While I'm at it, can someone tell me about PVD and CVD coatings?  How are they applied, how are they different and what are their advantages?

HVOF is done by feeding powder via a gas stream into a torch. Works for metals & ceramics.

PVD = physical vapor deposition; is done in a vacuum chamber. Can have solid source material. May involve heating the source & transferring by condensing onto substrate or use a voltage to effect the transfer.

CVD = chemical vapor deposition; is done in a chemical reactor chamber; source materials are gases (or vaporized solids) which combine at some elevated temperature onto the substrate.

Each of these is a vast topic in itself. Start below (& followup links given therein):
http://en.wikipedia.org/wiki/Physical_vapor_deposition
http://en.wikipedia.org/wiki/Chemical_vapor_deposition

This is a professional society: Society of Vacuum Coaters
http://www.svc.org/

HVOF is a high velocity spray.  It's common for applying dense metallic coatings. I am not familiar with ceramic application.  

PVD is applied by inserting your work piece into a "cloud" of vapor.  The vapor condenses onto the work piece.  Ceramic or metallic can be applied.

CVD is applied usually in a packed bed, with the work piece surrounded by granules of reactive media in a furnace.

Each coating likely requires some level of pre-treatment, which may be as simple as a cleaning or grit blast, or may go as far as requiring an additional coating to bond to.  How well the material sticks to your work piece depends on your work piece material and your coating material as well.  

From least to most expensive, (from memory): HVOF, CVD, PVD

Aaron A. Spearin
ASQ CSSBB
Engineering Six-S'$
www.Engineering6ss.com

"The only constant in life is change." -Bruce Lee

hello,

im currently a air-plasma/hvof operator and my shop also have cvd and pvd, and from what i know from cvd and pvd (this is my lack of true information)is that most of those furnace will cover the entire item or large area of surface with the application that you seek, now with hvof,(its my main job) you can shot a very dense and very hard metals that can be sized to proper dimention once finish, the nice thing about hvof is you can pin point the exact location of the coation area you wish to aim for and deposite from .001" to .100" depending on the powers.

the way hvof works is a mixed of gases, usaly oxygen and hydrogen, the speed of the molten powder is about 1800 fps and it works on impact density compared to air plasma which is intense heat.the real applications for hvof are mostly for areas of extreme wear,rust resistance,extreme heat and hardness.

some of the metals we do is tungsten,carbide,cobalt.
ceramic is usaly done with air-plasma due to its high heat needed to convert the powder ceramic form into an application coating

hope this helps