We are a group of final year students from Strathlclyde University in Glasgow and are currently working on a project concerning coating applications on wear rings for pump impellers. After researching the topic area we have decided to focus on the use of tungsten carbide and cold spray.

However, there are still some questions we have that are unanswered, such as:

>Is tungsten carbide compatible with cold spray, or is a ductile binder required?

>Is it possble to achieve a coating thickness of 150 microns?

>Would it provide good levels of uniformity, integrity, adhesiveness and chemical resistance?

Hi LLBHW

to the Surface Engineering Forum.

Quote:Is tungsten carbide compatible with cold spray, or is a ductile binder required?

With all thermal spray processes tungsten carbide is always applied in combination with a relatively ductile binder metal (cermet), usually cobalt, cobalt/chromium or nickel alloy. I am sure with sufficient development and optimisation of "cold spray" processes (depending on how we define cold spray) and powders, high quality WC/Co type coatings will eventually be achieved. HVOF and HVAF are probably currently the best method for applying tungsten carbide based coatings. Though these are not referred to as "cold spray" methods, the higher quality coatings are sprayed without melting the powder particles, so the differences in the processes are not as far apart as you may first think.

Quote:Is it possble to achieve a coating thickness of 150 microns?

Quite a lot thicker in fact.

Quote:Would it provide good levels of uniformity, integrity, adhesiveness and chemical resistance?

Relative to what? HVOF/HVAF WC based coatings provide very good solutions to many surface engineering applications, so lets say yes. When "cold spray" matures from R & D and if WC based coatings become commercial then I would suspect they would be better.
Chemical resistance really depends on what chemical. Co/Cr and Ni based binders tend to give better corrosion resistance than cobalt alone.

Hope that helps

Hi

There is a cold spray research group at the University of Ottawa who successfully deposited WC based cermet coatings on Aluminium using cold spray. Their result of the experiments can be found in the journal of "Surface & Coatings Technology 202 (2007) 382–390 ". Hope that helps

Regards
Tanvir