Vacuum plasma spray, also called low-pressure plasma spray (LPPS), carried out in a sealed chamber pumped down and backfilled with argon to a fraction of atmospheric pressure. With no oxygen, reactive alloys such as MCrAlY bond coats and titanium deposit dense and nearly oxide-free, and a reverse transferred arc can clean the part surface before spraying. The chamber adds cost and cycle time, so it is reserved for turbine hot-section and medical work.
Blades get the MCrAlY by VPS, the air plasma version has too much oxide for the engine spec.
Also heard as
- vacuum plasma spray
- LPPS
- low-pressure plasma spray
Related terms
Plasma spray
Spraying powder through an electric arc plasma jet hot enough to melt ceramics and refractory metals.
MCrAlY
Family of oxidation-resistant alloys of nickel or cobalt with chromium, aluminum and yttrium.
Oxides
Thin oxide films formed on metal particles in flight, showing as dark stringers between splats.
Bond coat
The first layer sprayed on a substrate to help the following coat stick and sometimes protect the metal.