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Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Thermal Barrier Coatings

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Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Thermal Barrier Coatings NASA/TM—2003-212516 Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Thermal Barrier Coatings Sung R. Choi Ohio Aerospace Institute, Brook Park, Ohio Dongming Zhu U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio Robert A. Miller Glenn Research Center, Cleveland, Ohio July 2003 The NASA STI Program Office . in Profile Since its founding, NASA has been dedicated to • CONFERENCE PUBLICATION. Collected the advancement of aeronautics and space papers from scientific and technical science. The NASA Scientific and Technical conferences, symposia, seminars, or other Information (STI) Program Office plays a key part meetings sponsored or cosponsored by in helping NASA maintain this important role. NASA. The NASA STI Program Office is operated by • SPECIAL PUBLICATION. 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Reports of Program Office’s diverse offerings include completed research or a major significant creating custom thesauri, building customized phase of research that present the results of databases, organizing and publishing research NASA programs and include extensive data results . even providing videos. or theoretical analysis. Includes compilations of significant scientific and technical data and For more information about the NASA STI information deemed to be of continuing Program Office, see the following: reference value. NASA’s counterpart of peer- reviewed formal professional papers but • Access the NASA STI Program Home Page has less stringent limitations on manuscript at http://www.sti.nasa.gov length and extent of graphic presentations. • E-mail your question via the Internet to • TECHNICAL MEMORANDUM. Scientific [email protected] and technical findings that are preliminary or of specialized interest, e.g., quick release • Fax your question to the NASA Access reports, working papers, and bibliographies Help Desk at 301–621–0134 that contain minimal annotation. Does not contain extensive analysis. • Telephone the NASA Access Help Desk at 301–621–0390 • CONTRACTOR REPORT. Scientific and technical findings by NASA-sponsored • Write to: contractors and grantees. NASA Access Help Desk NASA Center for AeroSpace Information 7121 Standard Drive Hanover, MD 21076 NASA/TM—2003-212516 Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Thermal Barrier Coatings Sung R. Choi Ohio Aerospace Institute, Brook Park, Ohio Dongming Zhu U.S. Army Research Laboratory, Glenn Research Center, Cleveland, Ohio Robert A. Miller Glenn Research Center, Cleveland, Ohio Prepared for the 27th Annual Cocoa Beach Conference and Exposition on Advanced Ceramics and Composites sponsored by the American Ceramic Society Cocoa Beach, Florida, January 26–31, 2003 National Aeronautics and Space Administration Glenn Research Center July 2003 Acknowledgments This work was supported by the Ultra-Efficient Engine Technology (UEET) program, NASA Glenn Research Center, Cleveland, Ohio. Thanks to R. Pawlik for mechanical testing and G. Leissler for the preparation of thermal barrier coating material. This report is a formal draft or working paper, intended to solicit comments and ideas from a technical peer group. This report contains preliminary findings, subject to revision as analysis proceeds. Contents were reproduced from author-provided presentation materials. 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. Available from NASA Center for Aerospace Information National Technical Information Service 7121 Standard Drive 5285 Port Royal Road Hanover, MD 21076 Springfield, VA 22100 Available electronically at http://gltrs.grc.nasa.gov Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Thermal Barrier Coatings Sung R. Choi, Dongming Zhu, and Robert A. Miller NASA Glenn Research Center, Cleveland, OH Presented at the 27th Annual Cocoa Beach Conference on Advanced Ceramics and Composites January 26-31, 2003 Cocoa Beach, Florida [Paper Number: ECD-S2-14-2003 (Invited)] Abstract Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-Standing Plasma-Sprayed Thermal Barrier Coatings Sung R. Choi, Dongming Zhu, and Robert A. Miller NASA Glenn Research Center, Cleveland, OH 44135 Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma- sprayed ZrO2-8wt% Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material’s unique constitutive relations. NASA/TM—2003-212516 1 Contents I. Background II. Processing III. Strength IV. Fracture toughness V. Fatigue/slow crack growth VI. Deformation VII. Sintering Effects VIII. Summary IX. Bibliography I. Backgrounds • Thermal Barrier coatings (TBCs), ZrO2-8 wt% Y2O3 – important coating materials due to low thermal conductivity, high thermal expansivity, and unique microstructure • Somewhat anisotropic nature of porosity, microcracks and splat structure - a challenge in routine mechanical testing and data interpretation • Mechanical testing for TBCs performed to characterize strength, fracture toughness, fatigue, and deformation, and also to establish database • Results of mechanical testing presented and discussed, and related issues discussed NASA/TM—2003-212516 2 II. Material Processing µ • ZrO2-8 wt% Y2O3 powder with an average particle size of 60 m • Plasma sprayed on a steel or graphite substrate •SULZER-METCO ATC-1 plasma coating system with a 6-axes industrial robot used • Free standing TBC billets fabricated • Test specimens machined from billets with appropriate configurations • Typical billets: Spray direction (S.D) S.D 90 mm 6 mm Test specimens to be cut 140 mm Test Specimen Billet Unique Microstructure of TBCs Spray direction ‘side’ view fracture surface • Layered, porous, microcracked, and splat (platelet) structure polished surface NASA/TM—2003-212516 3 III. Strength Testing Types of Testing/Test Specimens/Orientations Spray direction (S.D) 90 mm Uniaxial Trans-thickness Uniaxial tension tension compression 6 mm Test specimens to be cut 140 mm Billet Uniaxial flexure Biaxial flexure (four-point) (ring-on-ring) indicates spray direction Test Matrix (strength) Type of tests Specimen geometry No. of test Direction of specimens fracture* Uniaxial tension 15mm x 5mmφφφ 10 P Trans-thickness 15 mm x 3 mm (t) 10 N Tension (diameter x thick.) Uniaxial Trans-thickness Uniaxial tension tension compression Uniaxial 10mm x 5mmφφφ 10 P compression Uniaxial flexure 3mm x 4mm x 25mm 30 P (four-point) [10/20 mm spans] Uniaxial flexure Biaxial flexure Biaxial flexure 25mm x 3mm (t) 10 P (four-pt.) (ring-on-ring) (ring-on-ring) [11/22 mm rings] indicates spray direction * indicates the direction of fracture w.r.t plasma-spray direction. Test temperature: ambient temperature in air. NASA/TM—2003-212516 4 Experimental Results (strength) Type of tests No. of test Direction* Average Weibull specimens strength modulus valid (MPa)# Uniaxial tension 3 P 15(1) - Trans-thickness 10 N 11(1) 13 Uniaxial Trans-thickness Uniaxial Tension tension tension compression Uniaxial 10 P 300(77) 4 compression Uniaxial flexure 30 P 33(7) 6 (four-point) Uniaxial flexure Biaxial flexure Biaxial flexure 10 P 40(4) 12 (four-pt.) (ring-on-ring) (ring-on-ring) * indicates fracture direction w.r.t plasma-spray direction: indicates spray direction N: normal; P: parallel # represents ±1.0 standard deviation A basic assumption in strength calculation: a continuum mechanics (isotropic and linear-elastic) σσσ f = 10-15 MPa in tension = 30-40 MPa in flexure = 300 MPa in compression Choi, Zhu, and Miller (‘98,’99,’00,’01) Experimental Results (strength) Strength vs Type of Tests 500 ZrO2-8wt% Y2O3 TBCs ] (RT strengths) (10) 100 [MPa f σ σ σ σ , Uniaxial Trans-thickness Uniaxial tension tension compression H (10) T (30) 10 NG (3) (10) RE T S Uniaxial flexure Biaxial flexure (four-pt.) (ring-on-ring) 1 indicates spray direction Tension Trans-thick Uniaxial Biaxial Compression tension
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