COMMERCIAL ENGINE STANDARD PRACTICES MANUAL

	COMMERCIAL ENGINE STANDARD PRACTICES MANUAL	Dated: 02/09/2017
	SPM 70-49-37 TUNGSTEN CARBIDE/17% COBALT WEAR COATING APPLIED BY HIGH VELOCITY OXY-FUEL (HVOF) PROCESS

TASK 70-49-37-340-036

1 .

General.

This document provides guidelines for the spraying of tungsten carbide -17% cobalt using High Velocity Oxy-Fuel (HVOF). Tungsten carbide - cobalt produces a high-density coating for wear and fretting applications.

The tungsten carbide is supplied as a powder with cobalt forming a metallic matrix in the coating. The coating is self-bonding and will accept a high finish by grinding and lapping. This procedure is used when specified for individual parts in the repair procedures of applicable Engine/Shop Manuals.

Substantiation requirements are given in the repair procedures of the applicable Engine/Shop Manual.

2 .

Equipment.

Subtask 70-49-37-340-361

The equipment to do high density HVOF spraying consists of the following:

(1)

An HVOF gun system with a suitable controller.

(2)

A gas controller that can deliver up to 1,000 SCFH oxygen, 1,600 SCFH hydrogen, 300 SCFH propylene, and if required, 800 SCFH air. If liquid fuel is used, an appropriate controller is required. The unit shall provide gun power control and air delivery rate.

(3)

A pressurized powder feeder that can deliver powder between 4-15 lbs/hr (2-7 kg/hr).

(4)

A clean filtered air supply that can deliver up to 800 SCFH.

Commercially available equipment consists of the following:

Model

Supplier

Jet Kote 2000

Stellite Coatings Deloro Stellite, Inc. Refer to the List of Suppliers in Step 4 of 70-80-00.

Diamond Jet 2600 Hybrid

Sulzer Metco, Inc. Refer to the List of Suppliers in Step 4 of 70-80-00.

JP-5000

Praxair/TAFA Concord. Refer to the List of Suppliers in Step 4 of 70-80-00.

3 .

Materials.

Subtask 70-49-37-340-362

Tungsten Carbide C07-040 .

4 .

Spraying Parameters.

Subtask 70-49-37-340-364

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 70-49-37-340-365

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.

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.

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.

Hardness Tests.

(1)

Macrohardness.

(a)

Test specimens will be prepared for Rockwell hardness testing. The specimen material may be of a convenient size or shape but it should be at least 0.060 inch (1.52 mm) thick and of the same material as the coated part. The specimen must be coated with sufficient material to meet the thickness values of the part, the thickness values that are specified in TASK 70-49-00-340-001, Thermal Spraying, or the thickness requirements in TASK 70-34-03-220-009, Rockwell Hardness Testing and ASTM E-18 (whichever results in the maximum thickness). The Rockwell hardness for this coating shall be 89 minimum, based on an average of at least five readings on a Rockwell R15N scale.

(2)

Microhardness.

(a)

Test specimens will be prepared for microhardness testing. Test specimens shall meet a minimum average hardness DHP (Vickers) 950 using a 300 gram load. The specimen shall be prepared and tested in accordance with TASK 70-34-02-220-008, Vickers Hardness Testing, or ASTM E-384.

Tensile Bond Strength.

(1)

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. The tensile bond strength for this coating at room temperature shall be 10,000 psi (69 MPa) minimum.