TASK 70-49-32-340-033
1 . General.
CAUTION:
DO NOT APPLY THIS PROCESS TO ALUMINUM OR ALUMINUM ALLOY HARDWARE OR ASSEMBLIES, UNLESS APPROVED BY GEAE ENGINEERING.
A.Inconel 718 is a self-bonding, readily machinable coating that provides physical and chemical properties of wrought Inconel 718 Alloy. This coating is used, when specified in the applicable repair instructions of the Engine/Shop Manual, for salvage and build-up applications. This procedure covers application of the powder form by plasma arc spraying.
NOTE:
Inconel 718 may also be applied per TASK 70-49-45-340-044, Electric Arc Spraying Alloy 718 (Wire) as an acceptable alternative.
2 . Equipment.
Subtask 70-49-32-340-331
B.Refer to TASK 70-49-00-340-001, Thermal Spraying.
3 . Material.
Subtask 70-49-32-340-332
C.Inconel 718 Alloy Powder C07-038  .
4 . Spraying Parameters.
Subtask 70-49-32-340-333
D.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 70-49-32-340-334
E.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.
F.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 complete, uniform 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.
G.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 coatings 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 coatings 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.
H.Tensile.
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 Coatings. Tensile bond strength for this coating at room temperature shall be 7,000 psi (48.3 MPa) minimum.
I.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
 
Porosity
Less than or equal to V-1
Figure 25
TASK 70-71-04-700-005
None
 
Oxides
Oxides shall be uniformly distrib-uted. Reject Cluster oxides as shown in Figure 6 view X-3.
Figure 6
TASK 70-71-04-700-005
None
 
Oxide Clusters
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
 
Interface Contamina-tion
Less than or equal to I-2
Figure 7
TASK 70-71-04-700-005
None
 
Interface Separations
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
 
Transverse Cracks
None allowed
No figure for rating
TASK 70-71-04-700-005
None
 
Delamina-tions
None allowed
No figure for rating
TASK 70-71-04-700-005
See definition for ratable size
6 . Recoating Previously Coated (non-engine run coating) Surfaces.
Subtask 70-49-32-340-335
CAUTION:
THIS PROCEDURE IS NOT APPLICABLE FOR ENGINE RUN COATINGS, IT IS PERMITTED TO RESTORE FINISHING TO DIMENSION IN CASE OF INSUFFICIENT SPRAYING APPLIED PREVIOUSLY, OR IN CASE OF OVER MACHINING OF NEWLY APPLIED DIMENSIONAL REPAIR COATING.
CAUTION:
THIS PROCEDURE IS NOT APPLICABLE TO PARTS OR COMPONENTS THAT CONTAIN ALUMINUM ALLOYS OR ORGANIC COMPOSITES. DAMAGE CAN BE CAUSED TO PARTS OR COMPONENTS.
J.Surfaces previously coated per TASK 70-49-32-340-033, Thermal Spraying Inconel 718 (Powder), may be recoated without removing the original coating, subject to the following conditions:
(1)The repair procedure for the part specifies these materials and was applied for the purpose of restoring dimensional integrity.
(2)The part to be coated shall be thoroughly cleaned in the following sequence:
(a)Alkaline clean per TASK 70-21-09-110-007, Cleaning Method No. 9 - Light-Duty Alkaline Cleaning of Titanium Alloys.
(b)Steam clean per TASK 70-21-03-160-001, Cleaning Method No. 3 - Steam Cleaning.
(c)Bake part at 600° ± 25°F (316° ± 14°C) for 30 minutes in air.
(d)If surface to be coated exhibits evidence of oil or contamination repeat cleaning and baking operations.
(3)Apply masking and grit blast per TASK 70-49-00-340-001, Thermal Spraying, or applicable Engine/Shop Manual repair instructions.