Environmental barrier coatings are being developed and tested for use with SiC/SiC ceramic matrix composite (CMC) gas turbine engine components. Several oxide and silicate based compositons are being studied for use as top-coat and intermediate layers in a three or more layer environmental barrier coating system. Specifically, the room temperature Vickers-indentation-fracture-toughness testing and high-temperature stability reaction studies with Calcium Magnesium Alumino-Silicate (CMAS or "sand") are being conducted using advanced testing techniques such as high pressure burner rig tests as well as high heat flux laser tests

Miladinovich, Daniel S.

Zhu, Dongming

NASA Technical Reports Server

Introduction
Experimental Procedure
•Sample preparation
•Sintering 
•Polishing
•Indentation
•CMAS reaction
•SEM EDS
•X-ray diffraction
•Laser high heat flux testing
•High pressure burner rig
Environmental barrier coatings are being developed and tested for use with SiC/SiC ceramic matrix composite (CMC) gas turbine engine components. Several oxide 
and silicate based compositions are being studied for use as top-coat and intermediate layers in a three or more layer environmental barrier coating system. Specifically, 
the room temperature Vickers-indentation-fracture-toughness testing and high-temperature stability reaction studies with Calcium Magnesium Alumino-Silicate (CMAS 
or “sand”) are being conducted using advanced testing techniques such as high pressure burner rig tests as well as high heat flux laser tests .
Abstract
Mechanical Properties and Durability of Advanced Environmental Barrier 
Coatings in Calcium-Magnesium-Alumino-Silicate Environments
Daniel S. Miladinovich1, Dongming Zhu2
1.Illinois Institute of Technology, Chicago IL, 60616  
2. NASA John H. Glenn Research Center
EBC Materials Tested
•Vickers Indentation Fracture Toughness
• Oxides
•HfO2
•HfO2+50wt%Si
•HfO2+5wt%Y2O3
• ZrO2 + 4.5wt%Yb2O3 + 4wt%Gd2O3 + 3.5wt%Y2O3 (ZrO 311)
•Silicates
•Barium Strontium Alumino-Silicate (BSAS)
•Al6Si2O13 (Mullite) + 20wt% BSAS
•CMAS Reaction
•Oxides
•HfO2+5wt%Y2O3
•HfO2 + 50wt% (HfO2+5wt%Y2O3)
•HfO2 + 50wt% (HfO2+ 20wt%(Y, Gd, Yb)2O3
•ZrO2 + 3.0wt%Y2O3 + 3.2wt%Gd2O3 + 3.7wt%Yb2O3 (ZrO 312)
•ZrO2 + 4.5wt%Yb2O3 + 4wt%Gd2O3 + 3.5wt%Y2O 3 (ZrO 311)
•Silicate
•Yb2SiO5
•Al6Si2O13 (Mullite)
•BSAS+25wt% (ZrO2+14.3wt% (Y, Gd, Yb)2O3))
•Er2SiO5     
•Hybrid Electron Beam Physical vapor Deposition (EB-PVD)– plasma coating 
system consisting of ZrO2 and silicate system.
Sample Configurations
Hot press conditions
•Temperature   = 1300 ˚C to 1700 ˚C 
•Pressure   =  69MPa to 103MPa
•Atmosphere  =  Vacuum 
Results
Figure 2: The initial vickers indentation results of non-CMAS-reacted coatings. (a) the mean value of 
each samples Kc was measured from the crack lengths.  ZrO 311 was the toughest material.  (b) the 
samples Hv as measured using the length of the diagonals.  Hardness data was easily taken from the 
fracture toughness tests so (b) shows the hardest material as the HfO2 + 5wt%Y2O3.
CMAS Reaction and Behavior 
With Coatings
•Recession
•Melting
•Evaporation
•Reaction and chemical change
•Penetration and void generation
Figure 7 (left): SEM backscatter 
electron image with three images 
stitched together. Yb2SiO5 exposed 
to CMAS twice for a total of 100 
hr.  This photo illustrates the 
combined effects of penetration, 
void generation, reaction/chemical 
change, and melting.  
Figure 3 (above): SEM images that span ≈180µm  Right, secondary electron image showing the 
topology of HfO2 + 50wt% (HfO2+ 20wt%(Y, Gd, Yb)2O3.  Left, two EDS map images showing 
Hf (green) and Ca (yellow) locations.  This image illustrates the effect of penetration of CMAS 
into the material.  
Green: Hf
Yellow: Ca
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
400
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0 10 20 30 40 50 60
kcera
Tsurface
Tinterface
Tback
qthruTh
er
m
al
 c
on
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iv
ity
, W
/m
-K
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m
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re
, °
C;
 h
ea
t f
lu
x,
 W
/c
m
2
Time, hours
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
400
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0 10 20 30 40 50 60
kcera Tsurface
Tinterface
Tback
qthruTh
er
m
al
 c
on
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ct
iv
ity
, W
/m
-K
Te
m
pe
ra
tu
re
, °
C;
 h
ea
t f
lu
x,
 W
/c
m
2
Time, hours
After 50 hr testingAfter 50 hr testing
78.8mg/cm2 surface concentration34.9 mg/cm2 surface concentration
1.0
1.5
2.0
2.5
3.0
400
600
800
1000
1200
1400
1600
kcera
Tsurface
Tinterfacerm
al
 c
on
du
ct
iv
ity
, W
/m
-K
er
at
ur
e,
 °C
; h
ea
t f
lu
x,
 W
/c
m
2
 
After 100 hr testing
0 mg/cm2 surface concentration
Laser Heat flux Testing
Figure 4: (above) Laser-high-heat flux tests were conducted on three structurally 
identical samples. With surface concentration increasing from left to right is 
evident that the CMAS is causing damage and melting of the coatings. (Left) the 
increase in conductivity is due to the continued sintering from the high 
temperatures.
Figure 6: (right) Shows the 
increasing thickness of 
various layers of mullite.  
Each layer represents a 
different effect CMAS had. 
Time in hours is on the x 
axis.  Depth is on the y.
Bond coat
Intermediate coating or interlayer
Environmental barrier coating top coat
SiC/SiC CMC substrate
Figure 4: (above) is a hybrid EB-PVD coating system that 
consists of multiple layers.  The following list shows the 
layers of this system.
1. ZrO2+(Y, Gd,Yb)2O3+TiO2+Ta2O5
2. HfO2+Al2O3+SiO2+(Y, Gd,Yb)2O3
3. Yb2Si2O7
4. Yb2Si2O7 +20%BSAS   
5. Si
6. SiC/SiC CMC
Advanced SiC/SiC ceramic matrix composites (CMCs) developed for gas turbine 
engine hot section component applications are susceptible to environmental attack from 
harsh combustion and general operation. This is why it is necessary to apply layers of 
environmental barrier coatings (EBCs) to protect SiC/SiC CMCs. 
EBC materials have to withstand the extremely high temperature and corrosive 
environment, and integrate well with the CMCs to ensure excellent thermal cyclic 
durability.  Advanced multi-component oxide and silicate composites are being 
developed to improve the coating mechanical integrity and environmental stability for 
CMCs.
SiC/SiC CMC gas turbine components generally require a layered environmental 
barrier coating system for improved performance, stability, and durability.  EBCs are 
doped with rare earths and other metal oxides to improve their thermal mechanical and 
physical properties at high temperature. EBC top coats and intermediate coatings are 
typically made of rare-earth doped oxides and silicates. The coatings stability with 
calcium magnesium alumino-silicates (CMAS), which is sand and a common air born 
pollutant, is critical. The objective of this study is to determine the mechanical 
performance of several candidate EBC systems. The stability of candidate EBC material 
and coating systems in the presence of CMAS is also investigated. 
Figure 1:  Shows a schematic of an EBC system with all 3 layers of coatings shown on 
SiC/SiC CMC substrate.
Concluding Remarks
Initial fracture toughness testing using the Vickers indentation approach has shown 
that the ZrO2 and HfO2 coating materials are the most fracture resistant. Further testing 
is being considered to determine the strength and fracture toughness of materials reacted 
with CMAS.
Seven mechanisms of CMAS interactions with the coating materials have been 
identified.  While the oxides were more stable than the silicates, they were still affected 
by penetration and void generation from CMAS especially when initial high porosity is 
present.  Silicates reacted strongly with the CMAS generally decreasing the melting 
point and causing the coating to change phases as evidenced from x-ray diffraction such 
as in Yb2SiO5 case.  Some coating materials experienced combinations of all of the 
effects. The laser-high-heat flux tests showed the damage and potentially reduced 
temperature capability caused by the CMAS on a multilayer hybrid EB-PVD/Plasma 
Spray oxide-silicate EBC. This can be fatal to the coating structure as the operating 
temperature approaches the melting point of these materials after reacting with CMAS. 
The HPBR tests showed that the CMAS-reacted Er2SiO5 seemed to be damaged 
(delamination and disintegration) and had higher recession rates compared to the non-
reacted Er2SiO5.
While these studies are not complete, the current results easily showed that CMAS 
can cause serious damage to the coating or coating materials.  Coating that have 
improved resistance to CMAS must be designed and tested for advanced EBC systems.
High Pressure Burner Rig Test – Tyrannohex SA and Er2SiO5
0.001
0.010
0.100
1.000
10.000
0.0006 0.00065 0.0007 0.00075
TA SiC Composite No.7 - early study
TA SiC Composite No.8 - early study
TA SiC Composite No.11
TA SiC Composite No.12
Er2SiO5
Er2SiO5 with CMAS
Re
ce
ss
io
n 
ra
te
, m
g/
cm
2-
h
1/T, K-1
2500°F (1371°C)
2450°F (1343°C)
2300°F (1260°C)
Figure 5: (above) Shows the recession of TA 
(Tyrannohex SA) SiC Composite as well as the recession 
of the Er2SiO5 in the high pressure burner rig (HBPR).  It 
is shown that CMAS seemed to have a detrimental effect 
on the Er2SiO5 with a higher recession rate. The HBPR 
allows for gas turbine engine simulation testing at high 
pressure, temperature, and gas velocity.
Special Thanks To:
NASA Undergraduate Student Research Program
Joyce Dever: Branch Chief
Robert Angus: Hot Press Operator (Sample Creation) 
Robert Pastel: High Pressure Burner Rig Operator (Recession 
Testing)
Joy Buehler: Metalography Lab Technician (sample polishing)
Terry McCue: SEM Operator (SEM/EDS Analysis)
Rick Rogers: X-Ray Lab Manager (XRD Analysis)
•1in diameter x 1/8in thick disc specimens
•Hybrid Air EB-PVD coatings on CMC used 
for laser high heat flux tests
0
1
2
3
4
5
6
7
8
0 50 100 150
D
ep
th
 (m
m
)
Time (hrs)
Silicate-CMAS Reaction Depths
Recession Layer Melted Layer Reaction Layer Sample Initial Thickness
https://ntrs.nasa.gov/search.jsp?R=20110012056 2019-08-30T15:45:15+00:00Z


Mechanical Properties and Durability of Advanced Environmental Barrier Coatings in Calcium-Magnesium-Alumino-Silicate Environments

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