TASK 70-49-45-340-044
1 . General.
CAUTION:
DO NOT APPLY THIS PROCESS TO ALUMINUM OR ALUMINUM ALLOY HARDWARE OR ASSEMBLIES, UNLESS APPROVED BY GEAE ENGINEERING.
A.The Alloy 718 coating is self-bonding, easily machinable, and has the same physical and chemical properties as the plasma-sprayed Alloy 718. This coating is normally used for buildup and salvage applications as specified in repair instructions of the applicable Engine/Shop Manual.
NOTE:
Alloy 718 is also available in a powder form for electric-arc spraying per TASK 70-49-32-340-033, Thermal Spraying Inconel 718 (Powder). That procedure is an acceptable alternative.
B.Electric-arc wire spraying consists of an electric arc which is struck between two feed wires, resulting in complete melting of the wire and subsequent deposit of the molten atomized droplets on the part. The molten droplets are atomized and delivered to the part by a stream of air. The material is self-bonding, has a high bond strength, and can be deposited at rates in excess of 10-15 lbs/hr.
2 . Equipment.
Subtask 70-49-45-340-441
C.The equipment to do electric-arc wire spraying consists of the following.
(1)An arc-wire gun utilizing dual wire feed capable of melting, atomizing and depositing the molten droplets on the work piece.
(2)An arc-wire gun control unit that is capable of delivering spooled wire to the arc gun unit either manually or automatic with pneumatic or electrically driven motors. The unit shall also provide gun power control and air delivery rate.
(3)An electric-arc wire power supply that is capable of 50-350 amps at 20-38 open circuit volts.
(4)A clean filtered air supply that is capable of delivering 50 SCFM at 80 psi (552 kPa).
D.Commercially available equipment.
Model 8830, 8835, 8850, or 9000
Available from Praxair/TAFA Concord.
SmartArc™
Available from Sultzer Metco.
Refer to the List of Suppliers in Step 4 of TASK 70-80-00-800-803.
3 . Material.
Subtask 70-49-45-340-442
NOTE:
Alloy 718 wire material should have a chemical composition to GE Specification B50TF202, Class B, and conform to physical requirements of GE Specification B50TF69, Class A, except the wire diameter shall be 0.0625 in. (1.59 mm) nominal with spools up to 25 lb. (11.34 kg) permitted.
E.Alloy 718 Wire C07-049  .
4 . Spraying Parameters.
Subtask 70-49-45-340-443
F.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 70-49-45-340-444
G.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.
H.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.
I.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.
J.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 4,000 psi (27.6 MPa) minimum.
K.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 70-49-45-340-445
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 MAY BE CAUSED TO PARTS OR COMPONENTS.
L.Surfaces previously coated per TASK 70-49-45-340-044, Electric-Arc Wire Spraying Alloy 718 (Wire), 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.