10. J. Groh, “Spin Test of Superalloy Disks with Dual Grain Structure,” NASA/CR—2006-214266, April 

2006. 

TABLE I.—TENSILE DATA USED IN CURRENT ANALYSIS 

[Bore is fine grain and rim is coarse grain.] 

Rene 104 Yield (ksi) UTS (ksi) E (msi) Elong Density (lb/in.3

) 

Bore 170 244 32 24 percent 0.3 

Rim 160 230 32 20 percent 0.3 

Alloy 10 Yield (ksi) UTS (ksi) E (msi) Elong Density (lb/in.3

) 

Bore 165 240 32 25 percent 0.3 

Rim 155 225 32 23 percent 0.3 

TABLE II.—EXPERIMENTAL DATA FOR FIRST TEST SEGMENT TO 21000 RPM 

[Negligible growth and strains measured upon unloading to zero rpm.] 

 Coarse grain Rene 104 Dual grain Rene 104 Fine grain Alloy 10 Dual grain Alloy 10 

Growth 0.016 in. 0.014 in. 0.009 in. 0.010 in. 

Bore strain 0.6 percent 0.8 percent 0.6 percent 0.6 percent 

Web strain 0.3 percent 0.3 percent 0.3 percent 0.3 percent 

Rim strain 0.8 percent 0.7 percent 0.7 percent 0.8 percent 

TABLE III.—EXPERIMENTAL DATA FOR SECOND TEST SEGMENT TO 3 PERCENT TARGET RIM STRAIN 

[Data denoted with (1) refers to measurement at max speed and data denoted with 

(2) refers to measurements upon unloading to zero rpm.] 

 Coarse grain Rene 104 Dual grain Rene 104 Fine grain Alloy 10 Dual grain Alloy 10 

Max Speed 23 400 rpm 23 600 rpm 23 600 rpm 23 300 rpm 

Growth (1) 0.038 in. 0.030 in. 0.028 in. 0.021 in. 

Growth (2) 0.014 in. 0.012 in. 0.012 in. 0.007 in. 

Bore (1) 1.3 percent 1.5 percent 1.5 percent 1.0 percent 

Bore (2) 0.6 percent ------------- 0.8 percent 0.2 percent 

Web (1) 0.7 percent 0.9 percent 0.8 percent 0.8 percent 

Web (2) 0.1 percent 0.1 percent 0.4 percent 0.3 percent 

Rim (1) 2.8 percent 2.5 percent 3.0 percent 3.0 percent 

Rim (2) 1.8 percent ------------- ------------- 2.1 percent 

TABLE IV.—EXPERIMENTAL DATA FOR THIRD TEST SEGMENT TO BURST 

 Coarse grain Rene 104 Dual grain Rene 104 Fine grain Alloy 10 Dual grain Alloy 10 

Burst speed 24 670 rpm 25 030 rpm 24 240 rpm 24 005 rpm 

Growth 0.147 in. 0.137 in. 0.068 in. 0.067 in. 

TABLE V.—COMPARISON OF PREDICTED AND MEASURED BURST SPEEDS 

 Coarse grain Rene 104, 

rpm 

Dual grain Rene 104, 

rpm 

Fine grain Alloy 10, 

rpm 

Dual grain Alloy 10, 

rpm 

Predicted 24 800 25 100 25 200 24 800 

Measured 24 670 25 030 24 240 24 005 
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20

Burst Testing and Analysis of Superalloy Disks With a Dual Grain Microstructure

John Gayda and Pete Kantzos

Superalloy disks

Unclassified -Unlimited

Subject Category: 26

Elastic-plastic finite element analyses of room temperature burst tests on four superalloy disks were conducted and

reported in this paper. Two alloys, Rene 104 (General Electric Aircraft Engines) and Alloy 10 (Honeywell Engines &

Systems), were studied. For both alloys an advanced dual microstructure disk, fine grain bore and coarse grain rim, were

analyzed and compared with conventional disks with uniform microstructures, coarse grain for Rene 104 and fine grain

for Alloy 10. The analysis and experimental data were in good agreement up to burst. At burst, the analysis underestimated the speed and growth of the Rene 104 disks, but overestimated the speed and growth of the Alloy 10 disks.

Fractography revealed that the Alloy 10 disks displayed significant surface microcracking and coalescence in comparison to Rene 104 disks. This phenomenon may help explain the differences between the Alloy 10 disks and the Rene 104

disks, as well as the observed deviations between analytical and experimental data at burst.

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