Gabb, Tim P.

Gorman, Timothy T.

Hull, David R.

Sudbrack, Chantal K.

Yu, Jonathan D.

NASA Technical Reports Server

National Aeronautics and Space Administration 
www.nasa.gov 
Comparison of the High-Temperature Oxidation 
Behavior of Subsolvus and Supersolvus Treated 
Advanced Powder Metallurgy Disk Alloys 
Chantal K. Sudbrack, Tim P. Gabb, and David R. Hull 
NASA Glenn Research Center 
 
Jonathan D Yu 
Stanford University 
 
Timothy T Gorman 
University of Dayton 
 
Acknowledgements: James Smialek, Jack Telesman, Sue Draper, Mike Nathal for valuable 
discussions (NASA-GRC); Analytical Science Group for experimental support (NASA-GRC);  GE 
Engines and Honeywell International for providing samples  
 
Funding:  NASA’s Aviation Safety and Fundamental Aeronautics Programs 
 
March 6, 2012 
 
1 
TMS Annual Meeting:  Phase Transformation and Microstructural Evolution Symposium 
Session:  Scale and Subsurface Phase Transformations during High-Temperature Oxidation 
https://ntrs.nasa.gov/search.jsp?R=20150009926 2019-08-31T07:53:09+00:00Z
National Aeronautics and Space Administration 
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2 
•  The drive in aerospace propulsion applications towards higher turbine inlet 
temperatures, which should improve engine efficiency, is leading to higher disk rim 
temperatures. 
        Currently at  650 °C à Long-range goal of 800 °C       
 
•  Advanced powder metallurgy  (P/M) nickel based superalloys have been 
developed by industry, AFRL and NASA to address the properties needed at these 
elevated temperatures    e.g.  Alloy 10, LSHR, ME3 (R104), RR1000 
•  It is well-established that oxidation can reduce fatigue life in disk alloys above 
650°C by accelerated crack initiation and growth at defects, however it is not well-
studied yet in disk alloys at 650 °C - 800°C  Protective coatings? 
 
Background 
JOM, 51:1 (1999) 14-17.	

SX 
P/M  
hub	

rim	

blades	

disk	

Turbine stage 
schematic	

National Aeronautics and Space Administration 
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Oxidation of Disk Alloys 
•  Newer P/M disk alloys have substituted environmental resistance (Al, Cr levels) for 
strength (Mo, W, Ta, etc.) 
 
 
•  Stable, slow growth of protective Cr2O3  external scale with Al2O3 subscale by 
internal oxidation with fast growth deleterious TiO2 scale  
•  Cast-wrought disk alloy comparison shows Ti content is rate controlling 
 
⇑
  M
ec
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ni
ca
l P
ro
pe
rti
es
 
⇑
  Te
m
pe
ra
tu
re
 C
ap
ab
ili
ty
 
E
nv
iro
nm
en
ta
l R
es
is
ta
nc
e Disk Alloys  
wt.% 
Cr Al Cr+Al Cr/Al Ti 
Inconel 718    19.0 0.5 19.5 38 0.9 
Waspaloy 19.5 1.3 20.8 15.6 3.0 
Udimet 720 18.0 2.5 20.5 7.2 2.5 
RR1000 14.6 3.0 17.6 5.0 3.6 
ME3 13.0 3.4 16.4 3.9 3.8 
Alloy 10 11.5 3.5 15.0 3.3 3.5 
High Cr 
Low Al 
 
Cr2O3 
formers 
3 
•  Mass change data suggests classic parabolic growth (time1/2) consistent with 
high temperature oxidation of Ni alloys for the external oxide scale 
•  Simplified models also predict the penetration depth of the internal oxide by 
precipitation to be proportional to (time1/2)  
National Aeronautics and Space Administration 
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•  NASA research contracts with GE and Honeywell 
to identify coatings with good corrosion 
resistance.  In-house work now underway  
•  Walk before run:  oxidation is ubiquitous 
•  Supersolvus ME3 from GE 
•  Subsolvus Alloy10 from Honeywell 
•  Flat coupon exposures in air: 704 °C,           
760 °C and 815 °C up to 2,020 hours 
•  NASA progress on fatigue response published     
in Superalloys 2012 
Motivation: Environmental attack has the potential to limit turbine disk 
durability, particularly in next generation engines which will run hotter.   
 
Understand environmental attack and its effect on the fatigue 
resistance of disk alloys 
 
Approach:  
45k 55k 33k 15k 15k 7k 1.3k 0.4k 
Notched LCF testing at 704 °C 
σmax=855 MPa, R(σ)= 0.05, 0.333 Hz 
Each test is represented by a diamond 
Sudbrack et al. in Superalloys 2012, 863	

Dwell Notched LCF:  Telesman et al. in Superalloys 2012, 853.	

99% 
debit 
National Aeronautics and Space Administration 
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Both fine grained and coarse grained disks are in flight 
A fine grain size provides superior yield, tensile and                           
low cycle fatigue strength à  Subsolvus heat treated 
 
 
A coarse grain size provides superior creep and                             
crack growth resistance à Supersolvus heat treated 
 
 
Dual-structure processing techniques to produce a fine grain bore in 
combination with a coarse grain web and rim offer significant benefits 
for advanced engine designs 
 Dual microstructure 
heat treatment 
(DMHT) technology	

5 
J. Gayda et al. in Superalloys 
2004, 323  
National Aeronautics and Space Administration 
www.nasa.gov γ’ (L12): Al, Ti partitioning, γ (fcc):  Cr, Co, Mo partitioning 
20 um 
Volume Fraction:   0.55 
Primary γ‘: None 
Secondary γ’: 190 –330 nm 
Tertiary γ’, 18 – 39 nm 
 
Grain size: 25 um – 34 um 
Cr-rich M23C6  
•  carbides ornament GBs 
Ti,Ta,Nb-rich MC  
•  carbides in interior & GBs 
500 nm 
As-processed microstructure prior to exposures!
Supersolvus ME3 Etched Subsolvus A10 
6 
wt.% Cr Co Al Ti Nb Ta Mo W C B trace Ni 
ME3 13 21 3.4 3.7 0.8 2.4 3.8 2.1 0.05 0.02 Si, Fe, N, O, S, Zr 49.6 
Alloy 10 12 19 3.4 3.5 1.4 1.4 2.5 4.6 0.03 0.03 0.06 Zr bal 
10 um 
500 nm 
GS: 5.26  ± 0.28 um (95%CI) 
Micron sized W3B2 
Cr-rich M23C6  
•  carbides ornament GBs 
Ti,Ta,Nb-rich MC  
•  carbides in interior & GBs 
Volume Fraction:   0.57 
Primary γ‘: ~ 2 –5 um 
Secondary γ’: ~100-500 nm 
Tertiary γ’, ~20 –40 nm 
 
National Aeronautics and Space Administration 
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How these disk alloys oxidize 
•  Cr2O3 external scale is 
intermixed with  TiO2 grains 
•  Ti is driven towards the surface 
to form primarily superficial 
TiO2 grains 
•  Branched Al2O3 forms an 
internal oxide underneath the 
external scale  causing γ’-
precipitates to dissolve in the 
near surface region 
7 
Supersolvus ME3 
TiO2	

25 µm 
788 °C for 2020 h 
Cr2O3	
 Plan view  
BSE SEM 
Cr2O3+TiO2 
X-Ray Diffraction  
confirmed 
760 °C 2020 h 
Ni-plating 
Al2O3 fingers 
γ’-precipitate 
dissolution 
layer 
Large faceted 
TiO2 particles 
2 um Microprobe confirmed 
γ’-precipitates 
BSE SEM 
From cross sections, track evolution of 
 
1. Cr2O3-TiO2 external scale thickness 
2. Al2O3 finger penetration depth 
3. γ’-precipitate dissolution layer thickness 
€ 
y = k⋅ t( )n
Simple Power Law Fit k	  is	  the	  rate	  constant	  
n	  is	  the	  temporal	  exponent	  
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à SEM, DIC 
Dissolution  
layer 
10  um 
Differential Interference Contrast: 815 °C for 440 h 
10  um 
1        2       3       4       5       6       7        8 
Supersolvus ME3 
Track layer thicknesses precisely  
760	  °C	  for	  2020	  h	  
5	  um	   5	  um	  
1.	  	  Avg.	  Oxide	  Scale	  Thickness	  (µm)	  
2.	  	  Avg.	  Al2O3	  Finger	  Depth	  (µm)	  
3.	  	  Avg.	  γ’-­‐dissoluHon	  layer	  thickness	  (µm)	  
704	  °C	  	  for	  2020	  h	  
5	  um	  
Three  Areas 
8 
815	  °C	  for	  2020	  h	  
National Aeronautics and Space Administration 
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à SEM, DIC 
Dissolution  
layer 
10  um 
Differential Interference Contrast: 815 °C for 440 h 
10  um 
1        2       3       4       5       6       7        8 
Supersolvus ME3 
Track layer thicknesses precisely  
760	  °C	  for	  2020	  h	  
5	  um	   5	  um	  
1.	  	  Avg.	  Oxide	  Scale	  Thickness	  (µm)	  
2.	  	  Avg.	  Al2O3	  Finger	  Depth	  (µm)	  
3.	  	  Avg.	  γ’-­‐dissoluHon	  layer	  thickness	  (µm)	  
704	  °C	  	  for	  2020	  h	  
5	  um	  
Three  Areas 
9 
815	  °C	  for	  2020	  h	  
760	  °C	  for	  2020	  h	  
5	  um	   5	  um	  
704	  °C	  	  for	  2020	  h	  
5	  um	  
Subsolvus A10 
815	  °C	  for	  2020	  h	  
National Aeronautics and Space Administration 
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2020 h end points for three isotherms   
 
10 
Supersolvus 
ME3 
Scale Thickness 
(um) 
Alumina Penetration Depth 
(um) 
γ’-Dissolution Layer 
 (um) 
Technique SEM (3840) SEM (24) DIC (24) 
Distributed Log normal Normal Normal 
704°C 1.32 ± 0.61 2.88 ± 0.81 3.14 ± 1.01 
760°C 1.97 ± 0.67 5.23 ± 0.67 5.96 ± 1.20 
815°C 3.79 ± 1.57 10.00 ± 1.16 10.75 ± 1.13 
Subsolvus   
A10 
Scale Thickness 
(um) 
Alumina Penetration Depth 
(um) 
γ’-Dissolution Layer 
 (um) 
Technique SEM (3840) SEM (24) DIC (24) 
Distributed Log normal Normal Normal 
704°C 0.69 ± 0.22 1.32 ± 0.38 – 
760°C 1.77 ± 0.14 3.97 ± 0.66 5.80 ± 1.26 
815°C 4.17 ± 0.32 9.43 ± 0.82 12.76 ± 0.60 
slower 
compar-
able 
How do the reaction kinetics compare? 
National Aeronautics and Space Administration 
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Supersolvus ME3 
•  Branched Al2O3 penetration depth follows parabolic growth law 
•  Both external scale thickness and γ’-dissolution layer follow a cubic growth law 
•   γ’-­‐dissolu,on	  layer	  	  is	  three	  ,mes	  thicker	  than	  external	  oxide	  scale                          
      Scale Thickness          <         Al2O3 penetration    <             γ’-dissolution layer  
 
 
Average	  Scale	  Thickness	  (um)	   Average	  Al2O3	  PenetraHon	  (um)	   Average	  γ’-­‐dissoluHon	  layer	  (um)	  
Time	  (h)	   Time	  (h)	   Time	  (h)	  
k(704)=0.0077 ± 0.0018 um3/h 
k(760)=0.0031 ± 0.0006 um3/h 
k(815)=0.0190 ± 0.0026 um3/h 
k(704)upper=0.005 ± 0.004 um2/h 
k(760)=0.0142 ± 0.0011 um2/h 
k(815)=0.052 ± 0.004 um2/h 
k(704)=0.019 ± 0.0010 um3/h 
k(760)=0.076 ± 0.020 um3/h 
k(815)=0.510 ± 0.008 um3/h 
€ 
y = k⋅ t( )n
n= 1/3 
n= 1/3 n= 1/2 
11 
National Aeronautics and Space Administration 
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Grain growth in external oxide may be responsible for t1/3 kinetics 
10 h         100 h      440 h  1010 h   2020 h 
815 °C
 
Supersolvus  
ME3 
National Aeronautics and Space Administration 
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101 102 103
10 100 440 10102020
0.1
0.5
1
5
10
15
101 102 103
10 100 440 10102020
0.1
0.5
1
5
10
15
101 102 103
10 100 440 10102020
0.1
1
10
15
Subsolvus A10 
      Scale Thickness          > <         Al2O3 penetration     <         γ’-Dissolution Layer  
 
    
Average	  Scale	  Thickness	  (um)	   Average	  Al2O3	  PenetraHon	  (um)	   Average	  γ’-­‐dissoluHon	  layer	  (um)	  
Time	  (h)	   Time	  (h)	   Time	  (h)	  
k(704)=0.000164 ± 0.000026 um3/h 
k(760)=0.00231 ± 0.00020 um3/h 
k(815)=0.027 ± 0.003 um3/h 
k(704)= 0.00089 ± 0.00016 um1.5/h 
k(760)=  0.0042 ± 0.0003 um1.5/h  
k(815)=  0.0169 ± 0.0016 um1.5/h  
k(704)= Not Detected 
k(760)= 0.0157 ± 0.0007 um2/h  
k(815)= 0.07818 ± 0.0008 um2/h  
€ 
y = k⋅ t( )n
n= 1/3 n= 2/3 
n= 1/2 
13 
Agreement: External scale thickness shows a cubic growth law 
Difference: Al2O3 penetration depth shows larger temporal exponentà   Primary γ’-ppts. 
Difference: γ’-dissolution layer evolves parabolically à short circuit diffusion 
 
     
      
                                                   
National Aeronautics and Space Administration 
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oxide 
GPD 
 
 
bulk 
oxide 
GPD 
 
 
bulk 
Cr 
O Mo 
Al Ni 
Co 
20 um 
Microprobe chemical mapping:  insight into diffusional processes 
Higher content Lower content 
14 
Supersolvus ME3:  2020 h at 815°C 
 
100 
 
 
 
50 
 
 
 
0 
 
60 
 
 
 
30 
 
 
 
0 
 
20 
 
 
 
10 
 
 
 
0 
 
30 
 
 
 
15 
 
 
 
0 
 
12 
 
 
 
6 
 
 
 
0 
 
50 
 
 
 
25 
 
 
 
0 
at.% 
	  γ’-­‐dissoluHon	  layer=	  GPD	  
•  GPD: Depletion of the major 
oxide elements Ti, Al, Cr, Ta 
•  GPD is γ-like, enriched in Co, 
Mo, but not Cr 
•  Partitioning in primary γ' 
 
•  Interfacial volume between 
GPD and and bulk enriched in 
Cr and Ti 
•  A striking feature is the 
dissolution of coarsened (Cr, 
Mo)23C6 carbides past the GPD 
–  Associated GBs are depleted   
in Cr, Mo and Co 
•  More analysis planned! 
Cr 
O Mo 
Al Ni 
Co 
10 um 
 
100 
 
 
 
50 
 
 
 
0 
 
60 
 
 
 
30 
 
 
 
0 
 
20 
 
 
 
10 
 
 
 
0 
 
30 
 
 
 
15 
 
 
 
0 
 
6 
 
 
 
3 
 
 
 
0 
 
30 
 
 
 
15 
 
 
 
0 
oxide 
 
GPD 
 
bulk 
oxide 
 
GPD 
 
bulk 
wt.% Cr Co Al Mo C 
ME3 13 21 3.4 3.8 0.05 
Alloy 10 12 19 3.4 2.5 0.03 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
at.% 
Subsolvus A10:  2020 h at 815°C 	  γ’-­‐dissoluHon	  layer=	  GPD	  
D(Al) ≈ 3 D(Cr)  
National Aeronautics and Space Administration 
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Precise layer measurements give predictive 
capability for fatigue life models 
15 
€ 
y = κ1⋅ OST( )
m1
€ 
y = κ2 ⋅ GPD( )
m2
€ 
y = κ3 ⋅ CD( )
m3
€ 
y = κn ⋅ (kn (T)⋅ t)1/ 3( )
−3
∝  t −1
By substitution 
y = κ4 ⋅TDD( )
m4
m= -3 
Depth 
(Summation of fits) 
Supersolvus ME3: Notched LCF data at 704 °C 
Sudbrack et al. in Superalloys 2012, 863	

Future work à characterization of fatigue response for subsolvus Alloy 10 
To
ta
l D
am
ag
e 
D
ep
th
 
National Aeronautics and Space Administration 
www.nasa.gov 
Conclusions 
•  For isothermal static oxidation of such alloys at 704 °C, 760 °C, and 815 °C, fine-
grained subsolvus disks oxidize similarly to coarse-grained supersolvus 
disks despite their differences in alloy chemistry and microstructure: 
Ø  Oxidation by-products:  A continuous Cr2O3 external scale forms with superficial, faceted 
TiO2 grains primarily at the exposed surface with an internal subscale of branched Al2O3 
extends into a layer where the γ’-precipitates are dissolved. 
Ø  External oxide growth: Sustained partially by dissolution of Cr-rich M23C6 grain boundary 
carbides, it has a cubic growth likely due to non-negligible oxide grain growth.  
•  However, the fine-grained subsolvus disks with primary γ’-precipitates can respond 
differently than coarse-grained supersolvus for: 
Ø  Internal oxide growth:  Larger temporal exponent for penetration depth of (time)2/3 for 
subsolvus compared to (time)1/2 for supersolvus 
Ø  γ’-dissolution layer growth: Larger temporal exponent of (time)1/2 compared to (time)1/3  
•  Interestingly, over certain temperature exposures, the penetration depth of the 
internal oxide could be smaller for the subsolvus than supersolvus, suggesting that 
in addition to coarse γ’-precipitates other factors influence the growth process 
Ø  Additional experiments:  subsolvus ME3 and supersolvus Alloy 10 
16 


Comparison of the High-Temperature Oxidation Behavior of Subsolvus and Supersolvus Treated Advanced Powder Metallurgy Disk Alloys

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