thermal spray cr alternative-limited.pdf

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L I N K I N G G L O B A L T E C H N O L O G I E S W I T H M A R K E T S

1590 S. Milwaukee Ave., Suite 205, Libertyville, IL 60048, U.S.A 847-680-9420 Fax: 847-680-9682

Email: [email protected] www.rowantechnology.com

R T GOWAN ECHNOLOGY ROUP

Courtesy U.S. Navy. Photo by Ensign John Gay

Use of Therm al Spray

as an Aerospac e Chrom e

Plat i ng A lte rnat i ve

Report to:William GreenGeo-Centers

Rowan Project #: 3105JSF3

Contract Number: N00173-98-D-2006, D.O. 0002Subcontract Number: GC-3363-99-004P.O. Number: 28578MK

Report Number: Final

Date: October 27, 2000

Authors: Keith Legg(Rowan Technology Group, Principal Investigator)

John Sauer(Sauer Engineering)

UNCLASSIFIED NON-PROPRIETARY - Distribution Statement A

(mailto:[email protected])
mailto:[email protected]:[email protected]


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Rowan Technology Group

Project #: 3105JSF3 ; Report #: FinalPage i

EXECUTIVE SUMMARY

Thermal spray coatings have been used for many years in aircraft turbineengines as wear and erosion resistant coatings, thermal barriers, and

clearance control coatings. As increasing environmental and safetyissues have driven a search for chrome plating alternatives, engineershave found that thermal spray coating, long used for gas turbine engines,can be a very cost-effective alternative to hard chrome plating. Althoughthe initial driver for the substitution of thermal spray coatings for chromewas environmental, the alternatives are now being widely adoptedbecause of their better performance, higher reliability, and lower life-cyclecost.

This document summarizes the current state-of-the-art, property andperformance data, and usage of thermal spray coatings as replacementsfor hard chrome plating on aerospace components. The information coversthe use ofhard chrome for both original equipment and for overhaul and

repair. Its purpose is to provide in one place a summary of information onthermal spray coatings that will be useful for engineers engaged in the designand maintenance of aircraft components.

This document is designed as an electronic book, with links to guide theuser directly to information of interest. The document itself contains datasummaries and examples, with a large number of underlying full-textreferences (available at the click of a mouse) to provide as much detail aspossible. The information is current as of August 2000, but the documentis intended to be readily revised and updated as more information isgenerated. After a brief introduction, the document is broken into fourparts:

Part 1. Aerospace Usage of Chrome An overview of the types ofcomponents and applications in which hard chrome iscurrently used in the aircraft industry, and the requirementsfor chrome replacement.

Part 2 Overview of Thermal Spray Types and principles ofthermal spray, especially High Velocity Oxy-Fuel (HVOF) andPlasma Spray the two primary chrome replacementtechnologies. This Part includes thermal spray equipmentand powders, thermal spray producibility and quality control,stripping, and finishing.

Part 3. Thermal Spray Data Summary of current data on structure,

properties, and performance of thermal spray coatings hardness, adhesion, embrittlement, corrosion, fatigue, wear,hydraulic rig testing, landing gear rig testing, and flight testing.The text contains data summaries and graphs, with theunderlying data accessible via full-text documents.

Part 4. Specifications and Qualified Components Summary ofthermal spray specifications, and of thermal spray-qualifiedapplications and components.


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In summary, the data shows that in all critical respects HVOF coatingsperform as well as (and in most cases better than) hard chrome. This iscertainly true in critical areas, including hardness, wear, fatigue,corrosion, hydraulic testing, and extended flight testing. HVOF can beapplied to almost any material without causing hydrogen embrittlement,and in many cases the fatigue debit can be completely eliminated. As a

result HVOF coatings (primarily tungsten carbide cermets) are nowspecified on more than a hundred components on Boeing aircraft,and are used extensively for overhaul and repair of landing gearcylinders and axles, and flap and slat tracks. The new Boeing 767-400 is specified for HVOF-coated or chrome plated landing gear,whichever customers request. Parker-Hannifin is eliminating chromeplate, and using thermal spray coatings on all new aerospace hydraulicactuator designs. Airlines such as Delta, Lufthansa, and United are allqualifying HVOF for landing gear overhaul. There are several standardand widely used aerospace specifications for thermal spray processesand for the powder materials they employ. However, thermal spray is nota simple drop-in replacement for chrome plate. As a dry spraying

process rather than an electroplate it fits differently into the OEMproduction and overhaul sequence. Although it can be done in-house,and is in fact available at most repair shops and DoD depots, OEMsfrequently contract it out. Furthermore, HVOF coatings, the mostcommon chrome alternative, cannot be used on internal diameters,although plasma spray can be used on diameters down to about 2.Thermal spray cannot be used to replace thin dense or flash chrome,since it cannot be made thin enough.

The process lends itself to a large number of different coating materialsand a wide range of deposition conditions. This makes it highly flexiblebut more complex to use. Therefore the specifications for a thermal spraycoating must be properly defined, and the process optimized to fit boththe material being processed and the coating material being applied. Forexample:

Since it utilizes a torch or plasma gun, it is possible to overheatheat-sensitive components, making proper temperaturemeasurement and control an essential part of the processspecification.

The coating material must fit the substrate material. The mostcommon coating material is tungsten carbide, but thermal sprayedhard alloys, such as Tribaloy, give better fatigue performance onaluminum alloys.

The thermal spray coating must be optimized properly for theapplication. Some thermal spray coatings have performed poorlybecause they used the wrong coating material or used adeposition process that was optimized for the wrong application.For example, thermal spray coatings optimized for wearresistance may have as large a fatigue debit as chrome (or evenlarger). Re-optimizing the coating for fatigue has reduced, or eveneliminated, the fatigue debit while still retaining superior resistanceto wear.


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The finishing specifications for thermal spray coatings are notnecessarily the same as for chrome. Thermal spray coatingsmust in general be finish-ground or superfinished to a much finer

surface than is typical for chrome plate. For example, a 16 inchfinish is typically specified for chrome plated hydraulics. UsingHVOF coatings with this finish leads to very rapid seal failure.

With a 4 inch or better finish, however, both seal life and rod lifeare greatly extended.

In summary, the thermal spray process is highly recommended andgrowing as a replacement for hard chrome plate, but it must be usedproperly, with accurate specifications, a qualified sprayer, and properaccount taken for the materials and applications in which it is used.


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ACKNOWLEDGEMENTSThis compilation would not have been possible without the assistance of a greatmany people in the aerospace industry. We would therefore like to acknowledgethe many people and organizations that have contributed to this document.Funding for the work was provided by the Joint Strike FighterProgram Office,NADEP Jacksonville, poc Jean Hawkins. HCAT information has been providedby the members of the HCAT team, courtesy of Bruce Sartwell, NRL, the team leader.Many documents and other information have been provided by companies such asBoeing, Messier-Dowty, Praxair, Sulzer Metco, Southwest Aeroservice, MetcutResearch, and the National Research Council of Canada, among others. Many ofthe documents have been provided by courtesy of ASM International, MaterialsPark, OH 44073-0002, other documents by courtesy of Gorham Advanced Materials,Gorham, Maine, and by numerous individual authors as indicated in the text.


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HOW TO USE TH IS REPORT

This document is designed to be used electronically, so that it can be aliving document that can be updated with the latest information as it

becomes available. It is extensively hyperlinked to permit the reader tojump immediately to items of interest in the text.

Many items in the text figures, tables, references, section headings, etc. are hyperlinked, and can be identified by theirblue text. Clicking on thetext takes you to the item.

The report is designed to contain the most important information withinthe text. Details and backup information are provided in the form ofattached documents, which can be recognized by the yellow boxes, likethe one below. Clicking on the icon within the box brings up thedocument, making all the details readily available.

Later cross-references to these documents are shown in blue, and the

Document can be opened by clicking on the blue text.

When you have finished with the Document, just close it to return to theReport. If you need to keep it available you can switch betweenDocument and Report by clicking on the Window menu button and

choosing which item to view.

These documents were created by Adobe Acrobat in .PDF format, and

can be read with Acrobat Reader. Most computers already have thisutility installed for browsing the web. If yours does not, it can be obtainedfree of charge by clicking on the link below, which will take you to the

Adobe web site.

A note on the use of the Acrobat Reader - Make sure to open themenu item File/Preferences/General and uncheck the box Open Cross-Doc Links in Same Window. This will ensure that the Document opensin a separate window from the Report. Also click the button Shownavigation pane to put the Bookmarks and Thumbnails for navigation atthe left edge of the screen.

"HVOF ApplicationsListing SWA.PDF"
http://www.adobe.com/


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TABL E OF CONTENTS

Executive Summary........................................................iAcknowledgements ......................................................ivHow to use this report ...................................................vTable of Contents .........................................................viIndex of Tables.............................................................xvIndex of Figures..........................................................xixTable of Documents..................................................xxiiiTable of Acronyms ...................................................xxvi1. Introduction.............................................................................. 1

1.1. Documents........................................................................... 2

1.2. Recent data on health effects of Cr6+.................................... 2

1.3. Progress in chrome replacement .......................................... 3

Part 1. Aerospace usage of chrome ............................62. Typical Chrome Plated Components ....................................... 6

2.1. New equipment usage.......................................................... 6

2.2. Overhaul and repair usage ................................................... 7

2.3. Landing gear components .................................................... 7

2.4. Hydraulic actuators............................................................... 9

3. Chrome replacement options and requirements .................... 103.1. Hard chrome replacement criteria....................................... 11

3.2. Thermal spray for hard chrome replacement ...................... 13


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Part 2. Overview of thermal spray .............................144. Principles of thermal spray..................................................... 14

4.1. Summary............................................................................ 14

4.2. Documents......................................................................... 14

4.3. General .............................................................................. 15

4.4. Thermal spray processes ................................................... 16

4.5. Factors determining coating properties............................... 18

4.6. Applications of common thermal spray coatings................. 19

4.7. Limitations of thermal spray................................................ 20

4.7.1. Line of sight issues.......................................................... 21

4.7.2. Heating issues................................................................. 21

4.7.3. Coating thickness............................................................ 21

5. Thermal spray coatings ......................................................... 235.1. Summary............................................................................ 23

5.2. Thermal spray materials..................................................... 23

5.2.1. General ........................................................................... 23

5.2.2. Powders frequently used for chrome replacement 26

5.3. Typical structural properties of thermal spray coatings ....... 27

5.4. Typical applications of thermal spray coatings.................... 29

6. Types of thermal spray processes ......................................... 316.1. Flame spray........................................................................ 31

6.2. Arc spray............................................................................ 31

6.3. Plasma spray...................................................................... 32

6.4. High velocity oxy-fuel (HVOF) spray and detonation gun.... 33

7. Thermal spray producibility .................................................... 347.1. Summary............................................................................ 347.2. Documents......................................................................... 34

7.3. Quality Control Of the Thermal Spray Process ................... 35

7.3.1. Choice of powder ............................................................ 35

7.3.2. General ........................................................................... 35

7.3.3. Metallography.................................................................. 37


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7.3.4. Hardness......................................................................... 39

7.3.5. Tensile/Adhesion............................................................. 40

7.3.6. Temperature monitoring .................................................. 40

7.3.7. Monitoring residual stress................................................ 43

7.4. Process optimization and control ........................................ 44

7.4.1. General ........................................................................... 44

7.4.2. Example 1 Optimization of WC-Co ............................... 46

7.4.3. Example 2 Optimization of WC-CoCr ........................... 48

7.5. Stripping............................................................................. 52

7.5.1. Documents...................................................................... 52

7.5.2. Stripping of WC-Co ......................................................... 53

7.5.2.1. Southwest Aeroservice.............................................. 53

7.5.2.2. Sulzer-Metco............................................................. 547.5.2.3. Lufthansa .................................................................. 55

7.5.2.4. Other specifications................................................... 55

7.5.3. Stripping of WC-CoCr...................................................... 56

7.5.4. Stripping of Tribaloy 400 ................................................. 56

7.5.5. Water-jet stripping........................................................... 57

7.6. Finishing............................................................................. 57

7.6.1. Documents...................................................................... 57

7.6.2. General requirements...................................................... 57

7.6.3. Specifying the surface finish............................................ 58

7.6.4. Superfinishing ................................................................. 61

7.6.5. Rig test experience.......................................................... 63

7.6.6. Flight experience............................................................. 64

7.7. Inspection........................................................................... 65

8. Thermal spray equipment ...................................................... 66

9. Thermal spray services.......................................................... 67

Part 3. Thermal Spray Data ........................................6910. Coating structure................................................................ 70

10.1. Summary............................................................................ 70


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10.2. Documents......................................................................... 70

10.3. General .............................................................................. 71

10.4. Microstructure..................................................................... 71

10.4.1. General Description and Test Methods ........................ 71

10.4.2. Microstructural Features .............................................. 73

10.4.2.1. Porosity/Voids ......................................................... 73

10.4.2.1.1. Comparison of Porosity vs. Particle Velocity ..... 73

10.4.2.2. Matrix/Carbide Phases/Composition........................ 74

10.4.2.3. Transverse Cracks .................................................. 76

10.4.3. General trend of microstructural features ..................... 76

10.5. Phase Determination and Effect ......................................... 76


10.5.2. Phase Determination and Effect Results ...................... 7710.5.2.1. Carbide Phase Comparison vs. Process Type......... 77

10.5.2.2. Carbide Degradation Indexing................................. 79

10.5.3. General Trend of Carbide Phase Distribution............... 79

11. Coating properties.............................................................. 8111.1. Summary............................................................................ 81

11.2. General Background........................................................... 81

11.3. Hardness............................................................................ 82

11.3.1. Documents................................................................... 82


11.3.3. Hardness Results......................................................... 82

11.3.4. General Trend of Hardness Results............................. 85

11.4. Adhesion ............................................................................ 85

11.4.1. Documents................................................................... 85


11.4.3. Tensile/Adhesion Results............................................. 86

11.4.4. General Trend of Tensile Results................................. 86

11.5. Residual Stress .................................................................. 86

11.5.1. Documents................................................................... 86


11.5.3. Residual Stress Results ............................................... 89

11.5.3.1. Almen strip .............................................................. 89


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11.5.3.2. Almen/Residual Stress Comparison ........................ 90

11.5.3.3. Modified Layer Removal Technique ........................ 93

11.5.3.4. Residual Stress by X-ray Diffraction ........................ 95

11.5.3.5. Residual Stress by Neutron Diffraction.................... 96

11.5.4. General Trend of Residual Stress Results ................... 98

12. Coating performance.......................................................... 9912.1. Summary............................................................................ 99

12.2. General Background......................................................... 100

12.3. Documents....................................................................... 100

12.4. Test Protocol Summaries ................................................. 101

12.4.1. Start-up test Protocol ................................................. 101

12.4.2. JTP for Landing Gear................................................. 102

12.4.3. Other Protocols.......................................................... 102

12.5. Corrosion.......................................................................... 103

12.5.1. Documents................................................................. 103

12.5.2. Corrosion Test Methods............................................. 104

12.5.2.1. Atmospheric Methodology..................................... 104

12.5.2.2. Simulated Cabinet Testing..................................... 104

12.5.3. Corrosion Data........................................................... 108

12.5.3.1. Simulated Cabinet Results from Lufthansa............ 108

12.5.3.2. Cabinet and Atmospheric Testing - HCAT............. 111

12.5.3.2.1. ASTM B117 Salt Fog Testing.......................... 111

12.5.3.2.2. GM 9540P/B Testing....................................... 114

12.5.3.2.3. Atmospheric Testing ....................................... 114

12.5.3.2.4. Interpretation of results.................................... 115

12.5.3.3. Electrochemical Testing of Carbide Coatings ........ 115


12.5.3.4. Corrosion Work Planned in JTP Landing Gear ...... 117

12.5.4. General Trend of Corrosion Results........................... 118

12.6. Fatigue ............................................................................. 118

12.6.1. Documents................................................................. 118

12.6.2. General Description and Test Method........................ 119

12.6.3. Fatigue Results.......................................................... 123

12.6.3.1. Comparison of Hard Chrome vs. HVOF WC-Co and


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T400...................................................................... 123

12.6.3.2. Comparison of Hard Chrome vs. HVOF WC-Co forLanding Gear......................................................... 127

12.6.3.3. Comparison of Hard Chrome vs HVOF WC-CoCr . 132

12.6.3.4. Other ..................................................................... 13412.6.3.5. Comparative Study of Compressive Stress Effects on

Fatigue for HVOF .................................................. 134


12.6.4. General Trend of Fatigue Results .............................. 137

12.7. Wear Erosion, Abrasion, Sliding, Fretting ...................... 138

12.7.1. Documents................................................................. 138

12.7.2. General Description and Test Methods ...................... 139

12.7.3. Test Methods............................................................. 141

12.7.3.1. Erosion Testing per ASTM G 76............................ 141

12.7.3.2. Abrasion Testing ................................................... 142

12.7.3.3. Sliding/Fretting Wear Methods .............................. 142

12.7.4. Wear Results ............................................................. 143

12.7.4.1. ASTM G 65 Erosion Testing.................................. 143


12.7.4.2. ASTM G 76 Abrasion Testing................................ 145


12.7.4.3. Other Abrasion Tests............................................. 147

12.7.4.4. Sliding and Fretting Wear Results ......................... 148

12.7.4.4.1. DARPA program GEAE/NU.......................... 148

12.7.4.4.2. JTP for Landing Gear...................................... 150

12.7.5. General Trend of Wear Results.................................. 151

12.8. Impact .............................................................................. 152

12.8.1. General Description and Test Methods ...................... 152

12.8.2. Impact Test Results ................................................... 152

12.9. Hydrogen Embrittlement................................................... 15312.9.1. General Description and Test Methods ...................... 153

12.9.1.1. Embrittlement Testing:........................................... 153

12.9.2. Lufthansa embrittlement tests .................................... 153

12.9.3. Hydrogen Embrittlement Tests Planned - HCAT ........ 154

12.9.4. General Trend of Hydrogen Embrittlement Results ... 154


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12.10. Creep ............................................................................ 155

12.10.1. General Description and Test Methods...................... 155

12.10.2. Documents................................................................ 155

12.10.3. Creep Testing Results............................................... 156

12.10.3.1.Results for HVOF WC-Co and T400...................... 156

12.10.3.1.1. Test conditions.............................................. 156

12.10.3.1.2. Results.......................................................... 157

12.10.3.1.3. Interpretation of results.................................. 157

12.10.4. General Trend of Creep Results................................ 157

13. System performance ........................................................ 15813.1. Summary.......................................................................... 158

13.2. Rig tests ........................................................................... 159

13.2.1. Hydraulic Seals Green, Tweed Phase 2 hydraulic rigtest ........................................................................... 159

13.2.1.1. Documents............................................................ 159

13.2.1.2. Test Description .................................................... 159

13.2.1.3. Test Conditions ..................................................... 159

13.2.1.4. Results .................................................................. 160

13.2.1.5. Interpretation of Results ........................................ 161

13.2.1.6. Comments............................................................. 162

13.2.2. Landing Gear Pins Boeing landing gear rig test ...... 163

13.2.2.1. Documents............................................................ 163

13.2.2.2. Test Conditions ..................................................... 163

13.2.2.3. Results .................................................................. 164

13.2.2.4. Interpretation of results.......................................... 164

13.2.2.5. Comments............................................................. 164

13.2.3. Rig tests under development Messier-Dowty .......... 164

13.3. Flight tests........................................................................ 165

13.3.1. Lufthansa................................................................... 16513.3.1.1. Documents............................................................ 165

13.3.1.2. Test Conditions ..................................................... 165

13.3.1.3. Results .................................................................. 166


13.3.1.5. Comments............................................................. 166


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13.3.2. Delta .......................................................................... 166

13.3.2.1. Test Conditions ..................................................... 167

13.3.2.2. Results .................................................................. 169


13.3.2.4. Comments............................................................. 170

13.3.3. F-18 landing gear repair............................................. 170

13.3.4. Flight tests under way or under development............. 171

Part 4. Specifications and qualified components...17214. Specifications and standards for thermal spray ................ 172

14.1. Documents....................................................................... 172

14.2. Boeing thermal spray specs method, powder, grinding.. 172

14.2.1. Boeing Thermal Spray Spec BAC 5851 .................. 172

14.2.2. Boeing Powder Spec BMS 10-67............................ 174

14.2.3. Boeing Grinding Spec BAC 5855 ............................ 174

14.3. Hamilton-Sundstrand HS 4412 ...................................... 174

14.4. Society of Automotive Engineers - AMS 2447 .................. 174

14.5. American Welding Society AWS C.2-19-XX .................. 175

14.6. AMS standards under development.................................. 176

15. Qualified Thermal Sprayed Airframe Components............ 17715.1. Documents....................................................................... 177

15.2. Usage of thermal spray in Gas Turbine Engines............... 177

15.3. Summary of thermal spray coatings on non-enginecomponents ................................................................. 179

15.4. Boeing qualified thermal sprayed components .............. 180

15.5. Landing gear .................................................................... 181

15.5.1. OEM Production - Boeing 767-400 landing gear ........ 181

15.5.2. Flight tested landing gear repair - Canadian F-18 MLGaxle........................................................................... 183

15.5.3. Other qualified landing gear applications.................... 184

15.5.4. Boeing overhaul manual revision ............................... 184

15.5.5. Delta Airlines qualified landing gear repair Boeing 737,757, 767 ................................................................... 185

15.5.6. Qualified landing gear repair ...................................... 186


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15.6. Hydraulics ........................................................................ 186

15.6.1. P&W F-119 engine convergent nozzleactuator .................................................................... 187

15.6.2. Flight test Sikorsky CH-53 blade damper ................ 187

15.7. Production - Flap and slat tracks ...................................... 18815.7.1. OEM tracks - Boeing.................................................. 188

15.7.2. OEM tracks - Bombardier........................................... 188

15.7.3. Flap track repair Bombardier Dash 8....................... 189

15.7.4. O&R of tracks Boeing and other aircraft.................. 190

15.8. Other components............................................................ 191

References .................................................................193


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INDEX OF TABLES

Table 1. Hard Chrome Alternatives Team members (full list available onHCAT web site). ............................................................................... 4

Table 2. Some typical OEM chrome plated components......................... 6

Table 3. Some differences between OEM and O&R chromereplacement.................................................................................... 10

Table 4. Hard chrome replacement criteria. .......................................... 12

Table 5. Typical characteristics of thermal spray coating processes. .... 17

Table 6. Some fundamental terms that define the quality of thermal spraycoatings.......................................................................................... 19

Table 7. Some common thermal spray coatings, their structure,performance, and applications........................................................ 20

Table 8. Some major thermal spray powder classifications................... 24

Table 9. Important parameters defining thermal spray powders andelectric arc wire............................................................................... 25

Table 10. Examples of thermal spray powder used in chromereplacement operations. ................................................................. 26

Table 11 Comparison of thermal spray coating processes generalproperties. ...................................................................................... 28

Table 12. Comparison of thermal spray coating processes - permeability,thickness. ....................................................................................... 29

Table 13. Some applications of thermal spray coatings.. ...................... 30

Table 14. Producibility summary and links. ........................................... 34

Table 15 Commonly Used Quality Control Tests................................... 36

Table 16 Common Characteristics Evaluated in MetallographicSpecimens...................................................................................... 38

Table 17. Thermal spray process parameters....................................... 45

Table 18. Design of Experiment analysis tool. ...................................... 47

Table 19 Response vs. Coating Property............................................. 48

Table 20. Comparison of hydrogen versus propylene DOE. ................. 48

Table 21. Electrolytic stripping method for HVOF WC-Co (CourtesySouthwest Aeroservice).................................................................. 53

Table 22. Electrolytic stripping method for HVOF WC-Co (CourtesySulzer Metco). ................................................................................ 54

Table 23. Electrolytic stripping method for aged HVOF WC-Co(Courtesy Lufthansa). ..................................................................... 55

Table 24. Electrolytic stripping method for "new" HVOF WC-Co (Courtesy


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Lufthansa). ..................................................................................... 55

Table 25. Electrolytic stripping method for HVOF WC-Co (NTS/NADEPCherry Point). ................................................................................. 56

Table 26. Seal life in HVOF-WC-Co sprayed landing gear.18,................ 64

Table 27. Qualified providers for Boeing 5851 thermal spray coatings, asof June 2000 (Source, Boeing Aircraft Corporation)........................ 67

Table 28. Common microstructural Characteristics Observed in TungstenCarbide Materials. .......................................................................... 72

Table 29. Features seen in Figure 35. .................................................. 75

Table 30. Physical properties of coatings produced by different guns... 78

Table 31. Effect of Gas Flows and Cooling Gases on Retained Carbon........................................................................................................ 78

Table 32. Retained C and XRD phases. ............................................... 78

Table 33. Microhardness for various HVOF coatings and equipment

(Courtesy Praxair Surface Technology). ......................................... 83

Table 34. Comparison of Microhardness Values and Resultant Variation(Courtesy Sulzer Metco and SUNY Stony Brook). .......................... 84

Table 35. Qualitative techniques for measuring residual stress............. 88

Table 36. Common quantitative residual stress measurement techniques........................................................................................................ 89

Table 37. Zone analysis of thermal spray coatings. .............................. 92

Table 38. WC coating system designations for Document 24. .............. 93

Table 39. Comparison of Residual Stress by Varied Techniques.......... 96

Table 40. Experimental set-up for neutron diffraction............................ 96

Table 41. Summary of performance tests. ............................................ 99

Table 42. Chemistry of Tribaloys. ....................................................... 101

Table 43. Materials and heat treats for HCAT Landing Gear JTP. ...... 102

Table 44 Common Corrosion Testing Methods................................... 104

Table 45 GM9540 Protocol for Corrosion testing. .............................. 106

Table 46. Visual ranking criteria (ASTM B537-70). ............................. 107

Table 47. Coatings tested (Lufthansa). Note: 25m+0.001................ 109

Table 48. Summary of corrosion ratings for coatings tested by Lufthansa...................................................................................................... 110

Table 49. Coatings and substrates - HCAT corrosion testing.............. 111

Table 50. Corrosion of 4340 steel with HVOF and Cr coatings -appearance and protection rankings............................................. 113

Table 51. GM9540P/B corrosion of 4340 steel with HVOF and Crcoatings - appearance and protection rankings............................. 113


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Table 52. HVOF coatings used for Comparison of ElectrochemicalCorrosion Potential. ...................................................................... 116

Table 53. HCAT/C-HCAT corrosion test matrix for landing gear steelsand coatings. ................................................................................ 117

Table 54. Fatigue testing variables. .................................................... 122

Table 55. Materials and Substrates in Study....................................... 123

Table 56 Fatigue Test Parameters...................................................... 123

Table 57. Fatigue Matrix for Initial Validation ...................................... 124

Table 58. Substrate and coating materials - landing gear JTP. ........... 128

Table 59. Test conditions for landing gear JTP................................... 128

Table 60. Tungsten Carbide Coating System Designations (Volvo).... 135

Table 61. Fatigue Test Parameters for Volvo Evaluation .................... 136

Table 62. Four Primary Wear Mechanisms......................................... 140

Table 63. Erosion Results as Conducted By Praxair........................... 144

Table 64. ASTM G76 data from Praxair. ............................................. 146

Table 65. ASTM G76 Data from NRC. ................................................ 146

Table 66. ASTM G76 Data from NRL and Sulzer Metco. .................... 147

Table 67. Average wear coefficients, K, expressed in units of 10-4 mm3/N-m, for the various coating/substrate combinations. ....................... 148

Table 68. Fretting test parameters. ..................................................... 149

Table 69. Wear test variables for DOE factors. ................................... 151

Table 70. Creep test parameters ........................................................ 156

Table 71. Summary of rig and flight testing data. ................................ 158

Table 72. Hydraulic test conditions. .................................................... 159

Table 73. Stroke and frequency profile for hydraulic tests................... 160

Table 74. Military flight tests of HVOF-coated components................. 171

Table 75. Boeing thermal spray coating types. ................................... 173

Table 76. AMS 2447 HVOF Coating specifications. ............................ 175

Table 77. Summary of thermal spray-qualified non-engine components.(Click on links to access data directly.) ......................................... 179

Table 78. Summary of Boeing components specified for thermal spray...................................................................................................... 180

Table 79. Other landing gear components qualified for OEM HVOF WC-Co (Courtesy Southwest Aeroservice). ......................................... 184

Table 80. Landing gear components commonly repaired with HVOF WC-Co (Courtesy Southwest Aeroservice). ......................................... 186

Table 81. Flap and slat tracks specified for thermal spray coating with


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Super D-gun WC-18Co (Courtesy Boeing). .................................. 189

Table 82. Bombardier Dash 8-100, -200, -300 flap tracks qualified forHVOF repair (Courtesy Vac Aero). ............................................... 190

Table 83. Common flap/slat track repairs using HVOF WC-Co (CourtesySouthwest Aeroservice)................................................................ 191

Table 84. Other OEM HVOF WC-Co applications (Courtesy SouthwestAeroservice). ................................................................................ 192

Table 85. United Airlines O&R components qualified for HVOF in place ofchrome plate................................................................................. 193


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INDEX OF FIGURES

Figure 1. Boeing 737 nose landing gear inner cylinder. Shiny areas arechromed - piston and four axle journals (Courtesy Sulzer Metco). .... 8

Figure 2. Boeing 767 main landing gear (Courtesy Sulzer Metco). ......... 8

Figure 3. F-18 main landing gear Oleo Attach Pin (Courtesy Boeing). .... 9

Figure 4. F/A-18 E/F aileron servocylinder, manufactured by HR Textron(Courtesy Boeing)............................................................................. 9

Figure 5. Thermal spray process schematic (left); close-up view ofsurface (right). ................................................................................ 15

Figure 6. Types of thermal spray processes. Types covered in this reportshown in green.8 ............................................................................. 16

Figure 7. Structure of Thermal Spray Deposit at 100-500X.8................. 18

Figure 8. Example of powder definition for sintered irregularly shaped88/12 Tungsten Carbide Cobalt powder.......................................... 27

Figure 9. Components of a typical plasma spray system. ..................... 32

Figure 10. Typical HVOF coating cross sections; Ni-Al left (200x), WC-Coright (500x). (Courtesy Praxair-TAFA)............................................ 38

Figure 11 Tensile Assembly from ASTM C-633 .................................... 40

Figure 12. Typical non-contact temperature arrangement for HVOF..... 41

Figure 13 Typical Temperature Plot From a Spray Cycle (J. Schell,GEAE, Courtesy HCAT). ................................................................ 42

Figure 14. Almen N Test Strip. ........................................................... 43Figure 15. Almen holding fixtures (Electronics Inc.). ............................. 44

Figure 16. Almen measuring instrument (Electronics Inc). .................... 44

Figure 17. Kinetic versus thermal energy for the main thermal spraytechnologies. .................................................................................. 46

Figure 18. Best propylene results. Degradation index = 4.25. .............. 49

Figure 19. Best hydrogen results. Degradation index = 3.46................ 49

Figure 20. Graph showing the temperature/velocity profile with varied fueltypes............................................................................................... 50

Figure 21. Microstructure/morphology of selected powders. ................. 51

Figure 22. Particle size distribution for the three best powders. ............ 51

Figure 23. Typical surface profile. ......................................................... 59

Figure 24. Three different surfaces with the same Ra........................... 60

Figure 25. Other surface roughness parameters................................... 60

Figure 26. Definition of bearing ratio. .................................................... 61


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Figure 27. Effect of various finishing methods on an HVOF coating at175x (Courtesy Supfina). ................................................................ 62

Figure 28. Surface finishes obtained on Chrome and HVOF WC-CoCr byvarious finishing methods.18............................................................ 63

Figure 29. Sulzer Metco F210 ID plasma spray gun (Courtesy Sulzer

Metco). ........................................................................................... 66

Figure 30. HVOF spraying of WC-CoCr on landing gear with TAFA gun(Courtesy Praxair-TAFA). ............................................................... 66

Figure 31. Northwest Mettech Axial III tri-electrode plasma system(Courtesy Northwest Mettech).. ...................................................... 66

Figure 32. Stellite Jet-Kote HVOF gun (Courtesy Deloro Stellite).......... 66

Figure 33. Comparison of porosity at 200x and 1000x magnification. ... 73

Figure 34. Relationship between velocity and porosity.......................... 74

Figure 35. Comparison of Carbide Distributions in 88-12 WC-Co (left) vs.

83-17 WC-Co (right) at 500X (Courtesy Praxair/TAFA)................... 74Figure 36. Microstructure of WC-CoCr 1000X....................................... 75

Figure 37. Transverse cracking in plasma sprayed carbide coatings.25. 76

Figure 38. X-ray diffraction plot of powder(lower curve) and coating(upper curve). ................................................................................. 77

Figure 39. Comparison of carbide content in as-sprayed A-12 (12%cobalt ). Hybrid 2600 gun (left), air-cooled DiamondJet (right). ...... 79

Figure 40. Tensile assembly from ASTM C-633.................................... 85

Figure 41. Stress as a function of coating thickness for HVOF WC-CoCr.

....................................................................................................... 90Figure 42. Almen strip stress measurement.......................................... 91

Figure 43. Average residual stress as a function of spray distance....... 91

Figure 44. Average residual stress as a function of powder feed rate. . 92

Figure 45. Bend test technique, evaluation criteria, results. .................. 94

Figure 46. Typical stress profile for modified layer removal technique. . 95

Figure 47. Air Plasma Spray residual stress pattern. ............................ 97

Figure 48. Wire Arc Spray residual stress pattern. ................................ 98

Figure 49. HVOF Spray residual stress pattern..................................... 98

Figure 50. B117 Appearance Rankings for coatings on 4340 highstrength steel, PH13-8Mo stainless steel, and 7075 Al. ................ 112

Figure 51. GM9540P/B Appearance Rankings for coatings on 4340 highstrength steel, PH13-8Mo stainless steel, and 7075 Al. ................ 112

Figure 52. 4340 steel 18-month beach exposure tests, with and withoutscribing......................................................................................... 114


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Figure 53. 7075 Al 18-month beach exposure samples with and withoutscribing......................................................................................... 115

Figure 54. Corrosion Current for an Aerated 0.1 N HCl Solution.40 ..... 117

Figure 55. Typical hourglass-shaped fatigue bar................................. 121

Figure 56. Typical smooth fatigue bar................................................. 121Figure 57. Flat Kb fatigue bar.............................................................. 122

Figure 58. Comparison of Fatigue Data on Smooth Bars for 4340...... 125

Figure 59. Comparison of fatigue data on Kb bars for 4340................ 125

Figure 60. Fatigue of coated 4340 steel - hourglass samples. ............ 126

Figure 61. Fatigue Results for HVOF and Chrome on 7075 Aluminum127

Figure 62. Fatigue Curve for 300M with .24dia. hourglass tested in air coating thickness 0 .003. ............................................................. 129

Figure 63. Fatigue Curve for 300M with .24dia. hourglass comparing air

results with samples tested in NaCl and .003 Coating Thickness.130Figure 64. Fatigue Curve Comparing Thickness Effects 0.003 (.250

dia.) vs. 0.010 (.500 dia.) on 4340 using hourglass configurationtested in air................................................................................... 131

Figure 65. Fatigue of HVOF-coated and chrome plated high strengthsteels, Kt=1.5, Boeing qualification testing. (Courtesy EngelhardSurface Technology)..................................................................... 133

Figure 66. Comparison of fatigue for chrome and HVOF WC-CoCrdeposited with Jet Kote and Diamond Jet guns. (CourtesySouthwest Aeroservice.)............................................................... 133

Figure 67. Comparison of Residual Stress and Resistance of Coating toCrack Initiation.............................................................................. 136

Figure 68. Comparison of Final Fatigue Life with Residual Stress ...... 137

Figure 69. Typical Set-up of ASTM G76 erosion test. ........................ 141

Figure 70. ASTM G 76 set-up. ............................................................ 142

Figure 71. Schematic of Sliding Wear Apparatus for hydrualics......... 143

Figure 72. Side view of fretting apparatus........................................... 143

Figure 73. Erosion Results As Conducted By Stony Brook/Sulzer Metco..................................................................................................... 144

Figure 74. Comparison of HVOF Processes and WC-Co Powders..... 148Figure 75. Fretting wear of hard chrome, HVOF WC-17Co, and HVOF

T400. (Note the zero wear measurement resulted from materialtransfer from the uncoated block to the coated shoe, protecting itfrom wear.) ................................................................................... 150

Figure 76. Average creep measured by direct micrometer readings. .. 157

Figure 77. Cumulative hydraulic fluid leakage in rig tests.................... 161


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Figure 78. Seal wear during hydraulic rig tests..................................... 162

Figure 79. F/A-18E/F main landing gear, showing locations of HVOF-coated pins....................................................................................... 164

Figure 80. Landing gear components HVOF sprayed for flight testing byDelta Airlines (sprayed areas numbered). (Courtesy Delta Airlines.)

......................................................................................................... 168

Figure 81. Boeing 737 nose landing gear inner cylinder undergoing flighttest inspection at Delta Airlines (Courtesy Delta Airlines). ............. 168

Figure 82. Boeing 757 axle sleeves HVOF-sprayed with WC-CoCr(Courtesy Delta Airlines).................................................................. 169

Figure 83. Canadian F-18 main landing gear polygon repair (CourtesyMessier-Dowty)................................................................................ 171

Figure 84. Thermal spray coatings used in a typical gas turbine engine.(Courtesy GE Aircraft Engines)

50.................................................... 178

Figure 85. Boeing 767-400 with HVOF coated landing gear. ............... 181

Figure 86. Boeing 767-400 main landing gear (Courtesy Sulzer Metco).......................................................................................................... 181

Figure 87. Boeing 767 main landing gear axle (part # 2207-85-10),showing HVOF areas (engineering note 3). (Courtesy Sulzer Metco.)......................................................................................................... 182

Figure 88. Boeing 767-400 main landing gear inner cylinder (Part # 2207-4-10) with asterisks showing locations of HVOF coatings (CourtesySulzer Metco.).................................................................................. 183

Figure 89. Canadian F-18 main landing gear axle (Courtesy Messier-Dowty).............................................................................................. 183

Figure 90. Repair area of F-18 main landing gear polygon (CourtestyMessier-Dowty)................................................................................ 184

Figure 91. HVOF WC-Co repair of Boeing 737 nose landing gear innercylinder (Courtesty Southwest Aeroservice). .................................. 186

Figure 92. Thermal spray actuator coating system developed byPraxair.............................................................................................. 187

Figure 93. CH-53 helicopter (Sikorsky). ................................................ 188

Figure 94. Bombardier Q-400 (Courtesy Bombardier.)......................... 189

Figure 95. Typical flap track - Bombardier Dash 8 (Courtesy Vac Aero,Canada). .......................................................................................... 190

Figure 96. HVOF-sprayed Dash 8 flap track. Coated areas are dark.(Courtesy, Vac Aero, Canada.) ....................................................... 191

Figure 97. Flap and slat track repair by HVOF (Southwest Aeroservice).......................................................................................................... 191

Figure 98. Boeing 737 nose landing gear lower bearing shock strut, Part# 69-76508. HVOF WC-Co coated and super finished. (CourtesySulzer Metco.).................................................................................. 192


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TABL E OF DOCUMENTS

Document 1. Hard Chrome Coatings - Advanced Technology for WasteElimination, DARPA Grant MDA972-93-1-0006, Keith O. Legg, Jerry

Schell, George Nichols, Robert Altkorn............................................. 2Document 2. Lung Cancer Among Workers in Chromium Chemical

Production, Herman J. Gibb et. al., American Journal of IndustrialMedicine, 38, 115-126 (2000). (Courtesy of the authors and

American Journal of Industrial Medicine.) ......................................... 2

Document 3. Clinical Findings of Irritation Among Chromium ChemicalProduction Workers, Herman J. Gibb et. al., American Journal ofIndustrial Medicine, 38, 127-131 (2000). (Courtesy of the authorsand American Journal of Industrial Medicine.) .................................. 2

Document 4. JSF Phase 1 Report: Chrome Replacements for Internalsand Small Parts. (Rowan Technology Group)................................. 14

Document 5. JSF Phase 2 Report: Optimal Chrome ReplacementTechnologies for Internal Diameters and Heat-Sensitive Parts.(Rowan Technology Group)............................................................ 15

Document 6. Common thermal spray powder types.............................. 25

Document 7. Test standardization: a Key Tool in Coating SystemImplementation (Courtesy Sauer Engineering, Gorham AdvancedMaterials)........................................................................................ 34

Document 8. Training in Coating Evaluation Techniques: a UniqueApproach for Discussion (Courtesy Sauer Engineering). ................ 34

Document 9. The Use of Metallographic Standards in Calibration of thePolishing Process (Courtesy Sauer Engineering). .......................... 34

Document 10. Metallographic Preparation of Thermal Spray Coatings:Coating Sensitivity and the Effect of Polishing Intangibles (CourtesySauer Engineering)......................................................................... 35

Document 11. Tensile Bond Variance of Thermally Sprayed Coatingswith Respect to Adhesive Type. ..................................................... 35

Document 12. Almen Strips and Temperature Measurement DuringHVOF Processing (Courtesy, Sauer Engineering). ......................... 35

Document 13. Design of Experiment for HVOF WC-Co process(Courtesy HCAT, www.hcat.org)..................................................... 35

Document 14. Summary of DOE results for optimization of HVOF WC-CoCr (Courtesy NRC Montreal and C-HCAT). ................................ 35

Document 15. NTS Stripping Report,PDF. ........................................... 52

Document 16. NDCEE Evaluation of Stripping Methods. ..................... 52

Document 17. Stripping of WC Coatings from Aermet 100, SouthwestAeroservice, Menasco, Carpenter Technology (Courtesy SouthwestAeroservice). ................................................................................. 52


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Document 18. Surface Metrology Guide (Courtesy Precision Devices,Inc.). .............................................................................................. 57

Document 19. Superfinishing of Hard Chrome and HVOF CoatedWorkpieces (Courtesy Supfina and Gorham Advanced Materials). 57

Document 20. Surface Finishing of Tungsten Carbide Cobalt Coatings, J.

Nuse, J. Falkowski. ........................................................................ 57

Document 21. Barkhausen Noise as a Quality Control Tool (CourtesyStresstech Inc., Finland). ............................................................... 57

Document 22 Evaluation of Four High Velocity Thermal Spray GunsUsing WC-10Co-4Cr Cermets (Courtesy of J.G. Legoux,B.Arsenault, C. Moreau, V. Bouyer, L. Leblanc). ............................ 70

Document 23. Fracture Toughness of HVOF Sprayed WC-Co Coatings(Courtesy of S. De Palo, et al). ...................................................... 70

Document 24. Tungsten Carbide-Cobalt Coatings for IndustrialApplications (Courtesy of M. Dorfman, J Defalco, J. Karthikeyan). 70

Document 25. A Critical Evaluation of the Employment of MicrohardnessTechniques for Characterizing and Optimizing Thermal SprayCoatings 2000 (Courtesy of M. Factor and I. Roman, HebrewUniversity). .................................................................................... 82

Document 26 Behaviour of Tungsten Carbide Thermal Spray Coatings1995, J. Wigren et al....................................................................... 86

Document 27 An ASM Recommended Practice for Modified LayerRemoval Method (MLRM) to Evaluate Residual Stress in thermalSpray Coatings 2000, Ed Rybicki and ASM TSS Committee. ........ 86

Document 28 Properties of WC-Co Components Produced Using the

HVOF Thermal Spray Process 2000, J. Stokes and L. Looney. ..... 86Document 29 X-ray diffraction residual stress techniques, P.S. Prevey.

....................................................................................................... 86

Document 30 Processing Effects on Residual Stress in Ni+5%AlCoatings-Comparison of Different Spraying Methods 2000,J.Matejicek et al. ............................................................................ 87

Document 31 Residual Stress Measurement in Plasma SprayedCoatings by X-Ray Diffraction (Courtesy of J. Matejicek et al) 1997........................................................................................................ 95

Document 32 HCAT Test Protocol for Initial Work 1996 (Courtesy ofHCAT Team) ................................................................................ 100

Document 33 Joint Test Protocol (JTP) for Landing Gear 1998

(Courtesy of HCAT and CHCAT Teams) ...................................... 100

Document 34 Joint Test Protocol (JTP) for Propeller Hub Components2000 (Courtesy of HCAT, JG-PP, and C-HCAT Teams) .............. 100

Document 35 Joint Test Protocol (JTP) for Gas Turbine Engines 2000(Courtesy of HCAT and PEWG Teams......................................... 101


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Document 36. Report of Replacement of Chromium Electroplating UsingHVOF Thermal Spray Coatings AESF Plating Forum 1998 (Courtesyof Bruce Sartwell and HCAT Team). ............................................ 103

Document 37. Replacement of Chrome Plating by Thermal Spray Results of Corrosion Testing of HVOF Coatings 1996 (Courtesy of

Lufthansa). .................................................................................. 103Document 38. Replacement of chrome plating by thermal spray coatings

Summary of tests (Courtesy of Lufthansa). ............................... 103

Document 39 Performance of HVOF Sprayed Carbide Coatings inAqueous Corrosive Environments 2000 (Courtesy of S. Simard(NRC) et al). ................................................................................ 103

Document 40 Summary of 4340 Data from Initial HCAT Protocol(Courtesy of Phil Bretz Metcut) ..................................................... 118

Document 41 Summary of 7075 Al Data from Initial HCAT Protocol(Courtesy of Phil Bretz Metcut) ..................................................... 118

Document 42 Summary of 13-8 Stainless Data from Initial HCAT Protocol(Courtesy of Phil Bretz Metcut) ..................................................... 119

Document 43. HCAT landing gear JTP fatigue data - HVOF WC-Co on4340, 300M, AerMet 100 in air and NaCl solution......................... 119

Document 44 Advanced Thermal Spray Coatings for Fatigue SensitiveApplications (Courtesy of John Quets Praxair).............................. 119

Document 45 Compressive Creep Tests of Hard Chrome and HVOFcoatings 1998, J. Schell, GE Aircraft Engines............................... 155

Document 46. Evaluation of Chrome Rod Alternative Coatings, TonyDegennaro, Green Tweed, 1999................................................... 159

Document 47. F/A-18E/F Main Landing Gear HVOF-coated Pin Testingand Evaluation.............................................................................. 163

Document 48. Table of contents of BAC 5851 Thermal SpraySpecification, 2000 (Courtesy Boeing Aircraft Corp.). .................. 172

Document 49. Standards for the Thermal Spray Industry, Bhusari andSulit. ............................................................................................ 172

Document 50. HVOF WC aerospace applications for OEM and rebuild(Courtesy Southwest Aeroservice). .............................................. 177

Document 51. Thermal Spray Applications at GE Aircraft Engines(Dorothy Comassar, Courtesy GE Aircraft Engines). ................... 177

Document 52. OEM Approval for HVOF Wear Resistant and MCrAlYCoatings (Gary Naisbitt and Gorham Advanced Materials). .......... 177

Document 53. Replacement of Chromium Electroplating on Gas TurbineEngines. ....................................................................................... 177

Document 54. List of Boeing thermal sprayed parts (Courtesy, BoeingAircraft Corp). ............................................................................... 180


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TABLE OF ACRONYMS

AFRL Air Force Materials Lab (Dayton, OH)

ALC Air Logistics Center (Air Force maintenance depot)

AMS Aircraft Materials Specification (a specification of theSociety of Automotive Engineers)

APS, VPS Air Plasma Spray, Vacuum Plasma Spray

BFG B.F. Goodrich

C-HCAT Canadian Hard Chrome Alternatives Team

Cr6+

Hexavalent chrome

DARPA Defense Advanced Research Projects Agency

D-Gun Detonation gun (also Super D-Gun) high velocity

thermal spray method based on fuel detonation(proprietary to Praxair)

DND Department of National Defence (Canada)

DoD Department of Defense (US)

DOE Design of Experiment (statistically designed matrix ofexperiments used for process optimization)

EPA Environmental Protection Agency

ESTCP Environmental Security Technology CertificationProgram (funding HCAT)

GEAE General Electric Aircraft EnginesGTE Gas turbine engine

HCAT Hard Chrome Alternatives Team

HVOF High Velocity Oxy-Fuel thermal spray

ID Inside diameter

JG-PP Joint Group Pollution Prevention (DoD environmentalgroup assisting with qualifying clean processes)

JSF Joint Strike Fighter

JSF IPT Joint Strike Fighter Integrated Product Team

JTP Joint Test Protocol

NADEP Naval Aviation Depot (Navy Maintenance depot)

NAWC Naval Air Warfare Center

NDCEE National Defense Center for Environmental Excellence

NRC National Research Council of Canada


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NTS National Technical Systems, Inc.

O&R Overhaul and Repair

OD, ID Outside diameter, inside diameter

OEM Original Equipment Manufacturer

OSHA Occupational Health and Safety Administration

PC Personal computer

PEWG Propulsion Environmental Working Group (turbineengine environmental issues)

PVD Physical Vapor Deposition (vacuum coating depositionprocess)

P & W Pratt and Whitney

QPL Qualified Provider List

R&O Repair and Overhaul

SERDP Strategic Environmental Research and DevelopmentProgram (funding ID chrome replacements)

TPC Technology Partnerships Canada (funding C-HCAT)

WC Tungsten Carbide

WC-Co, WC-CoCr

Cobalt cemented WC (usually WC-17Co or WC-12Co)and cobalt-chrome alloy cemented WC (usually WC-10Co4Cr). (Percentages by weight.)