NASA Technical Reports Server (NTRS) 20110012056: Mechanical Properties and Durability of Advanced Environmental Barrier Coatings in Calcium-Magnesium-Alumino-Silicate Environments

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Mechanical Properties and Durability of Advanced Environmental Barrier
Coatings in Calcium-Magnesium-Alumino-Silicate Environments
1 2
Daniel S. Miladinovich , Dongming Zhu
1.Illinois Institute of Technology, Chicago IL, 60616
Abstract
2. NASA John H. Glenn Research Center
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 .
Introduction Results
Laser Heat flux Testing
0 mg/cm2 surface concentration 34.9 mg/cm2 surface concentration 78.8mg/cm2 surface concentration
Advanced SiC/SiC ceramic matrix composites (CMCs) developed for gas turbine 3.0 3.0
2 2
engine hot section component applications are susceptible to environmental attack from 1600 m 1600 m
K K
2.5 c 2.5 c
m- W/ m- W/
harsh combustion and general operation. This is why it is necessary to apply layers of
/ /
W , W ,
x x
2.0 1200 u 2.0 1200 u
environmental barrier coatings (EBCs) to protect SiC/SiC CMCs. y, fl y, fl
vit at vit at
EBC materials have to withstand the extremely high temperature and corrosive 3.0 1600 cti 1.5 he cti 1.5 he
u ; u ;
2 d 800 C d kcera 800 C
m n ° n °
environment, and integrate well with the CMCs to ensure excellent thermal cyclic m-K 2.5 1400 W/c l co 1.0 kcera Tsurface ure, l co 1.0 Tsurface ure,
durability. Advanced multi-component oxide and silicate composites are being / 1200 ma Tinterface at ma Tinterface at
W , 400 r 400 r
x r e r e
developed to improve the coating mechanical integrity and environmental stability for y, 2.0 1000 flu The 0.5 Tqtbharcuk mp The 0.5 Tqtbharcuk mp
vit at Te Te
i e
CMCs. ct 1.5 800 h 0.0 0 0.0 0
du kcera C; 0 10 20 30 40 50 60 0 10 20 30 40 50 60
n °
SiC/SiC CMC gas turbine components generally require a layered environmental o 600 , Time, hours Time, hours
c 1.0 Tsurface re
l u
barrier coating system for improved performance, stability, and durability. EBCs are a t
m Tinterface 400 a
r
r e
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
After 50 hr testing
pollutant, is critical. The objective of this study is to determine the mechanical
After 50 hr testing
After 100 hr testing
performance of several candidate EBC systems. The stability of candidate EBC material
and coating systems in the presence of CMAS is also investigated. Figure 4: (above) Laser-high-heat flux tests were conducted on three structurally Figure 4: (above) is a hybrid EB-PVD coating system that
Figure 2: The initial vickers indentation results of non-CMAS-reacted coatings. (a) the mean value of
identical samples. With surface concentration increasing from left to right is consists of multiple layers. The following list shows the
each samples Kc was measured from the crack lengths. ZrO 311 was the toughest material. (b) the
evident that the CMAS is causing damage and melting of the coatings. (Left) the layers of this system.
Environmental barrier coating top coat
samples Hv as measured using the length of the diagonals. Hardness data was easily taken from the
increase in conductivity is due to the continued sintering from the high 1. ZrO +(Y, Gd,Yb) O +TiO +Ta O
Intermediate coating or interlayer fracture toughness tests so (b) shows the hardest material as the HfO + 5wt%Y O 2 2 3 2 2 5
Bond coat 2 2 3. temperatures. 2. HfO +Al O +SiO +(Y, Gd,Yb) O
2 2 3 2 2 3
SiC/SiC CMC substrate
3. Yb Si O
2 2 7
4. Yb Si O +20%BSAS
CMAS Reaction and Behavior
2 2 7
Figure 1: Shows a schematic of an EBC system with all 3 layers of coatings shown on
5. Si
SiC/SiC CMC substrate.
High Pressure Burner Rig Test – Tyrannohex SA and Er2SiO5 6. SiC/SiC CMC
Experimental Procedure With Coatings
2500°F (1371°C)
Silicate-CMAS Reaction Depths
2450°F (1343°C)
2300°F (1260°C)
8
•Sample preparation •Recession
10.000 7
•Sintering •Melting
6
)
•Polishing •Evaporation m
5
h m
-
•Indentation •Reaction and chemical change m2 1.000 Figure 6: (right) Shows the (4
h
c t
•CMAS reaction •Penetration and void generation g/ increasing thickness of p3
e
m
D
2
•SEM EDS e, various layers of mullite.
0.100
t
Green: Hf a 1
r
•X-ray diffraction Each layer represents a
n
Yellow: Ca o TA SiC Composite No.7 - early study 0
i
•Laser high heat flux testing s TA SiC Composite No.8 - early study different effect CMAS had.
s
e 0 50 100 150
c 0.010 TA SiC Composite No.11
•High pressure burner rig Re TA SiC Composite No.12 Time in hours is on the x Time (hrs)
Er2SiO5
axis. Depth is on the y.
Er2SiO5 with CMAS Recession Layer Melted Layer Reaction Layer Sample Initial Thickness
EBC Materials Tested
0.001
0.0006 0.00065 0.0007 0.00075 Concluding Remarks
-1
1/T, K
•Vickers Indentation Fracture Toughness Figure 5: (above) Shows the recession of TA
• Oxides (Tyrannohex SA) SiC Composite as well as the recession Initial fracture toughness testing using the Vickers indentation approach has shown
•HfO of the Er SiO in the high pressure burner rig (HBPR). It that the ZrO and HfO coating materials are the most fracture resistant. Further testing
2 2 5 2 2
•HfO +50wt%Si Figure 3 (above): SEM images that span ≈180µm Right, secondary electron image showing the is shown that CMAS seemed to have a detrimental effect is being considered to determine the strength and fracture toughness of materials reacted
2
Er2SiO5 with a higher recession rate
•HfO +5wt%Y O topology of HfO + 50wt% (HfO + 20wt%(Y, Gd, Yb) O . Left, two EDS map images showing on the . The HBPR with CMAS.
2 2 3 2 2 2 3
• ZrO + 4.5wt%Yb O + 4wt%Gd O + 3.5wt%Y O (ZrO 311) Hf (green) and Ca (yellow) locations. This image illustrates the effect of penetration of CMAS allows for gas turbine engine simulation testing at high Seven mechanisms of CMAS interactions with the coating materials have been
2 2 3 2 3 2 3
•Silicates into the material. pressure, temperature, and gas velocity. identified. While the oxides were more stable than the silicates, they were still affected
•Barium Strontium Alumino-Silicate (BSAS) by penetration and void generation from CMAS especially when initial high porosity is
•Al Si O (Mullite) + 20wt% BSAS present. Silicates reacted strongly with the CMAS generally decreasing the melting
6 2 13
•CMAS Reaction point and causing the coating to change phases as evidenced from x-ray diffraction such
•Oxides as in Yb SiO case. Some coating materials experienced combinations of all of the
2 5
•HfO +5wt%Y O effects. The laser-high-heat flux tests showed the damage and potentially reduced
2 2 3
•HfO + 50wt% (HfO +5wt%Y O ) temperature capability caused by the CMAS on a multilayer hybrid EB-PVD/Plasma
2 2 2 3
•HfO + 50wt% (HfO + 20wt%(Y, Gd, Yb) O Spray oxide-silicate EBC. This can be fatal to the coating structure as the operating
2 2 2 3
•ZrO + 3.0wt%Y O + 3.2wt%Gd O + 3.7wt%Yb O (ZrO 312) temperature approaches the melting point of these materials after reacting with CMAS.
2 2 3 2 3 2 3
•ZrO + 4.5wt%Yb O + 4wt%Gd O + 3.5wt%Y O (ZrO 311) The HPBR tests showed that the CMAS-reacted Er SiO seemed to be damaged
2 2 3 2 3 2 3 2 5
•Silicate (delamination and disintegration) and had higher recession rates compared to the non-
•Yb SiO reacted Er SiO .
2 5 2 5
•Al Si O (Mullite) While these studies are not complete, the current results easily showed that CMAS
6 2 13
•BSAS+25wt% (ZrO +14.3wt% (Y, Gd, Yb) O )) can cause serious damage to the coating or coating materials. Coating that have
2 2 3
•Er SiO improved resistance to CMAS must be designed and tested for advanced EBC systems.
2 5
•Hybrid Electron Beam Physical vapor Deposition (EB-PVD)– plasma coating
Figure 7 (left): SEM backscatter Special Thanks To:
system consisting of ZrO and silicate system.
electron image with three images NASA Undergraduate Student Research Program
2
Sample Configurations
Joyce Dever: Branch Chief
stitched together. Yb SiO exposed
2 5
Robert Angus: Hot Press Operator (Sample Creation)
to CMAS twice for a total of 100
Robert Pastel: High Pressure Burner Rig Operator (Recession
hr. This photo illustrates the
•1in diameter x 1/8in thick disc specimens Hot press conditions
Testing)
combined effects of penetration,
•Hybrid Air EB-PVD coatings on CMC used •Temperature = 1300 ˚C to 1700 ˚C
Joy Buehler: Metalography Lab Technician (sample polishing)
void generation, reaction/chemical
for laser high heat flux tests •Pressure = 69MPa to 103MPa
Terry McCue: SEM Operator (SEM/EDS Analysis)
change, and melting.
•Atmosphere = Vacuum
Rick Rogers: X-Ray Lab Manager (XRD Analysis)