IN THE UNITED STATES PATENT AND TRADEMARK OFFICE
`
`
`Eaton et al.
`In re Patent of:
`7,060,360 Attorney Docket No.: 43498-0002IP1
`U.S. Patent No.:
`June 13, 2006
`
`Issue Date:
`Appl. Serial No.: 10/443,342
`
`Filing Date:
`May 22, 2003
`
`Title:
`BOND COAT FOR SILICON BASED SUBSTRATES
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`DECLARATION OF DR. DAVID R. CLARKE
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`1
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`UTC 2001
`General Electric v. United Technologies
`IPR2016-01289
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`

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`I. 
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`II. 
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`Table of Contents
`
`Introduction ...................................................................................................... 3 
`
`Qualifications ................................................................................................... 3 
`
`III.  Materials Considered ....................................................................................... 6 
`
`IV.  Applicable Legal Standards ............................................................................. 8 
`
`A.  My Understanding of Claim Construction ............................................ 8 
`
`B.  My Understanding of Anticipation ....................................................... 9 
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`C.  My Understanding of Obviousness ....................................................... 9 
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`V. 
`
`Level of Ordinary Skill in the Art ................................................................. 14 
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`VI.  Overview of Coating Technology ................................................................. 15 
`
`A. 
`
`B. 
`
`C. 
`
`D. 
`
`Introduction to Coatings ...................................................................... 15 
`
`Properties of Multilayer Coatings ....................................................... 18 
`
`Coatings Under Extreme Environmental Conditions .......................... 23 
`
`Residual Stress in Multilayer Coatings ............................................... 26 
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`VII.  Brief Overview of the ’360 Patent ................................................................. 27 
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`VIII.  Claim Construction ........................................................................................ 30 
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`IX.  U.S. Patent No. 5,677,060 to Terentieva (“Terentieva”) .............................. 32 
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`X.  U.S. Patent No. 6,387,456 to Eaton (“Eaton ’456”) ...................................... 35 
`
`XI. 
`
`J. D. Webster et al., Oxidation Protection Coatings for C/SiC Based on
`Yttrium Silicate, J. Eur. Cer. Soc., vol. 18, No. 16 (Dec. 1998) pp. 2345-50.
`(“Webster”) .................................................................................................... 37 
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`2
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`XII.  Yoshikazu Suzuki et al., Improvement in Mechanical Properties of Powder-
`Processed MoSi2 by the Addition of Sc2O3 and Y2O3, J. Am. Ceram. Soc.,
`vol. 81, No. 12 (Dec. 1998) pp. 3141-49. (“Suzuki”) ................................... 37 
`
`XIII.  Terentieva’s protective coating is not a bond layer ....................................... 38 
`
`XIV.  The combination of Terentieva and either Eaton ’456 or the ’360 Patent is
`not obvious ..................................................................................................... 40 
`
`A. 
`
`B. 
`
`C. 
`
`The functionality of the barrier layer of Eaton ’456 or of the ’360
`Patent is redundant with the functionality of Terentieva’s protective
`coating ................................................................................................. 40 
`
`A POSITA would not have had a reasonable expectation of success . 44 
`
`Dependent claim 4 is not obvious in view of Terentieva, Eaton ’456,
`and the background of the ’360 Patent ................................................ 49 
`
`XV.  Conclusions .................................................................................................... 50 
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`3
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`I.
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`Introduction
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`I, David R. Clarke, declare as follows:
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`1.
`
`I have been retained on behalf of United Technologies Corporation to
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`offer technical opinions relating to U.S. Patent No. 7,060,360 (the ’360 Patent),
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`and prior art references relating to its subject matter.
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`II. Qualifications
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`2. My name is Dr. David R. Clarke. I am the Extended Tarr Family
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`Chair of Materials at Harvard University. My current curriculum vitae is attached
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`and some highlights follow.
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`3.
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`I earned my B.Sc. (1968) with First Class Honors in Applied Sciences
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`from Sussex University in England and my Ph.D. (1974) in Physics from Cam-
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`bridge University, England. I carried out research on high temperature silicon-
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`containing materials and zirconia materials at Rockwell International Science Cen-
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`ter from 1977-1982. After employment in various capacities related to materials
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`research at IBM Research Division, Yorktown Heights, NY, I was subsequently a
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`Professor of Materials and Professor of Mechanical Engineering at the University
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`of California, Santa Barbara (UCSB), from 1990-2009, and served as the Chair of
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`the Materials Department from 1991-1998. I have been a Professor of Materials
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`and Applied Physics at Harvard University since 2009.
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`4. My record of professional service includes recognitions from several
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`professional organizations in my field of expertise. I was elected to the National
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`Academy of Engineering in 1999. I was named a Distinguished Life Member of
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`the American Ceramic Society (ACS) in 2009, and have been a Fellow of the
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`American Physical Society since 1986 and of the ACS since 1985. I have been the
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`recipient of a number of awards from the ACS, including James Mueller Award
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`from the Engineering Ceramics Division of the ACS in 2014, the Edward C. Henry
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`Award from the Electronics Division of the ACS in 1999, and the Sosman Memo-
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`rial Award from the ACS in 1999. I am the author of a scientific paper that was
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`identified as one of the 11 most significant papers in the 110 years of publication
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`of the journal Ceramics.1 I have served as an editor for the Annual Reviews of Ma-
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`terials Research since 1997 and as an associate editor for the Journal of the Ameri-
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`can Ceramic Society since 1986.
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`5. My work at Rockwell International, IBM, UCSB, and Harvard Uni-
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`versity has appeared in more than 400 refereed and archival publications on which
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`I am author or co-author. All publications are listed on my curriculum vitae. How-
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`ever, a few examples of recent publications that involve thermal barrier coatings
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`1 D.R. Clarke, On the Equilibrium Thickness of Intergranular Glass Phases in Ceramic
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`Materials, 70 Journal of the American Ceramic Society. 15-22 (1987).
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`5
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`for gas turbines include: Clarke and Levi (2003); Casadei, Bertoldi, and Clarke
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`(2014); Limarga, Shian, Leckie, Levi, and Clarke (2014); Evans, Levi, and Clarke
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`(2014); and Clarke, Oechsner, and Padture (2012).2,3,4,5,6
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`6.
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`I am a named inventor on 11 issued U.S. patents and 3 pending patent
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`applications. Many of these patents and applications relate generally to composites,
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`coatings, and glass-ceramic materials, inclusive of the following: U.S. Patent No.
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`7,070,866, titled “Nickel Aluminide Coating with Improved Oxide Stability;” U.S.
`
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`2 D. R. Clarke and C. Levi, Materials Design for the Next Generation Thermal Barrier
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`Coatings, 33 Annual Reviews of Materials Research. 383-417 (2003).
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`3 F. Casadei, K. Bertoldi, and D.R. Clarke, Vibration Damping of Thermal Barrier Coat-
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`ings Containing Ductile Metallic Layers, 81 Journal of Applied Mechanics. 101001-101001-10
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`(2014).
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`4 A. M. Limarga, S. Shian, R. M. Leckie, C. G. Levi, and D. R. Clarke, Thermal Conduc-
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`tivity of Single and Multi-phase Compositions in the ZrO2-Y2O3-Ta2O5 System, 34 Journal of
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`the European Ceramic Society. 3085-3094 (2014).
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`5 A. G. Evans, C. G. Levi, and D. R. Clarke. “Turbine Materials and Mechanics.” Turbine
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`Aerodynamics, Heat Transfer, Materials and Mechanics, edited by T. Shih and V. Yang. Ameri-
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`can Institute of Astronautics and Aeronautics, 2014.
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`6 D. R. Clarke, M. Oechsner, and N. P. Padture, Thermal-barrier coatings for more effi-
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`cient gas-turbine engines, 37 MRS Bulletin. 891-898 (2012).
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`6
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`Patent No. 6,072,568, titled “Thermal Barrier Coating Stress Measurement;” U.S.
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`Patent No. 5,277,725, titled “Process for Fabricating a Low Dielectric Composite
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`Substrate;” and U.S. Patent No. 5,185,215, titled “Zirconia Toughening of Glass-
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`Ceramic Materials.”
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`7. My Curriculum Vitae is provided as Exhibit UTC-2005, which con-
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`tains further details on my education, experience, publications, and other qualifica-
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`tions to render an expert opinion. My work on this case is being billed at an hourly
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`rate, with reimbursement for actual expenses. My compensation is not contingent
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`upon the outcome of these proceedings or on the content of my opinions.
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`III. Materials Considered
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`8.
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`In forming my opinions expressed in this declaration, I have consid-
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`ered and relied upon my education, background, and experience. I reviewed U.S.
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`Patent No. 7,060,360 (“the ’360 patent”) and its patent file history.
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`9.
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`Additionally, I have reviewed and relied upon the following list of
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`materials in preparation of this declaration:
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`
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`
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`
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`U.S. Patent No. 5,677,060 to Terentieva et al. (“Terentieva,” GE-1005)
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`U.S. Patent No. 6,387,456 to Eaton et al. (“Eaton ’456,” GE-1006)
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`U.S. Patent No. 5,985,470 to Spitsberg et al. (GE-1013)
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`- 6 -
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`7
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`
`
`Yoshikazu Suzuki et al., Improvement in Mechanical Properties of Pow-
`
`der-Processed MoSi2 by the Addition of Sc2O3 and Y2O3, J. Am. Ceram. Soc.,
`
`vol. 81, No. 12 (Dec. 1998) pp. 3141-49. (“Suzuki,” GE-1024”)
`
`
`
`J. D. Webster et al., Oxidation Protection Coatings for C/SiC Based on
`
`Yttrium Silicate, J. Eur. Cer. Soc., vol. 18, No. 16 (Dec. 1998) pp. 2345-50.
`
`(“Webster,” GE-1025)
`
`
`
`M.G. Hocking et al., Metallic & Ceramic Coatings: Production, High
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`Temperature Properties & Applications (1989). (UTC-2002)
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`
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`Excerpt of Merriam Webster’s Collegiate Dictionary (10th ed. 2002).
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`(UTC-2004)
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`
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`J.W. Hutchinson and A.G. Evans, On the delamination of thermal barrier
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`coatings in a thermal gradient, 149 Surface and Coatings Technology. 179-184
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`(2002). (UTC-2006)
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`
`
`D.R. Clarke and C.G. Levi, Materials Design for the Next Generation
`
`Thermal Barrier Coatings, 33 Annual Review of Materials Research. 383-417
`
`(2003). (UTC-2007)
`
`
`
`D. Zhu and R.A. Miller, Sintering and creep behavior of plasma-sprayed
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`zirconia- and hafnia-based thermal barrier coatings, 108-109 Surface and Coat-
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`ings Technology. 114-120 (1998). (UTC-2008)
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`8
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`
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`J.W. Hutchinson and Z. Suo, Mixed Mode Cracking in Layered Materi-
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`als, 29 Advances in Applied Mechanics. 63-191 (1991). (UTC-2009)
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`
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`A. Bagchi and A.G. Evans, The Mechanics and Physics of Thin Film
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`Decohesion and its Measurement, 3 Interface Science. 169-193 (1996). (UTC-
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`2010)
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`
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`D. Zhu and R.A. Miller, Investigation of thermal fatigue behavior of
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`thermal barrier coating systems, 94-95 Surface and Coatings Technology. 94-
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`101 (1997). (UTC-2011)
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`
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`A.G. Evans, D.R. Mumm, J.W. Hutchinson, G.H. Meier, and F.S. Pettit,
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`Mechanisms controlling the durability of thermal barrier coatings, 46 Progress
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`in Materials Science. 505-553 (2001). (UTC-2012)
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`10.
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`I have also considered all other materials cited herein.
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`IV. Applicable Legal Standards
`
`A. My Understanding of Claim Construction
`
`11.
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`I have been informed that claim terminology must be given the broad-
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`est reasonable interpretation during an IPR proceeding. I have been informed that
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`this means the claims should be interpreted as broadly as their terms reasonably al-
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`low, but that such interpretation should not be inconsistent with the patent’s speci-
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`fication and with usage of the terms by one of ordinary skill in the art at the time of
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`invention. I have been informed that this may yield interpretations that are broader
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`than the interpretation applied during a District Court proceeding.
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`12. For the purpose of this proceeding, I have used May 22, 2003, which
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`is the filing date of the ’360 patent, as the approximate time of the invention.
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`B. My Understanding of Anticipation
`13.
`I understand that documents and materials that qualify as prior art can
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`be used to invalidate a patent claim as anticipated or as obvious.
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`14.
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`I understand that, once the claims of a patent have been properly con-
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`strued, the second step in determining anticipation of a patent claim requires a
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`comparison of the properly construed claim language to the prior art on a limita-
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`tion-by-limitation basis.
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`15.
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`I understand that a prior art reference “anticipates” an asserted claim,
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`and thus renders the claim invalid, if all elements of the claim are disclosed in that
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`prior art reference, either explicitly or inherently (i.e., necessarily present).
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`16.
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`I understand that anticipation in an inter partes review must be shown
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`by a preponderance of the evidence.
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`C. My Understanding of Obviousness
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`17.
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`I understand that a patent claim is invalid if the claimed invention
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`would have been obvious to a person of ordinary skill in the field at the time of the
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`claimed invention. This means that even if all of the requirements of the claim
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`cannot be found in a single prior art reference that would anticipate the claim, the
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`claim can still be invalid.
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`18. As part of this inquiry, I have been asked to consider the level of ordi-
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`nary skill in the field that someone would have had at the time the claimed inven-
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`tion was made. In deciding the level of ordinary skill, I considered the following:
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`
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`
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`the levels of education and experience of persons working in the field;
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`the types of problems encountered in the field; and
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`the sophistication of the technology.
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`19. To obtain a patent, a claimed invention must have, as of the priority
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`date, been nonobvious in view of the prior art in the field. I understand that an in-
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`vention is obvious when the differences between the subject matter sought to be
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`patented and the prior art are such that the subject matter as a whole would have
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`been obvious at the time of the invention to a person having ordinary skill in the
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`art.
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`20.
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`I understand that a person of ordinary skill in the art provides a refer-
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`ence point from which the prior art and claimed invention should be viewed. This
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`reference point prevents one from using his or her own insight or hindsight in de-
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`ciding whether a claim is obvious.
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`21.
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`I also understand that an obviousness determination includes the con-
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`sideration of various factors such as (1) the scope and content of the prior art, (2)
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`the differences between the prior art and the asserted claims, (3) the level of ordi-
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`nary skill in the pertinent art, and (4) the existence of secondary considerations
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`such as commercial success, long-felt but unresolved needs, failure of others, etc.
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`22.
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`I understand that an obviousness evaluation can be based on a combi-
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`nation of multiple prior art references. I understand that the prior art references
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`themselves may provide a suggestion, motivation, or reason to combine, but other
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`times the nexus linking two or more prior art references is simple common sense. I
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`further understand that obviousness analysis recognizes that market demand, rather
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`than scientific literature, often drives innovation, and that a motivation to combine
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`references may be supplied by the direction of the marketplace.
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`23.
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`I understand that if a technique has been used to improve one device,
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`and a person of ordinary skill in the art would recognize that it would improve sim-
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`ilar devices in the same way, using the technique is obvious unless its actual appli-
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`cation is beyond his or her skill.
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`24.
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`I also understand that practical and common sense considerations
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`should guide a proper obviousness analysis, because familiar items may have ob-
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`vious uses beyond their primary purposes. I further understand that a person of or-
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`dinary skill in the art looking to overcome a problem will often be able to fit to-
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`gether the teachings of multiple publications. I understand that obviousness analy-
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`sis therefore takes into account the inferences and creative steps that a person of
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`ordinary skill in the art would employ under the circumstances.
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`25.
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`I understand that a particular combination may be proven obvious by
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`showing, among other things, that it was obvious to try the combination. For ex-
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`ample, when there is a design need or market pressure to solve a problem and there
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`are a finite number of identified, predictable solutions, a person of ordinary skill
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`has good reason to pursue the known options within his or her technical grasp be-
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`cause the result is likely the product not of innovation but of ordinary skill and
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`common sense.
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`26. The combination of familiar elements according to known methods is
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`likely to be obvious when it does no more than yield predictable results. When a
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`work is available in one field of endeavor, design incentives and other market forc-
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`es can prompt variations of it, either in the same field or a different one. If a person
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`of ordinary skill can implement a predictable variation, the patent claim is likely
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`obvious.
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`27.
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`It is further my understanding that a proper obviousness analysis fo-
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`cuses on what was known or obvious to a person of ordinary skill in the art, not
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`just the patentee. Accordingly, I understand that any need or problem known in the
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`field of endeavor at the time of invention and addressed by the patent can provide a
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`reason for combining the elements in the manner claimed.
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`28.
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`I understand that a claim can be obvious in light of a single reference,
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`without the need to combine references, if the elements of the claim that are not
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`found explicitly or inherently in the reference can be supplied by the common
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`sense of one of skill in the art.
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`29.
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`I understand that secondary indicia of non-obviousness may include
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`(1) a long felt but unmet need in the prior art that was satisfied by the invention of
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`the patent; (2) commercial success of processes covered by the patent; (3) unex-
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`pected results achieved by the invention; (4) praise of the invention by others
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`skilled in the art; (5) taking of licenses under the patent by others; (6) deliberate
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`copying of the invention; (7) failure of others to find a solution to the long felt
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`need; and (8) skepticism by experts. I understand that evidence of secondary indi-
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`cia of non-obviousness, if available, should be considered as part of the obvious-
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`ness analysis.
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`30.
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`I also understand that there must be a relationship between any such
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`secondary considerations and the invention. I further understand that contempora-
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`neous and independent invention by others is a secondary consideration supporting
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`an obviousness determination.
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`31.
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`In sum, my understanding is that prior art teachings are properly com-
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`bined where a person of ordinary skill in the art having the understanding and
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`knowledge reflected in the prior art and motivated by the general problem facing
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`the inventor, would have been led to make the combination of elements recited in
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`the claims. Under this analysis, the prior art references themselves, or any need or
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`problem known in the field of endeavor at the time of the invention, can provide a
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`reason for combining the elements of multiple prior art references in the claimed
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`manner.
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`32.
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`I understand that obviousness in an inter partes review must be shown
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`by a preponderance of the evidence.
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`V. Level of Ordinary Skill in the Art
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`33. A person of ordinary skill in the art (“POSITA”) at or before the time
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`of the invention of the ’360 patent7 would have had a Master’s degree in an aca-
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`demic area emphasizing Materials Science, Mechanical Engineering, Applied
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`Physics, or an equivalent field. Alternatively, a POSITA would have had a Bache-
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`lor’s degree in an academic area emphasizing Materials Science, Mechanical Engi-
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`neering, Applied Physics, or an equivalent field, as well as at least 2 years of in-
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`dustry experience in thin film deposition or characterization, high temperature
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`coating design, or mechanics. Additional education or industry experience in a rel-
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`7 Unless noted otherwise, references herein to what would have been known or under-
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`stood by a POSITA refers to the knowledge of a POSITA at or before the time of the invention
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`of the ’360 patent.
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`evant field, such as heat transfer, fluid flow, or materials engineering, may com-
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`pensate for a deficit in one of the other aspects of the requirements stated above. I
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`am familiar with the knowledge and capabilities of one of ordinary skill in these
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`areas based on my own industrial experience, experience working with colleagues
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`from academia, with undergraduate and graduate students, and with engineers
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`practicing in industry.
`
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`VI. Overview of Coating Technology
`
`A.
`Introduction to Coatings
`34. A coating is a thin layer of material that is formed on the surface of a
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`substrate. The coated substrate is sometimes referred to as a composite material.
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`35. A coating can be deposited or formed on the surface of a substrate by
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`any of a variety of methods, examples of which include physical vapor phase dep-
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`osition, electroplating, thermal or plasma spraying, dip coating, spin coating, and
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`printing. The resulting composite material is a “system [that] is invariably hybrid,
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`whether it has been achieved by means of a surface modification of the component
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`substrate itself or one or more other materials have been applied as a coating to the
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`component surface.” UTC-2002, p. 1.
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`36. Often, a coating is applied to a substrate to create a composite materi-
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`al that has properties that are not present in the substrate alone: “Coatings enable
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`the attributes of two or more materials [e.g., the coating and the substrate] to be
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`combined to form a composite having characteristics not readily available in a
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`monolithic material.” UTC-2002, p. xii. Properties of a coating can include me-
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`chanical properties, such as stiffness, toughness, and strength; protective proper-
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`ties, such as corrosion resistance; electrical properties, such as resistivity or con-
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`ductivity; optical properties, such as reflectivity or anti-reflectivity; adhesiveness;
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`and other properties. When a coating is applied to a substrate, the resulting compo-
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`site material generally inherits properties from both the coating and the substrate.
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`37. As an example, a protective coating can be formed on a substrate that
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`is susceptible to corrosion in the face of aggressive environmental conditions. Such
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`protective coatings are sometimes referred to as barrier layers or environmental
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`barrier layers. For instance, a metal component that oxidizes (e.g., corrodes) in the
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`presence of oxygen or water can be coated with a barrier layer to prevent oxidation
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`of the component when exposed to oxygen or water, thus expanding the range of
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`environmental conditions in which the metal substrate or component can be used.
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`38. To act as a barrier against aggressive environmental conditions (e.g.,
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`oxygen or water at high temperatures), an environmental barrier layer should be
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`more resistant to those environmental conditions than the underlying substrate:
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`“The primary requirement of a protective surface is to have qualities superior to
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`that of the substrate in order to shield the component from an aggressive environ-
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`ment.” UTC-2002, p. 1.
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`39. Many industrial applications involve the use of metal components un-
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`der extreme environmental conditions, such as at very high temperatures, in moist
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`environments in the presence of high velocity gas flows. Corrosion of metals is ac-
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`celerated under such conditions, and thus components exposed to these conditions
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`must be protected with an environmental barrier layer that is durable against high
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`temperature, water, or high velocity gas flows. For instance, in aerospace applica-
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`tions, metal components of jet turbine engines, such as the turbine sections, are
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`subject to extremely high temperatures, repeated heating and cooling cycles, and
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`are routinely in the presence of high velocity gas flows. Coating these turbine
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`components, whether metallic or silicon containing compounds, with a durable en-
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`vironmental barrier layer shields the components from these extreme, aggressive
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`conditions, improving the reliability and lifetime of the components.
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`40. A coating can sometimes include multiple layers of material formed
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`as a stack on the surface of a substrate. A coating including multiple layers of ma-
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`terials is called a multilayer coating and a substrate with a multilayer coating
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`formed thereon is sometimes referred to as a multilayer composite. Multilayer
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`composites are often formed to obtain a composite material having properties or a
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`combination of properties or functions not available from a single coating material.
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`41. The adhesion of a coating to a substrate depends on factors such as the
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`chemical composition of the coating and the substrate, the surface energy of the
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`coating and the substrate, residual or thermal stresses, and the method by which the
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`coating was formed on the substrate, among other factors. Some coatings may ad-
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`here well to some types of substrates but may adhere poorly to other types of sub-
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`strates.
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`42. When a layer of material with a desired property (e.g., an environmen-
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`tal barrier layer) does not adhere well to a desired substrate, an additional layer can
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`be incorporated between the environmental barrier layer and the substrate, forming
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`a multilayer composite. The additional layer, sometimes referred to as a bond coat
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`or a bond layer, has good adhesion to both the environmental barrier layer and the
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`substrate, and thus causes the environmental barrier layer to adhere better to the
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`substrate. For instance, the “adhesion of plasma sprayed ceramic coatings to metals
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`is generally poor but can be considerably improved” with a bond layer. UTC-2002,
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`p. 28.
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`B.
`Properties of Multilayer Coatings
`43. Multilayer coatings can bring valuable and diverse properties to a
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`composite material, but can be challenging to design: they “bring their own prob-
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`lems … and coatings technology has thus emerged as a challenging field for both
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`the fundamental and applied research worker.” UTC-2002, p. xiv.
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`44. One major challenge faced during the development of a multilayer
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`coating for use at high temperatures is that the component is also subjected to re-
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`peated heating and cooling (referred to as thermal cycling), which affects interac-
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`tions among the layers of the multilayer coating. This typically occurs during start-
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`up and shutting down an engine, but can also occur during engine operation. Com-
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`plex, coupled thermal-mechanical-chemical interactions can occur which can result
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`in the multilayer composite having unexpected or unpredicted properties. A layer
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`of material that exhibits a particular set of properties in isolation may behave dif-
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`ferently when combined into a single, multilayer coating on a substrate because of
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`such interactions. These interactions and the resulting changes in the properties of
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`the layers of a multilayer coating make it difficult or impossible to predict how a
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`multilayer coating will behave in service, even if the behavior of each constituent
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`layer in isolation is well understood.
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`45.
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`Interactions among layers in a multilayer coating can include thermal
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`interactions (e.g., due to a mismatch between the thermal expansion coefficients of
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`adjacent layers and the substrate) and diffusion of elements between the layers.
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`These interactions can be coupled; for instance, the inter-diffusion of elements be-
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`tween layers can alter the thermal expansion coefficients of the individual layers.
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`Such interactions can cause changes in the properties of a multilayer coating and
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`can lead to mechanical failure of the coating, such as delamination or cracking.
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`46. Thermal interactions between layers in a multilayer coating can arise
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`due to a mismatch in the thermal expansion coefficients of the layers in the coat-
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`ing. For instance, if adjacent layers in a multilayer coating, including the substrate,
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`have different thermal expansion coefficients, those layers will expand or contract
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`by a different amount when the multilayer coating is heated or cooled. These dif-
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`ferences in expansion or contraction can cause stresses to develop within one or all
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`of the layers, which in turn can have an effect on the properties of the multilayer
`
`coating or even compromise the structural integrity of the multilayer coating, for
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`instance by cracking or delamination. For instance, “some failure modes” in multi-
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`layer coatings are “caused by the large residual compression that develops in the
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`thin TGO [thermally grown oxide] layer upon thermal cycling.” UTC-2006, p. 179.
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`The effects of a mismatch in thermal expansion coefficients is exacerbated for
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`multilayer coatings that are exposed to high temperatures or wide variations in
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`temperature, such as for multilayer coatings used in aerospace applications, be-
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`cause the temperature changes are typically larger than in other applications.
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`Cracking can be manifest in a reduction in strength, for instance in four-point
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`bending strength measured at room temperature.
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`47.
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`In many engine applications, multilayer coatings are also exposed to
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`large temperature gradients. Because of differences in thermal expansion coeffi-
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`cients in the individual layers and the substrate, temperature gradients can lead to
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`stress gradients.
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`48. Diffusion is a process by which atoms or molecules move from one
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`region to another driven by differences in composition. In a multilayer coating,
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`material can diffuse from one layer into an adjacent layer, changing the sharpness
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`of the interface between the layers and the chemical composition of both layers in
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`the vicinity of the interface. In turn, these compositional changes alter the thermal
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`coefficient of expansion of the layers as well as the fracture energy of the interfac-
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`es. Both of these changes can result in changes to the properties of the multilayer
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`structure. Diffusion occurs more readily at high temperatures, and thus the effect of
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`diffusion on the properties of a multilayer coating is enhanced in multilayer coat-
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`ings that are exposed to high temperature environments, such as for multilayer
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`coatings used in aerospace applications.
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`49. There can also be changes in the coating layers with service at high
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`temperature associated with sintering or densification of the material. This can lead
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`to changes in the stresses in the composite coating as well as the onset of cracking.
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`For instance, densification “increases the elastic modulus [of the coating] and
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`thereby decreases the strain compliance of the coating.” UTC-2007, p. 399. This
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`“reduction in strain compliance produced by sintering and densification at higher
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`use temperatures is likely to control the life of coatings.” Id., p. 403. Indeed, “ce-
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`ramic coating sintering and creep at high temperature can result in coating shrink-
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`age and through-thickness cracking during cooling, thereby further accelerating the
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`coating failure process.” UTC-2008, p. 114.
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`50. Because of the complexity of these coupled inter-layer interactions,
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`rather than predicting the behavior of a multilayer coating based on the known be-
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`havior of the individual layers in isolation, a multilayer coating must be developed
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`and tested as an integrated system. “Duplex and multilayer coatings must be stud-
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`ied in a graded programme to enable assessment of the influence of each of the
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`coating layers.” UTC-2002, p. 563. A graded programme can be, for instance, a
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`“programme to test different properties of the same coating in a stand alone and in
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`a coating-substrate configuration,” e.g., for each layer of a multilayer coating. Id.,
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`p. 563.
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`51. Because of the com