Research supported by the Office of Naval Research

1
Experiences from the ONR-MURI Program on TBCs for
Aeroengines (Science Underpinning Prime Reliant
Coatings)
D.R. Clarke, A.G. Evans, C.G. Levi Materials
Department, University of California, Santa
Barbara
In collaboration with G.H. Meier and F. Pettit
(Pittsburg), J.W. Hutchinson and Z. Suo
(Harvard), A.H. Heuer (CWRU), H.N.G. Wadley
(Virginia), B. Gleeson (Iowa), R. Darolia and D.
Wortman (GE), M. Maloney (PW) and colleagues in
the NSF-HIPERCOAT and AFOSR-MEANS programs.
Workshop on Improving Ship Capabilities by
Insertion of Materials into Marine Gas Turbine
Engines Columbus, OH, May 24, 2006
Research supported by the Office of Naval
Research (Dr. S.G. Fishman/Dr. D. Shifler)
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Multidisciplinary Research on TBCs Overarching
Goals

• Extend the durability and reliability of TBCs by
  establishing an understanding of the mechanisms
  of failure, including the underlying phenomena
  and their associated dynamics.
• Enhance performance of TBCs, notably their
  ability to operate at higher temperatures and in
  more aggressive environments, by understanding
  the evolution of their structure and associated
  thermodynamic and kinetic fundamentals, and
  using that understanding to identify and develop
  potential alternative materials.
• Respond to problems identified by industry and/or
  the Navy that may arise in the course of the
  program notable examples are CMAS and
  Erosion/FOD.

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Mechanisms Limiting Durability in TBCs
A multidimensional problem, requiring an
interdisciplinary research effort
4
TBC Failure Driven by TGO Rumpling

• TGO growth provides strain energy available to
  drive spallation upon thermal cycling

5
Development of Mechanism Maps
Thermal Expansion Bond Coat Swelling
Micromechanics modeling essential to
understanding failure modes
6
Balint-Hutchinson model
Thermal Cycling Induced Rumpling
TGO
BC
Substrate
A multidisciplinary collaboration leading to the
development of a mechanics model that predicts
experimental findings
7
Erosion and FOD Mechanisms
8
Cracking/Erosion Threshold Map
ELASTO- DYNAMIC DOMAIN
High Toughness Soft at High Temperature
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t toughnessthe key to durability?
10
Ferroelastic Switching
11
Faulhaber, Krämer
Specimen provided by R. Darolia (GE)
TBC Degradation by CMAS
Airfoil
Shroud
Specimen provided by R. Kowalik (Navy)
Faulhaber, Krämer
12
Delamination Caused by Thermal Gradients
Raman piezo-spectroscopic measurement of stresses
in CMAS penetrated TBC on shroud, resulting from
rapid thermal cooling and alloy constraint.
13
Isothermal Infiltration with Model CMAS
7YSZ, 10mg, 7mm diam. pellet, 1300C Treatment
15 min
4h
14
Gd2Zr2O7 A CMAS Resistant TBC?
15
Leverage for Marine Turbines

• Outcomes that may help developments in Marine
  Turbines
• Models that incorporate the interaction between
  thermal, mechanical and chemical phenomena, e.g.
  cyclic oxidation, penetration by molten deposits.
  
• Microstructure science base, including phase
  stability in oxides and bond coats, morphological
  evolution of layered and porous systems,
  interdiffusion between BCs and superalloys.
• Concepts to guide material design, e.g. effect of
  dopants on toughness and phase stability in
  thermal barrier oxides.
• NDE and sensing concepts, e.g. those based on
  luminescence.
• Testing methods and implications.
• Synthesis and processing experiences.

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Broader Lessons

• Experiences with materials challenges in aircraft
  engines highlight the complex and multifaceted
  nature of these problems as well as the need for
  a systems perspective and a multidisciplinary
  approach in searching for solutions. The added
  chemical complexity of the marine turbine
  environment make those needs even more evident.
• A fundamental, mechanism-based approach is
  essential in understanding the performance and
  durability of materials in gas turbines, and in
  guiding the development of new materials systems
  that enable further advances in engine
  technology.
• Effective integration of modeling and experiments
  in a collaborative research environment
  accelerate the learning process and help develop
  new solutions.