John Gayda

Glenn Research Center, Cleveland, Ohio

Pete Kantzos

Ohio Aerospace Institute, Brook Park, Ohio

Jason Miller

University of Akron, Akron, Ohio

Quench Crack Behavior of Nickel-Base

Disk Superalloys

NASA/TM—2002-211984

November 2002

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John Gayda

Glenn Research Center, Cleveland, Ohio

Pete Kantzos

Ohio Aerospace Institute, Brook Park, Ohio

Jason Miller

University of Akron, Akron, Ohio

Quench Crack Behavior of Nickel-Base

Disk Superalloys

NASA/TM—2002-211984

November 2002

National Aeronautics and

Space Administration

Glenn Research Center
Acknowledgments

The authors gratefully acknowledge Dr. Gil London , Naval Air Warfare Center, for providing NF3 alloy.

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NASA/TMó2002-211984 1 

QUENCH CRACK BEHAVIOR OF NICKEL-BASE DISK SUPERALLOYS 

John Gayda 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Pete Kantzos 

Ohio Aerospace Institute 

Brook Park, Ohio 44142 

Jason Miller 

University of Akron 

Akron, Ohio 44325 

Abstract 

There is a need to increase the temperature capability of superalloy turbine disks 

to allow higher operating temperatures in advanced aircraft engines. When modifying 

processing and chemistry of disk alloys to achieve this capability, it is important to 

preserve the ability to use rapid cooling during supersolvus heat treatments to achieve 

coarse grain, fine gamma prime microstructures. An important step in this effort is an 

understanding of the key variables controlling the cracking tendencies of nickel-base disk 

alloys during quenching from supersolvus heat treatments. The objective of this study 

was to investigate the quench cracking tendencies of several advanced disk superalloys 

during simulated heat treatments. Miniature disk specimens were rapidly quenched after 

solution heat treatments. The responses and failure modes were compared and related to 

the quench cracking tendencies of actual disk forgings. Cracking along grain boundaries 

was generally observed to be operative. For the alloys examined in this study, the 

solution temperature not alloy chemistry was found to be the primary factor controlling 

quench cracking. Alloys with high solvus temperatures show greater tendency for quench 

cracking. 

Introduction 

 The understanding of the physics of any process can be of great importance in the 

design and manufacture of a product. Nickel-base superalloys, strengthened by gamma 

prime precipitates, are often heat treated during the manufacturing process to control 

mechanical properties of the alloy. As part of the overall heat treatment process the alloy 

is generally quenched from elevated temperatures to increase strength. However, the 

thermal stresses that build up in the part during the quenching process will sometimes 

exceed the alloyís ultimate strength. When this occurs, cracks will form, releasing the 

stresses built up in the alloy but also destroying the part. 

 This problem is especially troublesome for modern nickel-base superalloys used 

in aircraft turbine disks, as the size of these forged parts can be quite large. In addition, 

increasing turbine disk temperatures have resulted in the use of coarser grain size to 

increase creep resistance, which also, unfortunately, tends to increase the likelihood of 
NASA/TMó2002-211984 2 

quench cracking during supersolvus heat treatment of the disk (Ref. 1). The term 

supersolvus refers to temperatures at which all gamma prime precipitates in this class of 

alloy are completely dissolved thereby allowing rapid grain coarsening and subsequent 

precipitation of fine gamma prime particles upon quenching. To minimize the formation 

of quench cracks, one must understand the factors that can influence crack formation 

under these conditions. In this experiment two key variables were examined. First, there 

is the solution temperature of the superalloy. That is the temperature at which the alloy is 

heat treated to coarsen grain size, and this can vary from alloy to alloy based on 

chemistry. Secondly the chemical composition of each alloy was looked at, as it affects 

mechanical properties such as high temperature ductility that can influence the cracking 

propensity of the alloy upon quenching. Studying the effect that these two variables have 

on the cracking propensity of a superalloy will aid in the understanding of the quench 

cracking process, which could allow for the design of an improved quenching process or 

a more crack resistant superalloy. 

Materials and Procedures 

 A large number of small disk shaped specimens (0.9-in. diameter by 0.25-in. 

thick), of three next generation nickel-base disk alloys, were machined from forgings by 

EDM blanking followed by low stress grinding. While the shape of the specimen was 

similar to disk forgings used in aircraft engines, their size was much smaller to facilitate 

numerous quenching trials required in this study. The three superalloys used in this 

experiment were ME3 (Ref. 2), NF3, and Alloy 10 (Ref. 3). They were chosen for this 

study, as ME3 is known to be more resistant to quench crack formation than NF3 or 

Alloy 10 during supersolvus heat treatment of large forgings. 

 As previously stated, the quench cracking problem is most severe for the coarser 

grain size produced by a supersolvus heat treatment. For this reason all specimens were 

given a pre-solution heat treatment at their respective supersolvus temperature and aircooled. This was done to produce a uniformly coarse grain size, between ASTM 6 and 7, 

for all alloys before running the quench experiments. The supersolvus heat treatment 

temperatures chosen for the three alloys were: 2140 °F for ME3 and 2185 °F for NF3 

and Alloy 10. Each alloy was pre-solutioned at its respective supersolvus heat treatment 

temperature for one hour. None of the specimens cracked as a result of the air-cooling 

following the pre-solution treatment. 

With alloy grain size set via the pre-solution heat treatment, the effects of solution 

temperature and alloy composition on quench cracking could now be independently 

studied at a constant grain size. Specimens were re-heated at various temperatures 

ranging from 2080 °F to 2200 °F for 15 minutes before quenching in oil. This range of 

temperatures spans the range of practical solution temperatures for this class of alloys. 

Individual specimens were placed in the furnace on a sheet of superalloy. This was done 

so each specimen could be removed from the furnace by grabbing the superalloy sheet 

and not the specimen thereby eliminating any unwanted cooling effects introduced by 

direct manipulation of the specimen. 

After each specimen had received the solution heat treatment it was removed from 

the furnace and quenched in vacuum pump oil. Several quenching fluids were tried 

including water, oil, and antifreeze/water mixtures before settling on vacuum pump oil. 

Vacuum pump oil provided the rapid quenching rates required and also allowed 
NASA/TMó2002-211984 3 

maximum visibility of the specimen during the quench process. The oil was placed in a 

one-gallon can with a mesh platform in the bottom to suspend the specimen in the oil and 

thereby minimize cooling differences between the top and bottom of the specimen. The 

transfer time from furnace to quench media is very important in this experiment because 

the specimens are so small and loose heat very rapidly. A five second transfer time was 

as fast as the specimens could be quenched while still being consistent throughout the 

experiment. When the specimen had cooled it was visually checked for any quench 

cracks that might have formed. 

Results and Discussion 

Before presenting the experimental quench cracking results a short discussion of 

thermal stresses is warranted. Modeling of the specimen during the quench was done 

using a 2D axi-symmetric finite element model. Several assumptions were made which 

limited the accuracy of the analysis; nevertheless the analysis does allow one to 

approximate the temperature gradients along with the stress distribution in the specimen 

during the quench. The first and most significant approximation was the estimated heat 

transfer coefficient. Based on observation of glow time in oil, i.e., the time required for 

the specimen to stop glowing after immersion in oil, a heat transfer coefficient of 

1.1Btu/hr-F-in2 was utilized in the analysis. This number was arrived at by iteration until 

the predicted glow time (time for the top center location in the model to reach 1200 °F) 

matched the experimental glow time of 12 seconds. Other assumptions employed in the 

model included the following: the specimen temperature was 2140 °F when it entered the 

oil, all stresses were totally elastic, and the use of constant values for heat capacity and 

thermal conductivity, 0.2Btu/lb-F and 1Btu/hr-F-in, respectively. Cooling curves 

generated from the model for three key locations in the specimens are plotted in Figure 1. 

One should note that the cooling rates approach 100 °F/second on the skin and there is a 

significant thermal gradient between the interior and the surface of this specimen despite 

its relatively small size as seen in Figure 2. This temperature gradient produces the 

thermal stresses that cause quench cracking. The hoop or tangential stress distribution in 

the specimen is presented in Figure 3 after five seconds into the quench. The maximum 

thermal gradient and therefore the maximum thermal stresses are generated at this time. It 

should be noted that the surface of the specimen is in tension while the interior is in 

compression at this time. Continued cooling lowers the thermal gradient and therefore the 

thermal stresses. While this analysis shows the stresses are significant, the actual 

magnitude of the stresses is only approximate as a result of the assumptions that were 

previously mentioned. As expected, quench cracking initiated at the disk corners where 

the largest stresses were predicted. 

The results from the quench testing are presented in detail in Appendix 1. 

Pertinent data for all alloys is summarized in Figure 4 in bar graph format. Only two 

temperatures are shown in the graph, they are 2170 °F and 2200 °F. 2140 °F is not 

shown because only one specimen cracked at that temperature, and no specimens cracked 

at 2080 °F. From this graph it would appear that there is no difference in cracking 

propensity of the superalloys due to chemical composition. At these temperatures all 

alloys behaved in a similar manner. 

Figure 5 shows the cracking frequency of all alloys as a function of solution 

temperature. None of the specimens cracked in oil at 2080 °F, one out of 26 specimens 
NASA/TMó2002-211984 4 

cracked at 2140 °F, and at 2170 °F and 2200 °F about 50 percent of the specimens 

cracked. This leads one to conclude that solution temperature is more important than 

alloy chemistry with respect to quench cracking for the range of compositions studied in 

this paper. 

The cracking observed in the quench specimens was similar to what is found in 

large commercial disk forgings. The quench cracking of the test specimens was all 

intergranular, and this is exactly what is seen in commercial forgings. The quench cracks 

were also near the surface at the outer edge, which is where the highest tensile stresses 

are located. Shown in Figure 6 is the comparison of intergranular cracking in Alloy 10, 

between a full-scale forging and one of the test specimens. 

 It should be noted that quenching even from the highest temperature did not cause 

cracks in all of the specimens. Furthermore, many samples survived multiple quenches 

before cracking. This implies that the formation of quench cracks is a complex and 

perhaps stochastic process controlled by many variables. In order to study the evolution 

of cracking, quenched disks that did not show any cracking were sectioned and examined 

by metallography. Microscopic damage, in the form of small subsurface intergranular 

cracks, was observed in many of the visually un-cracked samples. The extent of damage 

also seemed to increase with temperature. Shown in Figure 7a and 7b is Alloy 10 

specimens after quenching from 2140 °F and 2170 °F. One can see evidence of micro 

cracking at grain boundaries at 2170 °F, which is absent at 2140 °F. This microscopic 

cracking has also been observed in large forgings as shown in Figure 7c for an ME3 

forging. 

 While chemistry differences between the three alloys were significant, all were 

high gamma prime content alloys (50 to 60%), typical of next generation disk alloys. 

Furthermore, all the alloys in this study had similar grain size. It appears that solvus 

temperature was the most important factor affecting quench crack tolerance, not alloy 

chemistry per say. However, alloy chemistry does change solvus temperature and 

therefore has an important indirect role on quench crack propensity. ME3 has a lower 

solvus temperature than Alloy 10 or NF3 and is therefore less likely to quench crack 

when it is given a ìcommercialî supersolvus solution treatment followed by an 

aggressive quench, Figure 8.

Summary and Conclusions 

 Quenching experiments on three next generation turbine disk alloys, ME3, NF3, 

and Alloy 10, were run on miniature disk specimens. Although there are significant 

differences in the cooling history between these specimens and larger, commercial 

forgings, these tests were successful in generating quench cracks similar to what is seen 

in the large forgings. 

 The design of this study allowed a clear separation of chemistry effects and 

solution temperature for coarse grain microstructures, ASTM 6 to 7. Based on the results 

of this study, it appeared that solution temperature, not alloy chemistry, was the primary 

factor controlling quench cracking of these alloys. This data suggests that alloy designers 

can increase alloying content to approach the strength levels of Alloy 10 or NF3 without 

increasing the risk of quench cracking by maintaining a lower solvus temperature similar 

to that of ME3. 
NASA/TMó2002-211984 5 

References

1. T.P. Gabb et al., ìThe Tensile Properties of Advanced Nickel-Base Disk 

Superalloy During Quenching Heat Treatments,î NASA/TMó2001-211218, 

October 2001. 

2. T.P. Gabb, J. Telesman, P. Kantzos, and K. OíConnor, ìCharacterization of the 

Temperature Capabilities of Advanced Disk Alloy ME3,î NASA/TMó2002-

211796, August 2002. 

3. S.K. Jain, ìHigh OPR Core Material (AoI 4.2.4), Regional Engine Disk 

Development,î AST Regional Disk Program Final Report, NAS3ñ27720, 

November 1999. 
NASA/TMó2002-211984 6 

Figure 1. Analytical cooling curves for selected locations in quench specimens. 

Figure 2. Temperature distribution in quench specimen. 
NASA/TMó2002-211984 7 

Figure 3. Hoop stress distribution in quench specimen. Note tensile component on surface 

and compressive component at interior of specimen. 

Figure 4. Quench crack frequency for each alloy at 2170 and 2200 °F. 

 

CRACK FREQUENCY FOR INDIVIDUAL ALLOYS COARSE GRAIN MICROSTRUCTURES 

QUENCHED IN OIL FROM VARIOUS SOLUTION T EMPERAT URES 

0%

10%

20%

30%

40%

50%

60%

70%

2170 2200

Temperature

Cracking F requency

Alloy 10

ME-3

NF-3
NASA/TMó2002-211984 8 

Figure 5. Quench crack frequency for all alloys at all solution temperatures. 

Figure 6. Comparison of quench cracks in Alloy 10 forgings and quench specimens. 

QUENCH CRACK FREQUENCY FOR ALL ALLOYS COARSE GRAIN 

MICROSTRUCTURE QUENCHED IN OIL

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2060 2080 2100 2120 2140 2160 2180 2200 2220

Temperature

Cracking Frequency

Minimum of 13 Quenches at Each Temperature

Quench Cracks

Alloy 10 Quench Cracks 

From Forgings

Alloy 10 Quench Cracks 

From Testing
NASA/TMó2002-211984 9 

 

a) b) 

c) 

Figure 7. Comparison of microcracking: a) in Alloy 10 at 2170 °F, b) Alloy 10 at 

2140 °F, and c) ME3 full-scale disk. 

Microscopic Cracking

2170°F

No Microscopic 

Damage

2140°F
NASA/TMó2002-211984 10 

Figure 8. Cracking frequencies of alloys at their respective solvus Temperatures 

0 %

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

ME3 Alloy 10 N F3

Cracking Frequency

2140°F

2170°F 2170°F
NASA/TMó2002-211984 11 

 APPENDIX 1 ñ QUENCH CRACK DATA 

ALLOY 10 TEMP(F) CRACK ME3 TEMP(F) CRACK NF3 TEMP(F) CRACK 

10A-1 2080 N 3D-1 2080 N 82A-1 2080 N 

10A-2 2080 N 3D-2 2080 N 82A-2 2080 N 

10A-3 2080 N 

10A-4 2080 N 3K-1 2140 N 82A-3 2140 N 

10A-6 2080 N 3K-2 2140 N 82A-4 2140 N 

10A-7 2080 N 3K-3 2140 N 82D-1 2140 N 

10B-1 2080 N 3K-4 2140 N 82D-2 2140 N 

 3K-5 2140 N 82D-3 2140 N 

10B-7 2140 N 3D-3 2140 N 82D-4 2140 N 

10D-1 2140 N 3D-4 2140 N 82D-5 2140 N 

10D-2 2140 N 3I-1 2140 N 

10D-3 2140 N 3I-2 2140 N 82E-1 2170 Y 

10D-4 2140 N 3I-3 2140 N 82E-2 2170 N 

 3I-4 2140 N 82E-3 2170 N 

10D-5 2170 N 3I-5 2140 Y 82E-4 2170 Y 

10D-6 2170 Y 82E-5 2170 N 

10D-7 2170 N 3M-1 2170 Y 

10E-1 2170 N 3M-2 2170 Y 82A-5 2200 Y 

10E-2 2170 Y 3M-3 2170 N 82C-1 2200 Y 

10E-3 2170 N 3M-4 2170 Y 82C-2 2200 Y 

10E-4 2170 N 3M-5 2170 N 82C-3 2200 N 

10E-5 2170 Y 82C-4 2200 N 

10E-6 2170 Y 3D-5 2200 N 82C-5 2200 Y 

10E-7 2170 N 3F-1 2200 Y 

 3F-2 2200 Y 

10A-5 2200 Y 3F-3 2200 N 

10B-2 2200 Y 3F-4 2200 N 

10B-3 2200 N 3F-5 2200 N 

10B-4 2200 Y 

10B-5 2200 N 

10B-6 2200 N 
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17

Quench Crack Behavior of Nickel-Base Disk Superalloys

John Gayda, Pete Kantzos, and Jason Miller

Superalloy disk heat treatment

Unclassified -Unlimited

Subject Category: 26 Distribution: Nonstandard

John Gayda, NASA Glenn Research Center; Pete Kantzos, Ohio Aerospace Institute, 22800 Cedar Point Road, Brook

Park, Ohio 44142; Jason Miller, University of Akron, Akron, Ohio 44325. Responsible person, John Gayda, organization

code 5120, 216–433–3273.

There is a need to increase the temperature capability of superalloy turbine disks to allow higher operating temperatures

in advanced aircraft engines. When modifying processing and chemistry of disk alloys to achieve this capability, it is

important to preserve the ability to use rapid cooling during supersolvus heat treatments to achieve coarse grain, fine

gamma prime microstructures. An important step in this effort is an understanding of the key variables controlling the

cracking tendencies of nickel-base disk alloys during quenching from supersolvus heat treatments. The objective of this

study was to investigate the quench cracking tendencies of several advanced disk superalloys during simulated heat

treatments. Miniature disk specimens were rapidly quenched after solution heat treatments. The responses and failure

modes were compared and related to the quench cracking tendencies of actual disk forgings. Cracking along grain

boundaries was generally observed to be operative. For the alloys examined in this study, the solution temperature not

alloy chemistry was found to be the primary factor controlling quench cracking. Alloys with high solvus temperatures

show greater tendency for quench cracking.