First of all, thank's for giving me access to this forum.

For some applications, I've got problems to decide which thermal spray process is most adequate...
Are there any established preferences/rules to use plasma spray or HVOF for the following coatings :

1) abradable coatings
2) coatings on composite and polymer substrates

Or does it depend on the coated materials (HVOF best for metal, carbide cermets..., plasma spray best for high t? ceramics...)

Hi Julio VALLES

Welcome to the Surface Engineering Forum.

Generally, I would say that plasma spray is the more versatile tool as it is capable of spraying a wider range of materials, but HVOF can produce superior quality coatings, particularly some of the metal and carbide based coatings (assuming powder is optimised for particular process).

Abradable coatings - from practical experience I can only really comment on aluminium silicon alloy/polymer composite abradable coatings through both processes. I believe HVOF can have benefits in this case (density, strength and deposit efficiency). It is important to note that powder composition and particle sizes need to be adjusted fairly radically to produce equivalent type coatings (abradability wise). A powder developed for plasma spraying will usually produce a softer coating when sprayed with HVOF, which at first seems surprising, but the polymer constituent appears to have better deposit efficiency and produces a coating richer in polymer and hence lower hardness. Generally, the only reasons I see for not using HVOF for other abradable coatings is where porosity is the main criteria for controlling abradability or for use with powders graded for use with plasma where equivalent coatings are required.

Coatings on composite and polymer substrates - In my experience plasma spray is very much easier and more successful in this case. It is difficult to control the aggressive nature of HVOF spray on very soft and thermally sensitive substrates.

Generally your last statement is correct. Substrate material and geometry can also be factors (HVOF requires longer spray distances and heats substrates more aggressively).
Note different equipment makes and processes usually require powders to be graded differently to produce optimum coatings, so take care with your choice of powder for your particular process.

Gordon,

Thank's for your prompt response, which I find much relevant

Julio

Julio,

What type of material are you spraying?

Danns