TASK 70-49-35-340-037
1 . General.
A.Thermal Barrier coatings (TBC) provide base metal protection against hot gas streams. They are used to reduce base metal temperatures to prolong part life. The applied TBC is resistant to thermal shock and has good durability. This process describes the deposition of a NiCrAlY powder bond coat and a YZRO3 powder top coat applied with air plasma system.
2 . Equipment.
Subtask 70-49-35-340-371
A.Refer to equipment requirements in TASK 70-49-00-340-001, Thermal Spraying.
3 . Materials.
Subtask 70-49-35-340-372
A.Bond Coat: Nickel Chromium Aluminum Yttrium Powder C07-032  .
B.Top Coat: Zirconium oxide - Yttrium oxide powder C07-035  .
4 . Spraying Parameters.
Subtask 70-49-35-340-373
A.Starting parameter sets will be listed in the spray equipment manuals or are readily available from the spray equipment manufacturers or powder suppliers. Modifications may be necessary for your location and product application. See sprayability testing per TASK 70-49-00-340-001, Thermal Spraying, and TASK 70-70-00-700-001, Testing and Quality Analysis. When the final spray parameter settings are developed, all values should be recorded to ensure consistent achievement of high quality coatings.
5 . Quality Assurance.
Subtask 70-49-35-340-374
A.Thickness.
Measure the coating thickness using a standard flat-anvil-and-spindle micrometer. The measurement may be made on either a coated production part or on a flat test specimen having a thickness of at least 0.060 inch (1.52 mm). Determine coating thickness to the nearest 0.001 inch (0.03 mm) at three different locations.
B.Appearance of coating.
(1)Visual examination of the coating shall be in accordance with the following:
(a)The coating shall exhibit no spalling or lifting.
(b)The coating shall exhibit complete, uniform coverage in those areas specified for coating in the Engine/Shop Manual.
(c)Coating is not permissible in areas other than those specified.
(d)The coating shall be uniform and free from cracks, blisters, spatter, chipping, and flaking.
C.Coating Microstructure.
Test specimens shall be prepared for microscopic examination, and evaluated in accordance with TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings. Metallographic examination of the prepared specimen shall be made for uniformity of coating, as well as for the following other conditions:
(1)Delaminations.
The coating shall be free of delaminations as defined for metallic (bond coat) and ceramic coatings (top coat) in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings.
(2)Integrity.
The coating shall show acceptable integrity as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings.
(3)Interface Separation.
The coating shall be free of interface separations as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings.
(4)Transverse Cracks.
The coating shall be free of transverse cracks as defined for metallic (bond coat) and ceramic coatings (top coat) in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings.
(5)Interface Contamination.
Interface contamination in the coating shall be identified as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings, and then rated per the guidelines of Table 1.
(6)Oxides and Oxide Clusters.
Oxides in the coating shall be identified as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings, and then rated as described in the guidelines of Table 1. The coating shall be free of oxide clusters as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings. Oxides shall be uniformly distributed.
(7)Porosity.
Porosity in the coating shall be classified for size as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings, and then rated per the guidelines of Table 1. Porosity shall be uniformly distributed.
(8)Unmelts.
Unmelts in the coating shall be classified for size, shape, and bonding as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatings, and then rated per the guidelines of Table 1.
D.Tensile.
Tensile specimens shall be prepared for tensile bond testing of the bond coat only and evaluated in accordance with TASK 70-71-01-700-002, Bond Strength Tensile Testing of Thermal Spray Coatings. Tensile bond strength for this coating at room temperature shall be 4,000 psi (27.6 MPa) minimum.
NOTE:
This test is only necessary for initial qualification and not required for testing of daily production hardware.
E.Bend Test.
The technical requirement for this test has been deleted and no longer needs to be performed when specified in the Engine/Shop Manual.
 
Acceptance Limits for Thermal Spray - Table 1
 
Feature
Acceptance Criteria
Rating Photograph
Task
Comments
 
General Features
Similar structure
Figure 20
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None
 
Bond Coat
 
Porosity
Less than or equal to V-2
Figure 1
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None
 
Oxides
Less than or equal to X-1
Figure 6
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None
 
Oxide Clusters
None allowed
No figure for rating
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See definition for ratable size
 
Interface Contamina-tion
Less than or equal to I-2
Figure 7
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None.
 
Interface Separations
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
 
Unmelts
Less than or equal to P-1
Figure 8
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See definition for ratable size
 
Transverse Cracks
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
 
Delamina-tions
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
 
Bond Coat/Top Coat Interface
 
Porosity
Less than or equal to 15%
No figure for rating
TASK 70-71-04-700-005
None
 
Top Coat
 
Porosity
Between 5-25%
Figure 17, 18, 19
TASK 70-71-04-700-005
None