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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Coatings for High-Temperature Structural Materials
Trends and Opportunities
Committee of Coatings for High-Temperature Structural Materials
National Materials Advisory Board
Commission on Engineering and Technical Systems
National Research Council
NATIONAL ACADEMY PRESS
Washington, D.C.
1996
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance.
This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.
The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Harold Liebowitz is president of the National Academy of Engineering.
The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.
The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Harold Liebowitz are chairman and vice chairman, respectively, of the National Research Council.
This study by the National Materials Advisory Board was conducted under Contract No. MDA-972-92-C-0028.
This report is available from the Defense Technical Information Center, Cameron Station, Alexandria, VA 22304-6145.
Library of Congress Catalog Card Number 96-68712
International Standard Book Number 0-309-05381-1
Available in limited supply from:
National Materials Advisory Board
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Additional copies are available for sale from:
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Copyright 1996 by the National Academy of Sciences. All rights reserved.
Printed in the United States of America.
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Abstract
This report assesses coatings materials and processes for gas-turbine blades and vanes; determines potential applications of coatings in high-temperature environments; identifies needs for improved coatings for performance enhancements, design considerations, and fabrication processes; assesses durability of advanced coating systems in potential service environments; and discusses required inspection, repair, and maintenance methods. Promising areas for research and development of materials and processes for improved coating systems and approaches for increased standardization of coatings are identified, with an emphasis on materials and processes with the potential for either improving performance, quality, or reproducibility or significantly reducing manufacturing costs.
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
COMMITTEE ON COATINGS FOR HIGH-TEMPERATURE STRUCTURAL MATERIALS
ROBERT V. HILLERY (chair),
GE Aircraft Engines, Cincinnati, Ohio
NEIL BARTLETT,
University of California, Berkeley
HENRY L. BERNSTEIN,
Southwest Research Institute, San Antonio, Texas
ROBERT F. DAVIS,
North Carolina State University, Raleigh
HERBERT HERMAN,
State University of New York, Stony Brook, New York
LULU L. HSU,
Solar Turbines, San Diego, California
WEN L. HSU,
Sandia National Laboratories, Livermore, California
JOHN C. MURPHY,
Johns Hopkins University, Laurel, Maryland
ROBERT A. RAPP,
Ohio State University, Columbus
JEFFERY S. SMITH,
Howmet Corporation, Whitehall, Michigan
JOHN STRINGER,
Electric Power Research Institute, Palo Alto, California
National Materials Advisory Board Staff
ROBERT M. EHRENREICH, Senior Program Officer
CHARLIE HACH, Program Officer
JACK HUGHES, Research Associate
AIDA C. NEEL, Senior Project Assistant
ROBERT E. SCHAFRIK, NMAB Director
ROBERT SPRAGUE, Consultant
JILL WILSON, Program Officer
Technical Advisors
WILLIAM J. BRINDLEY,
NASA Lewis Research Center, Cleveland, Ohio
STANLEY J. DAPKUNAS,
National Institute of Standards and Technology, Gaithersburg, Maryland
Government Liasion Representatives
WILLIAM BARKER,
ARPA, Arlington, Virginia
NORMAN GEYER,
Wright-Patterson Air Force Base, Ohio
DAWN MIGLIACCI,
Naval Air Warfare Center, Trenton, New Jersey
WILLIAM PARKS,
U.S. Department of Energy, Washington, D.C.
ROBERT R. REEBER,
Army Research Office, Research Triangle Park, North Carolina
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
NATIONAL MATERIALS ADVISORY BOARD
ROBERT A. LAUDISE (chair),
Lucent Technologies, Inc., Murray Hill, New Jersey
G.J. (REZA) ABBASCHIAN,
University of Florida, Gainesville
JAN D. ACHENBACH,
Northwestern University, Evanston, Illinois
MICHAEL I. BASKES,
Sandia-Livermore National Laboratory, Livermore, California
I. MELVIN BERNSTEIN,
Tufts University, Medford, Massachusetts
JOHN V. BUSCH,
IBIS Associates, Inc., Wellesley, Massachusetts
HARRY E. COOK,
University of Illinois, Urbana
EDWARD C. DOWLING,
Cyprus AMAX Minerals Company, Englewood, Colorado
ROBERT EAGAN,
Sandia National Laboratories, Albuquerque, New Mexico
ANTHONY G. EVANS,
Harvard University, Cambridge, Massachusetts
CAROLYN HANSSON,
University of Waterloo, Waterloo, Ontario, Canada
MICHAEL JAFFE,
Hoechst Celanese Research Division, Summit, New Jersey
LIONEL C. KIMERLING,
Massachusetts Institute of Technology, Cambridge
RICHARD S. MULLER,
University of California, Berkeley
ELSA REICHMANIS,
Lucent Technologies, Inc., Murray Hill, New Jersey
EDGAR A. STARKE,
University of Virginia, Charlottesville
KATHLEEN C. TAYLOR,
General Motors Corporation, Warren, Michigan
JAMES WAGNER,
The Johns Hopkins University, Baltimore, Maryland
JOSEPH WIRTH,
Raychem Corporation, Menlo Park, California
ROBERT E. SCHAFRIK, Director
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Acknowledgments
A great deal of work has gone into this study from its inception to the finished product. The committee is grateful for all the help it has received and expresses thanks to everyone who has participated. Without the patience and support provided by many individuals and organizations, this report could never have been completed.
The committee is grateful to those people who took time to brief the committee on the latest developments in coatings for high-temperature structural materials. The information and ideas from these briefings were essential to the study. Briefings were presented by Steve Balsone, Wright-Patterson Air Force Base; Andy Culbertson, Naval Air Warfare Center Trenton; Jack Devan, Oak Ridge National Laboratory; Dick Novak, Engineered Coatings; Randy Sands, Naval Air Warfare Center; Fred Soechting, Pratt & Whitney; Joseph Stephens, NASA Lewis Research Center; and Sharon Vukelich, Wright-Patterson Air Force Base.
The staff of the Southwest Research Institute (SWRI) did an excellent job of hosting one of the committee meetings, and the committee thanks Martin Goland, Henry Bernstein, and the SWRI staff for providing a tour of the facilities and accommodating the many needs of the meeting.
In particular, the committee thanks William Brindley of the NASA Lewis Research Center for making information available to the staff. The committee also thanks Stanley Dapkunas of the National Institute of Standards and Technology. Their support as technical advisors to the committee was invaluable.
The government liaisons who served this committee were also of enormous value. The committee thanks William Barker of ARPA, Dawn Migliacci of the Naval Air Warfare Center, William Parks of the U.S. Department of Energy, and Robert Reeber of the Army Research Office.
The chair of the committee thanks the members for their dedication and patience during the course of this study. This report could never have been completed without the diligence and goodwill of the members.
The committee thanks the staff of the National Materials Advisory Board, almost all of whom seemed to have been involved in the study at one time or another. Three program officers helped guide the study. In particular, the committee thanks Robert Ehrenreich for finishing the study. Tom Munns initiated the project and deserves thanks. Jill Wilson's support and guidance during the course of the study is greatly appreciated by the committee, as is Robert Sprague's, whose ideas as a consultant helped shape the report. Charles Hach and Jack Hughes were invaluable in the latter stages of the report. The committee also thanks Robert Schafrik for his support and direction along the way. Finally, the committee gratefully acknowledges the support of Aida C. Neel, senior project assistant.
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Preface
The U.S. Department of Defense and the National Aeronautics and Space Administration requested that the National Research Council conduct a study and provide recommendations on future research and development needs for high-temperature coatings systems. This report represents the work of the Committee on Coatings for High-Temperature Structural Materials, established by the National Research Council for this purpose.
Performance improvements in high-temperature mechanical systems have resulted in increasingly severe operating environments for high-temperature structural materials, particularly in gas turbines. This has sparked an increased demand for more reliable coatings that possess predictable failure mechanisms, improve the performance of structural materials, and extend the operating range of applications. With this background, the following objectives were outlined for this study:
assess the state of the art of coatings materials and processes
identify potential applications for coatings in high-temperature environments
identify needs for improved coatings for performance enhancements, design considerations, and fabrication processes
assess durability of advanced coating systems in expected service environments
identify required inspection, repair, and maintenance methods
recommend promising areas for materials and process research and development for improved coating systems and identify approaches to increased coating standardization
To address these objectives, the committee considered (1) propulsion systems for commercial and military aircraft and their marine and industrial derivatives and (2) land-based turbines for power generation and mechanical drives (excluding automotive, diesel engines, and space applications). The committee directed its efforts toward the hot section (combustor and turbine) of these gas-turbine systems, because this represents the most significant materials and coating challenges. To focus the study further, the committee considered a wide range of application and technology areas that might be covered under this broad charter and identified those that would be reviewed in detail. The intent was to concentrate on the materials systems and degradation modes in the hottest section of the identified power-generation systems and to consider the technology and application implications for coatings systems under these most severe conditions. A primary focus was on the needs for advanced machines under development by the U.S. Department of Energy, the U.S. Department of Defense, and the National Aeronautics and Space Administration sponsorship. This deliberation resulted in the list shown in table P-l, which defines the study focus, the areas not considered, and the areas that were only referenced by association with the primary focus.
Through a series of briefings from industry and government experts, the committee reviewed current coating systems, newly developed coating systems, and their implementation in products over the next five to eight years. To evaluate coating needs beyond this time frame, the committee reviewed the substrate materials (e.g., ceramics and intermetallics) being considered for future engine designs. The committee recognized that defining needs for many future systems would currently lack clarity, but a need was perceived to anticipate any fundamental changes that may demand longer-range research, process development, or manufacturing innovations.
This report reviews the state of the art for coating systems based on the following approach. First, the application needs were identified and a description of the domain of use was developed. Second, the environment that currently exists and the substrate materials that are now used in the hot section of gas-turbine engines were examined. This, in turn, led to a more complete definition of the coatings systems required. Third, the application processes, the industrial base, and the repair and overhaul requirements were discussed and the support capabilities (e.g., modeling, testing, and nondestructive evaluation) were assessed. This review provided a baseline for discussion of future trends and indicated how U.S. industry, government, and academia are planning to address the requirements of advanced propulsion systems.
To determine materials and coatings needs, advanced systems were assessed. The assessments on these advanced systems were obtained through presentations and information provided by the program managers for three major
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
TABLE P-1 Committee Focus
Focus
Associated/Referenced
Excluded
Industrial, marine, power generation, aircraft engine
Land-based systems
Auto, diesel engines, space
Structural materials superalloys (Ni, Co) intermetallics composites (IMC, CMC) monolithic ceramics
Refractories
Titanium alloys
700°C + temperatures (to capture Type II hot corrosion)
Oxidation, corrosion, erosion
Seal systems degradation caused by the service environment
Tribological wear
Gas-path coatings and clearance coatings
Gas-path seals
Combustor, transition piece, high-pressure turbine, power turbine
Off-line combustion
Compressor, fan
Diffusion coatings, overlays, TBC, surface modifications
Functionally graded materials, claddings, vitreous coatings
Low observable coatings, fiber coatings
Thermal spray, CVD, PVD, advanced processes
Plating, C/S/N/O-resistant coatings
Operating environment (air, fuel, water, particulates)
Combustion, emissions
Environmental impact: manufacturing, service, overhaul
Repair considerations
Lower-temperature coatings affected (e.g., impact-resistant coatings)
Repairs involving brazing, welding, etc.
Nondestructive evaluation (NDE)
Standards and standardization
Databases, modeling, engine condition sensors
Controls, intelligent processing of materials
Systems design (coating/substrate integration): advanced concepts
Material systems that might reduce or eliminate need for high-temperature coatings (e.g., Lamalloy)
Customer-DOD, DOE, NASA, original equipment manufacturers, suppliers
Airframe manufacturers, airlines, utilities
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
TABLE P-2 Primary Performance Goals for Advanced Engine Systems
Advanced Engine System
Requirements
Integrated High-Performance Turbine Engine Technology (IHPTET)
Cold section (fan and compressor): 2-3 times specific strength for materials 650-1000°C operating temperature
Hot section (the focus of this report; includes the combustor, turbine, augmenter, and nozzle subsytems): 3-5 times specific strength for materials 1650-2200°C with advanced cooling 1550°C uncooled
Nonstructural (bearing and lubes) up to 825°C
High-Speed Civil Transport (HSCT)
Range: 2 times greater than the Concorde Payload: 3 times greater than the Concorde Economics: 8 times greater than the Concorde Environmental emissions: 8 times lower than the Concorde Noise: 3 times quieter than the Concorde
Advanced Turbine Systems (ATS)
High efficiency, clean gas-turbine systems initially based on natural gas; adaptable to coal- or biomass-derived fuels
Power generation: >60% system efficiency
Industrial systems: >15% improvement
Environmental: 8 ppm NOx emissions; CO and HC < 20 ppm
Cost competitive: 10% reduction in busbar cost of electricity
government-sponsored materials efforts representing future military, commercial, and power-generation needs:
Integrated High-Performance Turbine Engine Technology—advanced military systems
High-Speed Civil Transport—aimed at the advanced supersonic commercial market
Advanced Turbine Systems—advanced utility and industrial power generation
Table P-2 summarizes the primary performance goals for each of these advanced systems. For each case, the committee obtained information on mission profile; systems needs; and specifics on time, temperature, and environmental requirements for materials in the propulsion system. This provided a perspective on what were the ultimate materials needs for propulsion systems reaching maturity early in the next century. In all cases, the goals underscored the demand for materials that can withstand significantly higher operating temperatures and service life than today's state-of-the-art devices. The reviews also provided information on significant changes that might be required as a result of new regulatory requirements, such as those that might stipulate permissible emissions from future propulsion systems. In addition, these reviews showed those areas common to aircraft engines and power-generation machines and changes to this commonality that might be demanded by derivative machines as, for example, the increased use of air to combat NOX in the combustor of land-based electric utility turbines. Some fundamental differences exist between aircraft and land-based systems that might cause a divergence in materials (and coatings) technologies. For instance, land-based systems are less affected by weight and can be supplemented with auxiliary systems, such as air supplies, steam supplies, or heat exchangers. The potential use of alternative fuels in nonaircraft systems might be another divergence affecting coatings type. Both aircraft and land-based gas turbines are moving toward higher temperatures and longer service-time requirements; this trend is causing increased emphasis on coatings needs. Finally, the committee heard presentations on the design requirements for coating systems and the engineered materials efforts that may have a bearing on the development and application of advanced coating systems.
In reviewing these briefings, the committee considered the following key questions:
Can the goals for the advanced systems be achieved simply by an evolution from today's materials?
Are programs and efforts in place to address the key potential barriers?
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Are there additional recommendations that can be made to enhance the chances for success in any of the key areas?
The committee then considered future opportunities for developing improved coatings by virtue of evolutionary development and by way of innovative concepts. The committee developed several innovative concepts for advanced coating systems and suggested how a wide variety of ideas could be integrated into coatings development and application advances. The members of the committee continually posed several key questions during their considerations of innovative approaches:
Are there concepts that have not been explored or that should be re-evaluated in light of recent knowledge?
Are there ideas or knowledge bases in other industries that can revolutionize thinking in the gas-turbine engine coating industry?
Are there ideas that can shorten the development cycle of existing efforts and thereby enhance the chance for success?
What are the latest developments in modeling, intelligent process manufacturing, and smart materials, and can these technologies be focused in the coatings area?
Are there new testing techniques that would be required and will new industry standards and procedures have to be defined?
Finally, the committee provides its conclusions and recommendations for the future as well as a bibliography of cited references and available texts.
Robert V. Hillery, chair
Committee on Coatings for High-Temperature Structural Materials
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Contents
EXECUTIVE SUMMARY
1
1
INTRODUCTION
8
2
APPLICATION NEEDS AND TRENDS
10
Application Needs
10
Current Component Design and Base Materials
13
Advanced Materials for Engine Components
13
3
MATERIALS AND PROCESSES
19
Coatings for High-Temperature Structures
19
Coating Processes
22
Coating Process Control
24
Summary
24
4
FAILURE MODES
26
Degradation Mechanisms of Structural Materials
26
Degradation Mechanisms of Coatings
26
A Case Study: Degradation of Thermal Barrier Coatings
30
Research Opportunities
32
5
ENGINEERING CONSIDERATIONS
34
Compatibility of Coatings with Structural Materials
34
Component Coatability
36
Other Engineering Considerations
36
Concurrent Coating Development
38
6
REFURBISHMENT OF COATED STRUCTURE
39
Factors Affecting Component Life
39
Repair of High-Temperature Coatings
40
Standard Designations for Coatings
41
Nondestructive Evaluation
41
7
NEAR-TERM TRENDS AND OPPORTUNITIES
43
Thermal Barrier Coating Development
43
Coating Processes
44
8
LONG-TERM OPPORTUNITIES AND INNOVATIVE SYSTEMS
46
Innovative Coating Architectures
46
Other Innovative Concepts
48
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
REFERENCES
51
APPENDICES
A
TESTING AND STANDARDS
57
B
RADIATION TRANSPORT IN THERMAL BARRIER COATINGS
65
C
SURVEY OF NONDESTRUCTIVE EVALUATION METHODS
67
D
MODELING OF COATING DEGRADATION
72
E
MANUFACTURING TECHNOLOGIES OF COATING PROCESSES
78
F
EXAMPLE OF A COATING DESIGNATION SYSTEM
83
G
BIOGRAPHICAL SKETCHES OF COMMITTEE MEMBERS
84
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
List of Figures and Tables
FIGURES
1-1
Typical ranges of a coating property compared with advanced engine requirements for a property
9
2-1
Cross section of a typical modern gas-turbine engine
10
2-2
Overview of transportation gas-turbine use
11
2-3
Overview of power-generation and mechanical-drive gas-turbine use
11
2-4
Approximate increases in firing temperature capabilities from 1980 to 2010
12
2-5
Turbine blade cooling methods
15
3-1
Coating compositions as related to oxidation and corrosion resistance
21
3-2
Schematic showing the benefit of development and deployment of manufacturing process control for high-temperature coatings
25
4-1
Types of high-temperature attack for metallic coatings (aluminide, chromide, MCrAlY, etc.) on nickel-base superalloys with approximate temperature regimes and severity of attack
28
4-2
Micrograph of service-exposed CoCrAlY overlay coatings showing internal oxidation of coating and base metal
29
4-3
Comparison of the microstructure of EB-PVD and plasma-sprayed TBCs
30
4-4
Photomicrograph of a plasma-sprayed TBC
31
4-5
Photomicrographs of EB-PVD TBCs before and after failure
32
5-1
Tradeoffs between first cost and operating cost
37
TABLES
P-2
Primary Performance Goals for Advanced Engine Systems,
xi
2-1
Typical Duty Cycles for Various Gas-Turbine Engines
12
2-2
Nickel-and Cobalt-Base Alloys Used in Land-Based and Aircraft Gas Turbines
14
2-3
Properties of Ceramic Materials that are Candidates for Hot-Section Use
16
2-4
Selected Properties of High-Temperature-Capable Intermetallics Compared to a Conventionally Cast and a Single-Crystal Superalloy
17
2-5
Properties of Refractory Metals and an Alloy Compared to B 1900 Nickel-Base Superalloy
18
3-1
Coating Functions and Coating Materials Characteristics
19
3-2
Types of Coatings Used in Hot-Section Components
20
3-3
Generic Information on Coating Types Used in Superalloy Hot-Section Components
21
3-4
Summary of the Benefits and Limitations of the Atomistic and Particulate Deposition Methods
22
4-1
Environmentally Induced High-Temperature Structural Material Failure Modes
27
4-2
Environmentally Induced High-Temperature Coating Failure Modes
28
6-1
Survey of Nondestructive Evaluation Techniques
42
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Coatings for High-Temperature Structural Materials: Trends and Opportunities
Acronyms
AISI
American Iron and Steel Institute
ASM
American Society for Materials
ASME
American Society of Mechanical Engineers
ASTM
American Society for Testing and Materials
ATS
Advanced Turbine Systems
CTE
coefficient of thermal expansion
CVD
chemical vapor deposition
DOD
U.S. Department of Defense
DOE
U.S. Department of Energy
EB-PVD
electron-beam physical vapor deposition
FGM
functionally graded materials
HSCT
High-Speed Civil Transport
HVAF
high-velocity air fuel
HVOF
high-velocity oxy fuel
IHPTET
Integrated High-Performance Turbine Engine Technology program
ISO
International Standards Organization
LPPS
low-pressure plasma spraying
NASA
National Aeronautics and Space Administration
NDE
nondestructive evaluation
PVD
physical vapor deposition
SNECMA
Société National d'Etude et de Construcion de Moteurs d'Aviation
STEP
Standard for the Exchange of Product
SVPA
SNECMA vapor phase aluminizing
TBC
thermal barrier coating
