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Surface Coatings Technology for Turbine Engine Applications

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Surface Coatings Technology for Turbine Engine Applications P r /JF Surface Coatings Tecnnology For Turbine Engine Applications By Dorothy M. Comassar Evolution in Design &Coatings The role of coatings In As operating temperatures in- 196O-J79 (Fighter Engine) creased in the 1970%more com- Simple aircraft gas turbine appllca- ponent protection was required. tlons Is increasingly impw - Solid turbine blade era Additionally, corrosion-resistant - 1500 "F (+) (822 "C) turbine temp tant. Higher engine operat- coatings were essential on more Coatings: ing temperatures, new components, such as disks, Anodized al alloys and component life blades, and vanes. Plasma- Ceramiccoated stainless steel alloy requirements all drive the sprayed, wear-resistant coatings combustors were also applied on compressor need for more durable Ceramic coated afterburner cases blade dovetails. AI-lacquer, heat-resistant systems. More and more, Throughout the 198Os, a typical compres sor case the engine component engine profile would include coat- designer 1s using new ings in every section of the engine. 1970479 (Fighter Engine) coatings systems to help The broad range of coating sys- . Expanded use of coatings tems addresses environmental Convection-cooled turbine provide the environmental conditions across the operating protection needed for these blade era spectrum of the engine. * 1800 "F (+) (990 "C) turbine temp increasingly stringent Coatings: demands.Thls article briefly Design Changes Corrosion-resistant coating for reviews the historical use Turbine airfoil design has evolved blades & vanes of coating systems in to allow increasing temperature Aluminum corrosion-resistant paint capability. (Seeexample in Fig. 1 .) aircraft turbine engine on casings The higher temperature environ- Co-dep on vanes, blades applications. Typical coat- ment has put increasing demands Corrosion-resistantcoatings on disks ing systems by engine on airfoil materials, as well as pro- Corrosion-resistant paint on shaft section (fan, compressor tective coating systems. Plasma-sprayed, wear-resistant and turbine) are described Improved cooling provided by coating (bearing load on shaft) the impingementifilm-cooled de- by material, coating pro- signs increase cooling capability; cess and environmental 1980-CF6 (Commercial Engine) all aspects, however-design, ma- - Coatings in every section of the challenges for each area. A terials, and manufacturing-are engine state-of-the-art process- being pushed to meet higher tem- All types of coatings I' Thermal Barrier Coating perature demands. .Impingementifilm cooled turbine (TBC)Aescribes coating As shown in Fig. 2, alloy devel- blade era opment has progressed signifi- process development - 2150°F(+)(1 186"C)turbinetemp cantly, providing additional tem- Coatings: challenges that typify future perature capability. Fan & compressor rub liners applications. Coating systems provide the Thermal barrier coatings additional protection required to Hot gas path seals satisfy total design life. Simple Dovetail & mid-span wear coatings aluminides satisfied early needs. Compressor erosion-resistant look at typical coating ap- Overlay coatings have been coatings plications in turbine en- added over the last 10 years for Oxidation & corrosion-resistant gines over the past few turther environmental protection. coatings EA decades shows increas- State-of-the-art systems, such as Labryinth seals ing use as well as complexity Thermal Barrier Coatings (TBC), In the 1960s, typical coatings were are being implemented today. simple anodized aluminum, aluminum Strategies for coating technolo- Historical perspective on design and coatings lacquer and ceramic coatings. gies are shown in Fig. 3. evolution over the past 30 )'ems. 20 Plating & Surface Finishing Are you still paying to haul water to the dump? You can remove the water portion of your "HAZARDOUS solutions and save barrels of money in hauling charges. 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Box 151, Atwood, California 92601 (714) 538-0701 FAX (714) 538-0691 FruO~allr:Clrcle114011 pwlpald readar rarvlcscard. .. resistant coating, WC-Co, to prevent wearand fatigue resulting from thecon- tinuous loading and unloading during engine operation. = 3000 The shroud is an abradable material Turbine Temperature .-m structuredesigned to wear awayduring 5 - contact with the fan blade. It also may 2 be configured to act as a component of - 2000 convection cooled the noise attenuation system. kL d Compressor Section i Solld Blade Year The compressor section of the modern I- 1000 Ngas turbine is a labyrinth of structures that compresses the incoming air for combustion. The environmental tem- peratures range from about 300 "F to 7g. 1-Turbine technology trends. 1200 "F. To achieve the most efficient compressor, leakage intothesumpand Engine Section Profile principally the dovetail and mid-span around the blade tips must be mini- Of Coating Systems damper (Fig. 4). Fan rub liners also mized. The airfoils are designed with Coating systems are tailored to the provide a rub surface for the fan blade specific contours to maximize pumping environmental conditions to which they tips; therefore, they usually contain soft, capability with a minimum of drag in as are subjected. Engine operating tem- abradable coatings. The selection of few compression steps as possible. perature increases dramatically from lightweight, high-strength materials, Increasingly, the role of specialized the fan to the turbine sections. There- such as titanium-based alloys for the coatings is to maintain the designed fore, the profile of coatings axiallywithin fan blades and disks, necessitates ac- clearancesand contours overthe lifeof the engine accommodates the chang- commodation of titanium's poor-wear the engine. Ingested particulateserode ing environment. capabilities. The fan blade attachment the contours of the airfoils, causing a surfaces, therefore, are clad with mate- loss of efficiency by changing the airfoil Fan Section rials such as CuNiln to prevent galling contour, opening clearances at the In the fan section of the engine, fan and fretting. Vibration dampener struts blade tip, and reducing stall margins. blades are coated at high-wear areas, are coated with a strong, hard, wear- Particulates raise the risk of fatigue Component Materials Trend 2000 Turbine Blade Materials = 1800 .-m z c Solidification vE" 1600 " 2! Yea,* ca Improved Aluminides m . simple. IneXpBnElYe k .Thin (c 3 m119) E 1400 MCrAlY Coatings . Complex chamlrlrlss require c PVD or VPS . Cr and Y Improve oxIdalion reslsfance. scale adherence . Thlck (> 4 mlls) 1200 Tailored Coatings .MalCh PhySIcol and mechanical pmpedles 10 substrate , .Salld solullon or oxide dlspernlon 340 1960 1980 2000 Blrenglhenlng Year .MalCh lo SUbSlrale July 1992 21 Typical Coating Scheme Typical Coating Scheme - Fan Airfoils and Liners Compressor Airfoils I - Honey Comb Fan Liner Coating at with Filler Tip and Around Leading wc Edge Impact Wear Resistance CuNiln I I Wear Resistance Fan Blade Comaressor Blade Front Stages - Titanium with WC Coating * Ooeratino Temoerature - 250°F I . Back Stages - In718 with CrC3 Coating 1 * Substrate Material - Titanium I Fig. 4-Typical coating scheme for the fan seclion. Fig. 5-Typical coaling scheme lor compressor section. failure by reducing the blade cross- damage by coating the pressure- walls vent wear of the rotor surface by the section and by defecting the highly near the tip with tungsten carbide for vanes. The blade mounts are coated stressed surfaces. lower temperature service, and with a with CuNiln and a solid film lubricant, The degree of severity of such par- chromium carbide-based coating in the and mate against the same coating ticulate damage is a function of the higher temperature regions. combination of knife-edge surfaces engine location, the use of the aircraft, The seals for the blade tips are main- coated with AI,O, to wear into filled and and the locale where flown. As ex- tained with an abradable coating ap- unfilled stationary surfaces. pected, helicopter engines, which are plied in segments, or directly to the required to hover in their own dust casing, as dictated by the engine de- Turbine Section storms, are prime victims, and have sign. The materials are generally ther- Theturbinesection representsthe most special centrifugal separators incorpo- mal-sprayed nickel graphite for lower challenging environment for the engine rated at the inlet to remove particu- temperature applications, and alumi- designer. Temperatures up to 2150 "F lates. Commercial engines ingest par- num bronze-nickel graphite or NiCrAl require both substrate materials and ticulates, especially when mounted in bentonitefor highertemperature needs. coating systems to be highly oxidation- low-hanging nacelles. Each material is designed to wear pref- and corrosion-resistant. To emphasize Typical coating schemes in the com- erentially with respect to the blade tips. again, new turbine airfoil alloys
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