HVAF & HVOF Tungsten Carbide Coating: How to Spray the Best

Tungsten Carbide WC-Co 88/12 Feedstock Properties

HVAF and HVOF Tungsten carbide coatings are sprayed with WC-Co agglomerated and sintered powder

Nominal composition	wt.%
Tungsten carbide	Base
Total carbon	5.3-5.4
Cobalt	11-13

Powders are available where cobalt is replaced with nickel.

The Properties of HVAF WC-Co Tungsten Carbide Coatings on Steel

WC-12Co thermal spray coatings are usually harder compared to coatings of WC-17Co as a result of higher tungsten carbide levels in the coating.

The tungsten carbide WC-12Co coatings are resistant to sliding wear, impact, abrasion and fretting at temperatures up to 510°C (950 °F), preferably in non-corrosive media. We recommend chromium carbide coatings for higher temperature applications.

Coatings that contain tungsten carbide protect substrates from the negative effects of fretting, abrasive grains, particle erosion and dynamic contact with hard surfaces.

These tungsten carbide coatings af steel can be used for abrasion-resistant coatings in dry, non-corrosive environments.

Although HVOF technology is frequently used for WC coating applications noticeable material oxidation and WC decomposition still occur during HVOF deposition.

The decomposition of WC-Co coatings is directly related to a high combustion temperature, usually more than 3,000^oC (5,432°F), as well as the presence of oxygen in HVOF combustion products. This results in coating embrittlement and subsequent reduction of its service lifetime in conditions of abrasive and erosive wear.

Kermetico High-Velocity Air Fuel (HVAF) systems use gas fuel and compressed air for combustion at substantially lower temperatures and produce higher velocities than HVOF coating systems.

With the HVAF combustion temperature below 2,000^oC (3,632°F), the surface temperature of Co-, Ni- and Fe-alloy particles usually remain near their melting point.

Depositing WC-Co coatings by the Kermetico HVAF spraying process eliminates WC coating embrittlement and improves its hardness and density.

It also reduces the production cost due to higher spray rates achieved and use of air instead of pure oxygen.

A distinguishing feature of the Kermetico HVAF process is that spray particles are heated but preferably not fused during spraying.

Kermetico HVAF WC-Co Coating Properties

Feature	S.I. Units	U.S. Units
apparent metallographic porosity, %	<0.1
bond strength of a tungsten carbide coating to carbon steel	80+MPa @100 µm	12,000+PSI @0.040”
hardness range, HV₃₀₀	1,150-1,600+
hardness deviation from a target value, HV₃₀₀	±6%
typical as-sprayed roughness	2-3.2 µm	80-130 µinch
maximum working temperature of the coating	510^oC	950^oF

A Typical Cross-Sectional Micrograph of a Kermetico HVAF WC-Co Coating

Kermetico HVAF HVOF Tungsten Carbide Coating WC-12Co

A Kermetico HVAF WC-12Co Tungsten Carbide Coating

Typical Applications of HVAF WC-Co Coatings

Heavy Abrasive Wear and Erosion Resistance:

Uniform high hardness and ductility, low stress and porosity lead to a substantial increase of service life of parts protected with Kermetico HVAF WC-Co coatings in comparison with HVOF tungsten carbide versions.

Kermetico HVAF Equipment to Spray Tungsten Carbide Cobalt Coatings

Most Kermetico guns are good to spray WC-12Co Coatings. We started to design our equipment to excel in the application of tungsten carbide coatings.

Convertible HVOF and HVAF equipment:
- C7 – an HVAF/HVOF gun for large parts
- C6 – a general purpose HVAF-HVOF gun
- CID – HVAF+HVOF system to spray WC-Co onto internal diameters
Multi-purpose HVAF AK systems, with a range of spray guns:
- AK7 – a high-power gun for the thermal spray of large parts
- AK6 – a tungsten carbide coating gun to spray a balanced mix of parts in a job shop
- AK5 – a compact gun to spray smaller parts, thin walls and complex surfaces
- AK-ID – an 80 mm (3.15”) and larger internal diameter spray gun
- AK-IDR – a rotating ID gun to spray 4” (100 mm) and larger bores
- AK-HH – a handheld gun for on-site coating
Additional equipment:
- A hot grit feeder for the grit blast preparation of parts to reduce coating costs
- A Gas Permeability Tester for an instant check of a coating through porosity

Kermetico, Inc. – HVAF and HVOF Material Science Excellence and Equipment Manufacturing Since 2006

We create equipment that helps material scientists, engineers, and business managers achieve their goals.

We have installed more than 60 Kermetico HVAF and HVOF systems in the USA, Europe, Japan and China.

Some of the systems are at work in Universities and National Labs, but most of them are used in production thermal spray shops.

We proudly design and produce our HVOF and HVAF thermal spray equipment in California and install it all over the world.

You can visit our R&D center in Benicia to meet our designers and see our HVAF and HVOF equipment in action or job shop of our partner in Beijing, China.

We also provide HVAF and HVOF thermal spray coating services for customers in the San Francisco Bay Area in California, USA.

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