Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

Florin Dimofte

University of Toledo, Toledo, Ohio

Raymond E. Chupp

General Electric Global Research Center, Niskayuna, New York

Bruce M. Steinetz

Glenn Research Center, Cleveland, Ohio

Interfaces—Weak Links, Yet Great Opportunities

NASA/TM—2011-214041

May 2011

140–ISROMAC–11
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Robert C. Hendricks

Glenn Research Center, Cleveland, Ohio

Florin Dimofte

University of Toledo, Toledo, Ohio

Raymond E. Chupp

General Electric Global Research Center, Niskayuna, New York

Bruce M. Steinetz

Glenn Research Center, Cleveland, Ohio

Interfaces—Weak Links, Yet Great Opportunities

NASA/TM—2011-214041

May 2011

140–ISROMAC–11

National Aeronautics and

Space Administration

Glenn Research Center

Cleveland, Ohio 44135

Prepared for the

11th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery

sponsored by the International Journal of Rotating Machinery (ISROMAC)

Honolulu, Hawaii, February 26–March 2, 2006
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at the NASA Glenn Research Center.
NASA/TM—2011-214041 1 

Interfaces—Weak Links, Yet Great Opportunities 

Robert C. Hendricks 

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Florin Dimofte

University of Toledo 

Toledo, Ohio 43606 

Raymond E. Chupp

General-Electric Global Research Center 

Niskayuna, New York 12309 

Bruce M. Steinetz

National Aeronautics and Space Administration 

Glenn Research Center 

Cleveland, Ohio 44135 

Abstract 

Inadequate turbomachine interface design can rapidly 

degrade system performance, yet provide great opportunity for 

improvements. Engineered coatings of seals and bearing 

interfaces are major issues in the operational life of power 

systems. Coatings, films, and combined use of both metals and 

ceramics play a major role in maintaining component life. 

Interface coatings, like lubricants, are sacrificial for the benefit 

of the component. Bearing and sealing surfaces are routinely 

protected by tribologically paired coatings such as silicon 

diamondlike coatings (SiDLC) in combination with an oillubricated wave bearing that prolongs bearing operational life. 

Likewise, of several methods used or researched for detecting 

interface failures, dopants within coatings show failures in 

functionally graded ceramic coatings. The Bozzolo-FerranteSmith (BFS) materials models and quantum mechanical tools, 

employed in interface design, are discussed. 

Introduction 

As designers seek to extract greater performance from 

turbine engines, all elements are being scrutinized for possible 

performance benefits including interfaces found in bearings and 

seals. 

How well and how long interfaces will be effective in doing 

their job depends directly on understanding the binding 

energies of those interfaces and the requirements for the 

application. Each application has unique requirements that 

depend on the integrity of their interfaces, which in turn depend 

on substrate coated materials. 

Conventional concepts of clearance interfaces in rotating 

machines involve bearing and seal interface coatings, materials, 

and fluid films [1,2]. Bearings control machine loads and 

dynamics. Sealing controls leakages, coolant flows, and “trim” 

dynamics (unrecovered bearing loads) and are usually the most 

cost-effective method of enhancing performance, Hendricks 

et al. [3,4]. 

Interface coating materials are subjected to abrasion, erosion, 

oxidation, incursive rubs, foreign object damage, and deposits. 

They are also exposed to extremes in thermal, mechanical, and 

aerodynamic loadings (Fig. 1), including positive and negative 

strain ranges, large case distortions, and impact loadings. No 

one coating material or sealing device can effectively satisfy 

these variations throughout an airframe or engine (Fig. 2) and 

must be properly tailored to maintain each interface. Most 

interface coatings are composites fabricated on substrates and 

can be readily refurbished either in situ or by removal. It is to 

be noted that fully decoupled turbomachine interfaces induce 

large electrostatic charge gradients which can be detrimental to 

the health and longevity of the engine. Such interfaces must 

have charge release paths designed into the system. 

Herein we look at some applications of coatings and 

materials to bearings and seals as well as some interface tools 

and advanced methods for detection of interface failure. 

Blade-Shroud Interface Abradable 

Materials and Coatings 

Baseline Studies 

Each system differs and as such, each abradable interface has 

to be tribologically designed for that application. Ghasripoor 

et al. [6] characterized three types of coating materials: (1) 

aluminum silicon polyester (AlSi-(PE), (2) aluminum silicon 

graphite (AlSiC), and (3) aluminum silicon hexagonal boron 

nitride (AlSi-hBN). The latter two are usually classified as solid 

lubricants while the polymer fillers of the first tend to burn out 

leaving a more porous structure contributing to relatively 

benign blade rubs. 
NASA/TM—2011-214041 2 

 AlSiC or AlSi-hBN materials are brittle, so they break more 

readily and have distributed networks. As a result they 

generally exhibit a benign microrupture wear mechanism. 

Material smears are minor even though the AlSi matrix may 

appear to have been partially molten. Graphite is abrasive to 

blade tips at temperatures below 200 °C (390 °F), yet the hBN 

should be less of a problem as it crushes more readily. AlSi 

without fillers tends not to microrupture and suffers from hot 

spot formation; AlSi and AlSi-PE can both rupture and spall 

with severe damage at high incursion rates with massive 

melting above 400 °C (750 °F). 

Gas Turbine 

Coatings that are created by adding a fugitive polymer such 

as PE or polyimide to the base metal alloy, together with a 

brittle intermetallic phase such as β-NiAl (325 mesh) increase 

the brittle nature of the metal matrix. This increases the 

abradability of the coating at elevated temperatures and 

improves oxidation resistance of the coating [7,8]. Coatings 

having about 12 wt% PE have been found to exhibit excellent 

abradability for turbine shroud coatings. An abradable coating 

thickness in the range between 1.016 and 1.524 mm (0.040 and 

0.060 in.) provides the best performance for turbine shrouds 

exposed to gas temperatures between 750 °C (1380 °F) and 

1010 °C (1850 °F). Tests included tip velocities to 375 m/s 

(1230 ft/s) comparable to Class E industrial machines. 

Aero-Fan 

Polymer-based shroud sealing, as in fan blade tip sealing, 

must have good casting properties as these materials are 

difficult to machine but can be ground or spot filled. 
NASA/TM—2011-214041 3 

Compressor 

CoNiCrAlY-hBN-15 wt% PE shows excellent abradability 

with nickel-based superalloy and steel blades to 700 °C 

(1290 °F) [9]. For titanium blades, CoNiCrAlY-hBN-20 wt% 

PE is a variant of those used for steel and Ni-superalloy 

materials and labeled as CoNi-20PE. The hardness is 

determined largely by the PE content. As-sprayed coatings with 

40 to 50 vol% nonmetallic and less than 12 percent PE gave 

repeatable coating hardness with moderate reductions due to 

heat treatment. Titanium has half the modulus of nickel-based 

alloys and a propensity to burn in high-pressure oxygen and 

nitrogen mixtures. Military aircraft have been lost to titanium 

fires as a result of blade-case interaction. 

Nava et al. [10] tested proprietary mixtures of flame spray 

(FS) and air plasma spray (APS) Ni-14Cr-8Fe-5.5BN-3.5Al 

(Metco 301 (Sulzer, Ltd., Winterthur, Switzerland)), APS Al8Si-20BN (Metco 320 (Sulzer, Ltd., Winterthur, Switzerland)), 

and APS Al-17Cu-15Cr-13Fe (Praxair AL–147 (Praxair, Inc., 

Danbury, CT)). A compromise between oxidation resistance and 

abradability is achieved using APS AlSi-BN. In an industrial 

application, the abradable shroud seal life was 30 000 hr at 

temperatures up to 482 °C (900 °F). Schmidt et al. [11] relates 

that initially compressor temperatures were limited to 350 °C 

(660 °F), but with α-titanium alloys, temperatures of 550 to 

600 °C (1020 to 1110 °F) are possible with creep and oxidation 

limiting life. Expectant life of compressor shroud seals are 

50 000 to 100 000 hr in commercial aero and industrial gas 

turbines while military operations may be in the 100s of hours. 

Other 

APS thermal barrier coatings (TBCs) are used in the 

combustor and, for some engines, first vanes (nozzles) and 

first-stage blades of the high-pressure compressor (HPT). EB–

PVD TBCs are used on the first-stage and some second-stage 

blades as well as first-stage vanes (nozzles). TBCs are not 

commonly used in the LPT due to lower heat flux and are less 

effective in decreasing component temperature. APS ceramics 

are also used on shroud seals (blade outer air seals) where they 

function as both a thermal barrier for the metallic shroud and 

abradable seal. 

Processing 

Vacuum brazing results in quality control problems, as it is 

difficult to ensure good bonding. Thermal spraying, such as 

APS and FS, are most widely used for compressor shroud seals; 

however, feltmetals are responsive to higher temperatures. 

Standardized testing needs to be addressed for use of 

abradables in engine design. 

Interface Rub Mechanics 

For blade and vane seal rubbing, the basic issues center on a 

material that mitigates blade wear while providing a durable 

interface that enhances engine efficiency. Blade rubs engender 

debris, which must be released to escape sliding contact wear of 

the blade tip and plowing of the interface [11]. In the highpressure turbine (HPT) (760 °C (1400 °F) to 1150 °C 

(2100 °F)) interface, yttria-stabilized zirconia (YSZ) with 

controlled porosity is used. If blade wear is a problem, 

designers have devised ways to put cubic BN or SiC grits on 

the tips to minimize the blade wear for tight running clearances; 

the shroud is then cut instead. (Note: With blade-cooling 

boundary layers, the interface temperatures are significantly 

less than gas path temperatures which can be >1400 °C 

(2550 °F) (e.g., Fig. 1). It is the weakness of the interface that is 

limiting and not the ceramic itself. 

Material released below surface speeds of 100 m/s is 

primarily forward expelled chips (cutting); while above 

100 m/s the expelled particles are released backward (grinding). 

Blade tip wear and material transfer are dominant issues. As 

such, the cutting tip needs to be thin (1 to 3 mm), as thicker tips 

trap materials and destroy the sealing interface. For these 

purposes, material release, porosity, and structural strength can 

be controlled in both thermal sprayed coatings and fibermetals. 

Some abradables are compacted when rubbed; blade tip wear 

increases and abradable porosity decreases. Other abradables, 

such as honeycomb, deform when impacted at high speeds, and 

the cell walls will rupture. Honeycomb wear is most 

pronounced at the brazed web where cell thickness doubles, 

which in turn impacts rotor wear. Blade tip coatings and saw 

teeth are employed to mitigate blade wear or damage. 

The better AlSi-plastic and Ni-graphite coatings avoid the 

onset of adhesive melting wear and favor cutting wear. Borel 

et al. [12] mapped incursion velocity as a function of tangential 

velocity. Figure 3 shows a typical map for an AlSi-PE coating 

on a 3-mm-thick titanium blade. Ideally one would want nearzero rubbing over the entire circumference, which would tend 

to optimize the running clearances. 
NASA/TM—2011-214041 4 

Standardization 

As gas velocities and tip speed increase in modern turbine 

engines, the task of selecting the best abradable materials 

becomes more challenging. Often materials that have low 

tensile strength exhibit the best abradability but have poor 

erosion resistance. The converse is also often true, as illustrated 

in Fig. 4 and characterized in Table 1. Because of these 

conflicting material characteristics, Chappel et al. [13,14] 

called for standardized test techniques to ensure effective 

selection of materials for the application. 

TABLE 1.—OVERALL PERFORMANCE RANKINGS OF 

ABRADABLE MATERIALS USED BY CHAPPEL [13,14] 

Abradable material Abradabilitya Erosion 

resistancea

High 

speed 

Low 

speed 

fiber metal 1 

Ultimate tensile 

strength, 

1050 psi; 

braze bonded; 

density, 22% 

1 1 3 

fiber metal 2 

Ultimate tensile 

strength, 

2150 psi; 

braze bonded; 

density, 23% 

1 1 1 

Honeycomb 

Hastelloy-Xb

 

0.05-mm foil, 

1.59-mm cell 

2 3 2 

Nickelgraphite Sulzer Metco 

307NS (spray) 3 1 2 

CoNiCrAlY/ 

hBN/PEc

Sulzer Metco 

2043 (spray) 3 3 1 

a

Where 1 = best and 3 = worst.

b

Haynes International, Inc., Kokomo, Indiana. 

c

Hexagonal boron nitride (hBN) acts as a release agent and 

polyester (PE) controls porosity. 

For industrial power systems under the conditions tested and 

the materials considered in Table 1, fibermetal has the best 

abradability-erosion characteristics. Honeycomb materials 

collected on the blade tips and sprayed materials are less 

satisfactory. These relative ratings are displayed in Table 1. 

Chupp et al. [15,16] report abradable seals afford tighter 

closure of cold clearances between the rotor and case. A 

general classification in terms of interface materials, coatings, 

location in a gas turbine engine and a type of process for 

application and operating temperatures are given in Table 2. 

TABLE 2.—ABRADABLE MATERIAL 

CLASSIFICATION [10, 12, 13, 14] 

Abradable 

material 

Locationa

AlSi + filler LPC: 400 °C (750 °F) 

Ni- or Co-based LPC, HPC: 

ambient to 760 °C (1400 °F) 

YSZ and cBN or SiC HPT: 760 °C (1400 °F) 

to 1150 °C (2100 °F) 

a

LPC is low-pressure compressor. 

 HPC is high-pressure compressor. 

 HPT is high-pressure turbine. 

Inroads to industrial standards have been initiated, yet more 

comparison tests are required before standardization becomes a 

reality. 

Liquid (Oil) Lubricated Interfaces 

One recent application for coatings in bearings to enhance 

conventional operational life as well as potential oil-out 

conditions was advanced by Dimofte et al. [17] who tested 

wave bearing coatings applied to both the rotor and stator (or 

sleeve). When the oil supply pressures are decreased, bearing 

interface surfaces can be destroyed due to rub, yet with the 
NASA/TM—2011-214041 5 

pumping action of a three-node wave bearing with three feed 

holes, decreasing the supply pressure did not significantly harm 

bearing operations until the supply was cut off (0 MPa). In 

these instances, residual particulates in the lubricant oil itself 

are major contributors to bearing damage and must be carefully 

controlled, and in these tests control could have been better. 

Nevertheless, Dimofte examined the following coatings with 

varying degrees of success: (1) SiDLC, (2) DLC, (3) tungsten 

carbide/carbon (WC/C), and (4) titanium carbide (TiC). SiDLC 

performed well for 1000 start-stop cycles followed by 50 oiloff cycles, where friction torque lockup occurred in about 

10 min. WC/C also did well except at oil-off, where it degraded 

rapidly due to higher friction. TiC failed at oil-off while DLC 

ran 20 min but seized on the first cycle thereafter. 

For new coated bearings operating at low supply pressures 

both SiDLC and WC/C performed well, yet at oil-off WC/C 

degraded rapidly—3 min versus 21⁄2 hr for SiDLC. 

The posttest rotor and stator SiDLC-coated interfaces are 

optically relatively smooth and uniform (Figs. 5 and 6). The 

uniformity is also confirmed by surface profiling after a 1000 

start-stop cycles test series (Fig. 7). Here the surface profiles of 

the SiDLC coatings illustrate the posttest surface roughness and 

consistency of the sleeve and rotor coatings (Figs. 7(a) and (b), 

respectively). The profilometer readings are quite uniform and 

generally within 2 μm, with the exception of the rotor where 

“scratches” up to 4.5 μm can be seen. The area examined is 

highlighted by the white line. 

Tribologically, SiDLC performed very well. 

Interface Tools 

There are many thermodynamic and computational methods 

used in characterizing materials. One of the better known is the 

BFS model, which has been successfully applied to known 

materials and developing new materials, [e.g., 18]. Yet more 

recently, Quantum mechanics (QM) tools are proving useful to 

macromechanics issues [19] and will play a prominent role in 

applications of coatings and thin films. Consider a typical 

layered thermal barrier coating (TBC) (250 to 500 μm yttria 

stabilized zirconia (YSZ); 10-25 μm Al2O3 (thermally grown); 

100 to 150 μm NiCoCrAlY (bond coat)) over a superalloy (Ni 

or Ni3Al base) turbine blade. QM predictions show that 

fracturing the ZrO2 requires a unit energy of 

2400 mJ/m2

, while Al2O3 requires 3000 mJ/m2. For the 

ZrO2/Al2O3 interface adhesion is 1200 mJ/m2

, and it is 

500 mJ/m2

 for the Al2O3/Ni interface (Fig. 8). Weaker adhesion 

and stress concentration at the interface are sources of failure. 

The transitional elements are suggested as the “interface glue.” 

Failure Detection Methods 

There are many methods used to determine interface failures 

such as dye penetration, ultrasound, surface waves, and 

rotational dynamics, to cite a few [20]. A recent novel method 

of incorporating material variants (dopants) to define interface 

failures also provides for health monitoring—crack and 

temperature detection. Europium oxide Eu2O3 fluoresces red or 

blue when illuminated by ultraviolet light, while terbium oxide 

Tb4O7 (terbia) produces green light. Bencic and Eldridge [21] 
NASA/TM—2011-214041 6 

 
NASA/TM—2011-214041 7 

noted that YSZ is opaque to ultraviolet excitation, but 

translucent to visible light: Tb3+ at 543 nm (green) and Eu3+ at 

606 nm (red). Tests were conducted on a Rene N5 (General 

Electric Company, Fairfield, CT) superalloy substrate with a 

PtAI bond coat and graded topcoat of 50 μm (7YSZ + 0.5Tb), 

50 μm (7YSZ + 0.5 Eu), and 50 μm (7YSZ) (nominal 

thicknesses). 

If the surface is flawed over 50 μm, ultraviolet excitation 

will reflect strong red light. With flaws >100 μm depth, strong 

green light becomes visible (Fig. 9). Further, the luminescence 

decay with time of pulsed ultraviolet light can be used to 

determine temperature. 
NASA/TM—2011-214041 8 

Summary 

Properly engineered interfaces can improve performance and 

external turbomachine service lives. No one geometry, coating, 

or material is satisfactory for general use. Each interface 

coating must be assessed in terms of its operational 

requirements. Coatings, films, and functionally graded 

materials (e.g. both metals and ceramics) play a major role in 

maintaining interface integrity for blade (or vane) shroud and 

platform performance. 

1. For the aeroturbomachine, the fan shroud seals have 

several forms but generally include polymers that can be 

repaired on the wing. 

2. For the low-pressure compressor (LPC) (ambient to 

400 °C (750 °F)) interface, feltmetals and AlSi with fillers are 

used. For the midrange (MPC) and high-pressure compressors 

(HPC) (ambient to 760 °C (1400 °F)), Ni- or Co-based 

materials are used. 

3. In the high-pressure turbine (HPT) interface, TBCs such 

as yttria-stabilized zirconia (YSZ) with controlled porosity are 

used. To mitigate wear, blade tips are often coated with cubic 

BN or SiC grits. For tight running clearances, the shroud is then 

cut instead of wearing the blade. 

4. The TBC can withstand high thermal loading, yet the 

metallic substrate cannot. Again, it is the weakness of the 

interface that is limiting and not the ceramic itself. 

5. Bearing and sealing surfaces are routinely protected by 

coatings. For instance, a recent application of silicon 

diamondlike coating (SiDLC) in combination with a wavebearing interface has proven very effective in prolonging 

bearing life even when the oil supply is intermittent or stopped 

altogether. This is an important advancement as it paves the 

way for future systems to continue to provide power while 

allowing for an orderly shut down of the machine. 

6. Several methods are being used or being developed for 

detecting interface failures, yet doping of coatings represents an 

innovative method of detecting such failures in coated ceramic 

materials. 

How well and how long interfaces will be effective in doing 

their jobs depends directly on understanding the binding 

energies of those interfaces and the requirements for the 

application. Of the many materials models, one of the better 

known is the Bozzolo-Ferrante-Smith (BFS) model to assist in 

designing interface materials. Recent developments in the 

application of quantum mechanical methods are also available 

to assist the designer in understanding the interface. 

REFERENCES 

[1] Zaretsky, Erwin V.: Tribology for Aerospace 

Applications. STLE SP−37, 1997. 

[2] Zaretsky, Erwin V.: STLE Life Factors for Rolling 

Bearings. STLE SP−34, 1992. 

[3] Hendricks, R.C.; Tam, L.T.; and Muszynska, A.: 

Turbomachine Sealing and Secondary Flows, Part 2—Review 

of Rotordynamics Issues in Inherently Unsteady Flow Systems 

With Small Clearances. NASA/TM⎯2004-211991-PART2, 2004. 

[4] Hendricks, Robert C., et al.: Turbomachine Interface 

Sealing. NASA/TM⎯2005-213633, 2005. 

[5] Sourmail, T.: Coatings for Turbine Blades. University of 

Cambridge, England, 2003. http://www.msm.cam.ac.uk/phasetrans/2003/Superalloys/coatings/ Accessed Jan. 13, 2006. 

[6] Ghasripoor, F., et al.: A Review of Clearance Control 

Wear Mechanisms for Low Temperature Aluminum Silicon 

Alloys. Proceedings of the International Thermal Spray 

Conference, Nice France, vol. 1, 1998, pp. 139−144. 

[7] Lau, Yuk-Chiu, et al.: High Temperature Abradable 

Coating for Turbine Shrouds Without Bucket Tipping. U.S. 

Patent 6,660,405 B2, Dec. 9, 2003. 

[8] Chupp, Raymond, et al.: Development of Higher 

Temperature Abradable Seals for Gas Turbine Applications. 

ASME GT2004−53029, 2004. 

[9] Wei, X., et al.: Microstructure and Property Control of 

CoNiCrAlY Based Abradable Coatings for Optimal 

Performance. Proceedings of the 1st International Thermal 

Spray Conference, Montreal, Canada, 2000, pp. 407−412. 

[10] Nava, Y.; Mutasim, Z.; and Coe, M.: Abradable Coatings 

for Low-Temperature Applications. Proceedings of the 

International Thermal Spray Conference, Singapore, 2001, 

pp. 263−268. 

[11] Schmid, R.K., et al.: An Overview of Compressor 

Abradables. Proceedings of the 1st International Thermal Spray 

Conference, Montreal, Canada, 2000, pp. 1087−1093. 

[12] Borel, M.O., et al.: Wear Mechanisms Occurring in 

Abradable Seals of Gas Turbines. Surf. Coat. Technol., 

vol. 39−40, nos. 1−3, pt. 1, 1989, pp. 117−126. 

[13] Chappel, Douglas E.; Vo, Ly; and Howe, Harold W.: Gas 

Path Blade Tip Seals: Abradable Seal Material Testing at 

Utility Gas and Steam Turbine Operating Conditions. ASME 

2001−GT−0583, 2001. 

[14] Chappel, D.; Howe, H.; and Vo, L.: Abradable Seal 

Testing⎯Blade Temperatures During Low Speed Rub Event. 

AIAA−2001−3479, 2001. 

[15] Chupp, R.; Ghasripoor, F.; and Moore, G.: Applying 

Abradable Seals to Industrial Gas Turbines. AIAA−2002−3795, 

2002. 

[16] Chupp, Raymond E., et al.: Advanced Seals for Industrial 

Turbine Applications: Dynamic Seal Development. J. Propul. 

P., vol. 18, no. 6, 2002, pp. 1260−1266. 

 
NASA/TM—2011-214041 9 

[17] Dimofte, F., et al.: Test of PVD Coatings in the Wave 

Bearing Environment Part I: One Thousand Start and Stop 

Tests and Oil-Off Tests at the End. Part II: Test of Coatings 

Under Low Oil Supply Pressure Down to Zero. Submitted to 

STLE. 

[18] Fan, W.; and Gong, X.G.: Monte Carlo Simulation of 

Surface De-Alloying of Au/Ni(110). Surf. Sci., vol. 562, nos. 

1−3, 2004, pp. 219−255. http://www.physics.fudan.edu.cn/ 

phyfaculty/personweb/xggong/publications/pdfs/2004_arx1.pdf 

Accessed Jan. 13, 2006. 

[19] Chaka, Ann: Mechanistic Insights Into the Corrosion 

Process From First Principles. Presented at the National 

Institute of Standards & Technology, Gaithersburg, MD, 

April 2005. 

[20] Sawicki, Jerzy T., et al.: Dynamic Behavior of Cracked 

Flexible Rotor Subjected to Constant Driving Torque. 

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Stability Control of Rotating Machinery, Zdzislaw Gosiewski 

and Agnes Muszynska, eds., Max Media, Warsaw, Poland, 

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[21] Bencic, Timothy J.; and Eldridge, Jeffrey I.: Smart 

Coatings for Health Monitoring and Nondestructive Evaluation. 

Proc. SPIE Int. Soc. Opt. Eng., vol. 5770, 2005, pp. 88−96. 
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WBS 561581.02.08.03.16.03 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

John H. Glenn Research Center at Lewis Field 

Cleveland, Ohio 44135-3191 

8. PERFORMING ORGANIZATION

 REPORT NUMBER

E-15398-2 

9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

National Aeronautics and Space Administration 

Washington, DC 20546-0001 

10. SPONSORING/MONITOR'S

 ACRONYM(S)

NASA 

11. SPONSORING/MONITORING

 REPORT NUMBER

NASA/TM-2011-214041 

12. DISTRIBUTION/AVAILABILITY STATEMENT

Unclassified-Unlimited 

Subject Categories: 07, 26, 27, 37, and 25 

Available electronically at http://www.sti.nasa.gov 

This publication is available from the NASA Center for AeroSpace Information, 443-757-5802

13. SUPPLEMENTARY NOTES

14. ABSTRACT

Inadequate turbomachine interface design can rapidly degrade system performance, yet provide great opportunity for improvements. 

Engineered coatings of seals and bearing interfaces are major issues in the operational life of power systems. Coatings, films, and combined 

use of both metals and ceramics play a major role in maintaining component life. Interface coatings, like lubricants, are sacrificial for the 

benefit of the component. Bearing and sealing surfaces are routinely protected by tribologically paired coatings such as silicon diamondlike 

coatings (SiDLC) in combination with an oil-lubricated wave bearing that prolongs bearing operational life. Likewise, of several methods 

used or researched for detecting interface failures, dopants within coatings show failures in functionally graded ceramic coatings. The 

Bozzolo-Ferrante-Smith (BFS) materials models and quantum mechanical tools, employed in interface design, are discussed. 

15. SUBJECT TERMS

Seals; Coatings; Thin films; Turbomachines; Life 

16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF

 ABSTRACT

UU 

18. NUMBER

 OF 

 PAGES

15 

19a. NAME OF RESPONSIBLE PERSON

STI Help Desk (email:help@sti.nasa.gov) 

a. REPORT

U 

b. ABSTRACT

U 

c. THIS 

PAGE

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19b. TELEPHONE NUMBER (include area code)

443-757-5802 

Standard Form 298 (Rev. 8-98)

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