A coating system which contains a bond coating and a thermal barrier coating is applied to metal surfaces such as turbine blades and provides both low thermal conductivity and improved adherence when exposed to high temperature gases or liquids. The bond coating contains NiCrAlY and the thermal barrier coating contains a reflective oxide. The reflective oxides ZrO2-Y2O3 and ZrO2-MgO have demonstrated significant utility in high temperature turbine applications

Leibert, C. H.

Stecura, S.

English

NASA Technical Reports Server

United States Patent [191 
Stecura et al. 
4,055,705 
[45] Oct. 25, 1977 
[54] THERMAL BARRIER COATING S Y m M  
[75] Inventors: S t e w  Stccurll, Parma; Curt H. 
Leibert, Middleburg Heights, both of 
Ohio 
[73] Assignee: The United States of America am 
rejmsented by the A- r of 
tbe N 8 t i d  Aeroupties 8ed Spsce 
Adminirtrition, Washington, D.C. 
[21] Appl. No.: 686,449 
[22] Filed: May 14,1976 
[Sl] Int. (3.2 .............................................. B32B 15/01 
[52] US. c1. .................................... 4 2 W a  428/652; 
428/667; 427/405; 427/419 A; 427/34; 427/423 
[58] Field of seucb .......... 29/197, 197.5, 183.5, 
29/194; 427/34,214; 428/632, 633,652,667, 
672 
[561 References Cited 
U.S. PATENT DOCUMENTS 
3,410,716 11/1968 Hilty ...................................... 427/34 
3,719,519 3/1973 Perugini ................................. 427/34 
3,879,831 4/1975 Rigncy et al. ......................... 29/197 
3,957,454 5/1976 &sscn .................................... 29/197 
Primary Examiner-Ralph S. Kendall 
Azrorney, Agent, or Firm-N. T. Musial; G. E. Shook; J. 
R. Manning 
A coating system which contains a bond coating and a 
thermal barrier coating is applied to metal surfaces such 
as turbine blades and which provides both low thermal 
conductivity and improved adherence when exposed to 
high temperature gases or liquids. The bond coating 
contains NiCrAlY and the thermal barrier coating con- 
tains a reflective oxide. The reflective oxides ZrOz. 
-Y203 and ZrOz-MgO have demonstrated significant 
utility in high temperature turbine applications. 
1571 ABSTRACT 
8 cliimr, No Drawings 
https://ntrs.nasa.gov/search.jsp?R=19780010412 2020-03-20T12:49:18+00:00Z
4,05 5,705 
3 1 
THERMAL BARRIER COATING SYSTEM 
ORIGIN O F  THE INVENTION 
The invention described herein was made by employ- 
ees of the United States government and may be manu- 
factured and used by and for the government for gov- 
ernmental purposes without the payment of any royali- 
ties thereon or therefore. 
FIELD OF THE INVENTION 
The invention relates to a thermal barrier coating 
system for metal surfaces that are subject to high tem- 
perature uses, such as the surfaces of turbine blades, 
vanes and the like. 
BACKGROUND OF THE INVENTION 
The operating temperatures of the combustion gases 
utilized in the turbines of jet aircraft such as the 747 and 
DClO reach approximately 2,000" F or more thus can 
produce melting of most commercially available metals. 
Because of this, engine designers have developed new 
alloys for use in fabricating turbine blades. Further, in 
order to permit the blades to effectively perform in the 
high temperature atmosphere, the blades are typically 
coated with intermetallic aluminide or metal-based 
overlay coatings. One ceramic based coating that was 
examined in the past is a Ni-20 chromium bond coating 
with a ZrOz-CaO barrier coating. The coating has only 
modest adherence and frequency suffers from partial or 
fatal barrier spallation or thermal shock cracking after 
relatively short periods of exposure to high temperature 
combustion gases. Further, the calcia stablized zirconia 
is gradually graded so that the surface layer is 100% 
stabilized zirconia. This causes quality control and ad- 
herence problems. Moreover, the method of application 
required to produce the graded layer is tedious, 
Coatings utilizing NiCrAlY and other complex alumi- 
nized coatings have been proposed (see, for example, 
U.S. Pat. Nos. 3,869,779; 3,846,159; and 3,676,085). 
Further, U.S. Pat. No. 3,410,716 (Hiltz) discloses that 
zirconium dioxide can form a component of an oxide 
L 
An important feature of the invention is that the coat- 
ing system demonstrates strong adherence to metal 
surfaces and, in particular, has been shown to form an 
especially strong bond to nickel. Further, the coating 
5 system of the invention is not sensitive to thermal shock 
cracking or barrier spallation. Moreover, the coating 
system can be polished to reduce aerodynamic frictional 
losses. 
Other features and advantages of the present inven- 
10 tion will be set forth in, or apparent from, the detailed 
description of the preferred embodiment found herein 
below. 
DESCRIPTION O F  THE PREFERRED 
EMBODIMENTS 
As previously described, the inventive coating system 
comprises a bond coating containing NiCrAlY to which 
a ceramic reflective oxide is applied. The reflective 
ceramic oxide is highly reflective and preferably con- 
20 tains Zr02-Y203. The oxide may also be ZrOz-MgO. 
The ceramic coatings have a low thermal conductiv- 
ity and thereby impose a thermal barrier between the 
high temperature combustion gases and air-cooled 
metal parts, such as the combustor or turbine blades and 
25 vanes of aircraft engines, power generating turbines or 
other airfliquid cooled components. The use of low 
thermal conduction ceramic coatings to provide a ther- 
mal barrier improves the efficiency of such gas turbine 
engines. Specifically, substantially higher operating 
30 temperatures can be utilized with no significant addi- 
tional losses due to the increased cooling while still 
maintaining the engine components at or below the 
temperatures that they are presently subjected to. this 
permits the use of such higher operating temperatures 
35 without requiring tlie use of the newer and more expen- 
sive turnbine alloys. Thus, low alloy content metals 
may be substituted for alloys presently utilized in high 
temperature power system components at significant 
monetary savings. 
As noted above, the coating system of the present 
invention comprises two layers which are able to with- 
stand both the thermal and centrifugal stresses to which 
gas turbine engine blades are subjected. The bond coat 
which comprises NiCrAlY is advantageously applied to 
15 
40 
composition that bonds Well to tunGten substrates. The 45 the substrate by plasma spraying, although cladding, 
Hilt2 Patent also discloses that magnesium oxide and slurry spray and sintering are examples of other suitable 
yttrium oxide in small amounts may be utilized for stabi- techniques that csuld be used for this purpose. The 
lization purposes. thermal barrier overlayer contains a Yz030r MgO stabi- 
lized zirconia composition (preferably Zr02-12- 
50 w/oYz03 or Zr02-3.4w/oMg0), and it can be applied SUMMARY OF THE INVENTION 
In accordance with the invention, a coating system is by plasma or flame spraying. The bond coating thick- 
provided which Overcomes the disadvantages of the ness is preferably from 0.003 inches to 0.007 inches and 
barrier coatings discussed above. The thermal barrier the zirconia-yttria and zirconia-magnesia barrier coat- 
coating system of the invention comprises a bond coat- 
ing containing NiCrAlY and a thermal barrier coating 
containing a ceramic reflective oxide. Suitable ceramic 
reflective oxides are those which are highly reflective in 
the 1-2p infrared band. Preferred reflective oxides are 
Zr02-Yz03 and ZrOz-MgO. 
The present invention also concerns a method of 
coating metal surfaces which comprises coating first 
with a bond coating containing NiCrAlY and subse- 
quently coating the bond coated surfaces with a thermal 
barrier coating containing a ceramic reflective oxide. 
The method of the invention has particular utility as 
applied to surfaces of components, such as blades or 
vanes, of turbines which are subjected to high tempera- 
ture gases and liquids. 
ings are prefkrably from 0.010 inches to 0.030 inches 
55 thick. It will be understood that the thickness of the 
coating layers may be varied to achieve a desired tem- 
perature drop across the coating system barrier. 
Each of the constituents of the coating system of the 
present invention may be produced by conventional 
60 techniques and, further, the temperatures used are those 
which are suitable for the particular method of applica- 
tion selected. 
The following examples illustrate the advantages of 
the coating system of the present invention: 
EXAMPLE I 
A metal substrate was coated with a Ni--20w/o Cr 
bond coating and a Zr02-Ca0 (partially stabilized) 
65 
4,055,705 
3 4 
barrier coating. A second metal substrate was coated 
with a NiCrAlY bond coating and a Zr02-5.4w/o 
CaO (partially stabilized) thermal barrier layer. The 
thermal barrier layer was found five times more adher- 
ent to NiCrAlY than to Ni--20w/oCr. 
EXAMPLE I1 
Metal substrates were prepared having a NiCrAlY 
bond coat. A first coated substrate was covered with an 
over-layer of ZrO2-12w/oY203, (totally stabilized) a 10 
second was coated with Zr02-3.4w/o MgO, (totally 
stabilized) a third was coated with Zr02-5.4w/oCa0 
(partially stabilized) as thermal barriers, a fourth was 
coated with zro2-5.4w/o CaO (totally stabilized). 
above. The first set was placed in a furnace for one hour 
exposure cycles at 975" C. The number of cycles that 
each work piece was capable of surviving without fail- 
ure is set forth in Table A. 
TABLE A 
5 
Three sets of metal work pieces were prepared as 15 
20 
ZrO2-Y2O3 673 cycles no failure 
ZrOZ-MgO 460 cycles failed 
Zr02-CaO 255 cycles failed 
(partially stabilized) 
Zr02-Ca0 87 cycles failed. 
(totallv stabilized) 25 
Sheet specimens were mounted in a gas oxygen torch 
rig. They were subjected to 25 minute cycles at 1,160" 
C. The number of cycles for each specimen that sur- 
vived is set forth in Table B. 30 
TABLE B 
Zr02-Y203 254 cycles cracked 
ZrOz-MgO 56 cycles cracked 
zro cao 35 cycles cracked 
(part?ally stabilized) 35 
Work pieces formed as air cooled blades were in- 
serted into a Mach 0.3 combustion rig. The cycle con- 
sisted of 40 second heat-up; 80 seconds at the tempera- 
ture; and 30 seconds cooling. The number of cycles and 
the surface temperatures required before erosion or 
cracking induced the termination of testing are set forth 
in Table C. 
40 
TABLE C 45 
Zr02-Y203 3200 cycles at 1280" C erosion 
Zr02-Mg0 1010 cycles at 1180" C erosion 
ZrO CaO 200 cycles at 1280" C cracked 
(pardhy stabilized) 
50 
The foregoing examples demonstrate the superior 
bonding capability of the NiCrAlY bond coat. These 
examples further demonstrate the effectiveness of 
Zr02-Y203 or Zr02-Mg0 as thermal barriers which 
resist thermal cracking. Further, the coatings are shown 
to increase the life of components subjected to high 
temperature use and thus will increase the life of those 
components in a turbine which are exposed to hot gases. 
Although the invention has been described relative to 
preferred embodiments thereof, it will be understood by 
those skilled in the art that variations and modifications 
can be effected in this preferred embodiment without 
departing from the scope and spirit of the invention. 
We claim: 
1. A coated article of manufacture having a thermal 
a substrate selected from the group consisting of nick- 
a bond coating consisting essentially of NiCrAlY 
a thermal barrier coating consisting essentially of 
2. The thermal barrier coating system of claim 1 
wherein said reflective oxide is selected from the group 
consisting of Zr02-Y203 and Zr02-MgO. 
3. The thermal barrier coating system of claim 1 
wherein the thickness of said bond coating is from 0.003 
inches to 0.007 inches. 
4. The thermal barrier coating system of claim 1 
wherein the thickness of said thermal barrier coating is 
0.010 inches to 0.030 inches. 
5. A method of coating surfaces of nickel-base and 
cobalt-base alloys comprising: 
a. coating said surfaces with a bond coating consisting 
essentially of NiCrAIY; and 
coating the coated surfaces formed in step (a) with a 
thermal barrier coating consisting essentially of an 
oxide stabilized zirconia. 
6. The method of coating a metal surface as claimed in 
claim 5 wherein said reflective oxide is selected from 
the group consisting of Zr02-Y203 and ZrO2-MgO. 
7. The method of coating a metal surface as claimed in 
claim 5 wherein the thickness of the bond coating is 
from 0.003 inches to 0.007 inches. 
8. The method of coating a metal surface as claimed in 
claim 5 wherein the thickness of the thermal barrier 
coating is 0.010 inches to 0.030 inches. 
barrier coating system comprising 
el-base alloys and cobalt-base alloys, 
covering said substrate, and 
zirconia stabilized with another oxide. 
* * * * *  
55 
60 
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Thermal barrier coating system

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