James K. Sutter

Glenn Research Center, Cleveland, Ohio

Subhash K. Naik

Rolls-Royce Corporation, Indianapolis, Indiana

Richard Horan

Allison Advanced Development Company, Indianapolis, Indiana

Kazuhisa Miyoshi and Cheryl Bowman

Glenn Research Center, Cleveland, Ohio

Kong Ma

Rolls-Royce Corporation, Indianapolis, Indiana

George Leissler

QSS Group, Inc., Cleveland, Ohio

Raymond Sinatra and Randall Cupp

Rolls-Royce Corporation, Indianapolis, Indiana

Erosion Resistant Coatings for Polymer Matrix

Composites in Propulsion Applications

NASA/TM—2003-212201

March 2003
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James K. Sutter

Glenn Research Center, Cleveland, Ohio

Subhash K. Naik

Rolls-Royce Corporation, Indianapolis, Indiana

Richard Horan

Allison Advanced Development Company, Indianapolis, Indiana

Kazuhisa Miyoshi and Cheryl Bowman

Glenn Research Center, Cleveland, Ohio

Kong Ma

Rolls-Royce Corporation, Indianapolis, Indiana

George Leissler

QSS Group, Inc., Cleveland, Ohio

Raymond Sinatra and Randall Cupp

Rolls-Royce Corporation, Indianapolis, Indiana

Erosion Resistant Coatings for Polymer Matrix

Composites in Propulsion Applications

NASA/TM—2003-212201

March 2003

National Aeronautics and

Space Administration

Glenn Research Center

Prepared for

SAMPE 2003

sponsored by the Society for the Advancement of Material and Process Engineering

Long Beach, California, May 11–15, 2003
Acknowledgments

We would like to thank Dr. Widen Tabakoff from the University of Cincinnati, Cincinnati, Ohio, for the many useful

discussions on the erosion rig testing aspects of this project. The cooperation and enthusiasm of his graduate

students is also well recognized. Our gratitude is expressed to Carol Ginty of the Aeropropulsion & Power Program

Office at NASA Glenn Research Center, Cleveland, Ohio, for her support of this project. We also acknowledge

Dr. H. S. Haller, of RealWorld Quality Systems for his contribution on the statistical analysis. Additionally, the

authors thank Daniel Scheiman, Rick Mondry, and Linda McCorkle for assistance producing and analyzing some of

the bondcoats used in this study. Finally, this paper is dedicated to the memories of two co-workers: Dennis Keller

of RealWorld Quality Systems and Dick Horan of AADC. Their contributions provided much of the foundation

that made this project a successful collaboration between many organizations.

Available from

NASA Center for Aerospace Information

7121 Standard Drive

Hanover, MD 21076

National Technical Information Service

5285 Port Royal Road

Springfield, VA 22100

This report is a preprint of a paper intended for presentation at a conference. Because

of changes that may be made before formal publication, this preprint is made

available with the understanding that it will not be cited or reproduced without the

permission of the author.

Trade names or manufacturers’ names are used in this report for

identification only. This usage does not constitute an official

endorsement, either expressed or implied, by the National

Aeronautics and Space Administration.

This report contains preliminary

findings, subject to revision as

analysis proceeds.

Available electronically at http://gltrs.grc.nasa.gov

The Propulsion and Power Program at

NASA Glenn Research Center sponsored this work.
NASA/TMó2003-212201 1 

EROSION RESISTANT COATINGS FOR POLYMER 

MATRIX COMPOSITES IN PROPULSION APPLICATIONS

James K. Sutter 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Subhash K. Naik 

Rolls-Royce Corporation 

Indianapolis, Indiana 46206 

Richard Horan 

Allison Advanced Development Company 

Indianapolis, Indiana 46206 

Kazuhisa Miyoshi and Cheryl Bowman 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

 Kong Ma 

Rolls-Royce Corporation 

Indianapolis, Indiana 46206 

George Leissler 

QSS Group, Inc. 

Cleveland, Ohio 44135 

Raymond Sinatra and Randall Cupp 

Rolls-Royce Corporation 

Indianapolis, Indiana 46206 

ABSTRACT 

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to 

other materials in many applications. High temperature PMCs are currently used in limited 

propulsion applications replacing metals. Yet in most cases, PMC propulsion applications are 

not in the direct engine flow path since particulate erosion degrades PMC component 

performance and therefore restricts their use in gas turbine engines. This paper compares two 

erosion resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and 

high temperature propulsion applications. Collaborating over a multi-year period, researchers at 

NASA Glenn Research Center, AADC, and Rolls-Royce Engines have optimized these coatings 

in terms of adhesion, surface roughness and erosion resistance. Results are described for 

vigorous hot gas/particulate erosion rig and engine testing of uncoated and coated PMC fan 

bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the structural 
NASA/TMó2003-212201 2 

durability of these coatings is described in long-term high cycle fatigue tests. Overall, both 

coatings performed well in all tests and will be considered for applications in both commercial 

and defense propulsion applications. 

1. INTRODUCTION 

Polymer Matrix Composites (PMCs) offer weight savings accompanied by strength 

improvements, reduced part count and reduced manufacturing costs. High temperature 

polyimide-based composites are of particular interest for next generation military aircraft engines 

because they exhibit outstanding thermal stability for many propulsion applications [1ñ3]. 

Examples of PMCs in advanced propulsion applications include the Joint Strike Fighter (JSF), 

JSF-Lift Fan and the Integrated High Performance Turbine Engine Technologies (IHPTET). 

In most cases, PMC propulsion component applications are not load bearing or in the direct 

engine flow path. Components residing in the engine flow path must withstand erosion to retain 

structural integrity and ensure acceptable surface finish to maintain aerodynamic performance 

[4, 5]. The survivability of PMC components is of major concern when long term operational life 

requirements for fan and compressor sections involve exposure to sand and grit erosion. One 

goal of NASAís HOTPC Project is to develop high temperature PMCs (HTPMCs) and 

associated surface protection coating technologies to allow for component integration into 

existing engines or advanced military engines. Over a multi-year period, NASA, AADC and 

Rolls-Royce Engines jointly developed an erosion resistant coating technology applicable to 

HTPMCs. A prior study detailing the performance of candidate erosion resistant coatings on a 

high temperature graphite fiber polymer composite, PMR-15, was reported [6] for flat coupon 

specimens. 

Although the use of erosion resistant coatings to reduce wear on metallic substrates is well 

documented, limited information is available for these coatings on PMCs [7ñ10]. To date, 

literature surveys reveal no references describing erosion coatings for these PMCs or the process 

to scale-up the coating process for PMC engine hardware. This paper describes a coating scaleup process, introduces a new coating system (SANPRES) that contains a new bondcoat and the 

testing of coated PMC hardware. Coated and uncoated PMC vanes were tested in three ways: a 

hot gas erosion rig, high cycle fatigue durability tests and in Rolls-Royce AE 3007 engine tests. 

Future testing will involve integrating this technology on high temperature PMC components for 

advanced engine applications. 

2. MATERIAL CONSIDERATIONS 

The objective of this project was to eliminate erosion wear issues and improve the durability of 

PMC components in order to incorporate them into civil and military engines. Therefore, two 

coating systems (SANRES and SANPRES) were applied to composite engine components and 

their performance was measured in rig and engine tests. These coatings included a bondcoat 

applied to the PMC substrate followed by a hard erosion resistant topcoat. The function of the 

bondcoat was to provide a ductile layer adhering well to both the PMC and the topcoat. 

Additionally, the bondcoat has a coefficient of thermal expansion (CTE) that bridged the CTE of 

the PMC and the topcoat. The primary difference between the SANRES and SANPRES coating 
NASA/TMó2003-212201 3 

systems was that the SANPRES coating contained a bondcoat with a polymer to improve 

adhesion to the PMC substrate. For both coating systems, tungsten carbide cobalt (WC-Co) was 

the primary topcoat constituent. 

The AE 3007 fan bypass vane (Figure 1) was selected due to the ready availability of this PMC 

component for engine tests within the project time frame. The vane material consists of a 

carbon-Kevlarô fiber-epoxy resin composite with a temperature capability up to 120 oC. A 

metallic strike strip is bonded onto the leading edge of the vane for added foreign object damage 

protection. This paper describes our approach for producing and testing coated PMC 

components used in subsonic engines. 

3. EXPERIMENTAL 

3.1 Coating Process Development

The coating process was selected such that prototype hardware could be fabricated for both 

erosion rig tests and engine tests. The SANRES coating system was applied using the 

combustion spray process for the bondcoat and plasma spray process for the top WC-Co coating. 

A plasma spray process was used for both the bond and topcoat layers in the SANPRES coating. 

Prior to coating, the AE3007 vanes were carefully grit-blasted with alumina to prepare the 

surface. Coating trials included coating a 3-vane (triplet) assembly as well as individual vanes. 

The manufacturing sequence was specified based on the results of extensive coating trials. The 

SANRES coating system was developed in earlier studies and therefore was considered the baseline coating in this study. The development of SANPRES coating system was a major focus of 

this research program. Another important aspect of this program was to adapt production-like 

coating methods for both coatings. 

A Metco 12E combustion gun with oxygen/acetylene gas setup was used to apply the bondcoat 

of SANRES coating to a thickness of about 0.076 mm. Coating trials were conducted with the 

part being held stationary or rotated with the gun moving vertically through an automated ladder 

step control program. A Sulzer Metco 7MB plasma spray gun was used to deposit the bondcoat 

of the SANPRES system to about 0.076 mm. Coating trials to optimize the bondcoat thickness 

and adhesion were also conducted by varying the gun traverse speed, number of passes, stand-off 

distance, part rotational speed and argon/nitrogen gas flow ratios. Finally, process parameters 

were established for the topcoat WC-Co (0.076 mm). This topcoat was applied to both coating 

systems using the 7MB gun. Engelhard Corporation applied all coatings. Once spray procedures 

were established, a design of experiments (DOE) was instituted to randomly apply the SANRES 

and SANPRES coating systems on three different days to remove potential biases due to spray 

and ambient conditions. Prior to coating, vanes were randomly chosen from a larger lot at the 

manufacturer. 

3.2 Erosion Rig Test Procedure

(Erosion testing was performed at the University of Cincinnati.) Specimens were cut from the 

coated AE 3007 bypass vanes at a set trailing edge location and placed in a test fixture 

(Figure 2). The fixture was designed to accommodate specimen curvature and to retain uneroded edge area for a nondestructive evaluation (NDE) baseline after the erosion test. In 

addition to the high temperatures, the University of Cincinnati erosion rig facility (Figure 3) 
NASA/TMó2003-212201 4 

realistically simulates all the erosion parameters that are deemed to be important from an 

aerodynamic point of view [4, 5]. These parameters include particle velocity, impingement 

angle, erodent particle and sample size. Varying the airflow in the erosion rig wind tunnel 

controlled particle velocities. Rotating the specimen relative to the flow stream direction set the 

particle impingement angles. Heating the flow stream with a combustible hydrocarbon gas or 

steam jacket varied the coated PMC sample temperature. The erosion test procedure used 

Arizona road-dust (ARD) impinging at 20o, 60o and 90o angles on both uncoated and coated vane 

specimens at a velocity of 228.6 m/sec. Room and elevated temperature (93 oC) tests were 

conducted using 15, 12 and 10 grams of ARD. A multiple correlation analysis was used to 

determine the effect of these operational variables on the erosion of the various coating systems.

3.2.1 Coating Effectiveness Analysis Procedure

The typical method to measure erosion is to weigh the mass of the specimen before and after 

testing. However, the SANRES and SANPRES coating systems each contain more than one 

constituent and each constituent has a different density. Therefore, typical erosion mass 

measurement methods may not provide a reliable means to evaluate erosion resistance. A more 

accurate method would measure the eroded volumes of the multi-component coating wear scar. 

Accurately measuring eroded volumes on coated materials with complex topographyís is also 

difficult. In order to gain a high level of confidence in our erosion measurements, several 

methods were used to measure the amount of material eroded from the coated PMCs. Some of 

the methods were employed for the first timeósuch as the method using optical interferometry. 

Other traditional methods such as coating weight loss or metallurgical sectioning/photo 

microscopy was also used to evaluate erosion. Results from each of these methods were 

compared with each other to determine if statistically valid correlations existed. 

Four independent response factors (Y1, Y2, Y3 and Y4) were measured to ascertain if there were 

significant statistical differences in the erosion resistance between the SANRES and SANPRES 

coating systems. The response factors for the statistical analysis were Mini-MoirÈ 

Interferometry, Optical Interferometry (both methods are nondestructive), metallurgical crosssectioning and weight loss methods. Since the topcoat for each coating system was WC-Co, it 

was presumed that the comparison analyzes the performance of each coating systemsí bondcoat. 

The specific erosion rate (Y1) was obtained through the weight loss measurement after the 

erosion test at the University of Cincinnati. The erosion depth (Y2) was measured at Rolls 

Royce using optical Mini-MoirÈ fringing based 3-D digitization (by EDIS Corp.) for generation 

of XYZ data points of surface profiles (Figure 4). For this measurement, the test specimen is 

mounted on a coordinate measurement machine and the ësurfacer-softwareí (SDRC Corp.) 

superimposes the before and after erosion test data to provide the erosion depth loss. The 

erosion coating volume loss (Y3), a second type of erosion rate (Y5) and the average wear scar 

depth (Y6) were measured by optical interferometer (VEECO Corp.) at NASA Glenn Research 

Center in Cleveland, OH (Figure 5). The optical interferometer or profiler quantifies critical 

dimensions such as area and volume of the damaged erosion wear scars, topographical features 

such as peaks and valleys in the coating, and surface roughness. This optical interferometer has 

3-D profiling capability with excellent precision and accuracy (e.g., profile heights ranging from 

< 1 nm up to 5000 μm with 0.1 nm height resolution). The shape and surface can be displayed 

as a digitally derived map from a three-dimensional interferogram of the surface. The volume 
NASA/TMó2003-212201 5 

and depth losses of an eroded surface are computed directly. Finally, specimens were 

metallurgically sectioned to determine the maximum depth measurements (Y4) in areas that 

indicated maximum coating loss as determined by optical interferometry. Again, all data were 

statistically analyzed to determine whether or not there were significant correlations between the 

various measurements and more importantly between the coating systems: SANRES and 

SANPRES. 

3.3 Laboratory Structural Durability Test Procedure 

Structural dynamic tests were performed at NASA Glenn to test the coatingsí high cycle fatigue 

durability, under vibration loading similar to the engine conditions experienced by AE 3007 

composite bypass fan vanes. The procedure for single vane durability testing is presented in the 

following description. A single vane was installed in a cantilevered fashion on a rigid test fixture 

mounted to a model C-60 electrodynamic Shaker with reciprocating slip table (MB Dynamics of 

Cleveland, OH) controlled by a Ling model DMA-48B/X amplifier. A clamping fixture was 

designed such that the tests could be performed on individual vanes or in triplet segments. This 

permitted an input acceleration of up to 539 m/s2

 (55gís) at the base of the vane with oscillatory 

frequencies up to 3000 Hz. An individual vaneís response to the range of slip table input 

variables was investigated using an uncoated vane instrumented with numerous strain gages and 

accelerometers. The strain survey provided the resonant mode locations on the uncoated vanes. 

A strain survey was then carried out with the coated vanes. These vanes were coated everywhere 

except at the gage locations by masking these areas to verify that the coating had no effect on 

vane dynamics. Vibratory testing was then carried out for long dwell times at the third flexural 

mode occurring at approximately 1500 Hz with 300ñ400 microstrain (μe). Fluorescent Penetrant 

Inspection (FPI) studies were conducted to identify any coating cracks that might result from the 

durability tests. 

 

3.4 AE 3007 Engine Durability Test Procedure 

 Table 1. Engine Cycle 

Six coated composite bypass vanes (3 each of SANRES 

and SANPRES) were assembled in a rainbow fashion 

in the AE 3007-fan section (Figure 6). The testing was 

conducted at the Rolls-Royce (Indianapolis) facility in 

an AE 3007 3000-cycle endurance test. The typical 

endurance test cycle is shown in Table 1. The elapsed 

time for each cycle was 22.5 min. Scheduled stops were 

made during the test to inspect the coated vanes and 

other components involved in this test. FPI studies were 

conducted to identify any coating cracks that resulted from the engine cycling. 

4. RESULTS AND DISCUSSION 

4.1 Coatings Process Development

The coating trials defined the optimized process parameters, as well as, the manufacturing 

sequence. Early coating trials with the 3-vane pack bypass vane component indicated that the 

coating thickness was not uniform due to the line-ofñsight limitations of the spray process. 

Therefore, the manufacturing sequence was re-defined as (1) applying the bondcoat and topcoat 

Condition Time, (min) 

Start to Ground Idle (GI) 2.5 

Maximum Take-off (T/O) 2.0 

Maximum Continuous 12.0 

Flight Idle (FI) 1.5 

Maximum Take-Off (T/O) 0.5 

Ground Idle (GI) 2.0 

Shutdown (Coast/stopped) 2.0 
NASA/TMó2003-212201 6 

to individual vanes and not the 3-pack of vanes, (2) then 

apply the leading edge metallic strip and finally, 

(3) adhesively bond the individually coated vanes into a 

3-pack vane assembly. 

The optimum range for the critical process parameters 

for the bondcoats of SANRES and SANPRES were 

identified as 250 rpm rotational speed, 12.7 cm standoff distance, 1200 to 1500 mm/sec gun traverse speed, 

2 mm gun displacement, and 18 to 24 passes. The 

optimized parameters of the WC-Co topcoat used for 

both SANRES and SANPRES coating system are listed 

in Table 2. Typical microstructures of SANRES and 

SANPRES are shown in Figs. 7 and 8, respectively. 

Each coating system adhered well to the PMC substrate. 

Another indicator that these coatings adhered well was 

demonstrated during the thermal shock test. Coated 

samples were ramped from room temperature to 93 oC 

followed by an air quench and then back to room 

temperature. This cycle was repeated for 10 times. Both 

coating systems remained intact after these tests. 

Results from the rotating and static modes of coating deposition indicate that the rotating mode 

was the preferred approach for both coating systems. By rotating the vanes, the SANRES and the 

SANPRES coatings thickness were quite uniform as shown in Figure 9 (a, b). Fine powder sizes 

(ñ325 mesh) were used to obtain the smoothest surface finish for the WC-Co topcoat. 

Regardless of the WC-Co powder size, topcoat surface roughness is predominantly determined 

by the roughness of the bondcoat. 

Earlier experiments showed that the surface roughness of the SANPRES coating, which 

contained a polymer added to its bondcoat, was 2ñ3 rougher than the more mature SANRES 

coating. However, after refining the powder size of the polymer additive, the typical surface 

finish for both coating systems was 350 Ra (average roughness). Note: this is a ten-fold increase 

in surface roughness compared to the uncoated PMC vanes. Aerodynamic analysis performed at 

Rolls-Royce Engines indicated that the increase in surface roughness for coated bypass vanes 

does not decrease engine performance. 

4.2 Coating Effectiveness in Erosion Prevention

Several independent erosion response factors were measured (Y1ñY6), as seen in Table 3. A 

statistical analysis was conducted on the four responses Y1, Y2, Y3, and Y4 to quantify the 

effect of coating system and performance parameters on erosion (Table 3) and to determine the 

correlation between these four independent measurements of erosion. Since WC-Co was used as 

the topcoat layer for both systems, the experiments essentially compared the bondcoat 

performance between the two systems, SANRES and SANPRES. Because of coating

Powder Praxair WC-106 

Gun Type 7MB 

Primary Gas Argon 

Secondary Gas Nitrogen 

Primary Flow 100 flow @100psi 

Secondary Flow 10 flow @ 50psi 

Nozzle GE 

Amps 400 

Volts 62 

Carrier 37 flow @ 100psi 

Powder Port #2 

Intersect-Air 7in. @ 60psi 

Stand-off 10.15mm 

Feeder Miller-1.90 rpm 

Feed Rate 2.58kg/hr 

Speed 1500 mm/sec 

Passes 28 

Thickness 0.003î 

Angle 0 o

Grit N/A 

Notes Traversed Horizontally 

Table 2. WC-Co Deposition Parameters
NASA/TMó2003-212201 7 

*Erosion Coating Breakthrough

1 Erosion tests performed at 228 m/sec 

2 SANRES, SANPRES and Uncoated Coupons are designated by S, SP, and U in Sample ID column above. 3

 Y1 = Erosion rate - measured by coating weight loss (mm3/gm = volume of coating weight loss/gm of erodent) 4

 Y2 = Wear scar maximum depth (mm) ñ measured by MoirÈ 

5

 Y3 = Erosion coating volume loss (mm3) ñ measured by optical interferometer 6

 Y4 = Wear scar maximum depth (mm) ñ measured by metallurgical cross section 

7

 Y5 = Erosion rate ñ measured by optical interferometer (mm3/gm = volume of coating weight loss/gm of erodent) 8

 Y6 = Average wear scar depth (mm) - measured by optical interferometer 

breakthrough for SANPRES coated specimens tested at 20o-impingement angle, there was no 

data available for Y4 (max. depth of wear scar) especially coupon SPD3-44. 

First, a statistical analysis compared the different methods (responses) used to calculate erosion 

resulted in four comparisons: the erosion rates (Y1 and Y5), the maximum eroded depths (Y2 

and Y4) and maximum and average eroded depths (Y2 and Y6), and the eroded weight and 

volume losses (Y1 and Y3). All four of the comparisons were significantly correlated with at 

least 95 percent confidence. In every one of these four cases, the correlation coefficient, r = √ R2, 

was greater than the tabulated value for a 5 percent risk factor. In fact or all but one case, the 

probability that such correlations could occur by chance alone were only 0.05 percent, i.e., the 

confidence is 99.95 percent that the relationship is significant. 

The effect of each coating system and the erosion process variables (angle of impingement and 

temperature) on erosion resistance were quantified for all six responses shown in Table 3. 

Because these correlations were all similar, only the case of Volume Loss (Y4) is summarized 

below. The effect of process variables (erodent angle of impingement and erosion test 

temperature) on the volume loss for the uncoated PMC vane, SANPRES and SANPRES coating 

systems are shown in Figures 10, 11, and 12, respectively. It is evident that both coating systems, 

SANPRES or SANRES, reduce the eroded volume by as much as 50 percent over the uncoated 

Table 3: Erosion Test Response Factors 1

Sample ID2 Test Temp. 

(°C) 

Erodent 

(g) Erosion Angle (Y1) 3 (Y2) 4 (Y3) 5

 (Y4) 6 (Y5) 7 (Y6) 8 

SD1-13 21 15 20 0.34 0.063 6.1 0.073 0.41 0.055 

UD3-37 21 15 20 2.40 0.191 24.3 - 1.62 0.128 

SPD1-8 93 15 20 0.69 0.140 9.8 0.157 0.65 0.076 

SPD3-44 93 15 20 0.76 0.165 14.0 * 0.93 0.089 

SD3-50 93 15 20 0.44 0.102 7.7 0.111 0.51 0.064 

UD2-20 93 15 20 3.10 0.254 30.5 - 2.03 0.155 

SPD2-27 21 12 60 0.68 0.102 6.8 0.119 0.57 0.063 

SD2-33 21 12 60 0.40 0.064 4.1 0.081 0.34 0.050 

UD1-3 21 12 60 1.48 0.114 14.8 - 1.23 0.077 

SPD1-10 93 12 60 0.72 0.089 7.5 0.081 0.83 0.066 

SD3-52 93 12 60 0.62 0.089 7.1 0.074 0.59 0.062 

UD2-22 93 12 60 2.52 0.165 21.1 - 1.76 0.102 

SPD3-47 21 10 90 0.39 0.064 2.6 0.076 0.26 0.044 

SD1-17 21 10 90 0.37 0.064 2.6 0.046 0.26 0.043 

UD3-41 21 10 90 1.23 0.114 14.1 - 1.41 0.070 

SPD2-30 93 10 90 0.84 0.102 9.4 0.119 0.94 0.074 

SD2-36 93 10 90 0.48 0.063 6.4 0.056 0.64 0.059 

UD1-6 93 10 90 2.78 0.140 19.1 - 1.91 0.093 
NASA/TMó2003-212201 8 

substrate. It should be noted that the surface of the bare substrate material has an under-layer of 

Kevlarô fabric that prevents further degradation due to erosion. A prior study on carbon fiber 

polyimide composites without Kevlarô subsurface reinforcement indicated that the WC-Co 

topcoat, in combination with these bondcoats, exhibited 3ñ8 fold erosion resistance improvement 

compared to the uncoated carbon fiber PMC [6]. 

Note that the SANPRES (Figure 11) is more sensitive to erosion at the low impingement angles 

than the SANRES (Figure 12); whereas at 90 degree impingement, the two systems are 

indistinguishable. It appears that the SANPRES coating with polymer additives does not enhance 

performance. In one case (20 degree impingement), the SANPRES erosion resistance is 

significantly less than the performance of the SANRES coating. This noticeable effect could be 

due to the presence of residual porosity in the bondcoat and/or a weaker interface with the 

WC-Co topcoat layer (Figure 8). At this time, these results are considered preliminary. It is 

important to note that the erosion results from these 18 vane specimens are a small subset 

(fractional factorial) of a larger experiment (54 vanes = full factorial). The results from the full 

factorial experimental design will be published in the future. 

4.3 Laboratory Structure Durability Tests 

Results from this study were based on two important questions: 

(1) What was the strain profile of the bypass vanes during certain flight profiles? 

(2) Where was the highest level of vane erosion? 

While it was not the intent of this study to fully model the flight profile experienced by the 

AE3007 bypass vanes, it was important to map the strain profile in the lab and correlate this 

strain profile to any potential coating failure. From earlier studies, specific strain responses were 

mapped for a given location on the bypass vanes. Therefore, two SANRES and two SANPRES 

coated vanes were tested to 40 million cycles while single SANRES and SANPRES coated vanes 

were tested to 80 million cycles (Table 4) at the third mode (1500 Hz with 300ñ400 μe). The 

applied force or level of acceleration shown in Table 4 was the actual constant acceleration 

applied to the fixture base. This force was chosen to achieve an initial strain of 250 microstrain 

(μe) on the vane leading edge. The planned μstrain level, 300ñ400 μe, equates to the maximum 

desired strain associated with the most responsive location identified in the strain survey of the 

bypass vane. For the third mode, the most responsive location was around the midpoint of the 

vane trailing edge. 

 Table 4: Structural Dynamic-Vibration Test Conditions

Sample ID Planned Excitation Conditions Input Total Cycles 

SANRES-DS1 40M cycles at 3rd mode (~400μe) 45 g 46,820,039 

SANPRES-DS1 40M cycles at 3rd mode (~400μe) 45 g 40,002,687 

SANRES-DS2 80M cycles at 3rd mode (~400μe) 45 g 80,002,851 

SANPRES-DS2 80M cycles at 3rd mode (~400μe) 45 g 80,002,980 

SANRES-DS31 40M cycles at 3rd mode (~400μe) 55 g 40,003,664 

SANPRES-DS31 40M cycles at 3rd mode (~400μe) 45 g 42,570,964 

Figures 13 and 14 show the frequency and leading edge strain response for the third mode 

dwells. The resonant mode dwells were not performed at a constant frequency, the frequency of 

the peak resonance dropped in a roughly asymptotic fashion during the dwells. Thus, the slip 
NASA/TMó2003-212201 9 

table was programmed to dwell at the 90-degree phase shift using an accelerometer located at the 

top of the outer vane shroud. This phase shift occurs at peak resonance. 

Fluorescent Penetrant Inspection (FPI) studies on the coated vanes were conducted after 

20 million, 40 million and 80 million cycles. Note the discontinuous shifts in figures 13 and 14 

that correspond to the inspection of the vanes during their durability tests. One of the three 

SANRES vanes (SANRES-DS2) exhibited a possible crack on the trailing edge (Figure 15) after 

40 million cycles. However, after this inspection, the same vane experienced an additional 40 

million cycles and the crack or flaw did not extend. A small number of filet cracks (Figure 16) 

were seen in SANRES and SANPRES specimens after 80 million cycles. In summary, the high 

frequency vibrating testing revealed only minor cracking in the filet region when the SANRES 

and SANPRES coated vanes were tested up to 80 million cycles at strain levels representative of 

engine conditions. Furthermore, both coatings endured extensive vibration testing and did not 

spall. 

4.4 Engine Tests

Engine tests were conducted to evaluate the performance of SANRES and SANPRES coatings in 

the presence of fan vibration and engine cycling. Three SANRES and three SANPRES coated 

triplet vane assemblies were installed in the AE 3007 endurance engine test (Figure 6) in a 

rainbow fashion. Two of the triplet vane packs had all three vanes coated with their respective 

coating systems as shown in Figure 17. While, the third vane assembly from each coating system 

had their two outer vanes coated and their center vane was installed without coating, as a 

reference for the test engineers. 

The engine test was scheduled for 3000 cycles with partial disassembly at approximately 1000 

cycle intervals. After the initial 1000 cycle interval, a visual examination of both the SANRES 

and SANPRES coated vanes indicated that the coatings adhered well to their PMC vanes. To 

date, the engine has completed 2088 cycles and all of the SANRES and SANPRES vane sets 

exhibited no coating spall. Visual examination of the engine tested vanes in their test stand show 

no obvious cracking. Subsequent FPI tests revealed 3ñ4 minor linear indications on some of the 

vanes trailing edge region on all three SANPRES 3-vane pack assemblies, while no indications 

were observed on any of the three SANRES 3-vane pack assemblies (Figure 17). There are no 

clear distinctions between SANRES and SANPRES coatings at this point. Further testing (up to 

3000 engine cycles) of all six of the aforementioned vane sets is schedule in the near future. 

Additionally, vane sets that have undergone ìengine-likeî high cycle fatigue testing and 

characterization in NASA GRC labs will be inserted into the planned engine tests. 

5. CONCLUSIONS

This work successfully identified the manufacturing process to coat AE 3007 bypass 3-vane pack 

assembly hardware. Rig erosion tests at both room and elevated temperature were conducted to 

verify the coating durability and erosion resistance. A new coating system, SANPRES that 

contains a polymer additive in its bondcoat was durable to thermal/engine cycling and erosion 

resistant. Optimum process parameters, in terms of coating uniformity, surface roughness and 

adhesion were identified for both the SANRES and SANPRES coating systems. In general, 
NASA/TMó2003-212201 10 

both of the candidate coatings provided a 2X improvement in erosion resistance benefit that is 

considered significant for this component. 

Multivariate statistical analyses of four independent response factors: erosion rate (Y1), MoirÈ 

maximum depth (Y2), optical interferometer volume loss (Y3), and metallurgical maximum 

eroded depth (Y4) for the 18 vanes tested indicate that there is a statistically significant 

difference in performance between SANRES and SANPRES. Specifically, the volume loss with 

SANRES is significantly less than with SANPRES at a 20-degree angle. While at 90 degrees, the 

performance of each coating system is comparable. Results from the full factorial design of 

experiments for 54 vanes will be reported in the near future. A new method was developed that 

uses optical interferometry to accurately determine eroded volume losses from complex coating 

surfaces. Verification of this optical interferometry method was correlated to three other wellestablished methods. Laboratory structural durability tests indicated that both SANRES and 

SANPRES coatings had good adherence and durability up to 80M cycles while at 300ñ400 

microstrain (μe) levels. Engine tests conducted to date (2088 cycles, ~800 hr) indicate that both 

SANRES and SANPRES coatings have good durability and adherence on PMC vane structures. 

Because of their two-fold improvement in erosion resistance and their durability for these bypass 

vanes, these coatings are being considered for several propulsion applications where PMC 

components suffer from erosion. 

7. REFERENCES 

 1. D. Wilson, ìPolyimide as Resin Matrices for Advanced Composites,î Polyimide, 

H. Stenzenberger and P. Hergenrother, Eds. Chapman and Hall, 1990, p. 187. 

 2. T. Stevens, Materials Engineering, 10, 34, (1990). 

 3. S.M. Hoff, Aerospace Engineering, 15 (2), 27, (1995). 

 4. W. Tabakoff and G. Simpson, 40th AIAA Aerospace Sciences Meeting and Exhibit, Paper 

No. AIAA 2002ñ0373, 1 (2002). 

 5. W. Tabakoff, and A. Hamed, ìErosion Characteristics of Coated and Uncoated 

Turbomachinery Blade Materials,î NATO RTOñMPñ34, 9/ 2000. 

 6. S.K. Naik, F.G. Macri, D. Keller, and J.K. Sutter, SAMPE Int.Symp, 44 (1), 68 (1999). 

 7. D.L. Chambers, et al., Surface Coating Technology, 41 (3), 315 (1990). 

 8. A.A. Ashari, R.C. Tucker, Thermal Spray: Meeting the Challenges of the 21st Century, ASM 

International, 2, 1998, p.1255. 

 9. S.J. Bull, 14th SAMPE International European Chapter, Birmingham, UK, 1993, p. 161. 

10. P. Lucchese et al., 9th National Thermal Spray Conference, ASM Int., 10, 1996, p. 239. 
NASA/TMó2003-212201 11 

 Bypass Vane 

 Fig. 1: AE 3007: Location of Bypass Vanes Fig. 2: Erosion Specimen ñ trailing edge 

Fig. 3: Univ. of Cincinnati Hot Erosion Rig Fig. 4: MoirÈ Optical Scanning System 
NASA/TMó2003-212201 12 

 

 

Fig. 5: Optical Interferometer System Fig. 6: AE3007 Engine - Coated Vanes 

Fig. 7: Typical SANRES microstructure Fig. 8: Typical SANPRES microstructure 

Fig. 9: Coating thickness comparison between a) rotating and b) Static Specimen Spray 

methods (bondcoat/topcoat thickness measured in mm) 

b) Static

a) Rotating 
NASA/TMó2003-212201 13 

O p tic a l In te rfe ro me try - Ero s io n Vo lu me Lo s s

S A N R ES C o a tin g

0

5

1 0

1 5

2 0

2 5

3 0

20 30 40 50 60 70 80 90

A n g le o f Imp in g e me n t (d e g re e s )

Erosion Volume Loss

 (mm 3

)

T =21

T =93

 Fig. 12. Optical Interferometry Erosion Volume Loss ñ SANRES Coating 

O p tical In terfero metry - Ero s io n Vo lu me Lo s s 

SA NPRES Co atin g

0

5

10

15

20

25

30

20 30 40 50 60 70 80 90

A n g le o f Imp in g eme n t (d eg ree s )

Ero s io n 

Vo lu me Lo s s 

(mm 3

)

T=21

T=93

 Fig. 11. Optical Interferometry Erosion Volume Loss ñ SANPRES Coating 

O p tic a l In te rfe ro me try - Ero s io n Vo lu me Lo s s

N o Co a tin g

0

5

10

15

20

25

30

20 30 40 50 60 70 80 90

An g le o f I m p in g em en t ( d eg r ees )

Ero s io n 

Vo lu me Lo s s 

(mm 3

) T=21

T=93

 Fig. 10. Optical Interferometry Erosion Volume Loss ñ No Coating 
NASA/TMó2003-212201 14 

 

 

 

Fig. 16. Minor indications in filet for 

SANRES & SANPRES after 80M cycles 

Cycles

0 2e+7 4e+7 6e+7 8e+7

Leading Edge Strain (microstrain)

0

100

200

300

400

500

SANPRES-DS1 

SANPRES-DS2

SANPRES-DS3 

SANRES-DS1 

SANRES-DS2

SANRES-DS3 

Fig. 13. Leading edge strain response 

for third mode dwell 

Fig. 15. FPI linear indication on 

SANRES-DS2 after 40M cycles 

Time (minutes)

0 200 400 600 800 1000

Frequency (Hz) 1400

1450

1500

1550

SANRES-DS1

SANRES-DS2 

SANRES-DS3

SANPRES-DS1 

SANPRES-DS2

SANPRES-DS3 

Fig. 14. Frequency response for 

third mode dwell 

SANRES

SANPRES 

Fig. 17. FPI tests on AE3007 vanes after 2088 engine test cycles. No Linear 

indication on SANPRES. No coating spall for either SANPRES or SANRES. 
This publication is available from the NASA Center for AeroSpace Information, 301–621–0390.

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20

Erosion Resistant Coatings for Polymer Matrix Composites in

Propulsion Applications

James K. Sutter, Subhash K. Naik, Richard Horan, Kazuhisa Miyoshi, Cheryl

Bowman, Kong Ma, George Leissler, Raymond Sinatra, and Randall Cupp

Coatings; Polymer; Composite materials; Aerospace; Aircraft

Unclassified -Unlimited

Subject Categories: 24 and 27 Distribution: Nonstandard

Prepared for SAMPE 2003 sponsored by the Society for the Advancement of Material and Process Engineering, Long Beach, California, May 11–15, 2003. James K. Sutter, Kazuhisa Miyoshi, and Cheryl Bowman, NASA Glenn Research Center; Subhash K. Naik,

Kong Ma, Raymond Sinatra, and Randall Cupp, Rolls-Royce Corporation, Indianapolis, Indiana 46206; Richard Horan, Allison

Advanced Development Company, Indianapolis, Indiana 46206; and George Leissler, QSS Group, Inc., Cleveland, Ohio 44135.

Responsible person, James K. Sutter, organization code 5150, 216–433–3226.

Polymer Matrix Composites (PMCs) offer lightweight and frequently low cost alternatives to other materials in many

applications. High temperature PMCs are currently used in limited propulsion applications replacing metals. Yet in

most cases, PMC propulsion applications are not in the direct engine flow path since particulate erosion degrades PMC

component performance and therefore restricts their use in gas turbine engines. This paper compares two erosion

resistant coatings (SANRES and SANPRES) on PMCs that are useful for both low and high temperature propulsion

applications. Collaborating over a multi-year period, researchers at NASA Glenn Research Center, Allison Advanced

Developed Company, and Rolls-Royce Corporation have optimized these coatings in terms of adhesion, surface

roughness, and erosion resistance. Results are described for vigorous hot gas/particulate erosion rig and engine testing

of uncoated and coated PMC fan bypass vanes from the AE 3007 regional jet gas turbine engine. Moreover, the

structural durability of these coatings is described in long-term high cycle fatigue tests. Overall, both coatings performed well in all tests and will be considered for applications in both commercial and defense propulsion applications.