GE Aircraft Engines
Monday PM
Diffusion Coatings
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1
GE Aircraft Engines
Turbine Coatings Specifications
E50TF579
Metallographic Preparation and Evaluation of Turbine Airfoil Coatings.
E50TF75
Metallographic Evaluation of Evaporative Metallic Coatings.
E50TF192
Metallographic Evaluation of Vapor Deposited Coatings.
F50TFxxx
Coating Finish Specifications.
P1TF33
Preparation of Technical Plans For Coating Application.
P16TF9
Turbine Diffusion Coatings.
P16TF10
Turbine Overlay Coatings.
P29TF22
Acceptability Limits for Metallic Diffusion Coatings After Oxidation Testion.
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Overview of Turbine Coatings
GE Aircraft Engines
1.1 Diffusion (Al, Pt-Al, Chromides)
1.1.1 Process and Specification
•Aluminides = F50TF8, F50TF26, F50TF86
•Pt-Al
•Chromides = F50TF37/ F50TF82
1.2 Overlays
1.2.1 Process
• CoCrAlHf (LPPS)
• APS TBC
1.3 Physical Vapor Deposition
1.3.1 Process
• MCrAlY (PVD)
• TBC (PVD)
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Aluminide Coatings (Codep, Pt-Al)
GE Aircraft Engines
•Produced by diffusion process
•Coating present below and above original interface
•Non line of sight process
•Ni-Aluminide or Co-Aluminide coating brittle
•Brittle coating subject to chipping
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Codep Coating
GE Aircraft Engines
• GEAE developed and licensed pack aluminide coating
process. This is the only process that will meet GEAE’S
F50TF8 or F50TF86 coating specification requirements.
Test Requirements
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# Metallography
# Oxidation
# Composition
5
GE – VPA Coating
•
GE Aircraft Engines
GEAE developed vapor phase aluminide coating process.
Test Requirements
# Metallography
# Oxidation
# Composition
Oxidation Aluminide Coating
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Aluminide Coatings
GE Aircraft Engines
• Modified Aluminide (Platinum Aluminide)
- diffused aluminum and additional elements(s) into surface
- additional elements may be from co-deposition or from prior
or subsequent surface treatment
Test Requirements
# Metallography
# Oxidation
# Composition
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Diffusion Coating Processes
GE Aircraft Engines
• Pack Cementation (e.g. Codep, pack aluminide , pack chromide)
- surfaces to be coated are packed in direct contact with powders used to form
desired coating
• Above Pack / Vapor Phase (e.g. GE – VPA, vapor phase chromide)
- surfaces to be coated are placed in a retort containing the source material
- parts are not in direct contact with donor
• Chemical Vapor Deposition (CVD)
- surfaces to be coated are contained in a retort, coating gas is flowed into the
retort from a separate source
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Coating Process – Cementation Diffusion
GE Aircraft Engines
Cementation Diffusion process has many names; CODEP, Pack, Aluminide, Chromide to name a few.
Cementation coating process consist of hardware being packed into a closed box with a powders
mixture. The mixture must consist of a Source of Aluminum or Chromium, and Activator, and inert
filler or diluant as the remainder (Al2 O powder). The pack is loaded into a retort where it is heated in
an inert gas (Ar) or reducing gas (H2). Activity in the pack is not proportional to metal content in the
Pack, but is proportional to state of Al in the pack, (e.g. activity of Al> Ti C- Al> CoAl> NiAl).
Powder & Coating Applied
Powder Composition
Powder Specification
Coating Specification
Calcined Aluminum Oxide
Ammonium Fluoride
CODEP Powder
A50TF100, CL-B/C
A50TF101, CL-A
B50TF93, CL-B/C
F50TF8,CL-A/B/C/D and
F50TF86
Calcined Aluminum Oxide
Ammonium Chloride
Chromium Powder
A50TF100,CL-B/C
D4G2
B10D5
F50TF37, CL-A/B
Stainless Steel
Fusible Silicate
Molyebdenum Can
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Coating Process – Chemical Vapor Deposition
GE Aircraft Engines
Chemical Vapor Deposition process supplies gas-phase materials to surfaces that have been elevated to
the optimum temperature for a specific chemical reaction. As a result of the reaction, the coating element
or compound is deposited onto the surface.
CVD can be generated by two methods; 1) Above the pack or 2) Chemical gases in reactor furnace. GEAE typical uses this
process to coat internal passages of turbine hardware. The above the pack method is the typical process used by GEAE
because it is very similar to VPA process. The only exception is the hardware is not packed into the powder mixture, actually
the hardware is position above the powder mixture of pellets.
The CVD chemical reaction are nearly the same as VPA reactions. The reactor furnace process does not use powder or
pellets, gas-phases materials are run through an aluminum chloride generator, where the gas mixture is pumped into the
reactor furnace. The gas mixture is channeled to the hardware (internal or external), where the coating elements are
deposited on the hardware. The exhaust gases are expelled from the retort into a exhaust gas scrubber.
Powder & Coating Applied
Coating Specification
F50TF68, CL-C Aluminide Coating
F50TF82, CL-A Chromium Coating
Furnace
Gases
Chlorine Generator
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Reactor
Exhaust Scrubber
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Overlay Coatings
GE Aircraft Engines
• Two main application processes
- Low Pressure Plasma Spray (LPPS)
- Physical Vapor Deposition (PVD)
• Line of sight processes
• LPPS higher compositional control
• LPPS less subject to chipping
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Overlay-LPPS
GE Aircraft Engines
Processes that will meet GEAE’S LPPS coating specification
requirements.
Tests
• Metallography
• Composition
• Oxidation
Shrouded Plasma PBC22
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Coating Process – Low Pressure Plasma
GE Aircraft Engines
Low Pressure Plasma (LPP) spraying, utilizes a plasma torch in an evacuated chamber substantially reducing
the degree of oxidation which occurs during deposition as a result of air(oxygen) in the plasma stream. The chambers
operates at pressures approximating 40 torr in a dynamically pumped system. The environmental pressure
is usually controlled by adding argon gas to the chamber. The normal range of conventional plasma feet per
seconds is 800-1000 ft./sec. Plasma gas velocity approaches Mach 3 in the lower pressure environment.
The oxygen content of a LPP deposits can be in the order of 150-750 ppm compared to 10,000 ppm or more
for conventional air plasma sprayed coatings.
Powder Feeder
Gun Manipulator
Heat Exchanger
Power Supplies
Mist Separator
Plasma
Gun
Vacuum Chamber
Plasma System
Vacuum Pump
Powder & Coating Applied
Powder Composition
Powder Specification
Coating Specification
Co-Ni-Cr-Al-Y
Co-Cr-Al-Hf
Co-Cr-Al-Hf-Pt
B50TF195, CL-A
B50TF201, CL-A
B50TF194, CL-A
F50TF51, CL-A
F50TF53, CL-A
F50TF52, CL-A
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Coating Process – Physical Vapor Deposition
GE Aircraft Engines
Physical Vapor Deposition (PVD) process used by GEAE primarily uses a Electron Beam source to generate
evaporation of the single bar-fed source. Evaporation in a high vacuum is a directional phenomena. To coat
an object uniformly, it is necessary to articulate the specimen over the evaporant. Critical parameters to control
the evaporant are to maintain temperature and volume of pool constant and allow equilibrium in the molten
pool to occur. The coating occurs from condensation of the vapor onto the substrate, followed by film growth.
Ingot & Coating Applied
Ingot Composition
Ingot Specification
Coating Specification
Co-Cr-Al
Co-Cr-Al-Y
Ni-Cr-Al-Y
Fe-Cr-Al-Y
ZrO28% Y2O3
B50TF128, CL-C
B50TF128, CL-A
B50TF129, CL-A
B50TF127, CL-A
A50TF299, CL-A
F50TF16, CL-D
F50TF16, CL-B
F50TF16, CL-C
F50TF16, CL-A
F50TF73, CL-A
Process Formation & Environment
Vacuum Chamber
Load Lock
Electron Beam Gun
Ingot Feed
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Thermal Barrier Coatings
GE Aircraft Engines
• Ceramic coating (Top Coat)
• Ceramic Insulator
• Metallic Bond Coat
• Ceramic applied by Air Plasma Spray (APS)
or Physical Vapor Deposition (PVD)
• Ceramic coatings more subject to chipping
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TBCs, APS Thermal Barrier Coatings and Tests
GE Aircraft Engines
Process that will meet GEAE’S coating specification requirements.
Coatings
• LPPS Bond Coat + Aluminide – APS Yttria Stabilized
Zirconia
Tests
• Metallography
• Tensile
• Jets Test
• Thermal Cycling
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PVD Thermal Barrier Coatings and Tests
GE Aircraft Engines
Process that will meet GEAE’S coating specification requirements.
Coatings
• Thermal Barrier Coating
Tests
• Metallography
• Composition
• Furnace Cycling
TBC Spalled
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Metallographic Evaluation of Diffusion Coatings
2.1 Aluminides
•Type I and II microstructure
•Interface
•Layer lines
2.2 Pt-Al
•Evaluation to photo standards (phases)
Single Phase, Two Phase
•Interface
2.3 Chromides
•Microstructural features
•Alpha Cr criteria in F50TF82
•Interface
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GE Aircraft Engines
2.4 Requirements of P16TF9
2.5 Definition of microstructural features
(E50TF579)
2.6 Illustration of microstructural features
•Aluminide, PtAl
2.7 Oxidation Testing
•Requirements of P29TF22
•Definition of oxidation features and example
2.8 Composition Requirements
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General Requirements For Metallographic Evaluation of Diffusion Coatings
GE Aircraft Engines
Microstructure
Aluminide (F50TF8 / F50TF68)
• Type I (outward), Type II (inward)
(ratio of additive layer to diffusion zone can establish type)
• Blue zone thickness (print driven)
• Interface (coating-base metal): Linear sum of discontinuous voids, 5% max;
No interconnected voids permitted (voids connected by cracks or oxide)
• Photostandards: Reference Photos for Type I & II in E50TF579.
• Layer Lines: No continuous or intermittent areas permitted. Report layer lines to GE.
• No Delta Phase (Purple Zone) Permitted (F50TF68)
• Core Reaction Products are not of coating evaluation.
Platinum Aluminide (F50TF59)
• Class A: Pack Cementation (two phase structure)
• Class B: Vapor Phase (two phase structure)
• Class C: Vapor Phase (single phase structure)
• Interface: same criteria as Aluminide
• Photo standards: Acceptable, transitional* and rejectable (worst field of view rule)
• Layer Lines: Same criteria as Aluminide
*Transitional microstructure acceptable only when coating composition requirements are met.
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General Requirements For Metallographic Evaluation of Diffusion Coatings
GE Aircraft Engines
(cont’d)
Chromide (F50TF37 / F50TF82)
• Class A (low temperature); Class B (high temperature)
• Photostandards: Alpha chromide thickness in F50TF82 only
(no photostandard for F50TF37)
• Interface: same criteria as Aluminide
Thickness
• Average of ten equally spaced readings obtained in a specific order
and location as designated
• No individual reading shall be outside designated min./max. percentage
• Sum of additive layer and diffusion zone
Plating for Edge Retention
Total Thickness
Note: Do not measure
secondary fingers/diffusion
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P16TF9 – Diffusion Coating Process Requirements Specification
GE Aircraft Engines
Terms
Test Specimens:
Specimen Preparation:
Referee Measurement:
Thickness
- QC specimens shall be processed identically and coated with the parts they represent
and must be at least ½” wide. QC specimens shall have the same geometry, material, and
heat treatment as the parts being coated.
- Sample shall be mounted and polished so that the freshly cut cross section can be
evaluated, the coating is kept at least 85% intact, and the outer edge of the coating
is clearly defined.
- In the event the average thickness measurement does not meet the requirements. Two
additional series of ten measurements each may be taken at different locations around the
same metallographic specimen. Average thickness values of both series shall meet thickness requirements.
- Ten individual measurements of the total additive and diffusion
zone thickness shall be taken at approximately equal distances around the specimen.
Oxidation Test:
- Specimens shall meet the requirements of applicable class of P29TF22.
Diffusion Coating:
- Thickness shall be determined by the metallographic examination at a minimum
Sectioning
Dimensions
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Mid Tip
Spans of interest
For Cavity Cut-Ups
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Diffusion Coating Characteristics
GE Aircraft Engines
Microstructure Characteristics Definitions
Additive Layer
Alloy Depletion
- The portion of the coating above or below the original interface, excluding
the diffusion zone.
- A condition at or adjacent to the surface of a part wherein the material is
deficient in one or more elements of its normal composition. This is usually
due to elevated temperature reactions associated with the casting or heat
treating process.
Base Metal Attack
- An area of oxidation attack, including an oxide layer or depletion area,
which has penetrated into the substrate material.
Blue Zone
- A layer of blue coloration extending from the surface inward in an aluminide
coating (when examined un-etched) indicating that the aluminum
concentration in the Ni or Co.
- In a coating process which is periodically interrupted for heat treatments or
other processing operations, a quantity of coating material deposited before,
after, or between interruptions.
- A zone beneath the additive layer and adjacent to/near the substrate interface
containing a mixture of phases.
- An area of continuous oxidation attack, including oxide layer and
depletion layer, which has a depth equal to or less than its width.
Coating Layer
Diffusion Zone
Frontal Oxidation
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Diffusion Coating Characteristics
GE Aircraft Engines
Interface - As of this presentation a clear or singular definition of interface is unavailable.
GEAE is working on this issue. In a diffusion coating, an interface can exist at
various locations:
1. The original metal surface as defined by presence of the base metal carbide,
casting or process related oxides and imbedded grit particles.
2. Additive Layer - Diffusion zone.
3. Secondary Diffusion Zone - Base metal.
Plating
External Surface
(1 & 2)
Coating
WWWWW
/ / / / / / / / / / / / / / / / (3)
The location of the original metal surface is influenced by coating parameters,
service temperature and oxidation testing.
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Diffusion Coating Characteristics
GE Aircraft Engines
Microstructure Characteristics Definitions
Inward Coating
- Inward aluminum diffusion associated with high aluminum activity (Type II).
Layer Line
- The interface between two coating layers.
Microblister
- An outer platinum-rich layer
Mold Interaction
Products
- Base metal surface irregularities indigenous to the casting process
such as extraneous contaminates/impurities and oxides (ZrO2 globules and fingers).
Orange Zone
- A layer of orange/yellow coloration extending from the surface inward in an aluminide
coating (when examined un-etched) indicating that the aluminum concentration in
the Ni or Co.
Outward Coating
- Predominate outward substrate element diffusion (nickel) associated with low
aluminum activity (Type I).
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Diffusion Coating Characteristics
GE Aircraft Engines
Definitions:
Overcoat
- The application of a coating over a presently coated part or existing coating.
Oxide Layer
Line
- An oxide line not associated with the original interface and which may be either
intermittent or continuous.
Pocket
- An irregular shaped indication in the coating which has a maximum width
and a depth equal to or less than its width.
Predominant
Thickness
- The average equally spaced thickness measurements taken at about
equal distances around the periphery of the specimen.
Primary Surface - The primary surface of the part is the one having the most critical requirements
for protection. On blades, the airfoil shall be the primary surface unless otherwise
specified.
Recoat
- A coating over a part stripped of a previous coating.
Spatter/ Fissure - A droplet of coating material ejected from the source pool and deposited on the part
surface during the evaporative coating process.
Spike
- An elongated oxide indication in the coating which has a depth greater than its width.
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Diffusion Coating Characteristics
GE Aircraft Engines
Definitions:
*Type I Coating
- A coating on nickel base alloys formed by the surface deposition of aluminum and a
predominant diffusion of nickel outward from the substrate, and defined as all
coatings not meeting the requirements for a Type II coating.
*Type II Coating - A coating on nickel base alloys formed by the deposition of aluminum at the surface
and a predominate diffusion of aluminum into the substrate, and characterized by the
simultaneous occurrence of:
A) A fine grained additive layer with the average diameter of the grains or less and
extending from the surface to the diffusion zone.
B) A fine white precipitate in the additive layer.
C) Substrate carbides in the additive layer.
D) An additive layer to diffusion zone ratio greater than 2:1.
E) An additive layer aluminum content greater than specific% with an aluminum concentration gradient across the additive thickness of less than 5%.
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Type I & Type II
GE Aircraft Engines
Simple Aluminide Coating Microstructure
Blue Zone
Additive Layer
Predominant
Coating
Thickness
Additive Layer
Diffusion Layer
Diffusion Layer
Type II - (inward diffusion)
CoAl Microstructure
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Type I - (outward diffusion)
NiAl Microstructure
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Aluminide Coating – Mold Interactive Product
GE Aircraft Engines
Aluminide coating on surface of blade
Example where oxides on the cast surface have prevented coating diffusion.
Etchant: None
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Aluminide Coating - Layer Lines
GE Aircraft Engines
Unacceptable layer lines in aluminide coating, separation/spalling along layer line (LEFT)
Etchant: None
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GE Aircraft Engines
Modified Aluminide Coating Microstructure
White PtAl and Dark NiAl Phases
Additive
Layer
Diffusion Layer
Predominant
Coating
Thickness
Two Phase Platinum aluminide Microstructure
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Platinum Aluminide Microstructures
GE Aircraft Engines
Two Phase
Single Phase
Ni(Pt)Al
Diffusion
Zone
Platinum Aluminide Coating
With An Acceptable Microstructure
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Acceptable Microstructure for Class A and B
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Platinum Aluminide Microstructures
B
A
A
GE Aircraft Engines
B
C
D
D
Acceptable
A = Additive Layer
B = Two Phase Field in outer portion of additive layer
composed of white PtAl2 phase and dark NiAl
phase.
D = Diffusion Zone
Transition
A = Additive Layer
B = Vague two phase field in outer portion of additive
layer.
C = Fine white chromium rich precipitates in inner
portion of additive layer.
D = Diffusion Zone
GE photostandards of Acceptable (Figure 1) and Transition (Figure 3) Microstructures in
Platinum Aluminide.
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Platinum Aluminide Microstructures
B
GE Aircraft Engines
A
A
C
D
D
Rejectable
A = Additive layer
B = Continuous and almost complete white PtAl2 layer
near surface.
C = Predominant PtAl2 inner layer containing NiAl
D = Diffusion Zone
Rejectable
A = Additive layer of single phase dark NiAl
(Absence if PtAl2) with fine discrete white
chromium-rich precipitates.
D = Diffusion Zone
GE photostandards of Rejectable Microstructure (Figure 4 & 5) in
Platinum Aluminide.
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Platinum Aluminide Microstructure
GE Aircraft Engines
2Φ (Rich in Pt)
Original Surface
Pt – Aluminide Coating on trailing edge tip of blade
(2Φ outer layer has higher than normal Pt)
Etchant: None
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Vapor Phase Chromide Coating Microstructure
GE Aircraft Engines
Chromide
Coating
Acceptable Vapor Deposited Chromium Coating with an Alpha Chromium layer Less
than Specification allowance.
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Alpha Chromium Layer
GE Aircraft Engines
Ni-Plating
Cr
Coating
Acceptable vapor deposited chromium coating with an
alpha chromium layer less than specification limit.
Unacceptable vapor deposited chromium coating with
an alpha chromium layer approximately limit
GE photostandards for Acceptable (Left) and Unacceptable (Right)
Alpha Chromium Layer.
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Chromide Coating F50TF37 (Class A) – Pack Cementation
GE Aircraft Engines
Coating
Chromide Coating
Etchant: None
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Diffusion Coating – Oxidation Testing
GE Aircraft Engines
* No Photostandards of Oxidation Characteristics
(i.e., Frontal, Pockets and Spikes)
* Features which may be mis-interpreted as oxidation effects are
illustrated on the following photo-standards
9203002
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Entrapped Particles
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9203001
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Diffusion Coatings – Oxidation Testing
GE Aircraft Engines
Oxidation Test and Evaluation (P29TF22; Classes A, B, C & D)
Aluminides
F50TF8
- Class A
Pt-Aluminides
F50TF59 - Class A or tech plan
Chromide
F50TF37 - Less than .0005” base metal attack permitted.
No spalling or irregular scaling.
F50TF82 - Testing not designated
Retesting criteria is the same for above diffusion coatings: repolish failed
specimen or examine metallographically a second oxidized sample
(cannot repolish second sample).
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P29TF22 – Coating Material Specification after Oxidation
GE Aircraft Engines
Photographs
Terms
Class A: - Oxidation not penetrating into the diffusion zone.
Class B: - Oxidation penetrating into the diffusion zone.
Class C: - Frontal oxidation.
Class D: - Oxidation penetrating into the diffusion zone .
Coated specimen requirements: After oxidation testing, coated specimens or parts shall reveal no
areas of separation coating or irregular scaling.
Sample:
Class A: - Pockets or spikes whose depths do not extend to within the additive layerdiffusion zone interface shall be permitted.
Class B: - Pockets or spikes having depths which are less than 50% of the post test
additives layer thickness shall be permitted. Maximum of two oxide pockets,
or two spikes, or one of each, which have depths greater than 50% of the post
additive thickness and are more than one lineal inch (25.4mm) apart and do
not contact the diffusion zone shall be permitted.
Class C: - Pockets or spikes are acceptable. Maximum frontal oxidation shall not
extend to within specification limit of the additive layer-diffusion zone.
Class D: - Pockets, spikes, or frontal oxidation are acceptable provided that no base
metal attack exist.
Oxidation Retest Rule: If failure: Repolish and re-examine for pass / fail.
or
Review additional / spare sample (from same test
lot) and examine for pass / fail (no repolish).
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Diffusion Coating Oxidation Characteristics GE Aircraft Engines
Definitions:
Spike - An elongated indication in the coating which has a depth greater than its width.
Base Metal Attack - An area of oxidation attack, including an oxide layer or depletion
area, which has penetrated into the substrate material.
Frontal Oxidation - An area of continuous oxidation attack, including oxide layer and
depletion layer, which has a depth equal to or less than its width.
Pocket - An irregular shaped indication in the coating which has a maximum width
and a depth equals to or less than its width.
Frontal Oxidation
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Oxidation Pocket
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Aluminide Coating – Oxidation Spikes
GE Aircraft Engines
Oxide Spikes
Aluminide coating subjected to oxidation testing
(oxidation failure)
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Composition of Diffusion Coatings (Via Microprobe)
Aluminides
F50TF8
GE Aircraft Engines
- Type II; additive layer > 30% Al (if blue zone requirement),
Al gradient < 5%.
Pt-Aluminides
F50TF59 - Class A and B
F50TF59 - Class C
Chromide
F50TF82
Al content in NiAl phase of two phase outer
layer, wt.% min. (outer 1/3 of additive
layer). Pt content in PtAl2 phase of two phase
outer layer shall be reported.
Al and Pt integration procedure
Pt /Al ratio: specification min.
wt.% Al cut-off distance – 15 microns min.
Cr > outer 15% of coating. α Cr
identified by EDS / microprobe where Cr
is.
Frequence of test, test location, number of determinations and retesting criteria may be
established by tech plan.
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Diffusion Coatings
GE Aircraft Engines
Element
K-Ratio
Z
A
F
ZAF
Atom%
Wt%
Cr-K
0.816
0.990
1.021
0.994
1.004
86.41
81.94
Ni-K
0.048
0.978
10112
1.000
1.087
4.92
5.27
Co-K
0.028
1.012
10145
1.000
10159
2.98
3.21
Mo-K
0.072
1.103
1.155
0.0993
1.265
5.18
9.06
Fe-K
0.004
0.989
1.186
0.995
1.168
0.51
0.52
Total
=
100%
Chromide Coating
SEM-BSE Image And Corresponding Quantitative X-Ray
Energy Spectrum / Analysis Of Thin Layer Of α Cr
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Evaluation of Overlay / TBC Coating
GE Aircraft Engines
• Microstructure Requirements and Features of;
Overlay, TBC.
• Requirements of P16TF10
• Thickness
• Chemical Composition
• Oxidation Testing
• Furnace Cycle Testing
• JETS Testing
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OVERLAY COATING - Characteristics
GE Aircraft Engines
Multiphase Structure of Plasma Sprayed BC23
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Overlay Coating - Characteristics
Maximum Allowable
Porosity
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GE Aircraft Engines
Unacceptable Porosity
47
Overlay Coating - Characteristics
GE Aircraft Engines
Porosity / Voids in PBC 22 Coating
Etchant: None
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Overlay Coating Characteristics
GE Aircraft Engines
Fissures in Evaporative Metallic Coating
Fissures Resulting from Spatter During the
Evaporative Process
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Overlay Coating Characteristic
GE Aircraft Engines
Original Magnification 500x
Delamination in Evaporative Metallic Coating
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GE Aircraft Engines
THERMAL BARRIER COATINGS – TBC
(APS – TBC,)
F50TF74 - Plasma TBC consisting of aluminided bond coat plus a zirconia APS
top-coat, classes A, B, C, D, & E.
Classes – low pressure or inert gas shrouded plasma
spray bond coat.
Class – APS bond coat
THICKNESS REQUIREMENTS (F50TF74)
• Measured at min. magnification
• Predominate thickness of bond coat and predominate thickness of top
coat – as specified on part drawing.
• Predominate – average equally spaced readings.
• If predominate not met, two additional series allowed (at different
locations) on same metallographic specimen. Predominate thickness
of both series shall meet requirement.
• Max. and min. requirements for individual measurements of top coat
and bond coat.
• Method of thickness measurement of top coat and bond coat shown
herein.
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GE Aircraft Engines
THERMAL BARRIER COATINGS
THICKNESS DETERMINATION OF PLASMA TBC
AND BOND COAT
T6
T5
T4
T3
T2
T0
T1
T0 = BOND COAT/SUBSTRATE INERFACE
T3 = AVERAGE OF BOND COAT PEAKS (T2)
AND VALLEYS (T1)
T6 = AVERAGE OF TOP COAT PEAKS (T5)
AND VALLEYS (T4)
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GE Proprietary Information Updated 10/01
BOND COAT THICKNESS = T 3 – T0
TOP COAT THICKNESS = T6 – T3
TOTAL THICKNESS = T6 – T0
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GE Aircraft Engines
THERMAL BARRIER COATINGS – TBC
(APS – TBC)
MICROSTUCTURE
• Examination for worst field of view
• Bond coat porosity - limits on percentage in a given length (after
aluminiding). Evaluation applies to entire bond coat thickness. (no
GE photo standards for porosity evaluation)
• Top coat porosity – limits on percentage (GE photo standards);
alternate measuring techniques or photo standards allowed when
included in tech plan.
• Bond coat - Substrate Interface Contamination – limits on size
and percent aggregate length in given interface length for voids,
entrapped grit or oxide.
• Uniform microstructure, free from delaminations and substrate –
coating interface separations. Limits on length of delaminations
and transverse cracks.
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GE Aircraft Engines
THERMAL BARRIER COATINGS
PLASMA TBC
EXCESSIVE POROSITY IN BOND COAT
ETCHANT ; NONE
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Thermal Barrier Coatings
5% porosity
GE Aircraft Engines
25% Porosity
From F50TF50; Photo standards
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