Tungsten Carbide Coating - Basic Information Required

[mands]

As a design engineer I am looking for basic information on tungsten carbide coating:-
Advantages / Disadvantages
Description of coating process
Substrate preparation,
Comparison to Hard Chrome Plating,
Hardness values

The substrate material is 17-4 Ph.

Thanks
Mandy

 

[mqas]

Mandy,

Coating application companies are Praxair Surface treatments and Deloro Stellite.

Both have their own proprietary application process which are essentially High Velocity Oxy Fuel processes (They might say different).

Substrate preparation depends on the component and material and for 17/4 I think this may only involve blasting with Al2O3.

I don't know the hardness in comparison to Hard Chrome however, there are numerous different grades of Tungsten Carbide and other carbides which can produce hardness ranges 63HRc ~ 90Hrc.

Advantages over hard chrome?

Hardness, Bond Strength?, Wear resistance

Try a search on HVOF Coatings and see what it yields

Regards

 

[EdDanzer]

Carbide spray applications will be rougher than chrome even after grinding, but will be harder. I don’t know about corrosion resistance, or adhesive strength, but there will be more distortion to the base part because of the heat imparted during carbide coating.

 

[unclesyd]

Mqas has started you in the right direction if WC is the route you have to go.
Depending on your end use I think a better solution would be liquid nitriding of the 17/4 instead of a coating or plating. I've used liquid nitrided 17/4 components in wear and galling resistance applications for many years with excellent results. The Kolene process QPQ is available if you need a smooth polished finish, otherwise the simple treat and go is used. There is some loss in corrosion resistance in certain media. Kolene has always been a great help.

http://www.kolene.com/index.asp

 

[EElmore]

Mandy:
Hard Chrome is usually applied over a nickle flash. It goes down highly stressed and cracks upon application, however but the hairline cracking does not affect it's preformance.
Because Hard Chrome entails the use of several environmentally unfriendly compounds we are supposed to be getting rid of it.

WC is applied in two parts. A bondcoat of something like NiCrAlly is applied before the WC can adhere.
The surface finish before the thermal spray needs to be rougher than a 50 RMS because the bond with the substrate is primarily mechanical engagement of the coating with the asperities of the prepared surface.

The HVOF process involves burning a fuel with O2 and using a DeLaval nozzle design to force the exhaust gas produced through a constriction and then let it expand to supersonic speed. The coating is introduced as powder into the gas stream and propelled against the substrate. Nozzle to work distances are in the neighborhood of 3 to 6 inches. Cooling jets impinge on the part during during application to prevent overheating of the part.

Extensive masking is required to keep the thermal spray from unwanted areas. This can be in the form of non-contact "shadow masking" or thermal tape. Shadow masking is more expensive, but the edge of the coating often chips off when the tape is removed.

The resulting coating has a bond strength of around 10,000-15,000 lbs max. it is essentially a ceramic and is suitable only for areas which will not see any flexure, since it has no ductility. From my experience it does not do very well when subjected to scraping or pressure loading such as that of ball bearings. If your part is big , and there is line of sight axcess to the area needing wear resistance and the contact is sliding, then WC might be a good choice

UncleSyd is right about the local nitride, also there is another process called ElectroSpark Deposition which Pacific Northwest National Labs has been using to apply wear resistant coatings to nuclear reactor components for a number of years. The no masking is needed and the coating is absolutely superior, but the process snail slow, though automatable.