The influence of cobalt content in U-700 type alloys on the behavior of aluminide coatings is studied in burner rig cyclic oxidation tests at 1100C. It is determined that aluminide coatings on alloys with higher cobalt offer better oxidation protection than the same coatings on alloys containing less cobalt

Zaplatynsky, I.

English

NASA Technical Reports Server

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NASA Technical Memorandum 87173 
NASA-TM-87173 19860003940 
I 
The Effect of Cobalt Content in U-700 
Type Alloys on Degradation of 
Aluminide Coatings 
I. Zaplatynsky 
Lewis Research Center 
Cleveland, Ohio 
November 1985 
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, NF01489 
https://ntrs.nasa.gov/search.jsp?R=19860003940 2020-03-20T15:54:29+00:00Z
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THE EFFECT OF COBALT CONTENT IN U-700 TYPE ALLOYS ON DEGRADATION 
OF ALUMINIDE COATINGS 
I. Zaplatynsky 
Nat10nal Aeronaut1cs and Space Adm1n1strat10n 
Lew1s Research Center 
Cleveland, Oh10 44135 
SUMMARY 
The 1nfluence of cobalt content 1n U-700 type alloys on the behav10r of 
alum1n1de coat1ngs was stud1ed 1n burner r1g cyc11c ox1dat10n tests at 1100 °C. 
It was determined that alum1n1de coat1ngs on alloys w1th h1gher cobalt offered 
better ox1dat10n protect1on than the same coat1ngs on alloys conta1n1ng less 
cobalt. 
INTRODUCTION 
The 1nfluence of n1ckel-based substrate alloys on the behav10r of n1ckel 
alum1n1de coat1ngs has been stud1ed by several 1nvest1gators (refs. 1 to 6). 
Because an extens1ve rev1ew of the work 1n th1s area has been recently pub-
11shed by Tomaszew1cz and Wallwork (ref. 7) we w1ll ment10n only 1ts essence. 
It has been demonstrated that the mechan1sm of coat1ng degradat10n 1s a func-
t10n of alloy substrate compos1t10n (refs. 1 to 4), test temperature (refs. 3 
and 4), and the env1ronmenta1 cond1t1ons of attack (refs. 3 and 4). The tem-
perature and t1me dependence of 1nterd1ffus10n 1s closely connected w1th the 
solub1l1ty of the var10us phases present 1n the alloy substrate and the se1f-
d1ffus10n coeff1c1ents of var10us atom1c spec1es (w1th1n the 1nterd1ffus10n 
zone). Also 1t has been proposed (ref. 2) that substrate alloys, r1ch 1n 
refractory elements (Nb, Ta, W, Mo, Cr), w111 produce a zone, wh1ch w111 act as 
a d1ffus10n barr1er and thus 1mprove the stab111ty of N1A1 coat1ngs. A related 
work (ref. 1) was 11m1ted to determ1nat10n of re1at1ve d1ffus10na1 stab111ty 
of N1A1 on some b1nary, ternary, and other n1cke1-base alloys. 
The work descr1bed here1n 1s a part of the Conservat10n of Strateg1c Aero-
space Mater1a1s (COSAM) program. Its object1ve has been to 1nvest1gate the 
effect of cobalt content 1n Ud1met 7001 type alloys on the stab1l1ty of N1Al 
coat1ng 1n burner r1g cyc11c ox1dat10n tests. Knowledge of th1s effect w1ll 
help determ1ne the 1mpact of mod1fy1ng alloys or sel~ct1ng a1ternat1ve alloys 
when cost and ava11ab1l1ty of strateg1c a11oy1ng elements are of concern. 
Ud1met 700 1s a n1cke1-based superalloy wh1ch conta1ns nom1nally by we1ght 
percent, 17 cobalt, 15 chrom1um, 5 molybdenum, 4 alum1num, and 3.5 t1tan1um. 
It 1s used 1n cast and wrought forms 1n turb1ne blades and turb1ne d1sks, and 
as 1sostat1ca11y hot pressed powder metallurgy products. 
1Trade name of Spec1al Metals Corp. 
.//,:,' 
Five alloys containing different ~mounts of cobalt were 6bta1ned in the wrought 
form and two alloys were available as ,powder metallurgical product. The a1um1-
n1de coating was applied by the RT-21 process. 2 Cyclic ox1dat10n tests were 
performed 1n a Mach 0.3 burner r1g f,or. 1.50.and 310 1-hr cycles with a sample 
temperature of 1100 .oC. Weight change of the spec1m~ns was determ1ned by 
remov1ng them per10d1ca11yfrom the burner rig and we1gh1ng. After test1ng, 
the spec1mens were subjected to metal16graph1c,.x-ray d1ffract10n (XRD), and 
x-ray fluorescence (XRF) analyses. . 
MATERIALS AND EXPERIMENTAL PROCEDURES 
Preparat10n of the.Spec1mens 
Several alloys, based on U-700 alloy, conta1n1ng var1ab1e amounts of 
cobalt were used 1n th1s 1nvest1gat1on. Five alloys conta1n1ng 0.1, 4.3, B.6, 
12.B, and 17 wt % cobalt were obta1ned 1n the form of wrought coupons and 
two alloys conta1n1ng 4.3 and 12.6 wt % cobalt were obta1ned as HIP-ed (Hot 
Isostatically Pressed) b111ets. The chem1ca1 ana1ys1s of the alloys 1s given 
in table I. The coupons and b111ets were machined 1nto cy11ndr1ca1 spec1mens 
10.16.cm (4 1n.) long and 0.9S2S, cm (3/B1n.) 1n d1ameter. T~e a1um1n1de coat-
1ng was applied to all spec1m'ens by the RT-21 procedure. 
Burner R1g Testing 
. The Mach 0.3 burner r1gused in these tests has been descr1bed in 
reference B. Eight specimens were placed 1n a carousel holder wh1ch was 
rotated at 400 rpm 1n front of the burner nozzle. T~e cent~~s of the specimens 
were evenly spaced on a 4.2 cm (approx1mate1y 1-3/8 1n.) d1ameter c1rc1e. In 
th1s cyclic ox1dat10n test, the specimens were heated for 1 hr and then cooled 
with a stream of compressed air for 3 m1n. The burner r1g was fired at a fue1-
to-a1r rat10 of aboutO.OS using Jet A fuel and combustion air preheated to 
260°C (SOO OF). The test temperature was 1100!20 °c (2012 Of) as determ1ned 
w1th a ca11brated (for em1ss1V1ty and w1ndo~. absorption) disappearing f11ament 
opt1ca1 pyrometer when focus1ng on the' center of the hot zone of the specimens, 
fac1ng the nozzle of the burner. The back side (not facing the nozzle) of the 
spec1mens was hotter than the front face by 20°C. Only the central part of 
the spec1mens,was exposed to the flame. About 4 m1n in the flame were required 
for the center of the spec1mens to reach the test temperature. After 1 hr at 
temperature, the specimens were cooled down to 80°C in 3 m1n by a stream of 
compressed air. Duration of tests was 1so and 310 1-hr cycles. The weight of 
the specimens was mon1tored per10d1ca11y by'remov1ng them from the holder and 
weighing. Thermograv1metr1c data are presented as total we1ght change (AW) 
versus the number of cycles. We1ght change per unit area (AW/A) was not used 
because the longitudinal d1str1btit10n.of temperature on the specimens was not 
un1form. The most heav11y ox1d1zed reg10n was the central part of the spec1-
mens w1th area of about 4 cm2. After test1ng, all the spec1mens were plasma 
sprayed w1th copper, for edge preservat10n, and cross-sect10ned through the 
center of the hot zone for meta110graph1c exam1nat10n,to ascertain the extent 
of ox1dation damage and accompany1ng m1crostructural changes. 
2Trade name of Chroma110y Amer1can Corporat10n. 
2 
Additional experiments were performed on that part of the specimens which 
was not affected by oxidation. About 1.5 cm long pieces were cut from the 
lower end of each specimen and subjected to cyclic oxidation at 1100 °C in a 
muffle furnace. Specimens were removed from the furnace after 20, 40, 100, 
and 150 l-hr cycles and XRD patterns were taken from the cylindrical surface 
in order to identify the phases present in ,the oxide scale. 
RESULTS AND DISCUSSION 
Before discussing the results obtained in this investigation it is neces-
sary to emphasize again that a limited amount of each alloy was available for 
the preparation of the test specimens. Only one specimen per alloy was used 
in each test. Meta110graph1c examination of the specimens in the as-coated 
condition (fig. 1) revealed that the coating consisted of two layers. The 
outer layer is a large grained, single phase 6-NiA1 with Cr, Mo, Co in solid 
solution. XRF determination of the elements in the selected alloys (sub-
strates) and the corresponding aluminide coatings indicated (table II) that 
the outer coatings contained significantly less Cr, Mo, Co, and Ti than the 
substrate. The content of these elements in NiA1, except for cobalt, was found 
to be independent of the cobalt content in the alloys. The inner layer next 
to the substrate, contained co1umnarNiA1,carbjdes, and sigma phases (ref. 3). 
The thickness of the coating was approximately the same for all the alloys, 
namely 0.003 cm. XRD patterns taken from the coatings confirmed the presence 
of N1Al (ao = 2.876 A). Figures 2 and 3 represent thermogravimetric data 
for wrought alloys and figures 4 and 5 for HIP-PM type alloys. 
All the alloys showed an initial weight gain due to oxidation of NiA1. 
After about 20 or more cycles the specimens began to lose weight. Also one 
can see that the weight loss was greater for the specimens with lower cobalt 
content. The curves representing data obtained during 150 cycles runs (figs. 2 
and 4) are in reasonable agreement with the initial portions of the curves 
representing data obtained during 310 cycles runs and give some idea of the 
reproducibility of results (figs. 3 and 5). The behavior of the specimen con-
taining 17 wt % Co departed from the general trend. After about 150 cycles 
it started to lose weight rapidly and after 310 cycles its weight loss was 
more than twice that of the specimen containing 0.1 wt % Co. Meta110graphic 
examination of the polished and etched cross sections of the specimens (figs. 6 
to 8) revealed that in all tases the NiA1 has disappeared through oxidation 
and interdiffusion with the substrate (ref. 6). The yl phase (N3A1) precip-
itate in the substrate became coarser. It is also apparent that the alloys 
with higher cobalt content retained more yl phase near the surface. The 
micrograph of the specimen, containing 17 wt % Co (fig. 8) shows that after 
310 cycles the substrate near the surface is void of yl phase, which means 
that the surface region is depleted of aluminum. This observation is consist-
ent with the significant and unexpected weight loss exhibited by this alloy. 
No significant difference was apparent between the oxidation behavior of 
the hot worked alloys and alloys prepared by HIP-PM technique. The thermo-
gravimetric curves for both types of alloys show the same general paralinear 
shape (figs. 2 and 4 or 3 and 5) and the microstructures resulting from the 
cyclic oxidation tests (figs. 6 and 7) are very similar. 
3 
XRD analysis of the surface of specimens subjected to cyclic oxidation at 
1100 °c in static air (table III) revealed the absence of NiAl coating after 
20 l-hr cycles. In general, the phases detected were alumina, NiSS, spinel, 
and rutile. The alloys with low cobalt content developed oxide scale composed 
of alumina or alumina plus spinel, whereas alloys with higher cobalt content 
produced oxide scale composed of alumina, rutile, a~d spinel. The amount of 
spinel and rutile in the oxide scale increased with the number of oxidation 
cycles. 
The data obtained here for coated U-700 type alloys can be compared to 
the results reported by Barrett (ref. 9) for the same alloys but in the 
uncoated condition. Barrett I s static ai r, cycl1c oxidation experiments were 
conducted at temperatures ranging from 1000 to 1150 °c for times to 500 l-hr 
cycles. He found 'that alloys with higher cobalt content underwent greater 
weight loss than those with lower cobalt content. Thus his findings are 
opposite to those of the present study where the aluminide coated alloys with 
higher cobalt content yielded reduced weight 10ss~ Barrett found also that 
the oxide scale on the low cobalt content samples was composed of Ni, NiTi03, 
and Cr203 while that on the higher cobalt content alloys was NiO, Cr203, 
and NiCr204. The offered explanation was that for erIAl ratio> 3.5 the tend-
ency to form Cr203 is accentuated by higher cobalt levels which leads an 
increased oxidation rate. 
SUMMARY OF RESULTS 
1. The aluminide coated cobalt rich alloys exhibited better oxidation 
resistance than alloys with low cobalt content, the weight loss being the 
criterion for such evaluation. 
2. The aluminide coatings contained significantly less Ti, Cr, Mo, and Co 
than their substrates. The content of these elements in the NiAl, except for 
cobalt, was found to be independent of the cobalt content in the alloys. 
3. The higher content of cobalt in the aluminide coated U-700 type alloys 
promoted the formation of spinel and rutile structures in the oxide scales, 
which could be the reason for improved oxidation resistance. 
4. There was no difference between the cyclic oxidation behavior of alumi-
nide coatings on wrought alloys and coatings on alloys of the same composition 
but prepared by HIP-PM technique. 
1. 
REFERENCES 
Talboom, F.P., and Petrusha, J.A.: Superalloy Coatings for Components of 
Gas Turbine Engine Applications. AFMl-TR-66-15, 1966. 
2. Fleetwood, M.J.: Influence on Nickel-Base Alloy Composition on the 
Behaviour of Protective Aluminide Coatings. J. Inst. Met., vol. 98, 1970, 
pp. 1-7. 
3. Redden, T.K.: Ni-Al Coating - Base Interactions in Several Nickel-Base 
Alloys." Trans. Am. Inst. Min., Metall. Pet. Eng., vol. 242, Aug. 1968, 
pp. 1695-1702. 
4 
4. Nejed11k, J.F.: Development of Improved Coat1ngs for N1ckel- and Cobalt-
Base Alloys. AFML-TR-70-20B, 1970. 
5. Goward, G.W.: Current Research on the Surface Protect10n of Superalloy 
for Gas Turb1neEng1nes. J. Met. vol. 22, no. 10, Oct. 1970, pp. 31-39. 
6. Sm1alek, J.L.; and Lowell, C.E.: Effects of D1ffus10n of Alum1num Deple-
t10n and Degradation of N1-Al Coat1ngs. J. Electrochem. Soc., vol. 121, 
no. 6, June 1974, pp. BOO-B05. 
7. Tomaszew1cz, P.; and Wallwork, G.R.: The Degradat10n of Alum1na-Form1ng 
Coating Systems on N1ckel, Cobalt, and Iron-Based Alloys by H1gh Tempera-
ture Ox1dat10n. Rev. H1gh Temp. Mater., vol. 5, no. 1,1982, pp. 49-91. 
8. Gray, H.R.; and Sanders, W.A.; Effect of Thermal Cyc11ng 1n a Mach 0.3 
Burner Rig on Properties and Structure of D1rect10n Solid1f1ed y/y' - 6 
Eutectic. Conference on In S1tu Composites, M.R. Jackson, et al., eds., 
Xerox Individualized Publishing, 1976, pp. 201-210. 
9. Barrett, C.A.: Oxidation of Low Cobalt Alloys. COSAM Program Overview, 
NASA TM-B3006, 19B2, pp. 89-98. 
5 
TABLE I. - CHEMICAL ANALYSES OF THE ALLOYS 
Alloy Co 
No. 
U_1a 0.10 
U_2a 4.30 
U-3a 8.6 
U-4a 12.8 
U-5a 17.0 
U-2-1b 4.3 
U-4-1b 12.6 
~Wrought. 
°HIP Alloys. 
Cr Mo 
15.1 5.00 
15.1 4.90 
15.0 5.05 
14.7 5.0 
14.9 5.03 
14.9 4.85 
14.8 5.10 
Ti A1 C B 
wt 6. 
3.46 4.12 0.06 0.025 
3.55 4.14 .07 .024 
3.51 4.05 .06 .025 
3.61 4.10 .06 .023 
3.60 4.08 .06 .028 
3.53 4.05 .07 .021 
3.56 4.03 .06 .024 
Ni 
Bal. 
TABLE II. - XR'F DETERMINATION OF ELEMENTS IN ALUMINIDE COATINGS 
AND THEIR SUBSTRATES 
Alloy Element Co Cr Mo Ti Al Ni 
(cobalt 
content) 
U-1 Coating aO.05 2.45 2.86 0.20 30.23 61.23 
(Co = 0.1) Substrate 0.16 15.20 4.41 3.39 6.42 68.90 
; 
U-3 Coating 4.01 2.87 2.80 .19 29.27 58.25 
(Co = 8.6) SUbstrate 7.80 14.97 4.45 3.25 3.40 64.36 
; 
U-5 Coating 8.64 2.90 2.87 .22 28.97 53.96 
(Co = 17.0) Substrate 14.44 14.74 4.20 3.12 3.43 57.99 
U-2-1 Coating 2.06 2.60 2.70 .19 31.24 58.21 
(Co = 4.3) Substrate 3.73 14.05 4.29 3.19 3.78 69.27 
aThe data are expressed in weight percent. For the a1uminide 
coating the precision is +10 percent and accuracy is +20 percent 
and for the substrate they are +5.0 percent and +15 percent, 
respect i ve ly. - -
6 
-....I 
TABLE III. - PHASES DETECTED BY XRD ON THE SURFACE OF THE SPECIMENS AFTER CYCLIC OXIDATION 
AT 1100 °c IN A MUFFLE FURNACE 
Alloy CODalt Number of cycles/phases detected 
content, 
wt I!. 20 40 100 150 
U-1 0.1 A1203(s),a NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(m) 
Spinel(s) 
U-2 4.3 A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(s) 
Spinel(w) Spinel(s) 
U-3 8.6 A1 203(s), NiSS(s) A1 203(s)., NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(m) 
I 
I 
1 
! 
I 
I 
Spinel(m) Spinel(s), Rutile(m) i 
U-4 12.8 A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(m) A1 203(s), NiSS(m) 
Rutile(w) Rutile(w) Rutile(m), Spinel(m) Spinel(s), Rutile(m) 
U-5 17.0 A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(s), NiSS(m) 
Rutile(w) Rutile(w) Rutile(m), Spinel~(w) Spinel(s), Rutile(m) 
U-2-1 4.3 A1 203(s), NiSS(s) A1 203(s), NiSS(s) A1 203(m), NiSS(m) A1 203(s), NiSS(m) 
Spinel(w), Rutile(m) 
----
~ . -- -- ------------
aRelative intensities of oxides are with respect to the other oxides only. 
s - strong; m - medium; w - weak. . 
(a) Alloy U -l,Co content O.l%,wrought. (b) Alloy U-5,Co content 17%,wrought. (c) Alloy U-4-1,Co content 12. 6%,HI P-PNI. 
Figure 1. - Microstructure of selected alloys after coating with aluminide by RT-21 process. 
0'> 
s:,-
<I 
• 02 
0 
-.02 
-.04 
-.06 
-.08 
-.10 
-.12 
-.14 
-.16 
0 
.04 
.02 
s:,- -,02 
<I 
-.04 
-,06 
Cobalt 
content, 
% 
U-1- 0.1 
U-2- 4.3 
U-3- 8.6 
U-4-12.8 
U-5-17.0 
-.08
0 
'----~----::-'--:----~ 
Figure 2. - Oxidation behavior of 
aluminized U-700 type alloys 
(wrought) in Mach 0.3 burner 
rig at 1100 °C . 
,------ " ......... ~, ...... 
~-----_ ............ U-4 
"... - ............ 
Cobalt 
content, 
% 
U-1 - 0.1 
U-2 - 4.3 
U-3 - 8.6 
U-4 -12.8 
U-5-17.0 
................ ............ U-3 
\ 
~--~ \~--- U-2 \ 
Number of cycles 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
U-I 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ 
\ U-5 
Figure 3. - Oxidation behavior of aluminized U-700 type alloys (wrought) in Mach 
0.3 bu rner rig at 1100 °C. 
• 02 
0 
-.02 
-.04 
-.06 
C"l 
:5:-
-.08 
<l 
-1. 0 
-1. 2 
-1.4 
-1. 6 
-1. 8 
0 
.02 
:5:- -.02 
<l 
-.04 
Cobalt 
content, 
% 
U-2-1- 4.3 
U-4-1-12.6 
Figure 4. - Oxidation behavior of 
aluminized U-700 type alloys 
(HIP-PM) in Mach 0.3 burner 
rig at 1100 °C . 
.",.------..................... _--- .... 
""--... 
U-2-1 
-- ................. 
.... -
.................. 
Cobalt 
content, 
% 
U-2-1 - 4.3 
U-4-1 -12.6 
.... - ... U-4-1 
\0201 
50 150 200 300 
Number of cycles 
350 
Figure 5. - Oxidation behavior of aluminized U-70 type alloys (HW-PM) in Mach 
0.3 burner rig at 1100 °C. 
(a) Alloy U-l,Co content O.I%,wrought. (b) Alloy U-3,Co content 8. 6%,wrought. (e) Alloy U-4-1,Cocontent 12.6%,HIP-PM. 
Figure 6. -Typical microstructures of aluminide coated U-700 type alloys after ISO oxidation cycles at 1100 °c in Mach 0.3 burner rig. 
(a) Alloy U-l,Co content -Q.l%,wrought. (b) Alloy U-3,Co content 8. ~wrought. (e) Alloy U-4-1.Co content 12. 6%.HI P-PM. 
Figure 7. - iypicai microstructures of aiuminide coated U-700 type alloys after 310 oxidation cycles at 1100 °c in Mach 0.3 burner rig. 
Figure 8, - Microstructure of U-5 alloy ( Cobalt content 17 w/o, wrought) after 310 
oxidati.on cycles at 1100 °c in Mach 0.3 burner rig. 
. 
1. Report No. 2. Government Accession No. 
NASA TM-87173 
4. Title and Subtitle 
The Effect of Cobalt Content 1n U-700 Type Alloys 
on Degradat10n of Alum1n1de Coat1ngs 
7. Author(s) 
I. Zaplatynsky 
9. Performing Organization Name and Address 
Nat10nal Aeronaut1cs and Spate Adm1n1strat10n 
Lew1s Research Center 
Cleveland, Oh10 44135 
12., Sponsoring Agency Name and Address 
Nat10nal Aeronaut1cs and Space Adm1n1strat10n 
Wash1ngton, D.C. 20546 
15. Supplementary Notes 
16. Abstract 
3. Recipient's Catalog No. 
5. Report Date 
November 1985 
6. Performing Organization Code 
505-63-11 
8. Performing Organization Report No. 
E-2798 
10. Work Unit No. 
11. Contract or Grant No. 
13. Type of Report and Period Covered 
Techn1cal Memorandum 
14. Sponsoring Agency Code 
The influence of cobalt content in U-700 type alloys on the behavior of aluminide 
coatings was studied in burner r1g cyclic oxidation tests at 1100 °C. It was 
determ1ned that aluminide coat1ngs on alloys w1th higher cobalt offered better 
oxidation protection than the same coat1ngs on alloys contain1ng less cobalt. 
17. Key Words (Suggested by Author(s)) 18. Distribution Statement 
Cyc11c oxidation; Coatings; Superalloys Unclassified - unlimited 
STAR Category 26 
19. Security Classlf. (of this report) 
UnclassHied 
20. Security Class If. (of this page) 
UnclassH1ed 
21. No. of pages 
"For sale by the National Technical Information Service, Springfield, Virginia 22161 
22. Price· 
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The effect of cobalt content in U-700 type alloys on degradation of aluminide coatings

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