TASK 70-49-61-340-000
1 . General.
A.Nickel-Chromium-Aluminum-Bentonite coating provides abradable clearance control coating that is both corrosion and oxidation resistant at temperatures up to 1200° F (649°C). This procedure covers application of the powder form by flame spray application.
B.Nickel-Chromium-Aluminum-Bentonite coating is an effective coating used in Low rub-heat generation coating for rotors (Class A) and High abradability coating for stators (Class B).
2 . Equipment.
Subtask 70-49-61-340-001
A.Refer to TASK 70-49-00-340-001, Thermal Spraying.
3 . Material.
Subtask 70-49-61-360-001
A.Bond Coat: Nickel-Aluminum Powder, C07-016  , Class A or B.
B.Top Coat: Nickel-Chromium-Aluminum-Bentonite Powder, C07-058  , Class A.
4 . Spraying Parameters.
Subtask 70-49-61-180-001
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 70-49-61-220-001
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. The tensile bond and erosivity number specimens for the coating system shall have a bond coat thickness as specified by the Engine/Shop Manual and an as-sprayed top coat thickness of 0.030 to 0.035 inches (0.76 to 0.89 mm).
B.Appearance.
Visual examination of the coating shall be in accordance with the following:
(1)Adhesion.
The coating shall exhibit no spalling or lifting.
(2)Coverage.
The coating shall exhibit acceptable coverage in those areas specified for coating in the Engine/Shop Manual. Coating is not permissible in areas other than those specified.
(3)Surface condition.
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)Delamination.
The coating shall show acceptable delamination as defined for bond coat and top coat in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatingsand then rated per the guidelines of Table 1.
(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.
Transverse cracks in the coating microstructure shall not be evaluated for acceptance/rejection.
(5)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.
(6)Microstructure.
Microstructure shall be identified as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Sppray Coatings, and then rated per the guidelines of Table 1.
(7)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.
(8)Interface Contamination.
Interface contamination in the coating shall be identified as defined in TASK 70-71-04-700-005, Metallographic Evaluation of Thermal Spray Coatingsand then rated per the guidelines of Table 1.
D.Tensile specimens shall be prepared for tensile bond testing and evaluated in accordance with TASK 70-71-01-700-002, Bond Strength Tensile Testing of Thermal Spray Coating.Tensile bond strength for coating system at room temperature must be 200 to 650 psi (1.38 to 4.48 MPa) for Class A. Tensile bond strength for coating system at room temperature must be 300 to 800 psi (2.07 to 5.52 MPa) for Class B. The coating system shall exhibit top coat cohesive failure within the Nickel-Chromium-Aluminum-Bentonite.
E.Erosion Testing.
Erosion specimens shall be prepared for erosion testing and evaluated in accordance with TASK 70-71-09-700-000, Erosion Testing of Thermal Spray Coatings. Erosion rate of NiCaAL/Bentonite top coat shall be within 1.0 to 4.0 seconds/mil for Class A and within 2.0 to 5.0 second/mil for Class B.
 
Acceptance Limits for Thermal Spray - Table 1
 
Feature
Acceptance Criteria
Rating Photograph
Task
Comments
 
Top Coat




 
Microstructure
Must be similar and uniform
Figure 48 and 49
TASK 70-71-04-700-005
Refer to Figure 48 and Figure 49 for a typical microstructure of an acceptable distribution
 
Bond Coat




 
Unmelts and porosity
Less than or equal to UV-2
Figure 45
TASK 70-71-04-700-005
Maximum 10 percent of total bond coat area may exhibit features less than or equal to UV-3
 
Interface Contamination
Less than or equal to I-2
Figure 50
TASK 70-71-04-700-005
Maximum 10 percent of total bond coat area may exhibit features less than or equal to I-3
 
Delamination
Less than or equal to D-2
Figure 47
TASK 70-71-04-700-005
Maximum 10 percent of total bond coat area may exhibit features less than or equal to D-3
 
Uniformity
Greater than or equal to C-2
Figure 46
TASK 70-71-04-700-005
Maximum 10 percent of total specimen interface length may exhibit uniformity greater than or equal to C-3